 Welcome to a special edition of RCE. We've moved back our regular interviews due to the situation in Japan and the situation with the Fukushima power plant. We have taken the opportunity to get a hold of some of my old faculty. I have a degree in nuclear engineering and we are going to talk about what happened at the plant and just better inform people that what kind of worries there are for the people in Japan, the people working on the plant and those of us around the world who are going to be affected by this. Yeah, thanks, Brock. This is, as we said, a special edition, but we do have that E in our name, Research, Computing and Engineering, and so we are talking to some nuclear engineers today. And really, there's a lot of information out there in the news media and whatnot, and I'm not sure that all of it is accurate, so I figured it would probably be good to talk to some people that, you know, from a well-established higher institution and with good educational pedigrees and actually are bona fide experts in this area to find out, you know, what's the real scoop? So, let's talk some technical details here. Yes, and also as a little side note, this is the first time I've had somebody that I've taken a class from on the show. So, our two guests today are Dr. Mike Hartman and Dr. Kim Keerfoot, both from the Department of Nuclear Engineering and Radiological Sciences at the University of Michigan. So, doctors, thank you very much for your time and take a moment to introduce yourselves. Mike? I was trying to be kind. Well, thank you for having me. My name is Professor Mike Hartman and I'm an Assistant Professor in the Nuclear Engineering and Radiological Sciences Department at the University of Michigan. My work focuses on the use of neutrons as a probe of atomistic processes, but I do have some tasks of both operational and theoretical experience in nuclear reactor design. And I'd be glad to answer your questions today and see if we can't clarify some issues with the current media reports that are out there. Hi, I'm Kim Keerfoot. I'm a Professor of Nuclear Engineering and Radiological Sciences. My area is special to your radiation safety as well as nuclear instrumentation. My research is focused on the development of passive dosimeters for monitoring networks. You should also note, because the situation is changing rapidly, we are recording this on Friday, March 25th. So, if anything occurs afterwards, it would not be reflected in this. So, before we get into this, can you get a little bit of a timeline of the events that happened that caused the Fukushima plant to be in a situation it is currently? Sure. So, I'll address this first. The magnitude 9 earthquake happened and when that happened seismic sensors at the various nuclear plants on the coast of Japan picked that up, it was sensed and those reactors were scrammed. And when I say scram, the automatic control system which shuts down the nuclear process occurred and so within seconds of the earthquake, the nuclear process within the reactor was stopped. And then subsequent to that, the tsunami came onshore and the wave that was onshore was beyond the design wave that the plants were built to. And apparently as a result of that, the diesel generators at the Fukushima-1 site were overwhelmed by that. And it's not clear whether that means that the diesels themselves were taken out, whether part of the switch gear that connects them or whether it was some ancillary system like the fuel oil system, but at any rate, the diesel generator capacity was rendered inoperable. And then subsequent to that, we've seen issues with cooling the core as well as the spent fuel pools. And it really has nothing to do with the nuclear process. Again, that was terminated and shut down. But we're looking at the removal of decay heat that exists within both the fuel in the reactor pressure vessel as well as in the spent fuel pools. From the viewpoint of radiation safety, the radiation levels on the plant sites have been jumping up and down. They have gone from very small levels to levels that would cause radiation sickness in time period with about five hours. However, the levels don't stay high very long. The recorded levels seem to be correlating with different transients and different changes that are going on within the reactors as well as in the spent fuel pools. In terms of public dose management, the initial exclusion zone was about 20 kilometers. The United States then put an exclusion zone of 50 miles for U.S. citizens. As of this morning, the Japanese increased their exclusion zone to 30 kilometers. The evacuation of the public was quite rapid, which was a really good news from the viewpoint of monitoring the public dose, minimizing the public dose. The evacuations were very timely in terms of minimizing public dose. There were 11 workers injured by some of the hydrogen blasts. Of these, there was one death. For the first week, the workers were able to operate under regular normal operational limits for occupational exposure. As the situation became less certain, permission was given to Tokyo Electric Power Company to operate under regularly accepted emergency limits for worker exposures. Recently, releases were noted as far away as Tokyo. In addition, this morning and last night, Iodine 131 was detected here in Michigan. So what is Iodine 131 and what does that mean that it was detected in Michigan? Iodine 131 is one of the fission products that would be released in incidents such as this. It happens to be one of the two fission products that we worry about for health and human safety. The other one is Cesium 137. Iodine has a very short half-life of about eight days, and the main effect that we worry about is thyroid cancer. So one of the nice things about this is that compared to dumping a hazardous chemical into the atmosphere that stays there, the radiation will die away. So a half-life of seven days means that half of the iodine is gone and is not coming back in seven days. That right? That's exactly correct. And since the reactors have been shut down, the total amount of iodine that could be released is decreasing in that same way. There's no further production of iodine going on in the plants without criticality. Now how much was actually detected in Michigan and elsewhere? Are these amounts to be concerned about even with a short half-life? What is the exposure risk? These are absolutely not amounts to be concerned about in the slightest. The issue is that we are able to detect such tiny amounts of radiation that the releases would be detectable across the globe at levels that are far below those where there would be even the slightest measurable increase in cancer risk. So when we hear reports that the level of activity in Tokyo is some multiple, sounds like a massive amount of increase over the background level of radiation, because radiation is around us all the time. Are they at levels anywhere in Japan close to the plant that is of worry to the public? The amount of radioactivity detected in water in Tokyo was such that if you consumed that water for a very extended time period, that the increase in dose would be equivalent to the difference in cosmic radiation between living in Los Angeles and living in Denver. That's a very small difference in dose. Minus some societal differences as well. Yes. Okay, so that's good for people worrying that it may have friends in Japan that yes, it's gone up a lot compared to what is normally in that area, but the amount is actually still nothing to worry about. So far the amount is nothing to worry about. The increases are far less than those that are normally gotten from typical medical procedures. In addition, food contamination only gives large doses if you consume contaminated food for an extended time period. Drinking small amounts of contaminated water at the highest levels I've seen detected would have negligible effects. In one calculation that I've looked at, it would take 58,000 glasses of water contaminated at the level seen in Tokyo before you would even begin to worry about a possible excess cancer. That's quite a bit of water. So it doesn't sound like that's at least currently as of this recording, not really an issue right now. Let me ask a couple of logistical questions here. So we had a nice timeline there in the beginning, but what kind of parameters are nuclear plants designed for, particularly in seismic areas such as the Ring of Fire in the Pacific and whatnot? What are they designed to withstand and how did we actually exceed that in this case? In terms of the design of a specific plant, they're designed on a plant specific basis. So when a utility wants to cite one of these reactors, they do an environmental study, review environmental conditions, determine what accidents are credible, and then design the plant and associated systems to withstand those credible accidents. And what we're seeing now is that the credible accident that was chosen for the Fukushima plants is either a magnitude 7 or 7.5 quake depending upon where you get your information. And the 9 simply exceeded that. And it should be pointed out that it wasn't actually the ground accelerations that caused the issues with the plant. It was the subsequent flooding of equipment as a result of the tsunami. So the tsunami was well above the design tsunami that everything was built around for the plant. So you mentioned that before that the tsunami took out the diesel generators and that had something to do with getting rid of the decay heat. What is decay heat and why is that a problem? Sure, actually we've already touched on it. So in the fission process, every time a fission occurs, when a uranium nucleus is split, we release 200 million electron volts worth of energy. And to put that in perspective, if you do a chemical reaction, the release is about an electron volt. And so every nuclear reaction is about 200 million times more exothermic than a chemical reaction. And that's exactly why we like nuclear for power production. It's a very compact, efficient way of producing large amounts of heat. And when we talk about decay heat, what we're really talking about is that the uranium nucleus fissions, typically pictured as splitting into two nuclei, then we call those fission products. And we've already talked about iodine-131 and cesium-137. Those are two examples of fission products. However, there literally are hundreds of potential fission products that can be emitted from the fission process. And if you look at the fission process, those fission products that are released are neutron rich. And so what that means is they're not stable nuclei, and they're all going to radioactively decay towards stability. Some with half-lives as short as fractions of a second, and others with half-lives that are tens of thousands of years. So on a very wide-ranging timescale, these things will decay. And the radioactive decay, again, moves them towards more and more stable nuclei, and eventually they will decay into a nucleus that's radioactively stable against radioactive decay. And so when we talk about decay heat, what we're really talking about is the energy that's released as these fission products decay towards stability. And that exists, again, for periods of time that are years. So how much heat are we thinking about here? Is it something that we could cool with the air conditioner in my car, a big fan, or is it a significant amount of heat? So that's a good question. Again, because many of the half-lives for these things vary from fractions of a second to tens of thousands of years, it turns out that the decay heat initially after a reactor is shut down is quite high, because you have a large inventory of short-lived radioactive nuclei that are decaying, but eventually they're going to decay, and they're going to decay quite quickly into longer-lived radioactive nuclei. And so the heat generation actually decreases as a function of time. Immediately after a reactor is shut down, the decay heat is 7% of whatever the full power operation in the reactor was. So to keep it simple, if we take a 1000 megawatt reactor and we immediately shut it down, so we terminate that nuclear process essentially instantaneously, we're going to be left with 70 megawatts of heat that are produced from the decay of these fission products. So as a percentage of full power it's quite low, but in terms of a total heat output that we need to remove, 70 megawatts of heat is still a large sum of heat to be removed, and it exists even in the spent fuel pools. So inside of the spent fuel pools is fuel that has resided in the core. It's been used during reactor operations. And then subsequent to that it's been removed and put in this fuel pool for either later use in the reactor or just cooling for eventual reprocessing or disposal. And that fuel is quite old, meaning that it hasn't been operated in the reactor for a long time, but there is still decay heat associated with that because now the longer lived radionuclides are still decaying and the energy from that radioactive decay process is deposited in the fuel rods themselves. So we're looking at needing to remove a lot of heat, so we need active cooling systems to cool these things and the generators dying remove that cooling capacity. Well, we should be clear on that. So the plants that are in operation, the 104 plants here in the U.S. and the plant of the design that we're talking about in Japan would be what we call a generation two plant. So all of the heat removal systems associated with accident scenarios in those plants are active. And active in this sense means that I need to have pumps and valves and power to operate those things in order to mitigate accident scenarios. Next generation nuclear plants that are being proposed to be built here and elsewhere in the world will have passive safety systems, which will have the ability to maintain core cooling for 72 hours following any event. But you're quite correct. In this case, the systems that were in place to remove the heat are what we would term active systems. So then let me ask this. If the Fukushima plant was a newer design, would we be having this discussion right now? If it were a design that incorporated these passive safety systems, and by definition passive safety means that there has to be no operator intervention for 72 hours. So an event happens and just by actuation of these passive systems, the plant will maintain the cooling for 72 hours. So I can't say that the event in Japan wouldn't have had consequences, but had there been passive safety systems, there would have been no need to respond for 72 hours and there would have been additional time to put some things in place to respond to the accident. So I think the next generation plant, I can say with confidence, I think would have gone through the accident. The initial stages of the accident, perhaps better than the plant that is currently there, but I think it's impossible at this point to say throughout the whole accident scenario would the ultimate performance have been better. Now such passive systems still must have their own design limits too, right? I mean this is engineering after all, there's no such thing as a free lunch. You design for what you can pay for and what you think will happen, such that even if there was a large enough tsunami that still could have taken out a passive system. Is that right or is it a fundamentally different kind of system protected differently? So the passive systems, you're right in that they would be designed to meet whatever the credible accident portfolio that the plant was designed to withstand. So they would have seismic restraints and would meet the design criterion to withstand any of the credible accidents. These systems are contained inside of the primary containment and if we look at what happened to the Fukushima plants, it wasn't the primary containment that was a problem, right? Even this older generation 2 plant that is the Fukushima design, the primary containment performed extremely well throughout the ground accelerations associated with the earthquake. It really was the tsunami and the ancillary equipment that was providing power for these active safety systems that was overwhelmed by the tsunami. So I think in this case the passive safety systems would have fared better because they're designed to be within the primary containment and that was unaffected by the current incident, the earthquake and subsequent tsunami. Interesting. So we've been talking about this as the older design in the last generation. How old are these plants? What kind of generation are we talking about here? Fukushima 1, let's see, initial criticality was October of 1970. So it's a little bit over 40 years old. And that was kind of the heyday back in the 70s when a number of plants were being built. So it was designed for a 40 year life cycle and it was near the end of its design life. So let's get back to cooling fuel from a shutdown system. We keep hearing about these spent fuel pools. What are they and why are they a worry? The spent fuel pool, again, when the fuel is used in the reactor, typically will be used for three reactor cycles. And when we say cycle, these things are typically 12 to 18 months depending on plant design. So the fuel will be loaded in and it will be physically moved throughout the core through three of these cycles and then removed from the reactor pressure vessel in the primary containment and put into the spent fuel pool. And again, it's necessary for the cooling of the fuel. So the spent fuel pool really is a large container of water that acts as a heat sink as well as a radiation shield for the fission, not the fission, the decay of radioactive nuclei that's taking place inside of the fuel. Why are they significant? Well, it's significant in this case because you have to maintain cooling in the spent fuel pool in order to keep that heat transfer from the decay heat from the fuel rod into the water. And if you lose that, then the fuel rod can heat up. And when that takes place, you can mechanically challenge the fuel pin. So the fuel in these is a uranium dioxide, essentially a ceramic, and it's contained inside of a zirconium tube. Well, as that heats up, you can challenge the zirconium tube, cause either cracking or failure of the zirconium tube. And as soon as you do that, any of these hundreds of fission products that may be in a gaseous form can leave and indeed that's what you see from venting of these plants is that gaseous fission products are allowed to escape out the stack and we subsequently see them in water systems in Tokyo and elsewhere over in Japan. And you also have the other fission product inventory that's in there as well, right? So if the rod gets hot enough, there's the potential to release some of the additional fission product inventory beyond the gaseous as well, and that's a significant concern. So a lot of people are seeing pictures of the reactor buildings crumbled from the hydrogen explosion. Where does hydrogen come into play in this whole accident and why is there such a volatile gas around? When the fuel heats up, so the zirconium that's surrounding the actual uranium dioxide fuel pin, when that gets hot enough somewhere around, let's say a thousand degrees C, you can get a zirconium water reaction. So the zirconium undergoes a rapid oxidation, becomes zirconium dioxide, and in that process you release hydrogen gas. And so again these fuel pins that are uncooled can heat to the point that they actually react with water to produce zirconium oxide and the hydrogen gas that has led to the hydrogen explosion explosion that we've all heard about in the media. Alright, so shifting gears a little bit here, let's go back to the current events here. So what exactly is still going on? What are they doing to clean up and to repair and whatnot? What are the ongoing efforts that are still occurring? From a reactor plant standpoint, they've restored power to the units and that's a very good thing because it opens up many more options in terms of combating any issues that are taking place at the plant. But the most important things are to provide water to the course and in the case of Fukushima 1, 2, and 3, they're currently doing seawater injection as well as keeping the spent fuel pools cool and they're doing that through a combination of cooling within the pools as well as the spraying of water from water cannons or helicopter drops like we've seen discussed in the media. We're having continuing issues of managing worker doses. In particular workers are going to places where they may not have gone before. These places might not be completely characterized. This is one of the reasons I believe this morning that we had some skin dose to workers entering an area for the first time after some stuff had changed. These stabilization processes, you have a lot of uncertainty in worker dose. Once the plants are fully stabilized and characterized, then robotics and other methods can be brought in to cut down on worker dose substantial amount. So at this point would you consider the plants in a safe condition? From a mechanical system standpoint, there's still work to be done. I think from what I can glean from the media reports and elsewhere, it sounds like the reactor pressure vessels and the cooling of the cores, that seems to be going forward in a positive direction. The status of the spent fuel pools and the proper cooling of those still seems to be somewhat of an issue and I think going forward in the next week or so, that would be my hope that they are able to solve that and provide adequate and sufficient cooling for both the reactors and the spent fuels. At that point, I think we can take a step back and as Kim says, we can characterize radiation fields, we can determine the status of systems and then come up with a good plan moving forward on how to minimize radiation release and how to recover the plants. So let's talk about the workers at the plant. What kind of risks are they experiencing? What kind of dose levels are they being managed at when we hear that they're receiving greater than the allowed annual dose for radiation workers in the U.S.? Is this a level to be worried about? The government and the power company appear to be behaving in a very responsible manner. They are attempting to keep worker doses below the international limits for workers under these circumstances. That limit is a factor of four protective for what are called deterministic effects. Those are high level dose effects. So they could still go a factor of four higher than their limit and not see effects on their blood. The highest doses reported to date are about two-thirds of the limit. Even so, I can't verify the highest dose that I've seen officially reported. There's a factor of 20 protection in the international emergency worker limit. That factor of 20 would be if someone went 20 times the limit then you would be getting in the range of radiation sickness. So those are pretty good safety factors from the viewpoint of operations. They seem to be working. The workers are being rotated in and out. They're being backed off when radiation levels jump up. But this is not a stress-free situation. The workers have to be very careful and vigilant to maintain their doses lower than the limits. So in terms of measuring radiation, we hear it's tasteless, colorless, odorless. How accurately can we actually measure radiation so that we know that the levels we're seeing are accurate and the amount of radiation these workers and public are getting are accurate? Although radiation is odorless, tasteless, you can't see it. It's in fact one of the absolute easiest things to detect. You can detect the decay of a single nucleus. The workers at Fukushima have a lot of experience using standard radiation detectors. They have both fixed detectors around the plant as well as portable detectors that they know how to use. But we'll be using them. In addition, more monitors have been installed on the site to track what's going on. I wonder if you could tell us a little bit of something. You hear it on the news and I admit I didn't really follow it closely but there's something about potassium iodide tablets. What are those and how do they come into play here? Iodine 131 or all iodines for that matter are taken up by the thyroid. The thyroid is like a sponge for iodine. It can only hold so much iodine at any given time. If you fill that sponge up with stable or non-radioactive iodine, then radioactive iodine can't get in. If radioactive iodine can't be taken up by the sponge, then the sponge is not going to get any radiation dose. No radiation dose, no increased risk of thyroid cancer. Potassium iodide has iodine in it of the stable variety. If you just take within either four hours before or within a few hours after exposure to radioactive iodine, if you take potassium iodide, then it blocks the thyroid. It fills up that sponge. It prevents dose from iodine 131. The problem with potassium iodide tablets are that they have other health effects. It's not a good idea to take a potassium iodide tablet unless it's under the direction of a physician or authorities. There are people who have iodine allergies. For those individuals, taking potassium iodide would be a very bad idea. One interesting thing is that most of the dose due to iodines is from the ingestion of iodine 131 in foodstuffs. Iodine settles on the grass, cows eat the grass, and the cow's milk concentrates the iodine. Then people drink the milk. It's through ingestion rather than inhalation that we take in iodine. The amount of time it takes for the iodine to get into cows' milk is a couple days, so there's usually a warning. There's also warnings, such as we saw in Tokyo, about contaminated water supplies and avoiding iodine intake that way. For the most part, potassium iodide tablets are not that useful for reducing dose. It's reducing consumption of iodine 131. Most of the 4,000 cancers from Chernobyl were thyroid cancers in children. A lot of those were preventable by having the children not drink contaminated milk for an extended time period. When we hear these stories that potassium iodide sold out in California and stuff, but we haven't heard anything from authorities and from the measurements you are seeing, we should not be taking those tablets currently. There's no reason to be worrying about the levels of iodine we're seeing currently. I would advise against taking those tablets. The levels that we're seeing now do not justify taking the tablets, and the tablets may have adverse health effects. So you mentioned the thyroid cancers in the children that were consuming food and milk around Chernobyl. How does this accident compare to the Chernobyl accident? The releases are much, much lower than the releases in Chernobyl. At the current time, it is premature to make a comparison, but it appears that the releases have been much, much less. One interesting thing about Chernobyl is that the total numbers of cancers that were predicted afterwards did not materialize. Even the most conservative scientists, given the total releases and calculating the distribution to the population of Europe, those scientists predicted 24,000 or more cancers, and all that was really seen were 4,000 thyroid cancers. And most of those, again, were preventable, and most of those were in children. The interesting thing about low-level health effects is that we can't measure them. You can't go on and say there were 500 cancer deaths as a result of that. We have to calculate them. The risks due to exposure to small amounts of radiation are so small they are postulated rather than actually counted. Everyone is still pretty much in my field puzzled by the lack of incidence of cancers in Europe following Chernobyl. So really, so far, the injuries from the plants come from the hydrogen explosion. Really, the effect on human life currently by the issue with the plant is small compared to the impact on human life from the tsunami just coming through and flooding over the land in the country. Yes, I think that's the same thing to say. I mean, what we've seen so far in terms of injuries to plant workers have been workplace injuries mostly due to trauma from the explosions. And ultimately, we'll have to wait until we can get in and characterize the amount of radiation that was emitted and the extent to which it was distributed through the environment to really make an assessment on what the ultimate environmental impact will be. At the moment, the health effects on the general public are like a Godzilla. If you remember, Godzilla was the sleeping monster that got awakened by the atomic bomb and then trampled all around Japan terrorizing people. Because it's premature to make health risk assessments and because in so far as we know, the releases have been relatively small at the date of this conversation. I would characterize them as a figment of people's imaginations. They are a Godzilla. That does not mean that the additional stress being caused by the uncertainties surrounding the plant and what is going on there are not significant. Certainly, we want to not have people be excessively stressed about things but vigilant and responsible. So as a side effect of this whole situation, what has happened to Japan's power capability? Are there other nuclear power plants that have quote-unquote picked up the slack? What has this done for the rest of Japan on a logistical basis? I believe Japan has 54 plants and at the moment the loss of the three, just to be clear, at Fukushima-1 there are six plants. Units 1 through 3 were operating at the time of the tsunami and units 4 through 6 were in scheduled refueling outages where they do the shuffling of the fuel and move some new fuel into the core and some older fuel into the spent fuel pool. So there is excess capacity in the way of nuclear power plants and presumably some of the excess capacity is being brought to bear. Certainly they will miss the presence of plants 1 through 3 on the grid but I think that that is something that they can make up for from other sources. And certainly in the area of the tsunami that may be a nonsensical question because there is no transmission lines, much of the infrastructure has been destroyed and so even if the plants were available there likely is no capacity to get it out to the public for use in that region at this point anyway. Reactors sit inside a strong set of containment made out of steel and concrete to withhold radiation and handle the plant in the event of an accident. Recently there was some reports that that primary containment may have failed. So the recent news reports suggest that the primary containment on unit number 3 may have failed and those seem to be based on the fact that these workers were exposed to water that contained 10,000 times the normal activity at water that they would expect to see at one of these facilities. And while it certainly would be uncommon to have water that had that kind of activity, I think it's premature to assume that that means that the primary containment which houses all of the reactor pressure vessel and the fuel inventory that sits inside of the pressure vessel has failed. Within one of these plants there would be several release paths that could lead to elevated radiation levels in water and none of those may involve failure of the primary containment. Certainly if the primary containment has failed then the elevated levels could likely be associated with that. But keep in mind that you've got to spend fuel pool and a number of fluid systems that may have been challenged throughout this accident scenario. So I would caution people that seeing these elevated radiation levels in the water doesn't lead one to conclusively believe that the primary containment has failed. Dr. Hartman, Dr. Kierfoot, thank you very much for your time for explaining the situation to us and hopefully we can get some good information out there for people who may be worried. Thank you. Really appreciate your time. Thank you very much. Pleasure being here. Nice meeting you guys.