The new operation system of DCA as subcriticality test facility and its applications

The reactor core of the DCA at Oarai Engineering Center, Power Reactor and Nuclear Fuel Development Corporation (PNC) was modified to compose two region core; the peripheral driver region (heavy water moderated as that of the Advanced Thermal Reactor) and the central test assembly region (ATR fuel or FBR MOX fuel, and light water or heavy water moderated). Because the scram interlock system became complex owing to the above modification, the system control by relay-system was replaced by that controlled by a microcomputer. The introduction of a microcomputer made the watching the operation condition easy and the maintenance work to detect malfunction or abnormal condition reasonable. It is expected to reduce the numerical errors of operating conditions such as water level, period etc. read by operator from the console by using those values obtained by online measurement with the new control system. The measurements of the inverse period and the level reactivity are already automated. This paper describes the new control system and reports a study of an online measurement of reactor power conversion factor (the factor to indicate the absolute power level on the console) as application of the system. Three methods were examined. One is a neutron source insertion of which neutron absorption is compensated by the water level adjustment at low power level. The second is also the neutron source insertion of which absorption reactivity is measured by period after withdrawing the source at relatively high power level. The third is the conventional Au wire activation method. Although there is a little deviation between the first and the second, these values show good agreement the third absolute measured value. One of them will be implemented into the system after investigation of the deviation. (Y.T.)