Keep in mind that between 90 and 160 tons of solidified core melt are in the recesses beneath the Unit 4 reactor room. NUKEFACT 24, "Inverse Multiplication and Fuel Loading - Part I: Fundamentals", showed that, in its simplest form, a reduction in shutdown reactivity is by the same factor as any increase in neutron level. And, if the worse case reports were true, then the solidified core melt was alarmingly close to criticality. The cause of the increased neutron level was not known at the time but one possibility given was that it was caused by leakage of rainwater under the sarcophagus. The water flowing in and around the solidified core melt would act as a moderator/reflector and increase the value of keff. We have seen no reports to indicate more definite findings since that time.
Now there are new developments being reported, as follows:
FUNDING IS SET FOR CHERNOBYL SHUTDOWN
BERLIN, July 5 –– After years of delay, the mammoth task of rebuilding a leaky cement shell encasing a ruined nuclear reactor near the Ukraine town of Chernobyl can now proceed after more than forty nations pledged here today to cover almost all of the estimated $768 million in construction costs. A temporary cover was hastily built by the Soviet Union shortly after the accident occurred but experts say a new concrete tomb is urgently needed to prevent further emissions of radioactivity from poisoning the surrounding region.
The last of Chernobyl's four reactors is due to be taken out of service by the end of this year; by 2005, the remains of the reactor that exploded and burned are to be encased in a vast cement shell to prevent further emissions of radiation. The country plans to build two nuclear reactors to replace it.
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CHERNOBYL REACTOR SHUT BECAUSE OF FLOODING
KIEV, Ukraine July 11, 2000 -- The only working reactor at the Chernobyl nuclear power plant was shut down early Monday due to flooding caused by a strong storm.
Workers started pumping water out of the reactor early Monday morning, said a statement from the Chernobyl press service. Several hours later, the reactor’s energy level was reduced and then shut down, the statement said.
There were no changes in the radiation level, it said.
Chernobyl was the site of the world’s worst nuclear accident, when a reactor at the plant exploded and caught fire in 1986.
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CHERNOBYL NUCLEAR PLANT RESTARTED AFTER REPAIRS
KIEV Ukraine July 19, 2000 -- The only working reactor at the Chernobyl atomic power plant, the site of the world's worst nuclear accident, was restarted this week after repairs, plant officials said Tuesday.
The reactor was shut down due to flooding caused by a storm July 10, 2000; two of its electric generators needed repairs.
On Monday evening, one electric generator was restarted. The other needs more work, the Chernobyl press service reported. The reactor will work at 50 percent of capacity until the second generator is restarted July 24, the press service said.
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NUKEFACT'S COMMENT
Hopefully, the design of the new sarchopagas will be such that any possibility of leakage of rainwater, ground water, or storm flooding into the regions of the solidified core melt will be completely eliminated.
The July 11 report indicates that "workers started pumping water out of the reactor". This is not very likely, since water is used as the reactor coolant, unless water was somehow penetrating into the graphite moderator. In any case, the report mentions a strong storm, which makes the situation appear more serious than the 1996 incident of just rain water. But, no mention is made of any monitoring of neutron level of the solidified core melt.
The July 11 report does indicate that "there were no changes in the radiation level". What is this suppose to mean? Could this refer to the monitoring of the solidified core melt? Who knows?
The July 19 report indicates that even though the shutdown was due to flooding of the reactor, it was necessary to repair the electric generators. The description of this whole event is very confusing and garbled. Maybe, the sooner the closure, the better.