omm remembering everybody in the last few lectures we touched upon the safety principles that we follow in citing a plant, designing a plant, commissioning a plant, operating a plant and so on. மற்றும் பார்வுகளை நடத்துக் கொண்டு இந்த சிறிக்கை வருப்பத்தில் நீங்கள் எடாத்தி வியாளைகள் என் சண்டாட்ச அனைக்கு இங்கே விஷதம் என்னுடன் attracting இந்த சுறிப் போள்மில் இந்த சிறிக்கை தெரியுகிறார்கள். ஆனால், இந்த மே wähரல்தில் கொண்டு salted பலிப்புவிலியினை வெளி yılற்சில் எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எது எ நான் நாம் வரணைப்பதிய விரையாடித்திருக்கிறோம் என் மிறைப்பள carriers реலவன 지ராவியற்றி சகுந்திருந்திருந்திரு ஜனிலியavaisத்திரு வைத்து எப்படிக்குமெல்லாம் பிரம் இருக்கிறது��மதீதுதல் இனிறையம் ஏற்சந்திரெண்டும் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல் நிறுதல இர்eyeற்டேன் இருக்zelிருந்து சொல்லாமதற்குconsciousness ராப்சோி ரேக்கட்டுற பதுதில் கத் удобடை கிடினம் இந்த உண்மையில் வந்திருக்கிறது நிறுத்திருந்த சந்தியாண swimming¿ தருப்பு நிெமூசம் செய்யில் சக வேண்சித் தொடர்ந்து ஆகின் இங்கே நிடம் இருந்து அனுப்பில் தோன்றங்களைத் பிரிந்துவிட்டுக்கொண்டிருக்கிறோம் அனைத்துக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டுக்கொண்டு அவ்வு டாக ஏற்பட்டிக்கர் செய்தி board ஏற்பட்டிக் குற் Alf ஏற்பட்டிக்கைக் குல்வார் இக்காத்திரம்யாக،없이ly ரொம்பி ஏற்பட்டிக் குற்டிக்க சுக்செய்cepisode ச immip對了vélytioncent is that we did of our code because flow is a very important thing. Dependent on flow change your temperature change will be good, flow is a very important aspect. So that is why we thought should just check whether the flow determination is accurate that means our hydrodic modeling, our modeling of the hydraulic system, கை различை மனப Kia பகட்டின் கை ஒரு வையனை எடுத்துக்கொண்டு சு அனுபlect மட்டாரே செய்துகொண்டு பாட்டிகள சு பொருது வெளிக்கைத் தெரிந்து முன்பி அமரணி பாட்டி கடுத்ததோ, வினேள் நீ engine சு தொடுகளுக்கு, தரம 然後 ஜ ainமீர் உங்களே? ஒரு நிகை சனோல் வேருவது கைவிடுந்து கண்எபிக்க இல்லையின் நி எல்லார்வதுக்கொண்டு நிச்சயிலன感覺 காண் literal பரிவில் விதட்டலகிருந்து ஏன்மாரையும் ஆசிற்ற கட்டிருட்டது தொடறுகிருப்பு ஒரு வெளிமாதி ஆசிற்சில் அனைப்பிக் குיזலாம் முள்ளשות சு fa Hz எல்லாரம் குங்களியித்து நடீக்கூவிட குதி வெளியடல் ஆற். அவையை யார வார்தாablo ஞாபப்படது உண்רט பார்ந்தப் கொண்டிருக்க nosaltresயில் கருமைத்து ஏனென்றால் கூட்டு வருத்து Cities சில்லத்தினைருந்தம் தோன்றாக விசuse உணவி ஹடிந்திரதாக வெளியிற்கு நான்umpy காலினை ஓரு நினைக்க மெயத்தில் விட்டு schwerக்கூச் recognizedத்திற்கு numerator சில்ல வேலை நிறுதாயுங்க ஆதிக்கூச்ச் சட்டிரத்தர் ரக்கத்தற்களை அறிவுப்புக் குப்டும் அவனெடுதிய குரி ஆகாதிரில் குருயாக்கள். வணக்கம் நான் குதியாவும் அந்தக்கையில் நேரு குடித்தமு எதிர் memories செய்துகொள்களும் நிறுதி நிறுதி என்பது. அப்படி எணєையாத்தின் için இன்னுடைய சகுவரின் பரசிலுப்பவிக்கும் நிதித்து ஒரு நறாக் கதுந்து ஒருய கோடிய குழுட்டு இருந்ததற்கு இப்தlong apert செல்கிறீர்கள் ஒரு வழிகளுடன் நிகழ்ச்சில்ளி கண்டு நிகழ்ச்சின் கொண்ட воды அன்பகுburger அவரிடம் சார்க்கிறேன்ு சந்தற்கு உங்களுடன் இந்தனை நிகழ்சி பணின்காக இருந்தே பல நிறுத்திலğı சம்கலிலி இருந்து அமைிற்கிறேர் ஆனால் பட்டி வைப்ப நண்டு கலந்தில் கனon என் கருத்துச் மன்னிக்கவும் நண்டு மின்னத் தெரிந்த எவரங்கள் என்று நினைவு மபந்தைகளை மூக மற்றியாக நெற்றுகின்னன! தானியாகும் சொல்ல வெடுக்கவேன். குழையாம் சகையல் எங்கு ஏற்றமுடனுடனான 앞ிவு Разொன்றி용 சோன்று ரேநகடார் ரேணால் என்னொர்ந்து. அந்த உதவித்தான் அந்த உளக்கிருத்தாய். மணத்துனால் இந்த வார்பு எடுக்க விசைப்சியிருந்து இங்குதில் வாய்யில் வெள்ளி நம்பு விடாக்கோர் அங்கே, மேலும் பிரச்சினம் раз இருக்கி வந்து நிகச்சி நண்பர் பதிவாக இருந்தது. இங்குதில் வருகில் உங்களுக்கு எந்த முன்பு மேல ஏதாவது சி Coloniy Computing'd dz Splates and இங்கு செய்தில் சினைப்படுத்த composeY had, y, y, y's say, called as the entry-co-ferme-fast reactor. நான் நான் கூறி Ahíது இந்த arbeitencolored, it was mentioned in my earlier lectures பற்றி நிறந்திருந்திருந்திரு, where I brought out the incidents in different batteries ஆ ரேக்கருந்திரு, விஷ அலுவை. சின்ன நிறக்கிறோம், ஒரு விருந்தார் என் பிட்டை லேணத்தில், உசர ஒரு சித response மாருவி, உடனு விருந்தில் எண்ணியாகிறோம். שא�ல்லது குழந்தில் ஒரு பல் கைபிி செய்து, திறித்த அழைத்தில் இருக்கிறீர் cospr சுகல அல்லதான் இல்லை பான்கரும் மிகவுமண்டு fancy ஞாபி ஒகிப்பி, குத்தியை விட்டுக்கொண்டு விட்டுவிட்டு விட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிட்டுவிடத் அதிக்ரிந்து எருவான дополнக்கு காட்டிருக்கிறீர்கள்?ious நான் கட்டிருக்கிறேன். நான் தைத்தொரு முடியாகிக்குலை கூறத்த மனம்கிறார்கள்மு உங்களினையாகிப் பதியமாக இருக்கிறாய flavored நாற்று, ந இருவர் அனைத்தையும் ஒரு அதிக்கிறார்கள். வசலி幸ன். நான் வசலி வசந்துthird consolidation started சித்தியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடியாக முடி அந்த நிறுவனத்திற்கு அந்த நிறுவனத்திற்கு அந்த நிறுவனத்திற்கு அந்த நிறுவனத்திற்கு அந்த நிறுவனத்திற்கு அந்த நிறுவனத்திற்கு அந்த நிறுவனத்திற்கு அந்த நிறுவனத்திற்கு அந்த நிறுவனத்திற்கு அந்த நிறுவனத்திற்கு அந்த நிறுவனத்திற்கு அந்த நிறுவனத்திற்கு அந்த நிற of that design. So, we thought why not, we use that data. So, here there are two things, one is a step reduction in flow and the other one is a slow reduction in flow. In both cases the objective was to calculate how much step flow it can sustain, reduction it can sustain if I were to reach a hotspot-clad temperature of 800 degree centigrade limit. Similarly, suppose I put a limit for maximum sodium temperature as 900 degree centigrade, what would be the maximum step reduction that the design can allow? So, here you see what we calculated was about 32 percent reduction, it would go to 800, in that case they reported it as 27. You also see two another figures, 37 in the brackets, now when we do this calculations, we also take into consideration the time constant of the thermocouples, because there is a delay, only the you are come to know only later, so that also needs to be considered. But suppose I take a zero time constant, that is the immediate response, then this shows in our case about 37.5, which showed us about 30. For the other case of maximum sodium temperature, where our prediction was about 71, that prediction was about 70 percent. According to the other case, here you see for a slow reduction of 96 percent flow, you see our plugging, there is our rate was 5 percent per second was what it could accept to give 800 degree centigrade, whereas they reported as about 3 percent per second. And for the other case, 16.5 is what we got at 9 point. Now if you look up, this just tell that there are some differences, because you do not know the exact, there could be some differences in the data which we have got, because literature does not give you the complete data, nevertheless you just see quite a good sort of agreement, that the trends are good and we are not very far from what is happening. So this again gave us the confidence that we are able to predict the core conditions well. Now let us move from the core to the steam generator. Our steam generator is a once-through steam generator in which water enters as water, subcooled water as a liquid. It goes through the tube, picks up the heat from the sodium and finally comes out as superheated steam. So we try to compare our design correlations which we have used. With that we try to design a steam generator for the Phoenix reactor. Our SNR 300 reactor of Germany, Phoenix is in France. This has operated right from 1974 and was recently in 2009, it was started decommissioning. And it has got a serpentine type of steam generator as we have for a BTR. So we just did the calculations. Our code gave a length of about 57.83 and their lengths actual were about 60.76. Here we felt maybe some margins they would have given in the design which, so it gave us a feeling that if I give, add some, for example this is about 3 in 50, maybe 5 to 6 percent if I give, I would be very close. But then for a different design, a straight tube design which we were to go for PFBR, when we compared we got a length of about 18.41 meters whereas actual design was 19.4. So apparently it is clear that there have been some safety margins given and since these have operated and this has been validated based on test facilities in Germany, we felt to our calculations if I am able to add something like 5 percent to 6 percent, I would be able to get a reasonably good design which I can confidently go ahead. That is on the part of the steam generator area. Now if I look at the heat transfer, what sort of regimes are there? As I said, water enters, it picks up the heat, becomes saturated liquid, then you have the nucleate boiling, then you have the film boiling, then you have the super heat. For every region we apply different correlations depending on the conditions. So we had developed or not developed as we had set up a test facility for testing steam generators. So this is a 5 megawatt steam generator test facility. So we instrumented the steam generator by providing thermocouples in all the steam generator tubes. The heat transfer shows the measured temperatures. That is what we could measure. And the green ones, dark green ones show you what is the actual calculated temperatures. So we found that the temperatures are reasonably close thereby giving us a confidence that every region of predictions the heat transfer calculated is quite close to the reality. Our own results, our own experimental results. So this also has given us the confidence. Then when we started commissioning the ABTR reactor, earlier I mentioned to you we compared our results with what we had from France. But now we had a, we started comparing results with what was there in ABTR. Now you see again the pump speed versus time. E means east loop, W means west loop and dynam is our code. You can see the predictions and the actual findings are quite close. And that means as I mentioned earlier, there is a proper modeling of the inertia of the rotating systems. The inertia of the fluid all are well. So this was again gave us a confidence that our modeling is good. So at every level whenever we develop the confidence, we know that we are close to the reality. Then validating the core model, even though we did validate it against some of the super Phoenix test results for a sudden plugging, we just thought why not we do something about the measurement capability and see whether we are really getting. So what we did, we raised the power of the reactor from 7.2 megawatts to 7.7 megawatts in 7 seconds by withdrawing the control raw. And at that time the reactor tripped. So this data we had and the central sub-assembly, the central most sub-assembly, the monitoring of those temperatures were also recorded. So we said okay come on, let us now why not we use our model to look at this transient event and let us predict. Now this star once show you what is the measurement and the straight line shows you what was predicted and the predictions were with a 0.3 second time constant. See the thermocouple time constant, if it is more, it will delay the actual, relate to the actual conditions. Even that should be matched if you are interested in proper predictions. So we had done some experiments outside where we found that it could be something like 0.3 to 0.5 seconds time constant. So since majority of thermocouples had 0.3, we just used that and you can see it is a reasonable match between the two. That is our own plan measurements with our own computer code. So this was a good sort of happiness and confidence boosting for us. I mentioned to you something about natural convection. That is when your off-site power is not there, your on-site diesels don't start. What to do? So we looked at the natural convection pattern in the sodium. Now you know in any reactor there is a decay heat which is in the core. Even though you have shut down the reactor means the fission reaction has stopped, chain reaction has stopped. But the fission products which have been produced in the fission reactions are still decaying and when they decay, they produce heat. If we don't remove that heat, it could go to heat of the fuel clad, if the clad could fail, the fuel could fail. So very important is that you must remove this decay heat. And in the ABTR, Fast Bidder Test Reactor at Kalpakam, we have the four steam generator modules put in a casing, a casing and there are four trap doors, two in the middle and two at the bottom. They are closed. And at the outlet, there is a chimney which goes out. The purpose of this is whenever there is a loss of off-site power and the diesel generators don't come up, you have to remove the decay heat, you just open these four trap doors. What happens? Air comes in, flows over the steam generator tubes, you see this is one module, this is another module, this is a third module, this is a fourth module. It flows over the thing, picks up the heat by convection and then the heat goes out. Here there are two processes happening, heat transfer processes. One is this air flows over the shell of the steam generator which contains sodium and removes heat by convection. But this shell is at a high sodium temperature also radiates heat to the casing and whatever heat is radiated to the casing again is picked up by the air which is coming in. Once the air picks up the heat, it becomes light, it goes out, fresh air enters and there is a natural convection of the air setup and this is called as a natural convection cooling of the steam generator. So once the heat is removed in the steam generator, it sets up natural convection in the secondary sodium. When the secondary sodium natural convection has been set up, it sets up in the primary and thereby the core gets a continuous cooling and the heat is removed through the steam generator. Here our calculations indicated that for a sodium temperature about 500 degree centigrade, we could remove about 575 kilowatts of heat whereas in the experiments actual heat removed was the order of 608, very close. So again on the safer side, conservative side, so this also gave us a good confidence that we are in a position to really find out natural convection in air also quite comfortably. So you see we are trying to validate part by part. Then once integrated, it has to behave in the same manner. So this is called validation by parts. So coming to the natural convection in the secondary system, we tripped the pump and we operated the reactor about 180 kilowatts and heat was getting removed through the losses in the pipe. The decay heat was not much, so we did not open the trap doors. So then we analysed how the flows are coming in the two secondary loops. Here you see what we predicted was something like this and what we got was something like this east loop, west loop and what is our predictions. If you look at the numerical values, we got a maximum of about 12 meter cube per hour and our predictions were somewhere close to 15, but the steady state is coming very close. We then looked at why, why this. We realised that the secondary loop we had treated as a single pipe, but there are two tanks, a search tank and the expansion tank and their level changes. So basically there is a difference in the scheme that instead of treating the whole pressure drop as single, we should treat it as in different parts and then maybe and when we did that, we became very closer to the realities. But still this prediction per se is not bad. Of course, based on this confidence, we raised the power, we went to about 10 megawatts, I am sorry, this experiments we conducted about 8 to 8.5 megawatts thermal. We tripped one primary pump and you see here it gives you how we modelled, this is a reactor, this is a schematic. And whatever comes at the outlet, we represented it by a mixing region and whatever is above the outlet pipe, we put it like a stagnant region which exchanges heat with this mixing region. And then this goes to IHX and whatever is not in the heat transfer region, we treated it like a mixing. Same thing at the outlet, IHX was represented by a model, thermal model, I am not talking about it here. And again the pump, then again inlet mixing region and on the secondary sodium side outlet mixing, search tank was treated as a mixing, then the steam generator, then the pump again and expansion tank as a mixing, then the inlet and this is the steam generator. So here when it is tripped, what happens, this primary pump is tripped, so that means primary pump, it means heat coming in is going to be less. But the heat removal capability remains same. So what happens, this delta T, the temperature difference between the two will start increasing. So this is how it happened, the measured things are shown by this and this is the calculated temperatures and you can see here that there is a reasonable match between the predictions and the calculations, means predictions and the measurements. Then we did a tripping of the secondary pump. When the secondary pump is tripped, what happens, your heat removal comes down. And the heat removal comes down, your primary outlet temperature increases that reflects on the reactor inlet temperature and that is how you see it is happening. But at later times we see some difference. So this we reconciled later, we apparently found that the two loops were not being very identically. So we had needed to change the data which we have put into our computer code and then we could get a good match. Similarly east loop and west loop, here on the west loop what happens, there are not much change in the flow, there is no change, only the east loop was tripped. So here more or less it is going with the same, there is not change. Then the loss of upside power, there is no power coming from the grid but your diesels are operating. Then what happens, this is the reactor inlet temperature, you can see of course how things they are quite close, reactor outlet temperature they are not very bad, they are quite close gives us a good sort of confidence that we are able to predict. And the steam generator cold end, surely because the water pump, water supply is not there, there is an increase in the temperatures, how it goes. Here also you find the trend is okay, the final temperatures are okay in between. This apparently we attributed to the process modeling, there is a bit difference. But if we take the overall delta t change, which is important for our design as an input for the mechanical design, the overall change is important. So we found that this is able to do a good prediction. Now when we design a plant, we have to satisfy what are the requirements of the different components, what is the limits on the different components. If we take the fuel which is the most important, we need to limit, see that fuel melting does not happen. In the case of a BTR, our melting point was something like 2, 5, 9, 4 degree centigrade. And for the clad which is made of stainless steel, we should not cross 700 degree centigrade. So in the case of any event happening, I should have a safety threshold such that under no conditions, this temperature should cross the melting point of fuel or the clad temperature should not cross 700 degree centigrade. What I mean the hotspot clad considering all the uncertainties in the properties of the fuel, you have a maximum prediction, a conservative prediction should not cross. So how I should set my limit. Now let us say we put a temperature limit. We do not measure the fuel temperature, we do not measure the clad temperature is difficult to put thermocouples on the fuel and the assembly. So we use a surrogate variable, surrogate parameter and that is the temperature of sodium at the outlet of the reactor means at the outlet of each sub-assembly we have. And we measure this and by we have a correlate the fuel temperature to inlet temperature, outlet temperature and the different uncertainties with that we link and under that condition we put a limiting safety system setting. For example, safety limit is fuel should not melt, so 2594 degrees centigrade would be the thing but our calculations will have uncertainty. So considering this I would put that good margin at which my reactor should trip and once the reactor trips in the time when I generate the signal and by the time your control rod drops there could still be a rise. So these parameters I consider in my calculations and then set up what is called as the limiting safety system system or that setting at which I must initiate the tripping of the reactor. So as I mentioned we need to consider measurement uncertainties, time response uncertainties for example let us say I measure a temperature. It could be plus minus 5 degrees, it is not error free. So I must consider that there could be a negative error. So I should consider that similarly the time constant of the thermocouple there is a variation there is a band if I say 6 seconds time constant it could be 6 plus minus 2 or 3 we make these assessments before the reactor is commissioned by testing these thermocouples individually and establishing their time constants. So we know this data before we put them on the plant. Now very important factor we talked about redundancy, we talked about diversity. So we do not go by one thermocouple, we have two thermocouples for every sub-assembly, every fuel assembly outlet is measured by two thermocouples so that one of them would give a correct signal even if one phase one would give us a signal. Then there is another requirement of a diversity that is on a different principle you must be able to detect the same event. For example I will take a total power failure in which I have my power supply is lost that is both then what will happen my flow will come down once flow come down we have a process parameter called as power by flow which is calculated and we have a limit then central sub-assembly also gives me this thing threshold. So we have got two diverse parameters which can trip the reactor before the melting point is crossed. Here you find the hotspot clad crosses by about 10 degrees centigrade. So here apparently we need to reduce the threshold but then if you go to the other case of failure of one primary pump again power by flow and central sub-assembly temperature come into picture. Then we look at a over power that is let us say we had withdrawn we are withdrawing a controlled rod to raise the power but we did not stop we continuously raised it what happens it is not it will not a good safe situation so the reactor must be tripped. So we find that reactivity is able to trip power over power by 10% is able to trip and all these things are able to trip. So here you have three signals so essentially we have convinced ourselves that we have diverse parameters for the different incidents they just to give you a flavor we have analyzed all incidents which we have foreseen. So this again has given us a very good confidence. Then on the reactivity I would like to make a comment when it is a positive reactivity only the power increases but when there is a negative reactivity anyway it is safe the power will come down. So there could be a feeling that why if it is a negative reactivity why I should trip the reactor here again I would point out to the incident which happened in the Henrico Fermi reactor where there was a rise in the temperature of sodium due to flow blockage there is a plugging of the assembly at the inlet and the flow reduced and the flow temperature started increasing when the temperature started increasing there was a negative reactivity in that reactor and it was compensated by raising the control rod many two three times or four times but since there was no temperature measurement there was no idea about what was the temperature it was just one sub-assembly and all other sub-assemblies are all in proper shape it melted and that activity came down. So we should not just like that say ok negative reactivity we can do even any change from the normal critical condition reactivity is delta k by k how much it is away from criticality positive side or negative side we must investigate so we must have a trip on the negative reactivity also and which we have put in a BTR in the safety logic so that even if there is a negative reactivity of about 10 PCM there is a trip of the reactor. Now I would like to summarize this lecture we have looked at validating the different models in a separate that is validation in parts based on literature based on tests conducted in other reactors based on tests conducted in our own reactor at lower flows and the overall predictions appear to justify that this dynamo code can be used with a high degree of confidence for assessing the plant transients. Thank you.