Document Control Desk

The NRC staff requested that GE-Hitachi Nuclear Energy (GEH) evaluate the potential non-conservatism in the GE Thermal-Mechanical Methodology, GESTR-M, identified in the ESBWR design certification review in accordance with the provisions of 10CFR Part 21. The staff was concerned that qualification of GESTR-M against high exposure fuel data could indicate that GESTR-M under-predicts fuel centerline temperature. GEH completed an extensive evaluation and concluded that GESTR-M and its associated statistical methodology, in conjunction with the exposure dependent Linear Heat Generate Rate (LHGR) limit, was adequate for fuel licensing and design calculations within its qualification domain and therefore did not constitute a reportable condition under 10CFR21. A summary of that evaluation was provided on January 21, 2007 in letter number MFN 07-040. Based upon review of MFN letter 07-040 the NRC concluded that the GESTR-M model and associated methodology are adequate to confirm compliance with fuel temperature and cladding strain SAFDLs but requested additional quantification of the conservatism in the calculation to confirm compliance with the rod internal pressure SAFDL. This quantificatio