ROP Trip Setpoints Update for GENTILLY-2 Since 2004

Abstract

Since the last ROP analysis documented in TTR-753 reference, a significant number of measurements of the pressure-tube internal diameters in Gentilly-2 has been done. This brought to 62 the number of Gentilly-2 pressure tubes for which the internal diameters have been measured. Evaluation of the diametral strains obtained from these measurements, as compared to the diametral strains predicted by the equation RC-1980, concluded that for the majority of the pressure tubes evaluated, the diametral creep strain rate is lower than that predicted by the equation RC-1980. Thus, the average ratio between measured and calculated maximum deformations is equal to 0.84 with 0.096 as a standard deviation. The last analysis used an average ratio between measured and calculated maximum deformations equal to 0.9188 with 0.1836 as a standard deviation. There are other changes that impact on the ROP base trip setpoints: the revision of the ROP trip setpoint uncertainties used in ROVER-F, the revision of flux shapes and the modifications of the ROP system during the 2005 plant outage. In addition, due to Primary Heat Transport System (PHTS) aging, revision over time of ROP base trip setpoints is required to ensure effectiveness. The methodology of the analyses is the same as in the last analysis documented in TTR-753 and it consists of: creating a revised PHT circuit model for NUCIRC to include up to date measurements of HTS conditions, calculating the Critical Channel Power (CCP) with NUCIRC at three points in time, 6211, 6800 and 7300 EFPD (Equivalent Full Power Days) based upon plant aging models including the measured diametral creep rates, and calculating ROP trip setpoints using ROVER-F for each of the three subsequent core ages and for 51 limiting ROP flux shapes. The calculations at the three points in time, 6211, 6800 and 7300 EFPD, resulted in a new trend in the ROP base trip set points as a function of EFPD that is at least 2.5% higher compared to the actual trend from the last ROP analysis (TTR-753). In addition, this new trend in the ROP base trip set points varies according to a quadratic curve that decreases at a reduced rate than the one documented in the last ROP analysis (TTR-753).