Interim report experience with PT IP-467-C reducing minimum downtime

The length of the minimum outage, or period of time during which a reactor must remain subcritical following a shutdown from equilibriu, is a direct function of the available excess reactivity. In reactors with unlimited safety system capacities, it is quite feasible to ``build in`` sufficient excess to allow complete override of the shutdown xenon transient, and thus, in effect, reduce the ``minimum downtime`` to zero. Present Hanford production reactors do not possess this unlimited capacity, and thus total pile reactivity must be restricted by minimum safety strength conditions. Any effort to increase the pile reactivity must therefore be tailored to satisfy existing Total control and Speed-of-control criteria. Production Test IP-467-C. ``Reducing Minimum Downtime,`` was designed to evaluate the economic benefits of a system in which base reactivity can be increased in periods of minimum control requirements, and correspondingly decreased when reactivity or safety considerations become more demanding. The purpose of this document is to summarize initial operating history and results obtained under the production test.