Rive said:Thanks for the ideas about fission/not fission difference.
About explosion/recriticality: IMHO every explosion were hydrogen explosion and maybe containment damage, but none of them were originated directly from any SFP. It would scatter at least some fuel, and scattered/damaged fuel rods would cause much more serious contamination nearby than the actually observed. It would end in Chernobyl-style radiation zones around the affected unit (with much stronger Uranium and Plutonium presence).
Not to me. As a nuclear engineer, fuel designer and fuel analyst, damage simply means 'Failure!', particularly in the context of an 'accident'. It means something happened that shouldn't have, so it is a failure - a violation of the prime directive - 'Thou shall not allow fission products into the environment!'. In the context of core damage, that is a BIG deal, and I would expect cladding breach (fuel failure).PietKuip said:"Damage" was a highly misleading euphemism. That is what I come to understand now.
My interpretation (I am not in the industry) of "damaged fuel rods" would be rather conservative. It could mean that they were bent or corroded. A damaged car can still be functional: a scratch, a dent. Maybe worse. But one would not describe a burnt-out car wreck as "a damaged car".Astronuc said:Not to me. As a nuclear engineer, fuel designer and fuel analyst, damage simply means 'Failure!', particularly in the context of an 'accident'. It means something happened that shouldn't have, so it is a failure - a violation of the prime directive - 'Thou shall not allow fission products into the environment!'. In the context of core damage, that is a BIG deal, and I would expect cladding breach (fuel failure).
More importantly is the fraction of core that has breached/ruptured cladding, and for that one has to go look at the activities being measured.
ascot317 said:We're not in the 80ies or 90ies anymore, making information available to masses is the easiest thing to do. In this situation, there's absolutely no reason to withhold information. We're beyond the stage of possible mass panic.
M. Bachmeier said:I don't think a 'cover-up' is the way most Japanese would perceive selective information dissemination. I think that most would either believe, or like to believe that information is controlled in the best interests of workers, people displaced, long term economic factors and the desire not to bring nuclear contamination shame to those exposed.
There are many Japanese who never reported suspected radiological effects upon they're children (Hiroshima, Nagasaki) because of stigma. There are some in Japan who might believe these events to be punishment for arrogance.
If there are errors in the degree of timely reporting of events, it most likely has to do with what (persons in the position of responsibility) feel is the path of least harm.
Astronuc said:Not to me. As a nuclear engineer, fuel designer and fuel analyst, damage simply means 'Failure!', particularly in the context of an 'accident'. It means something happened that shouldn't have, so it is a failure - a violation of the prime directive - 'Thou shall not allow fission products into the environment!'. In the context of core damage, that is a BIG deal, and I would expect cladding breach (fuel failure).
More importantly is the fraction of core that has breached/ruptured cladding, and for that one has to go look at the activities being measured.
The fuel in the SFP is 'spent', in addition to the fact that is started with low enrichment. The available reactivity is low because it is 'spent'. The rate a which positive reactivity could be inserted is relatively low, so a prompt critical event is unlikely. Coming out of a subcritical configuration with a very low neutron source, rather than starting at a critical configuration, I don't believe the configuration in the SFP supports prompt supercritical.TCups said:Question for Astronuc et al:
As I think about this, if the shape and depth of the SFP could focus the blast into a vertical mushroom, then the shape and depth of the SFP, particularly if there were water covering all or part of the spent fuel would also tend to focus the force of an explosion toward the bottom of the SFP. Might it be that either a blast from the primary containment or a blast from hydrogen + air in the service floor, "amplified" by the geometry of the SFP and efficiently transmitted by water in the SFP did indeed exert a hydrostatic, crushing force on the spent fuel assemblies?
This wouldn't be a shaped HE charge crushing two subcritical hemispheres of plutonium, but on a much larger scale, a large explosion crushing several tons of spent fuel racks -- at least in theory, the hypothesis of a sudden criticality in the SFP doesn't seem too far fetched to a lay person.
I see the international nuclear industrial complex colluding with them. The Swedish nuclear authority says that the French regulator was out of line to regard Fukushima as an INES level 6 accident when the Japanese said 4 (or later 5).MiceAndMen said:At some point, perhaps, the international community may find it desirable to take away the keys to the car, so to speak, and TELL them how to proceed with the cleanup.
Patience does not last forever, and Japans's political and industrial institutions are well aware of that. The longer they are able to prolong a "fog of war" type atmosphere surrounding this fiasco, the longer they can put off their day of reckoning.
DSamsom said:Mm, something's going wrong there. See webcam image 28/4 08:00 AM (Japan Time)
http://www.tepco.co.jp/nu/f1-np/camera/index-j.html
clancy688 said:So, let's take the following example for dummies like me:
Let's guess there's an RPV with only one fuel rod. Now there have been severe cooling problems. The fuel rod was uncovered for a short amount of time and has oxidated and ruptured. We don't know if it indeed has molten.
But because of the constant cooling, fission products such as iodine, cesium, cobalt, strontium etc. have been washed out and are now somewhere in the RPV, the dry- and wetwell.
CAMS is now measuring extremely high radiation, indicating that 30% of the radiating inventory is somewhere in the drywell and 5% somewhere in the wetwell.
Overall it doesn't necessarily mean that the fuel has molten. It's only indicating, that the fuel cladding ruptured and fission products can escape from the fuel rods?
Back to Fukushima: So 55% of Unit 1s core inventory of fission products is not contained by the fuel rods anymore but swimming in the cooling water? But there's NOT 55% of the core gone, like molten down? Or at least, those numbers do not indicate or show whether or how much of the core has molten?
Yes - I expect the fuel oxidized like heck, hydrided and broke apart. It might be rubble, but didn't necessarily melt - particularly if the actually had water in the bottom third of the core.M. Bachmeier said:Which I assume to mean fuel breaking up, but not melting. I'm sure it is not possible from the data (questionable, instruments and all, as it is) to know that melting has occurred? It may be sitting in lower containment, but not core melt? However, the events around #3 are disturbing and unresolved.
I would very much like to be there in person.DSamsom said:Mm, something's going wrong there. See webcam image 28/4 08:00 AM (Japan Time)
http://www.tepco.co.jp/nu/f1-np/camera/index-j.html
Astronuc said:I would very much like to be there in person.
My wife and I would very much like you to stay right here state-side so maybe we can see you and yours in years to come.Astronuc said:I would very much like to be there in person.
Yes - damage means some abnormality - a dent or ding - such that one cannot use the fuel anymore because it's outside of design spec. A damage fuel rod could be corroded, but still hermetic (sealed), but one would not use it, because it might fail. Similarly, a damaged fuel assembly means that it got dinged/dented, therefore is out of spec, and could lead to failure if used, so it's gone. Damage implies that a fuel rod or fuel assembly may not be able to perform its intended function.PietKuip said:My interpretation (I am not in the industry) of "damaged fuel rods" would be rather conservative. It could mean that they were bent or corroded. A damaged car can still be functional: a scratch, a dent. Maybe worse. But one would not describe a burnt-out car wreck as "a damaged car".
Of course, all the emissions meant that volatiles had escaped, so they would have burst open, I realized that. But I had not realized that it meant that rods had desintegrated, that their fuel pellets had fallen out.
No - I'm not being ironic. If TEPCO invited me, I'd be on-site ASAP.clancy688 said:Is that supposed to be ironic...? You saw the radiation maps. High radiation hotspots all over the plant. And now there's a plume... could be fog, could be a giant insect swarm, could be pure cesium... ^^;
NUCENG said:You have it as I understand it. And if you have used the SRVs venting steam from the RPV to the suppression pool some of that radioactivity went along. And then there are vacuum breakers that may have returned some of that radioactivity to the drywell outside the RPV and much less shielded from the CAMS detectors. If there has been a break in piping or instrument lines outside the RPV, the liquid and steam released directly into containment releases more radioactivity into containment. That will increase pressure in the drywell and spill over into the vent lines to the torus. And all that can happen while most of the core metal and core pellets remain inside the RPV. And hydrogen gas can go everywhere the fission products do.
Astronuc said:Yes - damage means some abnormality - a dent or ding - such that one cannot use the fuel anymore because it's outside of design spec. A damage fuel rod could be corroded, but still hermetic (sealed), but one would not use it, because it might fail. Similarly, a damaged fuel assembly means that it got dinged/dented, therefore is out of spec, and could lead to failure if used, so it's gone. Damage implies that a fuel rod or fuel assembly may not be able to perform its intended function.
Fuel failure means the cladding is breached - and fission products have escaped the first barrier between them and the environment. The industry takes fuel failures, even one, very seriously.
Core damage is a more significant context. It is a gravely serious matter, and then one would asked how damaged? How many failures? What's the off-gas and coolant activity? . . . . That's a very BIG deal.
Would a fast-neutron chain reaction in the plutonium be absolutely excluded?Astronuc said:The fuel in the SFP is 'spent', in addition to the fact that is started with low enrichment. The available reactivity is low because it is 'spent'. The rate a which positive reactivity could be inserted is relatively low, so a prompt critical event is unlikely. Coming out of a subcritical configuration with a very low neutron source, rather than starting at a critical configuration, I don't believe the configuration in the SFP supports prompt supercritical.
The explosions at Units 1 and 3 occurred well before the pools would have dried out, and it is more likely the hydrogen came from oxidation of the cladding in the cores.
I don't see the explosions being nuclear.
If the pools had dried out, there certainly wouldn't be any moderator to allow criticality.
In the core at power, the radiation field is so very different than simple radionuclide decay. The thermal and fast neutron fluxes are on the order of 1014 n/cm2-s. And the gamma and beta radiation is intense.elektrownik said:Questions: What is radiation in core at max reactor power, what is radiation in core after shutdown, what would be radiation of fuel rod/set from sfp, without water or any other protection ?
Astronuc said:No - I'm not being ironic. If TEPCO invited me, I'd be on-site ASAP.
I believe there is washout and dissolution of the fuel, but not nessarily melting - particularly if there was water in the bottom third of the cores. The question is - was there water in the bottom third of the cores?default.user said:Have I understood you correctly?
You believe that there was no damage to the nuclei in the reactors, and therefore no meltdown?
rowmag said:Searching through the file finds no other reference to the plastic covering, but some references to fiberscope searches for foreign matter in the assemblies (not much found), but no particular reason given why this should be a MOX-specific issue (to go to NUCENG's query). So perhaps such plastic covering may have been used in SFP4 as well?
Fast reactors use a tight fuel lattice configuration and 20% fissile inventory. LWRs have a maximum of 5%, and TEPCO probably uses 4% or less, based on annual cycles and between 1/4 and 1/3 core batch sizes. The spent fuel is even lower enrichment because of depletion of fissile inventory. So no fast-neutron chain reaction.PietKuip said:Would a fast-neutron chain reaction in the plutonium be absolutely excluded?
All utilities are concerned with 'foreign materials' on nuclear fuel, and all have a 'foreign materials exclusion' program - at least they should by now. Failure due to 'debris' has been a significant issue in the 1980s through 1990s. Debris-resistant features were added to the fuel, but more importantly, utilities implement programs to prevent contamination of fuel. Foreign materials do not belong in the fuel or the core.rowmag said:Further follow-up (context: cphoenix's superheated steam explosion theory):
I skimmed through a bunch of past press releases on the TEPCO site last night, particularly (but not exclusively) those related to Unit 4. There are several reports of foreign objects falling into the SFP or being found in the stored fuel assemblies over the years (bolts, washers, metal shavings, etc.), and the more recent reports mention that they are continuing strict countermeasures against foreign object introduction that were adopted a few years ago. The only enumeration I found of what those countermeasures consists of was basically different ways of saying, "we'll be more careful," and no mention was made of plastic covers being adopted on a regular basis. In fact the locations of where some of the foreign objects were found inside the fuel assemblies suggest that they are not using plastic covers on a regular basis. I also see no mention of plastic covers in the list of things to be done in the maintenance period that was underway when the earthquake hit.
So, not much support so far for the possibility of plastic covers being in place in SFP4.
Maybe the covers were a special-case for the MOX study after all?
PietKuip said:I see the international nuclear industrial complex colluding with them. The Swedish nuclear authority says that the French regulator was out of line to regard Fukushima as an INES level 6 accident when the Japanese said 4 (or later 5).
It needs a British professor Busby to produce alarming graphs of uranium spreading out over the Pacific from tabular EPA data. The EPA that does not want to monitor the radioactivity in fish.
The IAEA (with its Japanese boss) is completely passive.
DSamsom said:Mm, something's going wrong there. See webcam image 28/4 08:00 AM (Japan Time)
http://www.tepco.co.jp/nu/f1-np/camera/index-j.html
Astronuc said:In the core at power, the radiation field is so very different than simple radionuclide decay. The thermal and fast neutron fluxes are on the order of 1014 n/cm2-s. And the gamma and beta radiation is intense.
About 20 years ago, I was involved as a consultant to a utility where they managed to break a fuel rod outside of the core. It had failed during the cycle, and they managed to break it while moving the assembly during the refueling outage. The fuel rod was not discovered until they were draining the cavity above the RPV, and the radiation alarms went off. The operators stopped, reflooded the cavity and went to take a look.
The fuel rod was broken in 4 pieces. The top and bottom sections were about 2 ft each, and there were two 5-ft sections. One section was empty of fuel! It's activity was about 5000 R/hr, IIRC. Another section was about 2000 R/hr. I'd have to dig up my notes - but they were hot. The NRC wanted to know - where did 1 kg of UO2 go!? Well the answer was - it was distributed in the primary system as fuel particles and uranyl ions. The Np-239 in the reactor coolant (as well as increased Xe, Kr, I and Cs) was a really good indication that they had a degraded failure in the core. They just didn't bother to go look for it during the outage.
The senior plant management were fired.