Clock Ticks On Fukushima Unit 5 Cooling Outage As Typhoon Hits Japan

TEPCO reported over the weekend that they found a leak in a valve that is part of the cooling system used for the spent fuel pool of unit 5. The system was stopped as they identified the leak. TEPCO noted they have about 9 days before the spent fuel pool would reach a heat level that they are required to report it to authorities (65 Celsius).

The “reactor auxiliary cooling system” was found to have the leak on the sea water side of the system past the heat exchangers. The way this system is designed they could pull water into the three heat exchangers but have no way to expel that sea water back out to sea as all three exchangers share one outlet pipe. Without a way to bypass the section with the broken valve the system is out of service.

TEPCO managed a very bizarre repair with patch, wood and ratchet straps but says they must figure out an actual repair before the system can be restarted. This is where things became a little weird….

(photo TEPCO)

NHK reports that if TEPCO can not get the system back in service they would start using sea water to cool the pool. We are trying to confirm if this is a poor translation on NHK’s part. If it is indeed true it is a desperate step on TEPCO’s part to dump seawater directly into the spent fuel pool. This damages the pool chemistry and accelerates corrosion.

The quote from NHK: ” TEPCO says the temperature will reach the company’s safety limit of 65 degrees in a little over a week. The operator plans to channel seawater into the pool to curb the rise in temperature.

TEPCO’s daily reports, only available in Japanese seemed to indicate a different approach to keeping the pool cool. This seems less desperate and logical but TEPCO didn’t specify how they would do this. It is possible they have an existing method to share this system, or think they could improvise sharing it within the needed time frame. Since TEPCO doesn’t explain it leaves everyone guessing. The actual technical names of the systems in question are also left out.
Machine translation of the TEPCO report below:

“In the future, the fact that while looking at the spent fuel pool water temperature, switch back and forth emergency heat load operation cooling operation and (core cooling) and (spent fuel pool cooling) reactor shutdown due to the residual heat removal system, as required will do the cooling of the spent fuel pool, depending.”

Adding to the short time frame to determine a repair or come up with a replacement valve and conduct the work, is the typhoon making landfall in Japan. Super typhoon Neoguri is set to make landfall in Okinawa as a category 5 today. It is expected to eventually roll up the entire length of Japan with a downgrade to a tropical storm assumed by the time it reaches the region near Fukushima Daiichi. With most of the country under either typhoon or severe storm threat this could complicate bringing in parts to complete the repairs.

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