Design and experience with the BICOTH-type reactor water level gauge for the Dodewaard nuclear power plant

An alternative system for measuring operating water levels in The Netherlands´ Dodewaard BWR (200 MWt, natural circulation) was developed. Its design is based on BICOTH (binary coding thermocouples with heater) sensors that contain heater wires and multijunction differential thermocouple wires. Binary codes are obtained that correspond uniquely to stable water levels present in a standpipe mounted to the inside of the reactor vessel wall. From the experiments, it was found that the additional use of the analog information contained in the temperature transition functions of the thermocouple junctions results in very accurate and smooth water-level indications. An advanced water-level sensor called TRICOTH (trinary coding thermocouples with heater) is proposed that is based on the design and operating experience with the present system