 Good morning and welcome to Technical Session TH-21 titled R.V. observing more extreme weather events that affect the risk of nuclear power plants. My name is Mehdi Reisifart and I have the privilege of being the chair for this session today. In the past two years, we observed relatively important weather events that affected nuclear power plants. Although the risk of those events was mitigated because defense in depth and plant-wide safety margins were maintained, our observations prompted us to organize this forum to facilitate discussion on extreme weather events, if those events are affecting commercial nuclear power plants, and if so, the potential risk implications of those events. The presentations will explore what existing data are or are not telling us about how weather patterns are changing and any observed effects on the operation of nuclear power plants. Today we have distinguished experts and speakers from international and domestic organizations with diverse backgrounds and perspectives. Our first speaker is Dr. Paolo Contri from the International Atomic Energy Agency, and he will present on Climate Change Impact on the Safety of Nuclear Installations. For our second presentation, Dr. Ruby Loong and Dr. Rajiv Prasad from Pacific Northwest National Laboratory will discuss a regional perspective on climate change impact based on a study performed for the NRC. Our third speaker is Mr. Christopher Hunter from the Office of Nuclear Regulatory Research at the NRC. Chris will discuss recent insights from loss of offsite power trends and risk evaluations. And finally, our last speaker, Dr. Fernando Fronte from the Electric Power Research Institute will discuss observations on extreme weather and impacts on nuclear power plants. Before we start with the presentations, I'd like to thank all of our speakers for supporting this session, and I'd like to acknowledge and thank our session coordinator, Mr. John Lane, for all his efforts to make this session possible. Please feel free to submit your questions using the feature available in the platform. We will collect all questions and address as many as time allows at the end of the presentations. With that, I'll start with our first presentation, and I'll introduce our first speaker. Dr. Paolo Contri has a PhD in structural mechanics from the University of Parova in 1994. After a long experience in engineering consultancy in an international company in Italy, he joined the IAEA Engineering Safety Section in 1998, where he served until 2005. After four years at the European Commission, joint research center, Institute for Energy in Peren, the Netherlands. He joined NL in Rome, where he served as Head of Nuclear Safety Division in the Nuclear Engineering Department. In 2020, he joined the IAEA as Section Head of the External Events Safety Section in the Department of Nuclear Safety. Dr. Contri, the floor is yours. Thank you very much, Medi. Thank you very much indeed. I would like to focus my presentation today on the challenges that the climate change has on nuclear installation safety. Do I have to wait for the presentation? I cannot see the presentation. Medi, can you help me? The presentation is being streamed, Dr. Contri. Okay, it's fine. I will go ahead. I would like to focus my presentation, as I said, on the climate change impact on the nuclear installations. Next slide, please. First, we will have to start from discussion on the hazard, first of all, but actually our focus will be on the challenges posed to the safety of the plant. Next slide, please. In other parameters, we all know that the climate change is going to affect mainly the areas in the world which are posed in the extreme latitudes of the globe, and this is something that is very well known. We have many studies available and so on. What is more interesting for us as a nuclear safety experts is to understand which parameters of the climate change hazard are more relevant to the safety of the plants. In particular, if everybody can understand that the event magnitude is a typical parameter, the hazard type is less spontaneous, is less obvious, for example. We have sites where some scenarios have been screened out at the time of the sighting, while actually now they should be recovered because they are shown to have a high probability of occurrence. Typical case, for example, in Mediterranean, in Mediterranean the temperature of water just because of two, three degrees more make feasible, make possible some hurricane and some tornado that in the past were not even physically feasible. So that's why we have to add these types of scenarios to our hazard analysis. But also, of course, hazard sources. The permafrost melting is a typical scenario that was not considered in many high latitudes sites. It's a combination of hazard. Also, the combination is becoming an issue and because, again, many phenomena can happen in a contemporaneous scenario while in the past were screened out. There is an increase in frequency, of course, particularly affecting storminess and lightning, but also an increase of speed of development. So we have to think that the Ida hurricane jumped from category one to four in only one day recently in the in the in the Mexico Gulf. So just to say that hazard change is a genetic issue, but we have to concentrate on those specific parameters that make the post-major biggest challenges toward the safety of our plants. Next slide, please. I would like to support my statements on the basis of the analysis that we carried out in the agency on the databases of events that we collect. The database called IRS has been in operation since 1980 here and actually enables a very interesting analysis of the most recurrent events. This is interesting because the scenarios affected by climate change are the most common into the statistics. Meteorology precipitation and flooding are responsible for 30 over 60 reports in terms of genetic events and biological phenomenon as well, which means actually that the impact of external of this type of scenarios is growing into the list of potential incidents of incidents which happen in our sites, which are the most effective components by all types of events are electrical components, service water systems, primary system and structural protection. This gives us a good background for the understanding of the impact on safety. Next slide, please. Which are the major challenges that we recorded in our databases posed by the climate change effects? Well, this is a long list, but we can go in more in detail later. Of course, flooding, of course, high temperature damage to digital components in particular. Wildfires affecting site access and operation, sandstorms, salt sprays, impact on filters, impairment of vehicle access on site, damage to electrical station, water availability, and so on. These are a number of scenarios, of damage scenarios that we recorded on the in our database and that we have to keep in mind when we discuss on the potential, on the improvement of the protection measures that we may have in our sites. Next slide, please. Well, more in detail, we can see actually, I can show here a one very famous picture from the IPC program, for example, that was published in 2001 by NRC, where we see that the contribution of these type of scenarios to the CDF of a very large number of plants in the US has been very significant, which means actually that if the contribution of climate change is going to affect significantly the hazard in terms of flood, wind, lightning, and other related scenarios, we are going to suffer very much in terms of contribution to the overall CDF of the plants. In particular, the second slide can also show that which is the main effect that we recorded. Well, the main effect is in fact the gradation of barriers. And this is why actually most, if you see the ratio between the contribution of different, the external events into the different reporting categories, we see that most of the impact of the external events has been going into the degradation of barriers. Next slide, please. Even a more evident proof of what we are saying. This is an interesting picture based on the nuclear power disruptions. So the number of the business interruptions that we have recorded in years all over the world, in all the population of the nuclear plants in the world. And we can easily see that in the last 20 years, the impact of climate related events have been growing very significantly, in particular for river sites, where for plants I mean based on river sites. And in particular, we will see actually into the high latitude. So this is actually the best proof that something has to be developed in order to improve the hazard, to update the hazard, and to consider all the parameters that we discussed at the beginning. Next slide, please. This is the geographical distribution that I promised you to show. As you can see, most of the event have been recorded in Russia, Finland and Canada, which actually are showing this proportionally effects by climate change as compared to the other sites, and particularly in the last years. So this is a fact that there are some scenarios which are affecting our sites, particularly in the highlighted latitude in a specific way affecting the defense in depth. Next slide, please. Which is the lesson learned at this point, and which are the proposals for protection upgrading. For sure there is a need for an improved approach to scenario screening. Screening has been one of the major reasons why many scenarios have been screened out from the detailed hazard assessment, and therefore they are not considered into the design basis of many plants as they should be nowadays. We should have an improved hazard evaluation approach of course, particularly with uncertainty control, and of course with the simulation of climate change and load combination. The periodic hazard review that the agency recommends is something that should receive a major emphasis now than before. The periodic hazard review that should be carried out during the periodic safety review of any plant in the world is now becoming extremely urgent because of the reasons that we said before. There is an analysis for the assessment of the beyond design basis margin and cliff edge effect is more and is more and more important. This is a major lesson learned and we learned particularly after Fukushima, but now it's becoming absolutely a requirement even in the agency safety guides. So the analysis of the beyond design basis and the calculation of the margins, how big it has to be this margin beyond design basis. What is important is that there is also there should be an improvement of the monitoring there at the plant and in the region in relation to an event in order to support appropriate operational actions at the sites. This is something that has been pretty much overlooked in many sites in the world that we recorded that in many review missions. We believe that actually this issue should be really emphasized now. This is also regional because only by regional monitoring we can predict the potential impact of a major scenario into a site and therefore the plant can be prepared for such a type of impact. Of course, then at the site that we could have we could deploy some some specific measures like a movable on site safety emergency systems and movable protection devices. We could also have an improved the component qualification methods, but this I will say is is just on the side of the mitigation. We believe that we should work a lot also on the site of the prevention and the hazard calculation. Well, an additional provocation is that one at the end of my slide when I refer to the system resilience approach. Next slide please. This I believe is the is an important concept that has been underlined recently by even the international energy agency but also by April and so on. We realize that nuclear safety objective is not enough probably to face the challenge posed by climate changes. We also have to address the system resilience in general. So the overall energy supply system has to be able to to withstand a challenge opposed by climate climate change and in particular we have to address the climate resilience. Okay, the recovery time because these are the issues that are affecting the population. We realize that nuclear safety up to now has been addressing only the safe shutdown of a plant in case of major major challenge. We believe that nowadays we also have to address the resilience of the whole system. We realize that because because the business interruption could create major troubles to populations who are affected by by those effects. We realize that the components of the overall of the overall energy supply system may be managed by different type of administrations that's clear. They may have been designed according to different design basis, but this is probably a new challenge that we have to add to what to what we listed out in the in the previous in the previous slides. So I would like to end here my presentation opening for questions if needed, and I will be I will give it back to you maybe. Thank you very much power for very insightful presentation. We'll, we'll address questions after after all presentations. So moving to the, to the second presentation are, we have two speakers for our next presentation. Dr. Ruby Leung is a hotel fellow at Pacific Northwest National Laboratory, her research broadly cuts across multiple areas in modeling and analysis of climate and water cycle. Ruby is the chief scientist of the US department of energies energy exhale earth system model. She is an elected member of the National Academy of Engineering and Washington State Academy of Sciences. She's also a fellow of American meteorological society, AMS American Association for the advancement of science and American geophysical Union. She's the president of the AGU global environmental change bird bowling award and lecture in 2019 the AG atmospheric science Jacob Bjergnes lecture in 2020, and the AMS hydrological hydrologic sciences metal in 2022. She was awarded the deal we distinguish scientists fellow in 2021. She's a bachelor of science and physics and statistics from Chinese University of Hong Kong, and a master's in PhD in atmospheric sciences from Texas a and m university. She has published over 400 peer reviewed journal papers. Our second speaker for this presentation is Dr. Rajiv Prasad. He is an earth scientist in the earth system predictability and resiliency group within the energy and environment directed at Pacific Northwest National Laboratory. He has a PhD in civil and environmental engineering from from Utah State University. Since 2004, he has led hydrology related safety reviews and environmental analysis for supporting licensing of US nuclear power plants. He has contributed to the development of technical basis for flood hazard assessments including local scale flooding river river in flooding and tsunamis is currently developing probabilistic flood hazard assessment frameworks for local flood flooding at nuclear power plants. With Dr. Lung, he coauthored a series of reports that describe how hydro meteorological hazards to nuclear power plants can be affected by climate change. With that, I turn it over to you, Ruby and Rajiv. So in this presentation, I'm going to co present with my colleague, Rajiv, and we are going to talk about extreme weather hexes to nuclear power plants, particularly providing a regional perspective focusing on the United States. Next please. So this presentation is based on the PNNL climate change impact study that we performed for NRC during 2014 and 2019. We reviewed climate change literature very broadly and produced four different reports. The first one focusing on a national scope and then subsequently the three other reports focusing on particular region of the United States, including the South Eastern US, Midwestern US, and also the North Eastern US. So as you can see in this figure, we focus on extreme weather events and there are many different types. Some are common across different regions, but some regions also experience a particular type of extreme events. And we focus on reviewing those, how they have changed in the past and how they will project, how they are projected to change in the future. Next please. So the reason why we've been focusing on the three regions, I think should be obvious because most of the nuclear power plants in the United States are located east of the Rocky Mountains. And therefore we focus on the Midwestern US, the South Eastern US, and also the North Eastern US. And the definition of these regions, we use essentially come from the National Climate Science report. Next please. So climate change projections are produced by climate models following different scenarios of anthropogenic emissions of greenhouse gases, aerosols, and land use, land cover change. These scenarios are named by the radiative forcing, meaning the imbalance of the energy in the atmosphere. And for example in the high emission scenario, the radiative forcing or the energy imbalance towards the end of the century is 8.5 watts per meter square. And this usually is called the business as usual scenario. In another scenario that include climate mitigation greenhouse gas emission is lower as a result towards the end of the century, the radiative forcing is only 4.5 watts per meter square. These are the two most commonly used scenarios that are used in climate models to project future changes, and we would be focusing on these particular scenarios. Next please. In the first report, as I mentioned, we have a national scope and we introduced the general ideas about how climate change has and also will change different phenomena and different weather systems, particularly. For example, looking at extreme high temperature, the projection for the future towards the end of this century compared to the last, the end of the last century in the high emission scenario, show that the temperature of extreme hot days will increase during both winter on the left and also during summer on the on the right. But you can see that the projection shows larger warming for these extreme hot days for the summertime compared to the winter time. And this is partly because during summertime there's also drying, particularly of the soil moisture. And as a result, the reduced evaporative cooling can cause additional warming into the future. Next please. Now, looking at extreme precipitation, climate models or project changes, particularly increase in the future. And this is largely because with warmer temperature, the atmosphere can hold more moisture. And this is following a rule basically called the Clausius-Clapeyron relationship, showing that for each degree of warming, the atmosphere can hold 7% more moisture. And as a result, extreme precipitation is also projected to increase across all latitudes. And if you look at the figure, the green curve shows the mean changes in the future. Across the different latitudes, you can see roughly an increase of about 6% per degree of warming. But there are also quite a bit of uncertainty, particularly over the tropical area where models, some can project a really large increase of up to like 30% increase per degree of warming and some projected smaller increases. We are also of course very concerned about sea level rise. So sea level rise is because partly of the thermal expansion of the ocean as the earth warms, but it's also because of melting of the Greenland ice sheet and also the Antarctic ice sheet. So projecting into the future along the coastlines of different continents, you can see largely increase in the sea level. In the upper panel, for example, when you particularly look at the sea level rise along the coastlines of the United States, there are larger sea level, particularly in the Gulf Coast, but also increasing the east coast along the eastern seaboard as well. The lower panel showed the uncertainty in the projection of sea level rise, showing the increase between 17% and 83% range level. So in terms of uncertainty, there are larger uncertainties in projecting sea level rise over the northeastern United States, and this is partly because of uncertainty in projecting how ocean circulation is going to change in the future. Next please. Now, assuming into the United States, before we particularly dive into the different regions, let's take a look at across the US, the observed changes that has happened in the past. The three figures here show the observed change in the annual temperature on the upper left and the annual precipitation on the lower left as well as the change in the five year extreme precipitation on the right. So these are results based on comparison of roughly the last 30 years compared with the first half of the last century. So you can see annual temperature has increased almost everywhere in the United States except for the southeastern United States where there is some actually cooling and this is what has been called the warming hole. The warming hole has been studied a lot and partly related to the Kato variability that has happened in the last 30 years. When we look at annual precipitation, the changes are smaller, they are both increases and decreases, and the changes are not very significant. However, when you look at changes in extreme precipitation observed in the past, you can see increase everywhere in the United States, particularly on the eastern part where you see increases of several percent up to the northeastern United States, you see an increase of 17%. Next please. Now projecting into the future across the United States looking at changes in precipitation, let's particularly focus on the right-hand panel where we are showing the projected change in the extreme precipitation, particularly the annual precipitation for the exceeding the 90%ile, comparing the towards the end of this century with the end of the last century. We are showing the for the lower emission scenario on the left and then for the higher emission scenario on the right. You can see that as emission increases in the highest scenario, we'll see in larger increases in the extreme precipitation projected for the future. But generally you see larger change, especially for the western United States as well as the eastern United States, the regions where mostly affected by storms coming from the ocean. Next please. Now we go into a particular region for example the southeastern United States. A big concern in that region is sea level rise and that can result in these Sunday days floods or what we call nuisance tidal floods. On the left panel you can see that in the last 20 years or so, there has been accelerated increase in the rate of sea level rise, and you can see that particularly along the Gulf Coast as well as the eastern seaboard. As a result, as I mentioned, there would be, there are increasing the nuisance tidal floods, and this is particularly happening over the southeastern United States in states such as Florida as well as and also South Carolina. Over the years, you can see an increase of many days per year in these nuisance flood. Next please. Now projecting into the future on the left panel, as I mentioned before the projection for sea level rise, there would be a larger increase in the Gulf Coast as well as the northeastern United States and you can also see this very clearly. But also highlighting in the lower right panel are the projections for the tidal flood, the orange bars over there for the present day, but you can also see the projection into the future, suggesting that towards the end of the century, there would be almost like tidal flood every day in the year. So it's like over 300 days per year. Next please. Now I pass it to Rajiv to talk about the hydrological changes. Thank you Ruby. So here we reviewed several studies that use projected climate information that Ruby has been talking about to estimate hydrological changes. And really what happens in these studies is that they focus on mean annual or seasonal stream flow characteristics. While they're not particularly focused on extreme floods such as design basis floods that Dr country was mentioning these studies do provide information that are relevant to nuclear power plant operations. So this study actually looked at the results you should see on the screen, looked at the impacts of climate change on 28 southeastern US watersheds, using three what we call see me three scenarios and four see me five scenarios. And they generated daily future climate scenarios using synthetic weather generators, and then they use hydrologic models which were fed by these daily meteorology to estimate future stream flows. The study found that summer stream flows decreased for all watersheds under see me three scenarios and that can have implications on nuclear power plants that need to use water from those watersheds that a person streams see me five scenarios on the other hand only showed an increase in summer stream flow. So that was in contrast to see me three scenarios. So these results point to somewhat of a increased uncertainty when you go from climate scenarios to actually predicting future stream flow even for mean conditions. Next slide please. Okay, this slide is a little bit let's skip this one. This is only showing results from some climate change and organization scenarios what these studies usually found was increasing organization resulted in slightly higher stream flow because of imperviousness increasing, but the long term decrease in stream flow still persisted. Next slide please. Alright, so now let's move on to the Midwestern United States. So here we particularly look at projected changes in extreme precipitation in the in the Midwestern United States. So you see two panels over here, one showing the changes during summertime and the other one on the right showing the changes in wintertime. So we are comparing on the y axis, the future change in the peak precipitation versus the historical peak precipitation on the x axis. So what we are seeing is that during summertime, most of the climate models project that in the future the peak precipitation will actually decrease and therefore you see the red dogs falling below the diagonal line. But for wintertime, most of the climate models projects significant increase in the peak precipitation, as shown by all these red dogs that are above the diagonal diagonal line. Next please. We also look at Midwestern United States in terms of changes in what we call the metal scale convective systems. So these MCSS are the largest type of thunderstorms and they happen quite a lot during the warm season in the in the Midwestern United States. So this study shows that based on observation in the last 35 years, these metal scale convective systems have already been producing more precipitation shown by the blue patches of area in the middle panel showing the positive trend, as well as the extreme precipitation, the increase in the extreme precipitation produced by these metal scale convective systems shown by the lower right panel for all these different stations that we looked at. Next please. So this study also particularly look at MCSS, but based on climate model projections, particularly climate projections produced by very, very high resolution climate models of the order of four kilometer resolution compared to typical climate models that are run at roughly 100 kilometer resolution. So for these very high resolution climate models, one can actually look at individual storms simulated by the model and then they can composite the storms together. And what we show over here, the composite storm precipitation for the current climate on the left hand side, and for the future climate on the right hand side. So what you can see clearly is that in the future, the climate models project that the storms will become larger so you see larger increase in the area, as well as the color showing an increase in the intensity as well. Next please. Now I pass it back to Rajiv. Thank you, Ruby. So here we are showing results from two studies that analyze the annual maximum observed daily discharge from over 700 US year stream flow gauges in the Midwest. And they found that increases in observed flood magnitude tend to be clustered so if you look at the left figure you'll see that those there are those blue dots, and those red dots that tend to cluster together. On the other hand, the frequency of floods that is shown on the right panel is showing an increasing trend over much of the Midwest. So this is one of the findings that the study shows in the observed records. Next please. Based on that finding the army core in a 2015 study looked at what would be the effect of climate change on flood frequency go so probabilistically looking at extreme floods, how could that flood frequency go change. And the approach that took was to downscale climate model predictions to generate 90 day weather data sets that were used in turn to drive hydrologic models, and then from the model predictions flood frequency distributions were estimated. And that was concluded that the peak flow discharge increased for all future time periods so on the panel there you see the dotted line at the bottom that is the historical and everything on top of it are future conditions and they all show increases all throughout the flood frequency range. And the greatest increase they found to happen during the first half of the 21st century, which is really interesting. Advance please. So this table, actually it's pretty hard to read but I'll give you the gist of it the largest increase was up to 35% in the annual flood, and it was associated with a one in 200 chance flood event. So, as part of the mid western study we also looked at great lakes for the levels. And a lot of work has been done to understand what levels in the Great Lakes, both by the US agencies and agencies. The Great Lakes Environmental Research Lab develops and maintains runoff simulation models for the whole watershed is pretty big. While some of these models perform reasonably well as you see in those figures there. A large portion of Great Lakes water is still engaged, leading to uncertainties in the hydrologic model prediction a large part of that uncertainty actually comes from difficulty in characterizing various components of the water budget so how much you're infiltrating from the transportation, how much is getting lost to back if I have a transportation and things like that. And this uncertainty actually leads to predictions and future water levels in Great Lakes that show a range from a slight decrease to a slight increase. Next please, Ruby. Yep, so now let's move on to northeastern United States. So in this region, this region experiences a lot of extra tropical cyclones in both wintertime and summertime. So this particular study looked at the changes in extra tropical cyclones affecting the northeastern United States. And let's focus on just the upper panel as well as the lowest panel. The upper panel, the three panel show the frequency of extra tropical cyclones projected for the future, and then for the present day, as well as the change which is shown on the right hand side. And we see that if we consider all the extra tropical cyclones together, the climate models project a reduced frequency of extra tropical cyclones shown by the blue color on the upper right panel. But if we look at only the stronger or more intense extra tropical cyclones, which are shown in the lower three panels, we see that the projections suggest an increase in the more intense extra tropical cyclones, even though the total number of extra tropical cyclone is projected to be reduced in the future. Next, please. And here again, the northeastern United States, of course, the concern is sea level rise. So I'm not going to repeat this. This is again showing that in the last 20 years, sea level changes has accelerated in terms of weight, and this projected to continue into the future. Next, please. And this figure, let's take a look mainly on the left hand side. This is showing the projection for New York City in terms of the tide gauge. And on the X axis, you see the flood height in terms of the mean higher high water. And then the Y axis is the projected fraction of years that experienced the different flood height. So the blueish color shows the mid-century and then towards the ends of the century is shown in the red curve. So you can see projection of increase essentially for all different flood height, particularly towards the end of the century. Next, please. In this study also look at projected storm surge and flood levels, particularly looking at changes in tropical cyclones and the strong winds can induce storm surge. Mainly what you're seeing in terms of the blue color is the changes for the according to the present day and then the projection into the futures are shown by the reddish color. So what you are seeing is the projection of increase in the storm tide return levels, particularly for New York City that are shown over here, suggesting an increase in all levels of different flood return levels into the future. Next, please. Now I pass it back to Rajiv. So here we are showing a few climate projections for the watersheds in the northeast. And recall that Dr. Contra was talking about this issue also in the high latitudes, he was saying that riverine flooding hazards need to be reassessed because they are changing rapidly. This study actually shows why. Depending on latitude, the freezing threshold in many of these northeastern or high latitude watersheds are going to increase across the freezing threshold during various decades of the 21st century, and some of these is already happening. So that is what you see in the top panel. So the temperature increase, and those vertical lines are actually showing you different decades of the 21st century. And the horizontal line is the freezing threshold. So once this happens, what the watersheds start experiencing is decreased snowfall and increased precipitation. Plus, because of increased temperatures, you have more rapid snowmelt. So as the 21st century progresses, particularly for the business as usual scenario, the RCP 8.5 that Ruby was talking about, the flood hazards in these riverine conditions can increase quite rapidly. Next slide, please. Ruby. Okay, so let's summarize what we have been showing you for the different regions of the US. Essentially, we have highlighted several points. The first is that there have been changes in sea level that would affect coastal nuclear power plants. So changes have been observed in the past, and then changes are also projected for the future, combining the increase in the sea level together with changes in tropical and extra tropical storms. So that could potentially have significant impact on nuclear power plants. Secondly, we also look at changes in air temperature, although the changes are variable across different regions of the United States. Importantly, the increase in the extreme high temperature is basically seen almost everywhere. And so that could also have impacts on nuclear power plant operation related type of impacts. And then we also look at mesoscale convective systems. As I mentioned, the largest type of thunderstorms that produce a lot of flooding event, particularly in the Midwestern United States. We have seen, based on observational record, already see increases in MCS precipitation, but also projected into the future. That could result in increased flood risk, particularly for the Midwestern United States. And then we also look at the Great Lakes changes in the Great Lakes level, even though more uncertain, and then also changes in the seasonality of snow melt and springtime runoff in northern states that could result in changes to both flood magnitude and timing. So this current state of the information from climate science can be used to inform nuclear power plant operations related type of issues. And also the content represented based on the national climate assessment report called the fourth climate assessment report. And scientists are now currently working on the next climate assessment report that would be available by the middle of next year. So all of these information could be updated by then. Thank you very much. Thank you very much, Ruby and Rajiv for very insightful presentation. Our next presentation. Our next speaker is Mr. Christopher Hunter. Chris Hunter joined the NRC in 2002 as a member of the Accident Sequence Precursor, or the ASS program. He's the current ASS program manager and senior analyst. He has hundreds of precursor analyses, hundreds of screening analyses and has authored several annual ASS reports. Chris has a bachelor's in chemical engineering from the State University of New York at Buffalo, and was an enlisted nuclear operator in the US Navy for six years. Chris, I turned it over to you. Good morning, everyone. I think I think we're falling just a little bit behind so I'm going to try to cut this up. And so we'll just move forward. Next slide please. I'll just kind of a brief overview kind of just to frame this presentation. We believe evaluations of recent events caused by severe weather conditions have provided important risk insights. And that's part of that. Severe weather events that are very likely to lead to losses of off-site power. And so therefore, we believe a review of the current loss of off-site power loop data trends can be used to evaluate whether the more extreme events affect how they're affecting nuclear power plants. And so those trends are kind of indicators of how severe weather is affecting our current fleet. And some of the kind of key questions we're kind of asking ourselves, not necessarily that we'll be able to answer them using the existing data, but are there frequency and duration and weather-related loops changing? And also what do the results and insights from recent weather-related loops tell us? So, next slide please. First part of the presentation we'll be talking about the loop data and trends. And just for awareness, this information is all provided in a loop study completed by Idaho National Lab as part of a contract with the NRC. That loop study and past loop studies is on the Reactor Operating Experience Results and Database webpage on the NRC public site. Next slide. First, I want to talk about loop frequencies, initially, and then frequencies. And just for clarification, when I'm talking about the loop trends, we're talking about different date periods for some of these insights, so they're listed here, but just to prevent any confusion. So, the overall frequency of all loops is decreasing over the past 15 years. And this kind of decreasing trend is largely influenced by the decreasing trend in switcher related loops. There is no statistically significant trend for weather-related loops during the past decade. So, but I'll, next slide. I'll show you a figure here on weather-related loops. So this is the weather-related loops. You typically do not, you know, typically do not get a lot of weather-related loops, however, one to two. I mean, you can see here, based on the p-value of .052, that this is a nearly statistically significant trend. That's largely influenced by the trend starting at 2011 when we had five weather-related loops, which is the highest we've had in, you know, at least in decades. Next slide. This table is just showing you the weather-related loops from the past 15 years. Just know that in the previous, in the frequency and trend data, we do not include losses of off-site power that occurred during shutdown. So this is just a mixture of all weather-related loops, whether they were, they occurred at power or during shutdown, along with their durations and their cause. And you see there's a variety of causes from hurricanes, snow and wind, nice impacts, high winds, tornadoes, lightning, etc. Next slide. Loop duration. So we looked at the loop durations for since 1997 through 2020. The duration of all loops showed an increasing trend during that period. This increasing trend is largely influenced by the increasing duration of switch-yard loops. Again, switch-yard loops are happening in higher frequencies, so they're definitely having a stronger influence on the overall loop trend. There was no statistically significant trend for the duration of weather-related loops during the same period. However, the past couple of years have shown us we've had a couple severe weather-related loops recently, most notably the Dwayne-Arnold duration event in 2020. And even though it's not part of this data set, we had a loss of off-site power of Waterford during Hurricane Ida that was a pretty long duration loop. So next slide. Okay, this figure's a little bit busy, but this is showing all the different durations of loops since 1996. The weather-related events are noted in the dash marks. And this trend especially, the duration is a wider period, and I think in the future we're going to be looking at maybe making the data periods consistent for looking at frequencies and trends and even the duration. And so that could have an influence on future durations of the weather-related loops. And on the next slide we have the table of, next slide, please. Here we show the durations by loop type. We have the plant-centered, the switch-art-centered grid and weather-related loops. Again, these loop event counts include shutdown events. And they were the means, times are a log normal fit. You see the weather-related is 48 hours. This is significantly higher than the arithmetic mean. And that's largely, it's causing a skewed event. Some of these higher duration events is causing a skewing. So we're not sure exactly what they're showing us, and we're going to kind of have to re-look at this the way we're doing this in future studies. Next slide. This next part I'm going to talk about recent events. It's specifically events to analyze as part of the accident sequence precursor or ASP program. Next slide. First event I want to talk about is the Brunswick Loop during Hurricane Isias. There was a storm-generated debris that resulted in a loop to Unit 1 in August 2020. Unit 2 actually remained at 100% power. And so this is kind of a rare event in the sense of most of our severe weather events result in a loss of onset power at all units at the site. So this is one of the few, and I would say at least last decade or two, that actually only resulted in a single unit loop. The loop lasted approximately 14 hours, although there was some potential that operators could have restored power earlier. Sometimes the grid is showing some instabilities, but if they needed to, they could have potentially aligned a safety-related bus to off-site power sooner. The mean conditional core damage probability or CCDP was 2e-5. Now, and as part of that, the loop transient snares dominated risk and station blackout or SBO risk was minimal. Normally the station blackout risk is the dominant contributor when we're referring to loss of off-site power. However, Brunswick, being a multi-unit plant, they had access to, Unit 1 had access to not only their two diesels, but also share two diesels with Unit 2 and also there's an SBO diesel that can be shared between units. So that largely mitigated the risk of this event. Next slide. Dwayne Ireland, as I mentioned earlier, severe winds, approximately 100 to 130 miles per hour during a duration resulted in a loss of off-site power in August 2020. This storm caused severe damage to non-safety related cooling towers, basically totally demolished them, and also minor damage to some other buildings, reactor building, their flex storage building, et cetera. The high winds also resulted in increased debris loading to the central service water system and resulted in a clogged strainer. The operators were able to bypass that strainer and maintain the diesel generators, cooling to diesel generators. The loop lasted approximately 25 hours. The mean CCP was 80 miles for it, so significantly higher than the Brunswick event. And the station black ops scenarios were down the risk of triggers because of Dwayne Ireland being a two diesel generator plant and being a single unit that had no other resources there to share between units. Next slide. Water for loop during Hurricane Ida. So it wasn't a part of the loop trends, but we wanted to mention this loop because it was a severe loop. The high winds, heavy rain and localized flooding resulted in damage to both sources of off-site power. The supplemental diesel generator experiments have found battery due to rapid discharge after the loop occurred. However, there was definitely potential that that it started early in the event that supplemental diesel generator could have could have powered one of the safety related buses. How are both diesel generators actually work during the event so there was no demand on that. The loop lasted approximately 53 hours, which is the longest duration loop since actually Hurricane Katrina in 2005, I believe, what the cost of loop at Waterford. The preliminary ass analysis indicates a mean CCDP in the min one E minus four to low E minus three. That analysis is still in progress. The licensee is reviewing that analysis and providing comments on that. And again, the SBO scenarios were down the risk of triggers as well. And being again a single unit loop. However, the supplemental diesel generator mitigates the fact that they only have two safety related diesel generators. So it wasn't if the risk might not be as high as the twain Arnold event. Excellent. So I just want to go over some kind of general risk inside some of these I've already kind of pointed out. So the SBO risk is dominant for two emergency diesel generator plants for long duration loops. And so that's, again, not earth shattering not a surprise at all. Multi unit sites was shared diesel generators typically have much lower risk. And another point is having an EDG not included in the same common cause component group as the other safety related diesel generators can be a significant benefit. So having kind of a diverse, diverse, differently designed diesel generator can help help in that because a common cost value impact can can be a dominant contributor. So just modeling a common cost fairs across the units introduce significant uncertainties because the data do not support this modeling. So just kind of a mention that the energy spar models include common cost fair across certain systems, most notably diesel generators, but also service water pumps, etc. The common cost failure data is not collected in a manner that necessarily supports this modeling because data is collected on a single unit basis. However, you know, the, these, these equipment do share common cost failure coupling factors. So it is just something that we need to look at in the future. Loop duration has a significant impact on plants that have dominant SBO risk so the more recent events for at Dwayne Arnold and in Waterford this year, this past year. These longer duration events do do cause a significant impact, whereas looking at Brunswick due to the diesel generators and what they had is the offset power recovery time had minimal impact on risk. Flex credit can have a significant impact on the results. Again, not a real big surprise. However, some of the flux data that we have is showing pretty relatively high failure to run failure probabilities given a 24 emission time. And also the, the, the energy spar models currently right now the modeling is kind of a generic structure that has to be modified significantly by analysts. And so so this this kind of introduce uncertainties along with the data as well. I think that's it on my presentation. Thanks. Thank you very much Chris for your presentation. Our final speaker is Dr. Fernando front a Fernando is the principal principal program manager for the risk and safety management group in the nuclear sector of the Electric Power Research Institute in his role. He's responsible for multiple areas related to risk informed decision making application applications, development of research and guidance on probabilistic assessment modeling and why they're every efforts on climate change and plant resilience. Prior to joining a pre Dr front a health positions associated with risk assessment for large commercial nuclear reactors at the US and RC and for Department of Energy facilities at the defense nuclear facilities safety board. He also performed research and licensing activities at Southwest research institutes related to a potential high level nuclear waste repository. Fernando is a member of the joint committee on nuclear risk management and has supported international efforts in risk assessment your collaborations with every members as well as the international atomic energy agency, and the nuclear energy agency. He had he received a bachelor of science degree in mechanical engineering from University College in London, a master's degree in civil engineering from the University of Virginia, and a PhD in civil engineering from john johns Hopkins University. Fernando, please proceed. So let me start and go quickly to the next slide hopefully we'll we can still end in time. But I'm going to talk about a number of every activities that have been undertaken in this area. And so one of the things I want to do is highlight a couple of really key items I think the prior speakers have done a great job at already highlighting some of the things that are aligned with the research we've been doing. So the first thing to say, and this first slide is, we're looking at the impacts on nuclear in a more global scale and so actually every works in many areas not just nuclear generation. And so we're looking at the issue of climate change on the energy system as a whole, not just the generation assets, but as well as the transmission of the distribution assets. One of the things about the makes nuclear particularly special in this area is nuclear already has long history in trying to make sure it has sufficient robustness and a significant understanding of some of the stream phenomenon that can be associated with climate change. And so one of the things I'm highlighting in this slide is resiliency has been a topic that every has been pursuing as a whole, not just in the nuclear sector. Within the nuclear sector, a lot of the activities that can impact climate change have been already cover as well in the sense that the terrain is not necessarily new. But the understanding of how some of this information gets coupled with climate change and the particular impacts that I can do is something that we are adapting and moving forward on. And so seasonal and events, the change in seasonality for some areas the identification of external hazards for specific sites, given all the differences in regional impact, as well as how to optimize the operation of certain impacts that can come with different changes in the different areas of climate change such as biofouling is something that has definitely been on on work that every has been doing in the past, what has been changing is a little bit new is looking at the site specific information. The prior presenters made a great job at talking about the global impacts, of course, for different assets in different locations, and different regional effects, you have to understand how that information relates back to your site, since no site is going to have a single or unique or homogeneous impact with climate change. The other aspect is this broadening of the activity that we are undertaking that every to fully integrate the understanding of nuclear, the resiliency that nuclear power plants already have, and then the adaptation that is needed, not just within the nuclear power plant but thinking at the grid and the overall reliability of the energy system. So next slide. So in the next slide, you're going to see that one of the things that is critical to this effort has been highlighted in the prior presentations is collecting the information appropriately. And so, within the nuclear power plant framework, internationally and domestic of different countries, they have already been significant changes in terms of the expectation to collect the appropriate information. So we're not just looking at many of the events in the databases, as we once again discussed in the previous presentations, but as well considering the information in light of the overall performance of the plants. Is this changing significantly as Chris Hunter and the university presentation discussed, if there are changes, even if they're not as significant, where are they, and what's going on. And one of the staples that we are pursuing, and I think is in line with a lot of other activities is making sure the information is collected in real time, understood, and then catalog, so that sensitive understanding of is something changing what type of information is coming down in terms of the developments in the state of art and the state of practice and how does that impact ultimately nuclear power plants and then the entire energy system. Some of the efforts that we've been undertaking are in line with expectations after the Fukushima event, DNRC and other regulatory agencies have done. And we're also following the Institute of nuclear power operations guidance in terms of making sure that information is collected. So this understanding of what's going on in the area, and what are we observing all of the events and how does this link with the analysis is a key aspect. Next slide. So what's been going on in this already existing and ongoing effort that every in the nuclear sector has undertaken to look at information. So we have been performing an external hazards information compilation analysis. It's a fairly broad and structure approach to look at, not just operational events, but also developments in the sciences development, you know, such as the ones shown by the Pacific Northwest colleagues, developing in studies and the overall understanding of the global climate change analysis as well as regional impacts. And so we have been doing this for many years now in the last five years actually. We have collected and observed some of the same events that have been mentioned in the past, so I won't receive those. But we collect more than just that we collect changes in the information changes in risk, risk analysis is being performed. And we observe that for the most part plants have maintained the margins already existing in their design basis and so a lot of the events such as the straight wins the Rachel event that Chris mentioned were identified as interesting items from a climate change perspective as well from the general external events perspective, and the margins up to still over well over 100 miles per hour is this in many of those events and so again this is not to take the information as black and white, this is mean something is changing or not and doesn't mean that we can ignore or use information in a directly actionable way is not the overall intent of this to understand what information means how to put it in context and ultimately understand if the margin is significantly reduced or not at this point that we haven't seen the margins be significantly exceeded. But again it doesn't mean that climate change, you know, is not happening or that we believe this isn't something that adaptation shouldn't be considered for. So next slide. So we also did a white paper that was published recently, which focuses on the resiliency of nuclear power plants and again, this is the beginnings of developing of the understanding of the global climate change impacts, as well as the margins the plants have and the operational insights that we begin. And so one of the things that is very important to distinguish here is a lot of times when we look at data, we do see that the plants have to power down or have to shut down to a safe shutdown in advance of a event or potential impacts of the event may cause or may be causing in the beginning of the hazard. And of course, there's two aspects of this one is operational safety of the events that we have seen that can be impacted by climate change. We've seen that the plants can respond and have sufficient resiliency and robustness at this point in time as Chris indicated with his data and some of his discussion of the operating experience. Now, again, we were trying to understand not just what we're seeing, but what we might see in the future and connect that to the climate projections that we have gather and continue to be gathered by larger organizations such as the IPCC. And so, and then what a direction in terms of the framework that this needs to pursue to make sure that the adaptation of the resiliency continues to understand new information, including if future information may change some of the insights that we're having. And so, this effort also was strong in looking at not just the operational safety, but also the operational impacts that this can have in terms of lost electricity production. And so those two can be different. I mean, the plant can work, you know, operate safely through extreme events, but loss of generation is still something that can be a concern in terms of understanding what the risk is. So it's still risk analysis and it's still understanding what the overall risk currently and potentially the future is, but it's understanding that there is a two prong aspect to the issue. Not just, you know, whether a nuclear power plant can withstand some of the most extreme events that we may see in the future with global change in a regionalized way, but also trying to understand whether the operational side of, you know, the expectations that ultimately the sassets are expected to provide safe and reliable electricity source in terms of how that gets impacted in the overall picture of the energy system as a whole. And so in the next slide, we show a little bit of the insights that are contained in the documents I mentioned in the previous slide. And so we looked at some of the same data overall that Chris Hunter discussed in the US. We looked at it in a global level, as well as looked at it in terms of lost generation. And so not to take too much time here. Ultimately, we see what, for example, we saw in an IAA report in 2019 adapting the energy sector to climate change, which is the events, ultimately the extreme events that we may associate with climate change moving forward are very small in the overall picture. And so the vast majority of events we see at nuclear power plants are not extreme events. Number one, number two, even those events that we've seen where there was some impact, sometimes the impact is really lost generation in terms of grid instability that causes the grid operator to pass the plant to downpower or potential anticipatory shutdowns to make sure the plant can be secured and stay safe during the event, which again doesn't really speak to much to impacts to nuclear safety overall at this point in time. But it also speaks to electricity power generation is ultimately an important aspect of what needs to be considered. So we did look at the events and calculated a fairly high level but insightful study in terms of how many hours, how many megawatt hours per year were lost. And again, considering that plants, nuclear power plants in the overall energy system as generation assets provide already have a very high capacity factor. So even with plant shutdowns for refueling outages and so forth, the plants are already observing 95% capacity factors. With some of the unplanned shutdowns that we have to observe, even those that are not necessarily related to other events, the reduction goes down to 92.5%. And so the plants are still operating significantly. And that's a good thing because that means the power generation is also already significantly robust. But it's something to continue to look at, you know, overall, the nuclear power plants are producing, you know, true, you know, even more extreme events, the power that is needed, particularly in say a snowstorm homes and other facilities still need electricity, be able to operate for those events. And they're operating safely. And so far, we haven't seen a significant impact in the loss of margin. Again, the purpose of this discussion is not to say this doesn't mean, you know, that climate change is not important is to understand the current margin, understand whether it may be changing. And as we collect information, continue to be informed as to what needs to be done if adaptation is needed. So next slide please. So, some of, you know, the prior presentation that already kind of touched on the different impacts of climate change can have. And so clearly, for climate change, some phenomena that the plants have to be protected against, you know, our cover some are not necessarily impactful of climate change, losses of power can happen from a number of issues, some of them are not related to weather. And that's something as Chris Hunter highlighted in the NRC presentation can be looked at in some ways into the risk models that we have for nuclear power plants. And in some cases has to be adapted to be able to understand that better. And the white paper and some of the studies I was done in the past cover in detail changes in our temperature extreme storm events already in the design basis and from a probabilistic hazard point of view, sea level rise and cooling water impacts we can see charts can be impacted from weather events we understand in systems that are interfacing, which large waters of water can be impacted by changes in temperature by extreme phenomena. And so part of the question here is not just to say, well, we see a change in some of the natural phenomena coming but how can that impact the plant and then not just how can it impact the plant in terms of well, a loss of outside power can lead to a significant event, but how can the particular phenomena be considered, both in terms of the impacts to the site, as well as if it is our temperature, does that impact thermal limits that are imposed for a number of reasons on the amount of heat that is rejected to the environment and does that impact the operational aspect and ultimately electricity generation as well, from a perspective of the asset of the grid, the energy system and the global impact of climate change. So next slide please. So one of the things that we're trying to do is provide a fairly structured process to cover the information and to cover what we think is the best approach to go about this. Again, without going into all the detail and the time we have remaining. The thinking here is overall is there is a lot of good information already in the development of the science on the global climate aspects. What hasn't been as well developed and probably needs more information is saying that there is climate change coming is not really the end of the story from a proper way to deal with this complex issue. What is important is to gather the information continue to develop the science. There is a lot of uncertainty in some of the estimates and overall and dealing with extreme events and trying to understand whether there is a significant change, whether it covers something that has already sufficient margin and then highlight the vulnerabilities and ultimately develop a plan. And so if something is going to be impacted. What is that is that the most important thing that can reduce the risk and how can the nuclear energy system within the grid within the energy system continue to perform as key functions in provided safe electricity and survive potential climate change impacts. So next slide. So in the time we have available I won't cover everything that we're planning to do but there's a big activity I'll cover in a little bit more detail next that is very large and it I think our colleagues of Pacific Northwest already did a great job in discussing some of this. We are planning workshops we're planning collecting a lot of the community such as colleagues from the National Labs the NRC International Organizations NGOs to come together and look at this information as a whole and bring it together within the framework that can be used in terms of connecting the data to vulnerability assessments that truly understand the risk impact this phenomenon can produce in the future and ultimately develop a plan that those responsible for the assets can implement and efficient and and most appropriate manner. Next slide. And so the initiative I'm discussing is called ready stands for every climate resilience and adaptation initiative. And it is divided essentially works frames that will capture a lot of the concepts I mentioned, looking at the data understanding data continue to develop the science and support that aspects of the analysis. Look into a vulnerability assessment not just well is climate changing and can that impact our plans but how can it impact to what level and what does the analysis of the rest which ultimately needs to include both the hazard potentially changing as well as the existing margin and what can be done to improve if anything the resilience of the asset into one place and then ultimately the works frame tree just highlights the idea that there is many aspects just not just beyond looking at the global climate change data. But analyzing the vulnerabilities and then providing a framework that can both communicate to those that need to address potential challenges or questions about the capacity to deal with this issues. Manage that information continue to monitor and continue to consider what it does and then look at the options that are in front of them in terms of what can be enhanced what can be made more robust and how can operations continue to run efficiently while ensuring that they are cover for climate climatic changes. So next slide. So key takeaways I want to share with you here. The main one is that, you know, the robustness of the nuclear power plants is exists. It has been enhanced in the last 10 years, it will continue to be enhanced and understanding climate change is part of the continuing improvement of the activities that nuclear power plants have performed in the many decades of operations. So that doesn't mean that, you know, there isn't a need to continue to look at this issue. I think there is a need to make sure that it is informed that ultimately the high reliability and the power plants operate is considered within this context, and that adaptation is part of a risk informed approach that considers what can be done to provide the best improvements for risk, as well as make sure that improvement in risk reduction risk is justified under a science base and a technical engineering approach that looks at the best pathways to make sure that the assets continue to provide electricity in an energy system, a globalized approach. And so that's the end of my presentation and I'll take questions. Thank you Fernando. And all the speakers. We are almost out of time and we have received many questions. I'm going to start asking some of them. I don't know how far we can go but I'd ask the first question from Paulo. How do you reconcile the increase in interruptions with improved capacity factors and energy production by domestic nuclear facilities over the same time frame. I would say that this, of course, the picture that I presented is related to the worldwide population of plants, so not only the US, so this is clear. And in any case, my answer has to be related to what other speakers clearly stated that the business interruption related to extreme weather events, they have usually a very short recovery time. And this is why actually the capacity factor doesn't go down too much, even if we can count an increasing number of business interruption events. This is a very simple answer I would say. Thank you very much. Perhaps we have time for one more question. So the question is for Ruby. How does the extreme precipitation increase in all regions comport with those US regions that are observing severe drought? In the view of the questioner that doesn't seem to be consistent, are we observing severe drought and severe precipitation in the same area? If so, is there a risk from severe heat or drought? Yeah, I think this is a very good question. Yeah, often asked like, why do we expect like the two extremes might be happening at the same time and in fact it is possible that in the same regions in the future, it could experience an increase in drought as well as increase in extreme precipitation. And that's because drought is mainly caused by the heat, the increase in the evaporation, but the land surface is not able to provide enough of the moisture. And therefore, there is this increase in the aridity and drought. But at the same time, there could be weather systems that happen where the moisture is transported from the ocean over land. And because of the warmer temperature, there is more moisture in the air. And so in the right condition, the storm can produce more extreme precipitation because of the increased moisture. So this is actually projected to happen in some regions, both extreme dry and extreme precipitation. Thank you very much. And unfortunately, we are out of time and we don't have time to go over many questions that we've received. I like to thank everyone who attended this meeting. I'd like to thank you for all the questions you've sent. I'd like to especially thank our panelists for their time, informative presentations and their valuable insights. You can see on the last, if it's up on the last slide that we have, you can see our contact information. If there are any questions, feel free to reach out to us. And with that, our session is closed. Thank you very much.