Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[NUCENG]

Are they co-located with NPPs which already require the same?



A 90-year old spent fuel is more than 10 times less radioactive than 4-year old one, right? I imagine reprocessing plant designers would like this fact.

Not all spent fuel storage is at active plants, some are at decommissioned sites that have storage licenses. When you talk about 90 years, does that mean you expect plant license extensions that long? Obviously, if we can't eventually move this stuff offsite, the answer to your question will eventually be NO!

If your number is correct and spent fuel after 90 years is only 10% of the radiation levels of 4 year old fuel, I have to paraphrase a previous comment of mine, "10% of a big number is still a big number." I would like to see serious attention to reprocessing fuel. I believe we will still need geological storage of high level wastes.

 

[Rive]

An example of the sort of study I refer to is this one http://www.osti.gov/bridge/servlets/purl/6409677-0h1aot/6409677.pdf

Thanks.

It's interesting that the expected failure pressure is close to the expected containment cap failure pressure, if I take it right. So if this one failed then the other one might failed too.

Regarding the 'new' videos: did anybody managed to find the U3 FHM?

 

[nikkkom]

If your number is correct and spent fuel after 90 years is only 10% of the radiation levels of 4 year old fuel, I have to paraphrase a previous comment of mine, "10% of a big number is still a big number."

Sure. I am not implying that 90 year old fuel is harmless. Of course not. It is still so radioactive that it can kill nearby human in seconds if unshielded.

I would like to see serious attention to reprocessing fuel.

Me too.

I see no harm, though, in keeping spent fuel in dry casks for many years before reprocessing. It actually should make reprocessing easier. In 100 years, Kr-85 decreases by the factor of 1000 (meaning that airborne releases are greatly reduced), Cs-134 by 10^15 (practically zero), Cs-137 and Sr-90 by 10. What's not to like?

I believe we will still need geological storage of high level wastes.

Sure. Unless someone is willing to make an electric generator powered by heat of canisters filled by Cs-137 and Sr-90. :D

 

[SteveElbows]

Thanks.

It's interesting that the expected failure pressure is close to the expected containment cap failure pressure, if I take it right. So if this one failed then the other one might failed too.

Regarding the 'new' videos: did anybody managed to find the U3 FHM?

Given the locations of some of the steam we saw escaping from several reactors (most clearly number 3), I don't think many people would be at all surprised if drywall head was a leak point.

As for the FHM, I would not be at all surprised if it left the building during the explosion. There was more than enough debris to the immediate south of reactor 3 building to account for this, and I don't think the media or TEPCO were too interested in reporting its location. If it was ejected then I don't think it tells us much really.

 

[SteveElbows]

This one? Appears to be towards the SE corner of the Unit 4 SFP. We've never seen right into this SE corner of the pool perhaps due to the limitations of the camera rig they are using.

I didn't see any of the Unit 4 reactor void, which clip was that?

Yes that's the one. Any ideas about it? I wondered if perhaps it had been mishandled and damaged at some time in the past, and so was kept on its own? Or is there any such thing as a 'dummy' fuel bundle used for some purpose?

As for unit 4 reactor well, I made a stupid mistake having watched too many videos in one sitting. I knew it didn't look like the reactor well should, but I thought maybe it was something that had been temporarily placed in the region during the reactor shroud work. In fact it was the cask area of the fuel pool that you mention, my mistake.

 

[Rive]

As for the FHM, I would not be at all surprised if it left the building during the explosion.

Well, I would. Lot of other, less stable stuff remained there on the top...

But anyway, it's just my stupid theory about the falling overhead crane, pushing through the FHM on the drywell cap - no worth in discussing it without further details :-)

Yes that's the one. Any ideas about it?

IIRC the SE corner is where a 'Fuel Inspection Machine' or something like that were suspected. (It was around May, maybe...) I've posted a picture about it somewhere... It's for manual dry inspection of new bundles.

 

[SteveElbows]

Well, I would. Lot of other, less stable stuff remained there on the top...

But anyway, it's just my stupid theory about the falling overhead crane, pushing through the FHM on the drywell cap - no worth in discussing it without further details :-)

I don't see much other stuff remaining at that level of reactor 3. There is mostly just the overhead crane, and lots of roof debris.

I don't tend to see enough debris under the crane to account for the FHM, although the area is such a mess that I cannot be entirely certain. Certainly some portion of the circular plugs that sit above the drywall can be seen on a couple of different videos or images. A very small portion can be seen on old videos that showed steam escaping from the area where the edge of the reactor drywall connects to the storage pit/pool. Such footage tended to indicate that the overhead crane beam on this side had fallen quite neatly down to this level, quite parallel with the floor. And in the following image I believe we can see quite a portion of the eastern side of the cap. I will illustrate the area in question shortly.

http://www.tepco.co.jp/en/news/110311/images/111008_05.jpg

 

[SteveElbows]

OK so here is a version of the above image which I have marked. Within the yellow area is the edge of the circular drywell plug I mentioned. Within the orange area is possible another part of the plug edge, but I am less certain of this one. The X marks the spot where other images & video have shown steam escaping in the past.

This is a document which shows the area I marked with an X. The gap along the narrow edge of the removable pit gate is the main feature of interest due to the longstanding impression that this was a well visible point of containment failure, but in this case I am posting it so we can see what the edge of the drywell plugs looks like for comparison with above image.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110924_02-e.pdf

 

[SteveElbows]

Also please note that I cannot be certain that I have identified plug edges correctly in that photo, it could be something else, but the position seems about right.

 

[Rive]

... the position seems about right.

Agree. You can even see the FHM rails near the plug. Good find.
[URL]http://www.houseoffoust.com/fukushima/tepco_pics/R3_july21_1.jpg[/URL]
(The circle marks the pool gate: the rail is on the left near the reactor well.)

The 'spanner' (look it up in the thread here) was more in the way of the destruction than the FHM and it's still on the top level... More or less. So I think the FHM should be there too.

 

[SteveElbows]

The 'spanner' (look it up in the thread here) was more in the way of the destruction than the FHM and it's still on the top level... More or less. So I think the FHM should be there too.

Ah yes, also known by names such as the Stud Tensioner Carousel. I don't know why you think that equipment was more in the way of the destruction than the FHM. It was situated on floor that collapsed to a lower level, but I can't really do a meaningful comparison between what it experienced and the forces that the FHM may have been subjected to. I don't know as the FHM may have been launched far into the air, I could imagine it being blown more south than upwards, and it could have tipped over and tumbled out of the side of the building.

 

[LabratSR]

New Video From TEPCO - Radioactive Water Treatment 4: Fukushima Daiichi
http://youtu.be/Bglf9ZlwrpU

 

[NUCENG]

Sure. I am not implying that 90 year old fuel is harmless. Of course not. It is still so radioactive that it can kill nearby human in seconds if unshielded.



Me too.

I see no harm, though, in keeping spent fuel in dry casks for many years before reprocessing. It actually should make reprocessing easier. In 100 years, Kr-85 decreases by the factor of 1000 (meaning that airborne releases are greatly reduced), Cs-134 by 10^15 (practically zero), Cs-137 and Sr-90 by 10. What's not to like?



Sure. Unless someone is willing to make an electric generator powered by heat of canisters filled by Cs-137 and Sr-90. :D

A timely article about reprocessing. If we discuss this I would suggest we start a new thread.

http://green.blogs.nytimes.com/2011/11/16/a-long-long-road-to-recycling-nuclear-fuel/

Edit: And another article about Yucca Mountain. Note there is not one technical argument is this debate only Politics. That is not the right basis for a decision in either direction.

http://www.lvrj.com/news/illinois-senator-drops-amendment-to-revive-yucca-mountain-133978238.html

These two articles are examples of why I believe spent fuel is a significant issue. Failing to move forward on spent fuel increases risk. Failure to make decisions may be the decision that determines the future of nuclear power. It is irresponsible, but typical of other issues we face on energy, the environment, in the economy, in international affairs, in education, and on social services (and that applies to the world in general - not just the US).

 

[zapperzero]

Yes that's the one. Any ideas about it? I wondered if perhaps it had been mishandled and damaged at some time in the past, and so was kept on its own?

It does look a bit crooked, now that you mention. But I also saw a slant in the Unit 4 walls which wasn't there, so...

 

[LabratSR]

Preparations for the winter season in Fukushima Daiichi NPS

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111118_02-e.pdf

 

[etudiant]

TEPCO has issued its latest summary report on the efforts to control the Fukushima accident here:
http://www.tepco.co.jp/en/press/corp-com/release/11111701-e.html
The scale of the effort is somewhat reassuring, there does not seem to be any obvious cheeseparing.

What concerns me is that this scale of response is only possible in a rich society.
It is very unlikely that anything comparable could be done in say Pakistan, another country that has been known to experience large earthquakes, yet the growth in nuclear is in these poorer societies. Projecting out over the next 50 years, we can expect several other similar accidents. with gradually increasing global background burdens, unless a dramatically more robust reactor design is found.
Is this even a consideration currently in the international regulatory apparatus?

 

[clancy688]

unless a dramatically more robust reactor design is found.

It is probably already found. With all those (yet unbuild) GenIII reactors. But that won't help us the slightest when there are still literally hundreds of reactors from the sixties and seventies in use. And probably will be for the next 20 years.

 

[Rive]

... Projecting out over the next 50 years, we can expect several other similar accidents.

Are you sure? Do you know about more old designs built on such stupid places, with underestimated environmental risks?

It's still not the reactor what failed there on the first place, but the placement and the risk analysis.

 

[etudiant]

Are you sure? Do you know about more old designs built on such stupid places, with underestimated environmental risks?

It's still not the reactor what failed there on the first place, but the placement and the risk analysis.

Of course I'm not sure, but the experience to date seems to suggest that.
Afaik, we have somewhere around 500 reactors in service for generating commercial power.
Three have experienced destructive failure, through operator error or external events, during at most 50 years of operation, so we have about 1 major failure per 10,000 reactor years of operation.
It would seem important to try to improve that by at least a factor of 10, preferably a factor of 100.
Is that even possible, given that we are apparently not very good at identifying, much less managing low probability events?

 

[rmattila]

If you aim at
-operational occurrence rate of less than once per year
-limiting functions capable of preventing 99 % of occurrences from propagating into accidents
-safety functions capable of preventing core damage in 99 % of accidents
-containment capable of preventing a large release in 99 % of meltdowns

you will not have to deal with smaller probabilities than 1e-2. Instead, you will have to deterministically ensure that each of the levels reaches its goal and is independent of the other levels. If this can be guaranteed, the probability of a large release is around 1e-6 per annum, which is generally deemed acceptable.

Old plants fail miserably with the last bullet, and have to try to compensate the incapacity to deal with consequences of a severe accident with somehow even more improved preventive measures. This will inevitably result into a more challenging safety case to ensure the acceptable safety level.

 

[NUCENG]

If you aim at
-operational occurrence rate of less than once per year
-limiting functions capable of preventing 99 % of occurrences from propagating into accidents
-safety functions capable of preventing core damage in 99 % of accidents
-containment capable of preventing a large release in 99 % of meltdowns

you will not have to deal with smaller probabilities than 1e-2. Instead, you will have to deterministically ensure that each of the levels reaches its goal and is independent of the other levels. If this can be guaranteed, the probability of a large release is around 1e-6 per annum, which is generally deemed acceptable.

Old plants fail miserably with the last bullet, and have to try to compensate the incapacity to deal with consequences of a severe accident with somehow even more improved preventive measures. This will inevitably result into a more challenging safety case to ensure the acceptable safety level.

Your point of generalizing old plants fails by example. TMI2 was a meltdown accident in an older plant with no large release.

Chernobyl was a deliberately initiated event, the safety systems had been deliberately disabled, and there was no containment.

Fukushima was a 1E-3 event (earthquake/tsunami), the safety systems worked initiially, but failed due to lack of protection from flooding. I am not sure that containment failures at Fukushima would have occurred in a plant that didn't have such a glaring design deficiency.

And finally on your risk targets. PRA has exactly those kinds of targets. The problem comes when estimating probabilities for rare events and anticipating all the threats. TEPCO underestimated the threat of tsunami and didn't design turbine buildings to resist flooding. I understand they had completed the IPE level analysis (internal events) and some level of IPEEE analysis (External Events). I am guessing their results showed that they met the acceptable risk goal you describe.

The 1E-3 tsunami greater than 5.5 m was not recognized. failures of individual safety systems and power sources had probably already met or exceeded your 1E-2 failure probabilities. But that had not recognized the common failure mode of flooding. Suddenly all of the safety systems had a failure probability of 1.0. Containment never had a chance.

The biggest lesson to be learned from Fukushima is the importance of safety culture at all levels from National Regulators, to vendors, to the utility management, to operators, to engineers, and technicians, security and general laborers. The single biggest tool for safety is maintaining a questioning attitude. Thus when the geological evidence of large tsunamis was made known the question should have triggered action by regulators, managers, and techical staff. It didn't, and I attribute that to complacency, and a lack of integrity. Anyone with knowledge of the risk who didn't force the issue is at fault.

I don't know how to measure safety culture or include it in a PRA. Rare accidents are obvious triggers of attention to safety, but the real need is to use every issue, equipment failure, and problem, no matter how small, as a similar trigger. If a breaker trips or a fuse blows, don't just reset or replace it. Consider the circumstances when it blew. Was the operation abnormal? Was the circuit overloaded? Is the fuse or breaker the right size or rating? This sort of thinking becomes a habit. If you know people who have worked in the US nuclear industry, you may have observed this kind of thinking. It is why I believe that Fukushima technical solutions will be applied in US plants. It is not enough to simply implement techical solutions from from Japan, the safety culture must also be part of the mix.

 

[Most Curious]

TMI2 was a meltdown accident in an older plant with no large release.

An older design but, in fact, a reactor that had not been in operation for very long.

No appreciable release to the environmnet, of course.

Man made machines can and do fail - in spite of our best efforts. We learn from those incidents and make the next one LESS likely.

 

[NUCENG]

An older design but, in fact, a reactor that had not been in operation for very long.

No appreciable release to the environmnet, of course.

Man made machines can and do fail - in spite of our best efforts. We learn from those incidents and make the next one LESS likely.

I initially posted before I completed my thoughts - fat finger syndrome. I think what I added is consistent with your point.

 

[Most Curious]

Yes, NUCENG, we agree. I just wanted to make sure the "aging plants" folks did not get any more ammunition through misunderstanding what you meant.

Two ways to look at "aging plants": One is that old designs like Fukushima, even if newly constructed, have many of the faults of the original design on which the plant is built. The other is the accumulated operating hours and "wear out" of the components, buildings etc. The shroud failures in old BWR plants, as an example.


Designs evolve, including NPP. Hopefully, if engineers are guided by science, not politics or cost savings at the expense of safety, each newer generation design addresses safety issues of previous designs, particularly those revealed by accidents like Fukushima. Of course, there are thousands of other less dramatic issues that get addressed as well, such as materials, maintenance access to critical componets, etc.

The "build no new NPP" folks effectively doom us to obsolete designs that are less safe than later generations, just the opposite of what they profess to want. In addition, if we wait for the "perfect design" that has zero risk, no progress will EVER be made, no new plants will EVER be built.

 

[tsutsuji]

http://www.fnn-news.com/news/headlines/articles/CONN00211924.html Tepco says that the work to remove outdoor debris is almost finished.

http://www.47news.jp/47topics/e/222695.php 1.6 Sv was found on unit 3's first floor on 20 November. On 16 November 1.3 Sv had been found nearby.

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201111180006 Aerial photograph showing the large areas covered with water storage tanks.

 

[etudiant]

Imho the discussion of safety culture is not enough. For one, there is no evidence a safety culture can be maintained over many decades without getting ritualistic and stale, as it did in Japan. It did not in the US Navy either, afaik, as the Thresher accident demonstrated.
There has to be a serious focus on minimizing the failure at every level, just as rmattila said.
Otherwise it means we have learned nothing from Fukushimas finding out that events can be beyond plan.
Just as an example, the largest earthquakes in the US were about M8, centered on New Madrid, MO, about 200 years ago. Would current nuclear plants in the area shut down gracefully in the event of a recurrence or would the resultant large scale blackout have severe consequences?

 

[NUCENG]

Imho the discussion of safety culture is not enough. For one, there is no evidence a safety culture can be maintained over many decades without getting ritualistic and stale, as it did in Japan. It did not in the US Navy either, afaik, as the Thresher accident demonstrated.
There has to be a serious focus on minimizing the failure at every level, just as rmattila said.
Otherwise it means we have learned nothing from Fukushimas finding out that events can be beyond plan.
Just as an example, the largest earthquakes in the US were about M8, centered on New Madrid, MO, about 200 years ago. Would current nuclear plants in the area shut down gracefully in the event of a recurrence or would the resultant large scale blackout have severe consequences?

If you have a well implemented safety culture, actions to minimize risk happen automatically. I absolutely agree with you that we must continue to reduce risks where possible and especially when something happens to raise new issues.

As a US Navy officer, I was qualified as Engineer Officer for nuclear submarines. As a SUBSAFE coordinator during a submarine refueling overhaul after the loss of the Thresher, I respectfully disagree. The Thresher accident was caused by a non-nuclear seawater pipe rupture. The pipe had been weakened in explosive shock testing before the yard period. There are reports that the sub made a navigation error during testing which put them closer to the detonation than planned. The sinking occurred during sea trials following repairs. The Navy instituted the SUBSAFE program to require rigorous testing and inspections of non-nuclear systems exposed to sea pressure following the accident. Nuclear systems were already tested to those standards and were not included in the program. I learned much of the habit of safety conscious thought wile I was in the Navy. Perhaps your experience was different. But I believe the Thresher is a poor example when indicting the Navy nuclear safety culture.

My understanding and reading are the basis for the following. I am not presenting myself as a civil/structural or mechanical engineer. The New Madrid earthquake was a series of three main shocks over short time in 1811/1812 and the estimates I have seen indicated they were about M7.4. The new Madrid earthquake was closer to the type of earthquake we just saw in Virginia in a region of low seismic activity with a relatively solid (unfractured) crust. Japan and the west coast of the US are in a region of high seismic activity with well fragmented crust. North Anna saw high acceleration at high frequencies and lower total energy than the basis of the plant design. If the energy is at lower frequencies it has a larger effect on the structures. Current USGS estimates are only about a 10% chance of an relatively small earthquake on the New Madrid fault in the next 50 years. I reviewed information for one plant located several hundred miles from the New Madrid fault. Their evaluation of the effects of the 1811/1812 earthquakes would not result in significant damage at the plant site. I also reviewed the hazard maps on the USGS website and confirmed that those predictions are still valid even relatively close to the New Madrid area.

That said the NRC is preparing regulatory guidance (a Generic Letter) that will require plants in the central and eastern states to reevaluate seismic risk and design based on recent findings of higher potential ground acceleration during earthquakes than USGS had previously estimated. The plant I reviewed is on the list of plants affected by the pending guidance. So like TEPCO, they are aware of the risk AND, unlike TEPCO, are taking action to address that risk. NRC has also concluded from both the GI-199 issue and the North Anna Earthquake that there is no immediate safety concern. A large scale blackout could occur if the grid is brought down, but a tsunami is not much concern in that area. On site emergency diesel generators should remain available. So I would expect a better result than Fukushima. (See the point I made earlier - that doesn't mean we can ignore Fukushima!)

 

[etudiant]

The Thresher disaster surely showed that safety is indivisible, that it is not enough for the reactor to be secure if the surrounding systems are not. To me, the analogy to Fukushima is very direct, in both instances the reactors functioned as expected and nevertheless disaster followed, because of unexpected ancillary failures. That is why as rmattila suggested there must be specific provision to allow for a relatively graceful reactor failure, because somehow over many thousands of reactor years of operations it will happen.

 

[NUCENG]

The Thresher disaster surely showed that safety is indivisible, that it is not enough for the reactor to be secure if the surrounding systems are not. To me, the analogy to Fukushima is very direct, in both instances the reactors functioned as expected and nevertheless disaster followed, because of unexpected ancillary failures. That is why as rmattila suggested there must be specific provision to allow for a relatively graceful reactor failure, because somehow over many thousands of reactor years of operations it will happen.

All I have said is that safety culture makes complacency less likely. It is not a substitute for implementing lessons learned but makes those improvements almost in automatic. In addition by taking action on little problems it makes cascading small problems into big problems much less likely.

I really don't think there is an argument here. The link between Fukushima and the Thresher may be direct in your opinion, but it certainly is not current. USS Thresher sank in 1963. The Navy implemented your "INDIVISIBLE" safety concept 48 years ago. You used it as an example of why safety cultures don't endure. I don't think the Thresher era has any current validity. Heck that was even before I entered the Navy, and I haven't seen any SUBSUNK reports lately. Sounds to me like a pretty good safety record for nearly 5 decades.

But I have also agreed with rmattila and you that actions need to be taken based on Fukushima. And finally that action is needed even though there is a high probability a similar initiator (earthquake) in the US would show successful mitigation. And I believe that action is underway to take that action. So what is missing?

 

[Borek]

My understanding is that Tresher reactor doesn't pose any risk to the environment. In a twisted way it proves that correct design makes reactor safe even in the case of a serious disaster.

 

[dezzert]

The "build no new NPP" folks effectively doom us to obsolete designs that are less safe than later generations, just the opposite of what they profess to want. In addition, if we wait for the "perfect design" that has zero risk, no progress will EVER be made, no new plants will EVER be built.

And you have also just given the reason why in the near future all old plants will be shutdown. And I am amazed at anyone at this point in time who still tries to justify the need for the most dangerous resource ever created, nuclear power. Thank god there are intelligent people on this planet that know better.

 

[Shinjukusam]

And you have also just given the reason why in the near future all old plants will be shutdown. And I am amazed at anyone at this point in time who still tries to justify the need for the most dangerous resource ever created, nuclear power. Thank god there are intelligent people on this planet that know better.

You know, there is a thread specifically for more political discussion...

 

[NUCENG]

And you have also just given the reason why in the near future all old plants will be shutdown. And I am amazed at anyone at this point in time who still tries to justify the need for the most dangerous resource ever created, nuclear power. Thank god there are intelligent people on this planet that know better.

Sorry, in a list of the most the most dangerous resource ever created on this planet, nuclear isn't anywhere near coal (including TMI2, Chernobyl and Fukushima). Even if you don't believe in man-made global warming (or climate change), acid rain, mining accidents, transportation accidents, health effects of particulates and other emmissions, and waste issues make your overstatement clear and your prediction dubious.

Returning to my point of a safety program that has workd, when NASA restarted benchmarking efforts to improve their safety culture and performance they went to the Navy Nuclear Propulsion and SUBSAFE Programs.

They found:

"It is important to note that NASA’s benchmarking of the Navy submarine program has
been focused on the SUBSAFE and Naval Nuclear Propulsion Programs with full
understanding that these programs represent only two of the Navy submarine safety
domains ... This deliberate selectivity results from an early consensus of
the NNBE management team that these two high reliability programs would provide the
most meaningful comparison to NASA’s human rated space flight programs."

Specifically, they noted the record of the US Navy Nuclear propulsion safety record:
Through 2003... "Since its inception in 1948, the NR program has developed 27 different plant designs,installed them in 210 nuclear powered ships, taken 500 reactor cores into operation, and accumulated over 5,400 reactor years of operation and 128,000,000 miles safely steamed. Additionally, 98 nuclear submarines and six nuclear cruisers have been recycled."

There has never been a nuclear accident in any US Naval Nuclear Propulsion Plant or prototype.

Reference: http://www.nasa.gov/pdf/45608main_NNBE_Progress_Report2_7-15-03.pdf

 

[rmattila]

Your point of generalizing old plants fails by example. TMI2 was a meltdown accident in an older plant with no large release.

Chernobyl was a deliberately initiated event, the safety systems had been deliberately disabled, and there was no containment.

Fukushima was a 1E-3 event (earthquake/tsunami), the safety systems worked initiially, but failed due to lack of protection from flooding. I am not sure that containment failures at Fukushima would have occurred in a plant that didn't have such a glaring design deficiency.

You have a point there. However, I was not thinking so much of the experiences we have had so far (the number of which is fortunately very limited), but rather the design bases of the containments. If you don't have large enough volume to accommodate all hydrogen produced by cladding oxidation, a full meltdown will probably result into a release. And if you don't have filters in the vent line, you will probably have a rather large release (and even if you have filters, they will not be able to catch noble gases or organic iodine, unless it's a large dry bed instead of the more compact wet scrubber type).

If you don't have a core catcher, and your containment does not allow for flooding of the drywell in case of melt-through (either due to the pools sitting lower than the drywell or due to fear of steam explosions), you have difficulty controlling the core-concrete interaction, which may result into a containment failure.

Etc. My point was simply that if a full-scale meltdown is not included in the original design basis of the containment, it's difficult to prove it can prevent release in 99 % of the cases, which would be a plausible target for new reactor designs.

 

[dezzert]

You know, there is a thread specifically for more political discussion...

I apologize. I was having a bad hair day. No more political stuff from me. Except the below post ;>)