RS-07-039, Request for Safety Evaluation Revision Regarding Backup Stability Protection Methodology

Request for Safety Evaluation Revision Regarding Backup Stability Protection Methodology

ML070720134
Person / Time
Site:	Dresden, Quad Cities
Issue date:	03/09/2007
From:	Simpson P Exelon Nuclear
To:	Document Control Desk, NRC/NRR/ADRO
References
RS-07-039
Download: ML070720134 (2)

Text

Exelom, Exelon Generation 4300 WSnIjeld Road www_exeloncorp.r_om Nuclear WarrenvilleAL 60555 RS-07-039 March 9, 2007 U . S. Nuclear Regulatory Commission ATTN : Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Units 2 and 3 Renewed Facility Operating License Nos. DPR-19 and DPR-25 NRC Docket Nos. 50-237 and 50-249 Quad Cities Nuclear Power Station, Units 1 and 2 Renewed Facility Operating License Nos. DPR-29 and DPR-30 NRC Docket Nos . 50-254 and 50-265

Subject:

Request for Safety Evaluation Revision Regarding Backup Stability Protection Methodology References : 1 . Letter from M. Banerjee (NRC) to C. M. Crane (Exelon Generation Company, LLC), "Dresden Nuclear Power Station, Units 2 and 3, and Quad Cities Nuclear Power Station, Units 1 and 2 - Issuance of Amendment Re:

Transition to Westinghouse Fuel and Minimum Critical Power Ratio Safety Limits (TAC Nos . MC7323, MC7324, MC7325 and MC7326)," dated April 4, 2006

2. Letter from K. R. Jury (Exelon Generation Company, LLC) to U.S . NRC, "Clarification Regarding Backup Stability Protection Methodology," dated July 25, 2006

3. Letter from R. C. Jones (NRC) to D. B. Ebeling-Koning (ABB Combustion Engineering Nuclear Fuel), "Acceptance for Referencing of ABB/CE Topical Report CENPD-295-P : Thermal Hydraulic Stability Methodology for Boiling Water Reactors (TAC No. M93648)," dated February 22, 1996 In Reference 1, the NRC issued license amendments for Dresden Nuclear Power Station (DNPS), Units 2 and 3, and Quad Cities Nuclear Power Station (QCNPS), Units 1 and 2. The license amendments support the transition to Westinghouse SVEA-96 Optima2 fuel .

March 9, 2007 U. S. Nuclear Regulatory Commission Page 2 During review of the NRC safety evaluation for the Reference 1 amendment, Exelon Generation Company, LLC (EGC) identified that the NRC safety evaluation discussed the backup stability protection (BSP) methodology in a manner that was not consistent with information provided in EGC's submittals requesting the license amendment. This was discussed with the NRC during a conference call on May 2, 2006. During that call, the NRC requested EGC to submit information to summarize the Westinghouse methodology for BSP calculations . As requested by the NRC, EGC submitted the requested information in Reference 2. The information provided in Reference 2 is consistent with the stability calculations that were reviewed by the NRC during audits supporting the Reference 1 amendment.

Specifically, Reference 2 clarified that the immediate scram region for DNPS and QCNPS was defined by a RAMONA-3 decay ratio > (1 .0 - cu - 6), and the controlled entry region was defined by a RAMONA-3 decay ratio > (0.8 - cu). The term "cu" accounts for cycle uncertainty, and the term "6" accounts for the standard deviation of RAMONA-3 predictions against benchmark plant decay ratio measurements.

Several discussions with the NRC have occurred subsequent to the Reference 2 submittal. In these discussions, it was clarified that the NRC safety evaluation for the RAMONA methodology (i .e., Reference 3) for stability calculations specifies an uncertainty of +/- 0.2 for the decay ratio of all three instability modes (i.e ., core-wide, channel, and regional) . The +/- 0.2 uncertainty term implicitly includes the cycle uncertainty term "cu ." Therefore, the approved stability region calculation methodology for the immediate scram region is defined as the area in the power-flow map where the decay ratio is > 1 - 0.2, or 0.8. For DNPS and QCNPS, defining the immediate scram region as the area in the power-flow map where the decay ratio is > 0.8 is essentially equivalent to the approach stated in Reference 2 (i .e., decay ratio > 1 .0 - cu - (T) .

In order to reach final resolution of this issue, EGC requests the NRC to revise the safety evaluation for the Reference 1 amendment to reflect that the immediate scram region is defined as the area in the power-flow map where the decay ratio is > 0.8, and the controlled entry region is defined as the area in the power-flow map where the decay ratio is > 0.8 - cu .

There are no regulatory commitments contained in this letter . Should you have any questions related to this letter, please contact Mr. Kenneth M . Nicely at (630) 657-2803 .

Patrick R. Simpson Manager, Licensing cc : NRC Senior Resident Inspector NRC Regional Administrator, Region III