Before today’s relatively brief list of updates, there seems to be some confusing information on both the Japanese Atomic Industrial Forum (JAIF) and International Atomic Energy Association (IAEA) charts for the status of the three Fukushima Daiichi Units that remain in an emergency condition. Specifically, the water levels in each reactor pressure vessel. Both the JAIF and IAEA charts say that all three reactor fuel cores are currently partially uncovered (present tense phrasing), and the charts have been displaying this for more than two weeks! Paradoxically, scrolling down from the JAIF chart on page 2, to page 5 (of 6), we find that all three reactors have water levels listed. This becomes very curious at best. Here’s why.
With all Boiling Water Reactors (BWR), water levels are not measured relative to the fuel core, but rather well above the top of the fuel cells. In fact, all water levels displayed are actually located in the steam separator (#6 in the below diagram), which is between 10 to 15 feet above the top of the fuel cell (# 15 in diagram).
There are no water level detection devices that monitor the fuel core itself. This is because during routine operation, the water in the reactor core boils at a terrific rate. Thus there is always a roiling mixture of water and steam in the fuel core. Yes… the fuel cells are built to operate in a steam environment. They are necessarily much, much tougher to damage than the Pressurized Water Reactor fuel cores (like TMI) which have no boiling in the core. In the BWR, if a full automatic shutdown (SCRAM) happens, the control rods are literally rammed into the core, stopping the chain reaction in less than a second. This immediately stops the majority of the boiling, and the level of the steam and water mixture drops, suddenly and rather dramatically, because most of the steam bubbles collapse. By keeping the range of operating water level way up above the core, the fuel core below never gets uncovered, even if the rector experiences SCRAM from 100% power. Thus, the water level detectors only measure water levels beginning many feet above the top of the fuel in the core! Any water level shown on the water level monitors means the core is completely covered and there’s lot’s of water on top of that. Many feet of water, in fact. JAIF’s data page (5 of 6) displays detected water levels in all three reactors, and because of the well-above-the-core location of the detectors, there’s at least 15 feet of water indicated to be on top of each fuel core!
The cores cannot be partially uncovered on charts and then shown to be totally immersed using the data the charts are supposed to be based on. This is a terrible contradiction.
And, in a hot reactor condition driven by decay heat, like we had at Fukushima for at least 5 days before fire truck pumps were available to supplement the steam-driven feedwater pumps, there was unquestionably steam engulfing the fuel cells sticking out above the water levels during partial uncoverage periods between feedwater injections. In other words, the hot, uncovered fuel cells in the reactor cores were probably never really dry! All the water inside the reactor pressure vessel must be boiled off before the steam temperature can increase to temperatures capable of causing severe fuel damage like TMI (severe meltdown – NRC, 2009). We don’t know if a complete loss of water level was ever the case in any of the three Fukushima cores of concern. And, we won’t know until the pressure vessels are opened and visually inspected.
Further, no licensed reactor operator in the world would intentionally leave the fuel cores of three at-risk reactors partially uncovered for two weeks. As soon as the ability to pump enough water into the reactor to keep the core covered is available, the operator will keep the core covered, with many feet of water level above the core to provide an appropriate margin of safety. No reactor operator in the world would neglect doing this. For JAIF and IAEA, posting status reports that say the fuel cells are, and have been partially uncovered for two weeks, is an insult to reactor operators everywhere! I have refrained from mentioning this out of respect for JAIF and IAEA, but the resolution of the the posted water level contradiction is way over-due.
Now, for today’s relatively few available items of update…
- Work continues to remove the water from all four turbine building basements. Further improvement in the ability to bring all three reactors into the optimum safety condition of cold shutdown, and restoring normal cooling and water cleaning systems on the spent fuel pools, will not happen until the contaminated water is removed from these areas.
- Plant workers are testing the spray of synthetic resin on debris outside the common spent fuel pool building. Before further spraying happens, it should be determined whether or not it is effective in keeping dust and debris from becoming airborne.
- Radiological monitoring devices located at the outer boundary of the TEPCO property have been re-energized and are providing radiological data.
- Asahi Shimbun today reports that “External power has been restored to all four reactors and lights have been turned on in the central control rooms.” This is an example of misleading information being broadcast in all news media reports around the world. The reactor is inside the reactor building. The reactor building (RB), as well as the concrete vault rooms for pumps and piping located between the turbine buildings, and the control rooms for each unit, are NOT the reactors. None of the equipment in these areas needed for cold shutdown have been re-connected. Only the control rooms. The reactors are equipment inside the RBs. To indicate that the four RBS and control rooms are “all four reactors” is a gross mis-statement. All news media ought to get it right on this point, at least.
- To make matters worse, Japan’s Nuclear and Industrial Safety Agency (NISA) is doing essentially the same thing. Kyodo News reports the discovery of a cracked concrete pit completely outside one of the Fukushima buildings (see below) has NISA saying, ”We will also check whether there are cracks at other reactors as soon as possible.” This makes it sound like the discovered crack is possibly on something attached to the reactor itself, or perhaps physically part of the reactor pressure vessel. I hope this is a translational problem, and not something endemic to future NISA statements.
- On another note, Asahi is entirely correct in saying that the current situation with high radiation levels will limit the amount of time workers can do their jobs. Once the substantial radiation sources from the four pools of turbine basement contaminated waters have been removed… radiation levels in the most important areas of work needed to bring all three reactors to a cold shutdown condition… work can progress.
- NHK, Asahi, and Kyodo News report that one source of seawater contamination has been “confirmed”. A relatively small 2 meter deep pit for plant power cables was found to have 4 to 8 inches of contaminated water in it, and it’s walls were cracked. TEPCO says this cracking lets the contaminated water get into the ocean. Concrete will be used to fill the cracking and stop the leak. However, this discovery is but one straw in a rather large bale of hay. The volumes of water that must have been leaking into the ocean in order to cause the concentrations of contamination detected to date, are far, far, far more than could ever have come from a relatively small cable pit. NHK seems to believe TEPCO has found the source of the entire flow of contaminated water into the sea. No way! Not even four cracked pits could do it.
- Massachusetts Institute of Technology reports that “All units are currently being cooled by injection of fresh water, using temporary pumps, with backup power supplies in place in case of further electrical power issues. TEPCO reports that water temperatures in the units are below 100 C in the pressure suppression chambers, and that no reactor coolant is being leaked to containment.” Lots of good news indeed.
- MIT also reports “The EPA has continued to monitor the potential pathways for radiation exposure of the U.S. population. To date, radiation detected in milk is on the order of picocuries (10-12 Curie) per liter. This is 5,000 times lower than the FDA’s Derived Intervention Level. A Derived Intervention Level is the point at which the FDA would act to take the food in question out of our food supply.”
