During full-power operation, numerous “fission products” are in approximate steady-state equilibrium, meaning roughly equal becquerel of I-131 and Cs-134, with a slow buildup of Cs-137. But they all cease to be created when the reactors are scrammed. Japanese regulators NISA and MEXT seem oblivious of the mysterious fact that I-131 Bq “reactor density” is still often reported double the Cs-134/137 Bq. The TEPCO data suggest that fission is ongoing despite the reactor shutdowns. This is bad news.
It seemed very bad taste for April Fool’s jokes, but a few weeks ago there were some very bizarre indications of ongoing criticalities suggested by TEPCO’s own reporting of Cl-38 in “stagnant water” of a drywell, plus, a “neutron beam” again implausibly claimed by Kyodo news to be observed at 2-km distance. All those things seemed to defy the laws of physics and were highly suspect, but they led Arnie Gunderson, Arjun Makhijani, and Chris Martenson all to conclude that the evidence pointed to ongoing fission in the Units 1-4 scrammed reactors and their SNF pools in warm shutdown. Maybe so.
Everyone with just a very basic understanding of reactor safety should know that once a reactor is scrammed, U-235 is no longer fissioning, and I-131 has no parent which can be decaying to create it in an ongoing process. SNF pools contain the million-year halflife I-129 which is difficult to measure, but the water circulating in intact SNF pools should have absolutely no detectable I-131 in them.
Units 1-131 all scrammed 3/11/2011, so it has been almost five full 8-day halflives for their I-131 to decay to stable xenon. At t=0, as we say, the Bq of I-131 and Cs-134 and Cs-137 would all be approximately equal, but, after five I-131 halflives, the “reactor density” radioactivity of I-131 should be only 1/2**5=~3% of what it was originally. Go look at all the data of relative radioactivity that TEPCO is reporting with dates of April 19, 2011 and you’ll see that instead of I-131 being below the levels of the two cesiums, I-131 is often twice as high as the two cesiums always reported.
Sure, iodine is more volatile than cesium, so, when you have an almost total fuel melt (in a “classic” release to atmosphere accident), 100% of the iodines can be released while maybe at most 35% of the cesium is released outside containment because the iodine can come out as vapor, while the cesium comes out as aerosol subject to agglomeration and also chemical binding with the concrete basemat.
The fact that nobody in Japan seems to know basics of reactor accident progression that I learned at Sandia Labs in early 1980s is truly scary, because it suggests they are playing with these broken/leaking reactors and SNF pools inside at least three buildings totally destroyed by steam explosions … as if the reactors and their SNF pools are broken toys that they’re using trial and error to try fixing.
April 19, 2011
Source: Gerson Lehrman Group