Reactivity calculations of the Chernobyl accident

Conference · Fri Jan 01 04:00:00 EST 1988 · Transactions of the American Nuclear Society; (USA)

OSTI ID:5579856

Martinez-Val, J M; Aragones, J M

The objective of this study was to analyze the physical causes of the Chernobyl accident, in particular, the role of reactivity effects along its evolution. The best source of information about the accident is the official report presented by the Soviet authorities at the International Atomic Energy Agency meeting in August 1986, but it had to be completed with earlier papers on the physics of RBMK reactors, including some articles on reactivity effects. Reactivity coefficients were calculated with WIMS-D4 in a multicell scheme to take into account different ratios of fuel channels to control and water channels. The most critical effect in RBMK reactors is the water density coefficient. The graphite reactivity coefficient was also positive in the quasi-steady state but it did not play a significant role in the accident because the graphite temperature varied very slowly (<1{degree}C per 800{degree}C rise in fuel temperature). Xenon reactivity effects were of interest before the accident itself, but their influence was null during the reactivity trip. It can be concluded from this analysis that the initiating mechanism was primarily related to the pressure drop at the reactor inlet after starting the experiment on the generator trip, together with the positive void coefficient in the nuclear conditions. It is work emphasizing that an undermoderated light water reactor cannot undergo this type of sequence of events, which is very specific of overmoderated reactors with a solid main moderator.

• OSTI ID: 5579856
• Report Number(s): CONF-881011--
• Conference Information: Journal Name: Transactions of the American Nuclear Society; (USA) Journal Volume: 57
• Country of Publication: United States
• Language: English

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