Japan Reactor Shut Down After Water Coolant Leak Full Coverage Japan News TOKYO (Reuters) - A Japanese commercial nuclear reactor on the Sea of Japan coast was shut down Monday after officials found radioactive cooling water leaking within the reactor container.

In what could turn into the worst-ever water coolant leak in Japan, the No. 2 reactor at the Tsuruga nuclear station in Fukui Prefecture had leaked 82 tons of primary cooling water by 7 p.m. (1000 GMT), according the Japan Atomic Power Company.

Japan's worst leak of primary coolant water, which is radiated, was in 1979 when Kansai Electric Power Co Inc's Takahama No. 2 reactor leaked about 95 tons.

The coolant still appeared to be leaking at a rate of about five tons an hour at Tsuruga, a spokeswoman for Japan Atomic Power said, adding there was no radioactive impact on the environment.

The spokeswoman said cooling facilities at the 1.16-gigawatt reactor in Fukui prefecture was being refilled to the normal capacity of about 260 tons.

The reactor was manually shut down following fire alarms and anomalies in monitor indications at 6:48 a.m.

Five officials entered the reactor late Monday to investigate the cause of the leak, officials said.

The Ministry of International Trade and Industry (MITI) said the accident was rated 1 on the International Nuclear Event Scale (INES). A rating of 1 is the third-lowest, following ``out of scale'' and 0, while 7 is the most serious rating.

The worst nuclear accident in Japan was an explosion in 1997 at a state-run nuclear reprocessing plant in Tokaimura village north of Tokyo, which was rated 3.

There was also a leak of about 55 tons of primary cooling water in 1991 at Kansai Electric's Mihama No. 2 reactor in 1991, the MITI official said.

The Mihama leak was contained within water pipes. But at Tsuruga Monday and Takahama in 1979, primary cooling water leaked out of the water circulation system onto the container floor, the MITI official said.

Japan currently has 51 commercial nuclear power plants that provide one-third of the country's electricity.

******* got KI?*********

-- justme (justme@justme.net), July 12, 1999

Answers

Here is a stupid question for the "It takes 4 months to shut down a reactor croud." If the problem was found at 6:45 am monday, and the 1.16 gig reactor was shut down, How could 5 people walk into the reactor lator that same night. Lets assume that Late Monday was 11 pm. Thus, the reactor was cooled for 14 hours before 5 people could walk in to determine the cause of the leak. If it takes 4-6 months to shut down the reactor, how could these people go in to investigate 14 hours lator without being burned a little?

Sorry, I said it was a stupid question.

-- Ned P Zimmer (ned@nednet.com), July 12, 1999.

Ned - to confirm your question - I've shutdown and cooled down smaller reactors in two shifts to room temperature.

For these size reactors, it takes a little longer (18-30 hours to room temperature), but cooldown is still a fairly straight forward routine procedure. Though in this case, they probably didn't need to get that cool, they only need reduce pressure an dtemperature a little to allow safe access to inspect - it will depend on what the failure was, and on what the repair will be to know what final pressure and temperature will need to be.

The loss of coolant in this case appears to be to the cooldown pool under the reactor - which is designed to allow recirc and capture and reuse for cooling of the contaminated water. This is why there is no environmental impact - the water stayed inside the containment dome. Note that many Russian designs do NOT have such containment structures, nor the under-reactor recovery coolant chambers like this.

The report didn't say why the leak occurred. Stay tuned.

-- Robert A Cook, PE (Kennesaw, GA) (cook.r@csaatl.com), July 12, 1999.