Press Release Back Number(2007)

Concerning Shutdown of Hamaoka Nuclear Power Station Reactor No. 4 to Repair Moisture Separation Heater Drain Tank Instrumentation Pipes

February 23, 2007
Chubu Electric Power Co., Inc.

Chubu Electric has confirmed that on February 8, 2007 during rated thermal output operations at Hamaoka Nuclear Power Station Reactor No. 4 (rated electric output 1,137 MW), water flowed into a drainage pit from the drainage pipe of instrumentation piping that measures the water level of a moisture separation heater(*1) drain tank (B-2)(*2).

The drainage pipe's drain valve was tightened, but a slight amount of water continued to flow to the drainage pit, so that Chubu Electric installed a camera for better monitoring the flow to the drainage pit. This phenomenon is not having any effect on the plant, where operations remain stable.

At this time we have not seen any changes in flow and we suspect that the situation developed because the inside of the drain valve was corroded by water flow.

Presently there is still a channel of water flowing even when the drainage valve is shut off, so we do not expect any improvement in the phenomenon beyond this. Based on this and the concern that the channel could expand and the flow increase, Chubu Electric will practice preventive maintenance by shutting down the reactor and repairing the part tomorrow.

To make sure the leakage is stopped, the repair job will include removing the drain valve(*3) and welding on a closure lid.

There are in addition seven other points with similar construction, and we will take the same steps there, even though they are not currently experiencing problems.

If the work proceeds as planned, the reactor will restart the same day and resume power generation on the 25th.

This incident has not caused any leakage of radioactivity.

(*1) A moisture separation heater enhances plant thermal efficiency by removing and heating moisture from the steam that is put out by high pressure turbines and sent to low-pressure turbines. Reactor No. 4 has two moisture separation heaters, each of which has stage 1 and stage 2 heaters.

(*2) The moisture separation heater drain tank recovers the moisture separation heater's drainage (water which will form when heating is complete and the steam cools into water) and returns it to a condenser.

(*3) The drain valve may be safely eliminated because it is not used during operations.