Testing the dynamics of shutdown systems instrumentation in reactor trip measurements

Abstract

Periodic testing of the dynamics of the shutdown systems and their instrumentation is performed in the CANDU nuclear power plants of Ontario Power Generation (OPG) and Bruce Power. Measurements of in-core flux detector (ICFD) and ion chamber (I/C) signals responding to the insertion of shut-off rods (shutdown system No. 1, SDS1), or to the injection of neutron absorbing poison (shutdown system No.2, SDS2) are regularly carried out at the beginning of planned outages. A reactor trip is manually initiated at high power and the trip response signals of ICFDs and I/Cs are recorded by multi-channel high-speed high-resolution data acquisition systems set up temporarily at various locations in the station. The sampling of the seaprate data acquisition systems are synchronized through the headset communication systems of the station. A total of 120 station signals can be sampled simultaneously up to 2500 samples per second. The effective prompt fractions of the ICFDs are estimated from the measured trip response. Effectiveness and the timeline of the trip mechanism are assessed in the measurement as well. The measurement can identify ICFDs with abnormally slow response (under-prompt) or overshooting response (over-prompt) at the beginning of the outage. The time required for the signals to drop to predefined fractions of their pre-trip values (level crossing time) is plotted as a function of detector position and compared against safety requirements. The propagating effect of shut-off rod insertion or poison injection on the flux is monitored by the level crossing times of ICFDs and ion chambers.