Fault Tree Analysis of System Anomaly Leading to Red Oil Explosion in Plutonium Evaporator

Abstract

Results of scenario identification, preparation of reliability data, fault tree construction and its analysis, are rendered for a system anomaly considered liable to lead to a red oil explosion in a Pu evaporator of a typical model of reprocessing facility.

Japan Atomic Energy Research Institute has introduced the model plant data, the basic failure frequency data together with the fault tree analysis code FTL from NUKEM GmbH, Germany, and used to execute the above analyses.

The frequency of occurrence of the system anomaly initiated by failures of the Pu purification process such as a pulse column failure or a mixer settler failure has been evaluated to be 2.6×10-³/yr for the solvent carry over into the evaporator for the German model reprocessing facility. In addition to this event, if an abnormal state such as continuously heating the solution to over 150°C inside the evaporator would happen with the analyzed occurrence probability of 1.0×10⁻⁸, it would be the more possible to result in the red oil explosion. The occurrence frequency for the combined events has been calculated to be 2.6×10⁻¹¹/yr, so small compared with the public acceptance limit which might be set as 1×10-⁶/yr.

KEYWORDS:

• fault tree analysis
• red oil explosion
• reliability data
• plutonium evaporator
• fuel reprocessing plants
• accident occurrence frequency
• system failure analysis