Replacing control rod worth minimizers in the Gundremmingen Nuclear Power Station

In units B and C of the Gundremmingen Nuclear Power Station the control rod worth minimizers were replaced by new systems based on type-tested stored program control systems because of mounting difficulties in obtaining spare parts for the old installations. These are the basic characteristics of the systems concept for the new control rod worth minimizers: (1) Functions are distributed over independent subsystems with functional redundancy. (2) Type-tested platforms are used so as to minimize the expense involved in qualification tests. (3) A process simulator is integrated in the control rod worth minimizer which simulates the environment of the control rod worth minimizer for the works test and for subsequent in-service inspections. The minimizers were replaced during refueling and revision outages, respectively. Since they were commissioned, the control rod worth minimizers have functioned as required. Minor defects. which were detected neither in the works inspection nor during assembly tests, despite careful planning and execution of these tests, were remedied with the plant in operation without in any way impairing minimizer functions.