DR ball 3X drop: Operation Physics report

摘要

An accidental ball 3X trip occurred at DR Reactor on July 11, 1961. Startup was attempted on July 21, 1961, subsequent to the ball recovery operations, at which time a large reactivity loss was apparent. The loss was assigned to inaccessible poison balls remaining within the graphite structure. Enriched uranium (0.947% U(sup 235)) columns were charged during successive outages to immediately recover the minimum excess reactivity required for operational transients and effective control. The large increase in enrichment inventory in the reactor complicated evaluation of total control and speed-of-control requirements necessary to comply with the control criteria. An additional effect of the remaining ball poison was observed as a skewed front-to-rear klux distribution with downstream peaking, indicating a much larger concentration of the balls in the upstream regions of the reactor. Summaries of various physics analyses performed as a result of the ball drop and some of the analytical techniques used in evaluating and resolving the flux distribution and reactivity and control problems are outlined in the report. The ball boron burnout rate and total estimated costs incurred due to the decreased conversion ratio, reduced operating level, and increased rupture potential are also provided.