From on-going Japanese Press reports, it seems TEPCO and NISA believe Unit #2 reactor fuel cell has the most damage, compared to reactors 1 & 3. In fact, they think much of Unit #2’s fuel cell has melted. As a result, this writer has been puzzled for more than two weeks. More fuel damage usually means more hydrogen. So, why was there no hydrogen explosion in the upper spent fuel handling area of Unit #2? Just wondering…
- Speaking of spent fuel (weak segue), The Japanese news media reports TEPCO has remotely sampled the water in unit #4 spent fuel pool and found I-131 and Cs-137 levels indicative of some fuel damage. In fact, TEPCO says that most of the fuel bundles appear undamaged. NISA says the isotopic levels are about 100,000 times higher than would be typical for pool water with no damaged fuel, but much lower than expected in a worst case scenario. The levels reported indicate that relatively few fuel bundles are actually damaged. Western Press generally speaks of over-heating as the cause. While over-heating is one possibility, there are also two others which are at least as likely, as reported in Japan. First, a considerable volume of debris and structural steel fell into and on top of the pool. Plus, the large, multi-ton polar crane used to move fuel bundles in the pool, collapsed on top of it all. This could have caused physical damage to at least some of the fuel bundles sufficient to release the I-131 and Cs-137 in the sample. Further, the heavy debris lying on top of the fuel bundles may have restricted water flow through some of the fuel clusters resulting in localized pockets of over-heating. Second, several rain showers and storms have probably washed the isotopes coating the debris over the pool, into the pool. However, no-where in the Japanese Press do we find speculation that the water level in the pool ever dropped low enough to expose the fuel clusters. NISA says this possibility cannot be totally eliminated, but the debris-damage scenarios are now possible since remote cameras have shown the considerable amount of debris coverage over the entire spent fuel handling deck. In this writer’s opinion, the debris did the damage…not overheating.
- Asahi Shimbun reports that TEPCO and NISA are putting together plans for the removal of all spent fuel bundles in #4 spent fuel pool. The recent remote camera images and the relatively low isotopic activity level of the water in the pool make them feel removal of the fuel bundles is possible. Their preliminary idea is to fabricate a metal structure around the pool area. While radiation levels right now would make this impossible, by raising the water level to maximum the radiation levels would drop considerably. Camera images indicate there was at least 2 meters of water above the fuel bundles when the sample was taken, then 195 tons of water was injected into the pool, raising the level another meter. Radiation level was detected at 84 millisievert/hr. By adding four more meters of water level ( ~740 tons) and filling the pool, radiation levels will plummet. One foot of water lowers radiation levels by a factor of ten. Four meters of added water shielding will drop rad levels by a factor of more than a trillion. (ten to the twelfth power) Once the fuel pool cooling and cleaning system is functional, much of the isotopic concentration in the water can be filtered out which will further lower the rad level. Cleaner water and higher water levels ought to provide a relatively safe condition for the construction of the metal enclosure.
The actual removal and storage of the fuel bundles is preliminarily planned to utilize the process and equipment developed for the removal of the severely melted fuel cell at TMI. Because it is not thought there is widespread meltage of the fuel cells in the #4 pool (if any), removal of the cells and their examination for possible damage level will be much, much easier than the TMI experience. The fuel clusters can then be loaded into 100 ton casks (under water, of course), and the casks then removed by cranes for storage at a yet-to-be-determined location at Fukushima Daiichi. In addition, the equipment used at TMI was remote-operated in order to keep radiation exposure to the operators as low as reasonably achievable. (ALARA) However, what will actually be done at Fukushima depends on how low radiation levels become after the pool is filled, the water fully filtered and cleaned, and all the contaminated debris has been removed from the upper deck.
One thought-provoking aside…wouldn’t it be interesting if one of the most important outcomes of the TMI meltdown turns out to be the procedures and equipment used for the safe and successful clean-up of Fukushima?
- It now seems (Asahi, again) there are three emergency power lines that have been strung into Fukushima Daiichi. All three come from a Tohoku Power Company transmission station about a km. inland. Two of the lines are connected to Units 3 through 6, and the other to Units 1 & 2. Monday’s earthquake temporarily interrupted power through the line to Units 1 & 2 (50 minutes), but did not interrupt the flow of electricity through the other two lines. One encouraging implication is that the Japanese companies have put their competitive differences aside for the good of everyone. (Standing-O)
In addition, the emergency mobile generators and many of the fire trucks used to pump water into the reactors before the emergency power lines were completed, are still on-site. They were available if the loss of power to Units 1 & 2 became extended.
- The milk from the farms surrounding 7 cities and towns in Fukushima Prefecture is now available in local stores. Tests on the milk by three separate labs all agreed that the milk was safe for unrestricted consumption. This indicates, not only are the conditions at the Fukushima power complex calming down, but the world around the power complex is beginning to recover, as well.
- NHK Japan reports TEPCO’s April 12 seawater samples show that activity levels of the water next to Unit #2 have dropped by a factor of 1000 since April 2. (from 7.5 million Bq/cc down to 2,500 Bq/cc) This was not in the levels supplied by the JAIF report yesterday.
- Kyodo News reports that the April 7 earthquake aftershock exceeded the design basis for the Onagawa Nuclear Power Station. The Onagawa design basis is 451 gal (a vertical acceleration unit), while actual vertical acceleration was 471 gal. The was no damage to any of the Onagawa equipment, and there should not have been. Be reminded, the design basis is the minimum specification required to be met or exceeded in order to be licensed to build the plant. What the actual as-built specifications might be are never given political or legal credit. As it turns out, the GE design used for reactor and containment construction in Japan has a generic design criteria (as built) approaching 1000 gal. Isn’t it about time that governments give political and legal credit to as-built specifications for nuclear plant safety, and not the preliminary specifications used to decide the make and model of plant to be built?
- TEPCO is now using double-layered “silt dams” in the further attempt to restrict contaminated leakage from Units 3 & 4 to the open sea. Silt dams are reasonably good at collecting suspended solids from water flowing through them, but the dissolved stuff passes right on through. Iodine is mostly in a suspended form, but a small fraction is necessarily dissolved. Thus, the silt dams should restrict most of the I-131 leaking, but not all of it.
- TEPCO measurements of the radiation level at the property boundary is now below the 5 microsievert/hr limit.
- TEPCO reports that water level in a trench outside Unit#2 was lowered 6 cm by pumping the water into Unit #2 condenser. Several hours later, the water level had re-risen 4.5 cm. It seems the trench will not be drained until the waters inside the turbine basements are removed. The water in the #2 turbine basement began to be pumped into the condenser using a submersible pump on April 12.
Finally, TEPCO says they will begin inspection of the Kariwa nuclear power station on April 15. After inspection, they will decide if any “restoration” work needs to be done before restarting the power plants. The restarting of the seven units at Kariwa would increase Japan’s electrical capacity by nearly 8,000 Megawatts. The delay in doing this was in order to provide all available resources to the Fukushima Daiichi emergency. Now that things have become relatively stable, efforts to restrat Kariwa’s power plants can begin.
So, what’s more important? Recovery from a disaster that kills more 25,000 and makes hundreds of thousands homeless, or mitigation of a grossly exaggerated nuclear emergency’s risk because of fears predicated on misunderstanding and misconception? The Hiroshima Syndrome strikes again.