Day 35: Parts of the fuel has fallen to the bottom of the vessels

Last updated on March 1, 2013

10:00(CET)/08:00(UTC)/17:00(JST)

Just a short update for today. The number 2 turbine building basement is filling up with water as quickly as TEPCO is pumping it out. No word is said about how the similar work in number 1 and 3 is proceeding. Temperatures are on a downwards trend in all reactors. Pressure in the number 1 pressure vessel continues to climb slowly, containment pressures are stable. Not much new happening on that front.

The Japanese Nuclear Society has reported that their analysis shows that parts of the fuel of all 3 reactors has melted and dropped down to the bottom of the vessels. Small parts of molten fuel has according to their analysis dropped from the rods, solidified when hitting the water and then sunk to the bottom forming small grains. The grains are easily cooled since they have large surface area to volume ratio and they don’t form a geometry that is prone to re-criticality.

They also state it is unlikely that there is a large amount of molten fuel at the bottom due to the low temperature readings in the bottom head. Nothing really surprising there either and I pointed it out some time ago. None of this is really surprising.

Zeolite containing sandbags have been put outside the water intake for the number 2 reactors. Zeolite is a porous material that readily adsorbs different molecules (adsorbption is the process of molecules sticking to the surface layers of a material, as opposed to absorption that means its sucked into the material itself). It was used to clean contaminated water within the TMI power planet after the meltdown there.

TEPCO has ordered storage tanks from the US to use to store radioactive water in. IMO I think TEPCO is trying to do perfect when perhaps they should think about doing things adequate. It seems like the volume of water is so large that temporary solutions, like erecting temporary pools, should be considered. But then again it is always easy to be an armchair quarterback on opposite side of the Eurasian continent (other seems to share my general idea though). I haven’t seen any new published analysis of the radionuclide content of the water in the number 2 basement, it would be interesting to see what it contains. The dose rates from the water should be going down due to the I-131 decay. Over 95% of the I-131 has decayed now.

Nitrogen injection into the number 1 containment continues, but pressure in the containment has stabilized. Meaning there must be a leakage somewhere. The leakage can’t be very large however.

The radiation levels in the groundwater is increasing in the plant area. Otherwise radiation trends are all downwards around Fukushima. From IAEA

Gamma dose rates are measured daily in all 47 prefectures. The values tend to decrease over time. For Fukushima, on 13 April a dose rate of 2.0 µSv/h was reported. In the Ibaraki prefecture, a gamma dose rate of 0.14 µSv/h was reported. The gamma dose rates in all other prefectures were below 0.1 µSv/h.

Dose rates are also reported specifically for the Eastern part of the Fukushima prefecture, for distances beyond 30 km from Fukushima-Daiichi. On 13 April, the values in this area ranged from 0.2 to 26 µSv/h.

In addition to the 7 measurements referred to in yesterday’s brief, (note- these measurements were made at distances of 25 km and 33 km not 32 km and 62 km as reported), 13 more measurements were made on 12 April at distances of 25 to 33 km, West and Northwest from the Fukushima Nuclear Power Plant by the IAEA team. At these locations, the dose rates ranged from 0.5 to 16.5 µSv/h. At the same locations, results of beta-gamma contamination measurements ranged from 0.05 to 2.1 Megabecquerel/m2.

Analytical results related to food contamination were reported by the Japanese Ministry of Health, Labour and Welfare on 13 April that covered a total of 98 samples taken on 4 and 11 to 13 April. Analytical results for 76 of the samples of various vegetables, pork, seafood and unprocessed raw milk in nine prefectures (Chiba, Fukushima, Gunma, Ibaraki, Kanagawa, Miyagi, Niigata, Saitama and Yamagata) indicated that I-131, Cs-134 and/or Cs-137 were either not detected or were below the regulation values set by the Japanese authorities. In Fukushima prefecture on 11 April, twenty samples of various vegetables were above the regulation values set by the Japanese authorities for Cs-134/Cs-137, and one sample of seafood (sand lance) and one sample of spinach were above the regulation values set by the Japanese authorities for both I-131 and Cs-134/Cs-137.