I am sending you a copy of the book by David R. Marples, The Social Impact of the Chernobyl Disaster, which is a thorough compilation of Soviet sources concerning the accident. Unfortunately, the introduction is written by Victor G. Snell, who on page 19 writes: "The destruction was not, of course, a result of a nuclear explosion, but rather of steam and perhaps chemical explosions, so the damage was confined to unit 4." I, of course, disagree with this statement completely. In my opinion, a "steam" explosion as a result of over-pressurization of the reactor vessel could not possibly have resulted in an ejection of large chunks of graphite and pressure tubes over several square kilometres around the reactor site. Such ejection indicates the presence of highly supersonic shock waves originating in the central regions of the core.
I am enclosing a letter which I wrote to the Ukrainian Weekly (published Sept. 25, 1988) concerning the description of the explosion in a book by Fredrik Pohl.
To confuse the issue still further, I recently read a 109 page article in Russian by Hryhorii Medvedev, Novy Mir #6, June 1989. He claims that the explosion did not occur 4 seconds after the AZ-5 button was pushed as stated in the USSR Report to the IAEA August 24-26, 1986 and assumed by all Western scientists but at least 18 to 20 seconds later (i.e. at 01:23:58 or later). He refers to the testimony of Valerij Perevozchenko who between 01:23:40 and 01:23:58 presumably ran down several flights of stairs to attempt to warn the operators that something was wrong.
I found the article extremely interesting because it states the names of the people who were involved in the accident and the investigation. There are several other contradictions between his and the "official" version. He states that there were 3 or more explosions; that the reactor fire stopped because all the graphite had burned up rather than because it was extinguished by sand and the use of liquid nitrogen to keep oxygen away from the graphite. He also states that the director, Bryukhanov, had asked permission in the early morning of Saturday, April 26, 1986 to evacuate Prypiat but had been told not to cause panic and to wait until officials from Moscow had arrived on the scene. Still in July 1987 Bryukhanov, Fomin and Djatlov were convicted for misleading the authorities as to the severity of the accident and thus delaying the evacuation of Prypiat.
I have two questions to ask of you, Yoshi. It is repeatedly emphasized that the major cause of the accident was the positive void coefficient of light water (i.e. the reactivity increases markedly when light water turns to steam). It is my understanding that the positive void coefficient of heavy water is much less than that of light water (i.e. deuterium absorbs far fewer neutrons than hydrogen). Is there any reason why heavy water could not be used to replace light water in RBMK reactors and thus alleviate the problem? (Canada has a large surplus of heavy water and would be pleased to supply it!) It would also allow for a decrease in enrichment to less than 2.0%. [It is ironic that one of the proposed solutions is to increase the enrichment to 2.4% and insert the control rods deeper to compensate for the increased reactivity. In my opinion, the higher the enrichment the greater the danger of an explosion in an accident situation.]
Secondly, it has been stated repeatedly that at 11:10 p.m., April 25, 1989 when the operators attempted to continue ramping down the power from 1600 MWt towards 900 MWt, they overshot and went down to 30 MWt. They then struggled for a long time before bringing the power back up to 200 MWt by 1:00 a.m. I was under the impression that about 7% of reactor power is due to "after-heat" associated with the radioactive decay of the fission products. If this is true, then I would have expected the lowest attainable reactor power would be somewhere between 112 and 224 MWt, unless this "after-heat" decays very rapidly. Could you comment on this?
Lily and Will Zuzak
CHORN_90.L25 = Letter to Yoshi 1990-12-25
Excerpt from a letter to Yoshi and Masami Hayamizu (1990-12-25)
Copyright © 1990 Dr. W. Zuzak