Application of Statistical Combination of Uncertainties to the Three Mile Island Unit 1 Flux/Flow Reactor Trip Setpoint

Typical reactor trip setpoints established for the reactor protection system may be unduly restrictive, depending on how the uncertainties are handled in the plant safety analyses. The current deterministic approaches to establishing specific setpoints contain a substantial amount of conservatism, which can be reduced through the use of a statistical combination of uncertainties process. Using this approach for Three Mile Island Unit 1 indicates that the flux/flow trip set-point can be relaxed to 1.1 from the existing technical specification value of 1.08. This provides an increased plant operating margin and reduction in the probability of spurious scrams.