San Onofre Experience with Apparent Power Mismatch and Reactor Coolant Temperature Anomalies

摘要

In January 1968, the upper limit for operation at the San Onofre Nuclear Generating Station was set at 90% power (405 MWe). The reason for imposing this ceiling was that discrepancies had been noted in reactor thermal power as reckoned by different methods. Calculations from the temperature differentials across the steam generator in the primary loops gave one value; calorimetrics in the secondary system gave another. It appeared that coolant flow was less than the design value. Extensive testing during March, September, and October 1968 revealed that temperature sensors gave misleading indications because of their locations. Accordingly, additional direct-immersion Resistance Temperature Detectors (RTDs) were installed downstream of each coolant pump to give accurate cold-leg mixed mean temperatures. Accurate core outlet temperatures were already being provided by core thermocouples. The data provided by the new RTDs made it possible to prove that coolant flow actually was equal to or greater than design. On the strength of this knowledge, operation at 100% power rating (450 MWe) was begun in December 1968, after an 18-month investigation of the anomaly. The problem demonstrated the great need for instrumentation to accurately read two performance parameters in large pressurized-water reactors: (1) mixed-mean hotand cold-leg temperatures, and (2) flow of primary coolant. (Author)