Fukushima Unit 6 Cooling Pump Fails

An RHR (reactor heat removal) pump at Fukushima Daiichi unit 6 failed on  November 19th.
The suppression chamber suction valve for the RHR B pump suffered a broken drive shaft. TEPCO didn’t inform the national government until November 26th. This is a piece of safety critical equipment that requires notification to Japan’s nuclear regulator.

The valve leak was first noticed on October 17, the leak was noticed to increase on November 19th. Later that day it was discovered that the pump shaft was broken. The reactor no longer contains any fuel and other methods remained to cool the spent fuel pool. This appears to have caused some confusion at TEPCO, if this required notification to the nuclear regulator or not.

The unit 6 RHR pump A currently has the sea front pump down for inspection. TEPCO was able to cross tie the internal portions of the RHR pump A system to the RHR pump B system to hobble together one functioning system. This means this system currently does not have a back up system.

Translation of graphic text:
Cooling spent fuel pools
Can be cooled by RHR(A) and (B)
Replenishing spent fuel pools
Resupply is possible by RHR(A)

The RHR A system is under inspection of the seawater pump, so it is
Use tie line with RHR B-based seawater pump.
(end)

The suspected cause of the valve failure is over tightening of the valve. They plan to eventually replace the broken valve.

TEPCO document
https://www4.tepco.co.jp/decommission/information/committee/roadmap_progress/pdf/2019/d191128_13-j.pdf

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