Fukushima Daiichi crisis – April 1 perspective
Posted on 1 April 2011 by Barry Brook
The Fukushima Daiichi nuclear crisis has moved off the front page of most newspapers, but a lot continues to happen, and the situation remains unresolved. Below I offer some personal perspectives on some of the things that have been widely reported over the last few days, and then I conclude with some official updates.
Disclaimer: What follows is
my interpretation of the sparse and often confusing information being made available by TEPCO, NHK etc. Take or leave at your discretion.
Will the GE Advanced Boiling Water Reactor (a Gen III unit) be built at Fukushima Daiichi to replace units 1-4?
1. Plutonium detected in the soil around the plant. A few isotopes of plutonium (Pu) have been found in soil at various test sites at the FD plant. This has
sent some folks on Twitter apoplectic. So where does it come from?
One theory, and quite a reasonable one, is that it is the global residual left over from the extensive atmospheric atomic weapons testing of the 1950s ”” 1970s. That would help explain the presence of Pu-238, for instance ”” an isotope not readily created in a power reactor.
Another thought is that there was a local source, either from volatilisation of sloughed material in the drying spent fuel ponds, or perhaps from the reactor cores (that was then carried away in minute traces via the vented steam). Being a heavy metal, however, the Pu would not mobilse readily and would deposit very locally. Remember, Pu is present in all spent fuel, via the U-238 –> Pu-239 transmutation pathway.
All reactor fuel elements that have been fissioning will contain plutonium. It is not something peculiar to mixed-oxide (MOX) fuel (which was being used in FD unit 3), as some have implied ”” there has been a lot of nonsense written about this during the past few weeks.
In short, Pu is a metal, not a demon. Indeed, from my perspective on the
Integral Fast Reactor technology, I see Pu as THE fuel of the future, and boldly predict that it will be looked back on, by some far distant civilisation, as among the most important elements humankind ever encountered. However, that’s for another post for another day. But if you want the full review now,
please read Cohen.
2. Containment integrity and core damage. The story that hit the headlines
was this…
Richard T. Lahey, former chair of nuclear engineering at Rensellaer Polytechnic Institute, in Troy, N.Y., was quoted as saying that the evidence he had seen indicated that fuel melted through the pressure vessel of reactor No. 2 at some point after the crisis began. He told The Guardian:
“The indications we have, from the reactor to radiation readings and the materials they are seeing, suggest that the core has melted through the bottom of the pressure vessel in unit two, and at least some of it is down on the floor of the drywell.”
While I respect his personal opinion as an engineer with professional experience with GE BWRs, I
really don’t think he’s correct– to me, as a logical analyst, it’s just not consistent with the recent data. The reactor pressure vessel (RPV) outlet temperature, RPV internal pressure, and drywell pressure readings, have all remained relatively stable over the last few days (see latest FEPC and JAIF reports at the foot of this blog entry). I can’t see that this could possibly have been the case if chunks of molten metal had burned a gaping hole through the 8″ thick steel vessel and then fizzed through the concrete floor to boot. It certainly didn’t happen at TMI-2 in 1979, and I don’t think that it happened at Fukushima unit 2 either. Lahey seems to think his theory is supported by the high radiation readings in the water trench adjacent to unit 2… however, I disagree, as I explain in point 3.
3. Trench water. I think
World Nuclear News had done an excellent recap on this:
Tsunami likely filled trenches. In short:
Analysis of the trenches at Fukushima Daiichi indicates they were probably flooded by the tsunami. Low radioactivity in one trench may result from capture of radionuclides from the air but high levels in another are unexplained…
…But while an answer appears close on the presence of the water, the levels of radioactivity remain unexplained. The trench at unit 2 is a serious concern due to radiation levels from surface measurement in excess of 1000 millisieverts per hour. Further sampling has not yet taken place due to this extraordinary level, and it is not clear if the dose rate is representative of the whole 6000 cubic metre body of water, although it does match the level in the basement of the turbine building. Unit 2 suffered suspected damage to its torus suppression chamber on the morning of 15 March.
The key to this riddle, I think, is the wetwell torus breech (which is likely to be a pinhole or crack) ”” there has clearly been damage to containment at unit 2, but NOT, I think, to the RPV. The radioactive water in the trench could also plausibly have come from cracked/burst piping or seals elsewhere in the containment/primary system (remembering that in a BWR, the cooling water/moderator also runs through the turbine directly, unlike in a PWR). But there is no reason to think that this water comes directly from the RPV or drywell (which is where the fuel would be if it had melted through the RPV). Indeed, I think the chances of a large steam explosion at this stage of events ”” more than two weeks out from the core damage event ”” is remote in the extreme, and even if this highly unlikely chain of events did occur, it would still not spread reactor fuel over a wide area, because most of the heavier material is very difficult to mobilise and disperse (remembering that there is no burning graphite in this situation, unlike Chernobyl, and even in that accident most of the actinides stayed put).
The
weird theories of Caldicott and her ilk, in which she fantasises about some ‘magical’ mechanism that is able to spread fine particulates of Pu across the landscape and into the lungs of millions of humans, and so (she outrageously claims) render the Japanese islands uninhabitable as a result, is simply beyond a joke (from
many angles). Actually, it’s nothing short of appalling, grossly unscientific, hyper-alarmism.
4. Spent fuel ponds. These continue to get serious attention, with regular injections of water. They have likely been the primary source of the Cs-137 releases. The current TEPCO plan is to
switch to fresh water injection ASAP. The pools in units 5 and 6 are now stable and both below 40C (see reports given at the end of this post), but there is still some concern of the pools in units 2, 3 and 4 especially. There was even a report that authorities are still
considering entombing them in concrete. It’s possible, but I really don’t think that will happen because it may solve a few short-term problems, and create other longer-term site-management headaches (
personal judgement).