November 20, 2013
In 2012, Japan’s congressional investigation into the Fukushima accident (NAIIC) said it was possible that the unit #1 accident was started by the 3/11/11 earthquake. A few plant workers said they saw water leaking in the vicinity of the unit’s Isolation Condenser before the tsunami hit, and the NAIIC said it had to be proven that it was not an indication of emergency cooling failure. Several months ago, the Nuclear Regulatory Authority sent in a team to find out what may have happened. They said there was no evidence of earthquake damage and the water had probably sloshed from the pool on the next-higher floor and ran down the walls. That should have put an end to the “earthquake caused the accident” speculations.
But…not so fast.
This past Monday, the Japan Times published an English translation of an article from the Japanese-only magazine Sentaku. A former Tepco “plant engineer”, Toshio Kimura, believes that key components in unit #1 were seriously damaged by the quake before the tsunami hit. He worked for Tepco for 17 years (1983-2000), 12 of which were at F. Daiichi. He says Tepco’s own data suggests his claim is factual. He explains, “An effective means of determining the true cause of the accident would have been to analyze recorded data related to transient phenomena — data that show what happened near the reactor cores.” This data was released by the company in August, but Kimura says it was incomplete. In September, Kimura prepared a report titled “Leakage from the piping in the Fukushima No. 1 nuclear power plant caused by vibrations from the earthquake” where he delineated his claim. Unfortunately, Mr. Kimura’s view is based on gross naivety relative to how Boiling Water Reactors operate, and an obvious misreading of the time-line of the accident.
Mr. Kimura’s interpretation of the data immediately following the earthquake seems to be based on misconceptions relative to BWR operating phenomena. He says that as soon as the quake ceased, “about 30 percent of coolant inside the core started flowing backwards and that after the coolant flow returned to the normal flow direction, the core flow fluctuated and eventually became less than zero.” If he had any operational training or experience with a BWR, he would have known what really happened.
During full-power operation of a BWR, a massive amount of steam is constantly being produced inside the fuel core of the reactor vessel. Two large pumps are constantly recirculating the water flow through the core to uniformly admix the steam with the water. The monitored steam/water level is actually several feet above the fuel bundles showing the top of the mixture. When the reactor experiences a full, rapid automatic shutdown (SCRAM), the steam is quickly washed from the fuel core. Indicated water level necessarily drops due to the volume of steam no longer in the core area. Reactor operators and operation’s engineers call this phenomenon “shrink”. A reasonable analogy would be what happens when a pan of hot liquid boils-over on the household stove. When the pan is removed from the heat, the boiling almost immediately stops and the roiling mixture of bubbles and hot liquid rapidly “shrinks” down to only hot fluid.
The amount of shrink after a reactor SCRAM is in the 25-30% range, depending on the model type and size of the fuel core. Soon after the earthquake-induced SCRAM on F. Daiichi unit #1, the typical “shrink” occurred. Mr. Kimura, obviously unaware of this fundamental BWR operating phenomena, erroneously assumes the flow through the core had reversed! He further tries to support his misconception by making another, even wilder assumption. He says that if all flow through the core stops, natural circulation should keep flow through the core at about 10% of full-power level. He says that the apparent reversal of flow is evidence that a pipe must have broken somewhere in the systems attached to the reactor vessel during the quake. Kimura also says a pump “designed to draw up water from the bottom of the containment vessel” was operated occasionally, indicating a leak from the reactor into the containment. There is nothing about such a pump being operated in the operator records kept by the control room staff between the quake and the tsunami-induced power blackout. For that matter, all records kept by the control room staff show that all emergency systems were operating precisely as they were designed and the water level in the reactor was exactly where it was supposed to be.
But, this is not Kimura’s only misrepresentation. He says the water level in the reactor reached the top of the fuel core (TAF) and at radioactive vapor leakage out of the containment began 5:46pm, less than three hours after the quake. Kimura adds that plant management restricted access to the reactor building at 5:19pm, further proving that the meltdown had begun. However, where he got these times from is an absolute mystery. Unit #1 staff records show that the entry restriction due to high radiation exposure was at 9:51pm. Further, at 10pm, the water level inside unit #1 reactor was 55 centimeters (about 22 inches) above TAF. The meltdown hadn’t started yet.
Based on his naïve assumptions, Kimura claims that Tepco is covering up the fact that the earthquake, not the tsunami, caused the nuclear accident at Fukushima Daiichi’s unit #1. He says the cover-up is designed to try and persuade Japan that other, undamaged nukes can be restarted so that Tepco can turn their circling-the-drain finances around. The article itself adds, “Behind Tepco’s continued refusal to release all the data and to admit that the earthquake damaged the piping is a fear that serious doubts will arise about the safety of its Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture, which it hopes to restart as soon as possible.”
Kimura also claims that if his “truths” were known, no bank would loan money to Tepco and they would quickly go bankrupt. But, alas, the man’s words are not worth the fonts used to write the magazine article and the Japan Times translation.
The Sentaku article closes with the following statement, “It likely will not be long before ‘lies’ by Tepco are brought to light.” To the contrary, it likely will not be long before the “gross misconceptions and base assumptions” by Toshio Kimura are brought to light.