The popular Press has a new buzz-word with which to prolong the public’s angst related to nuclear energy in general, and Fukushima in specific. It’s “recriticality”. Actually, the term is being used out of context. Recriticality is a term intended for use with respect to fuel bundles stored in spent fuel pools (SPF). Numerous measures are in place (including a insertion of neutron-scavenging control rods and boric acid) inside SPFs to prevent the exceedingly low probability of a self-sustaining fission chain reaction from happening. With respect to Fukushima, the term is being used to denote the possibility of the solidified corium in the bottoms of RPVs 1, 2 &3 re-liquifying with a subsequent uncontrollable re-start of the chain reaction. Actually, the concept should be described as “impossible”.
Here’s why. First, before the corium could re-liquify, it would have to be uncooled and dry for at least 38 hours (at this point in decay heat generation) to achieve temperatures in excess of 2500 oC. Second, the concentration of fissile isotopes in the corium is so low that water is needed to slow down free neutrons so that a “criticality accident” could occur. No water equals no acceleration of the sub-critical chain reaction. Third, even if it were possible to simultaneously dry out the corium and impregnate it with enough water for an escalation of the chain-reaction (which is patently contradictory), the Boron-based control rod material dissolved in the corium prevents the nuclear excursion. The corium in all three Fukushima RPVs could re-liquify from now until the next millennium and “recriticality” could not happen.
If it’s impossible with respect to three melted fuel cells at Fukushima, then why is recriticality being broadcast at all? Only a vastly tiny fraction of the world’s public knows what recriticality means. The term sounds scary. Anxiety naturally diminishes with the passage of time. “Recriticality” is used to perpetuate the public’s nuclear anxiety level since there’s very little scary news currently coming out of Japan. The Press doesn’t care a bit as to whether or not the foundation of a story it true. If the Press can find someone to quote (including other news media), the story will be broadcast because it is good for business. Besides, most media reporters wouldn’t know a neutron from a ping-pong ball, so reporter ignorance only serves to exacerbate the misconception. Regardless, if something is “newsworthy”, what you don’t know will be used against you. Adding to the problem are Japanese “experts” saying corium recriticality is “highly unlikely” and/or “not impossible”. Tell it like it is! It’s a unicorn…mentally conceivable but not ever going to happen.
For a more detailed explanation of “criticality” and “recriticality”, go to…
Now…back to Fukushima…
- TEPCO has announced that it’s company’s manual for nuclear emergencies was essentially useless during the accident phase at Fukushima. They say that a complete loss of AC power for an extended period of time was considered too unlikely to be worth mentioning, so procedures were never devised to mitigate accident conditions like those which occurred at Fukushima Daiichi. TEPCO, and it seems the governmental regulatory agencies who approved the procedures, worked on the assumption that the installed emergency diesel generators would operate “no matter what”. (Kyodo News Services)
- TEPCO also announced something that should come as no surprise to readers of this update page…there was no hydrogen explosion inside the reactor building of unit #2 on March 15. TEPCO says they “erroneously recognized” something akin to an explosion had occurred at No. 2 unit at the same time unit #4’s refueling deck exploded. (Kyodo News Services) It seems the TEPCO home office staff also failed to recognize their plant control room records. The unit #2 entry at 6am on March 15, is “large impulsive sound around suppression chamber”, whereas the refueling deck demolition events of units 1, 3 & 4 are entered into the operator records as explosions. Why has it taken so long for the TEPCO home office to get it right?
- The TEPCO announcement also contains a re-statement of their belief that unit #2 sustained the most extreme meltdown of the three RPV’s of concern. They continue this questionable speculation because it has taken longer than units 1 and 3 to bring the #2 RPV temperature below the desired 100 oC criteria. Further, TEPCO points to the “blowout” panel on the west wall of the unit #2 refueling deck being open to the atmosphere, which may have been caused by the hydrogen explosion of unit #1.
Some of the hydrogen that reached the refueling deck may have wafted out to the external atmosphere and kept the internal mixture below the explosive point. TEPCO says this is why the unit #2 reactor building remains intact. (Kyodo News Services)
But, there’s also another reasonable possibility. The #2 fuel cell was uncovered and without any cooling water injection for about 2.5 hours on March 14. Because the depressurization of the Reactor Vessel was successful (not the containment structure), fire truck pumps began injecting cooling water into the RPV at the end of the 2.5-hour period and never stopped, thereafter. (From control room records, again) Plus, the decay heat production rate for unit #2’s core was unquestionably the lowest of the three units. These two facts strongly suggest the level of fuel damage within the unit #2 fuel cell was the least of the three units of concern, and by a wide margin. In fact, it is not unlikely there was actually very little melting in unit #2, if any at all! Was there fuel overheating and significant hydrogen production? Unquestionably. Was there a massive meltdown in excess of units # 1 and 3? Questionable, if not utterly doubtful.
- The TEPCO announcement further adds that the hydrogen build-ups on the unit #1 and 3 refueling decks may have resulted from the silicon-based seals around the containment vessel’s upper heads (lids), separating the primary containment from the refueling deck, may have over-heated and “not functioned properly”. (Kyodo News Services) We find this to perhaps be another overly-simplistic rationale by TEPCO. Possible? Well, not impossible. Likely? Not unlikely, without a doubt. Actual or likely? Probably not.
- The TEPCO statement goes on to say that Prime Minister Naoto Kan’s visit to Fukushima Daiichi the morning of March 12 did not cause any delays in venting (depressurizing) the unit #1 primary containment. (Kyodo News) This changes nothing. Kan’s insistence on a complete 3km evacuation and national press conference before venting could start, was the most significant reason for the delay in venting on March 12. His visit to the site later that morning never had anything to do with it.
- The Tokyo government (i.e. NISA) has reported that TEPCO had found a 10 meter tsunami to be possible for Fukushima Daiichi in 2008, but didn’t report it to anyone until a few weeks before March 11. (NHK World) Again, this should come as no surprise to regular readers of this update. IAEA’s preliminary findings relative to the Fukushima accident included the above back in June.
- The European Union has announced that the stress tests run on the continent’s 143 reactors found “no major problems”. (NHK World) Already, some of the more notorious prophets of nuclear energy doom have called this a whitewashing of truth, and another example of their “international nuclear conspiracy” superstition.