RS-07-039, 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
Exelon Generation www_exeloncorp.r_om 4300 WSnIjeld Road WarrenvilleA L 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
- Exelom, Nuclear
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