KK-7 stopped due to radioactive leak KK-6 begins start-up tests Nuke Info Tokyo No. 132

Tokyo Electric Power Company (TEPCO) was hoping that Unit 7 (ABWR, 1,356 MW) would soon be the first plant at its Kashiwazaki-Kariwa Nuclear Power Station (KK) to resume commercial operations since the July 2007 Chuetsu-oki Earthquake. However, on July 23, the day before the plant was scheduled to enter commercial operations, there was a leak of radioactivity in the reactor’s primary circuit. It was suspected that the leak came from a damaged fuel rod. The governor of Niigata Prefecture responded by choosing to prioritize safety and public confidence. As a result, approval for commercial operation has been postponed for several months.

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The reading for xenon-133 (a noble gas with a half life of 5.24 days) in the primary circuit, where steam or hot water flow from the reactor to the turbine through the condenser and back to the reactor, was found to be six times the normal level. The following day (July 24), the reading had increased to 450 times the normal level.

Apparently, the xenon-133 gas (a fission product) had escaped from a small hole in the casing of a fuel rod. Several questions arose as a result of the leak. Was the hole formed as a result of the Chuetsu-oki Earthquake? Will it increase in size? Are there holes in any other fuel rods?

TEPCO claims that by inserting and withdrawing control rods it was able to identify the fuel assembly containing the leaking fuel rod. This assembly was not inspected before start-up tests began on May 8. KK-7 has 872 fuel assemblies, just 20 of which were inspected using an underwater camera. These visual inspections did not reveal any problems, but when two of these 20 fuel assemblies were further inspected using a fiberscope, foreign matter was discovered in one of the assemblies. This fuel assembly was removed and disposed of. Not surprisingly, TEPCO was criticized for the inadequacy of its original inspection.

The upshot is that KK-7 will not resume commercial operations as scheduled. The plant is currently undergoing tests at below full power. However, on September 1 TEPCO announced that it would not wait for the next scheduled periodic inspection, but that instead it would shut down the reactor at the end of the month to check the other fuel assemblies.

In March this year Niigata Prefecture’s technical review committee allowed the plant to begin start-up tests, ignoring warnings from some committee members. Considering the way things have turned out, it is fair to state that the committee shares responsibility for the current situation. The experts who warned the committee in March have pointed out that unless the leaking fuel assemblies are taken apart, it will not be possible to find precisely where the radioactivity is coming from or the cause of the leak. Debate on the issue within the technical review committee and the subcommittee looking into equipment integrity and earthquake resistance is continuing.

Meanwhile, KK-6 began start-up tests on August 31. TEPCO intends to bring it up to full power by mid September. The three local groups opposed to nuclear power, along with concerned citizens, are demanding that start-up tests be suspended until the investigations into KK-7’s leaking fuel rod problem have been concluded. On September 4 they submitted demands to Niigata Prefecture and Kashiwazaki City for both KK-6 and KK-7 to be immediately shut down and for thorough inspections to be carried out.

Yukio Yamaguchi (CNIC Co-Director)

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