Safety Analysis And Countermeasure Reserch On Verification Test Of The Calibration Pressure Of Main Steam Safety Valves During Power Operation

It can reduces the critical path time of refueling outage that verification tests of the calibration pressure of main steam safety valves are scheduled to be performed at power operation state from hot shutdown state just after disconnecting with the grid of the unit, and it can assures well certainty of the outage schedule.Reactor reactivity balance calculation and systems'operations showed that it was feasible performing verification test of the calibration pressure of main steam safety valve under 83 %FP power operation at the end of life.Safety injection actuation test was performed at Full-scale Simulator of Qinshanâ…¡NPP, the initial condition for the test was same as one for the SI actuation test of Unit 1 during commissioning. SI signal was triggered by low-low steam pressure through opening the steam dump valves to atmosphere. Comparing the results obtained from the simulator and real data from the commissioning of Unit 1 showed that the results from the simulator were more conservative from view points of safety, so the models and parameters for the simulator were credible.One main steam safety valve was opened spuriously at Full-scale Simulator, evolution of key parameters of nuclear steam supply system after spurious opening was observed. The results from the simulator showed that it was feasible to perform verification tests of the calibration pressure of main steam safety valves at 81 %FP power level. After spurious full opening of the safety valve, under all related control systems being kept in normal operation, the reactor power increased about 9.6 %FP, reactor protection system and turbine protection system didn't actuate, then the unit kept power operation. According to the relation between flow-rate and differential pressure dumping flow-rate of main steam safety valve under the test pressure were deduced from the characteristics of main steam safety valve, then the results from the simulator were verified.As to spurious opening and getting stuck of main steam safety valve, some countermeasures are made; key operations for accident processing and key points of outage schedule regulating are given. Through comparative Analysis on simulator tests, precautions for verification tests of the calibration pressure of main steam safety valve are presented, increasing the levels of steam generators and pressurizer can prolong the SI actuation time greatly.Finally, scheduling and precautions for verification tests of the calibration pressure of main steam safety valve under 83 %FP power level are given.