(351.3484) WISE Amsterdam - This latest report shows more equipment problems than previously revealed. Two pressurizer valves -- not one -- stuck closed, a main steam isolation valve stuck open, and operators, apparently trying to avoid overfilling the primary system, shut down high-pressure injection and residual heat removal pumps earlier than previously reported.
Kansai did report previously that, because one pressurizer relief valve stuck closed, operators used the pressurizer spray system to cool the primary system, but it had not reported the problem in achieving isolation of the damaged A steam generator or operator maneuvers with the emergency cooling pumps.
While the earlier report said isolation of the rupture was achieved at 1:56 pm, the new report says operators determined that the A steam generator was the damaged one and flipped switches at 1:55 pm for isolation. However, the switch indicator light for the main steam isolation valve of the damaged generator showed it was still open. An operator was sent to manually close it at 2:02 pm. In the intervening seven minutes, radioactive primary coolant continued to pour into the secondary system while a leak path outside containment was still open. (The fact that the main steam isolation valve could not be activated from the control room was only revealed three weeks after the accident.) The earlier report also said high-pressure injection was terminated at 2:38 pm, but the latest says emergency injection was halted at 2:14 pm, as operators were struggling to cool the primary system with the two relief valves failing. They were apparently afraid continued injection would set off other problems in the primary system.
There are still many unknowns concerning the accident and the release of radioactivity, with Kepco and MITI releasing important facts only a few at a time. And the most recent official estimates for the release of radio-activity appear to be very questionable. Even though these estimates are now greater than those given earlier, they are without a clear basis. (The figures now given on the releases are approximately 20 billion Bq in rare gases and 700 million Bq in liquids -- as opposed to the earlier figures of five billion for rare gases and seven million for liquids -- and 400 million Bq of radioactive iodine.)
It has become clear to Japanese groups that the work of discovering the direct causes of the accident has just begun. It is equally clear that the root cause is the attitude of the government and power company in ignoring safety. According to the Citizens' Nuclear Information Center in Tokyo, activists across Japan are now calling for a complete phase out of nuclear power and are working on this in various ways. They hope to create a national groundswell of opposition even greater than in 1988. The Center, in the meantime, is demanding that the cause of the accident be thoroughly investigated by an independent body and, until the cause is discovered, all 17 operating PWRs in Japan be shut down, as they all are now considered to be subject to the danger of sudden rupture. (Mihama-2 is 500 MW PWR.)
Sources:
- Nucleonics Week (US), 7 Mar. 1991
- Nuke Info Tokyo (Japan), Mar/Apr 1991
- Nuke Info Tokyo, Extra, 28 Feb. 1991; "A Major Accident that Nearly Ended in a Meltdown", by Takagi Jinzaburo.
Contact: For a full account (or at least a full account of what is presently known), write to the Citizens' Nuclear Information Center, 4F Yoshinobu Bldg., 2-10-11, Mo-toasakusa, Taito-ku, Tokyo 111, Japan, tel: 03-3843-0596.
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