ML110770296
| ML110770296 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 03/18/2011 |
| From: | David Helker Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML110770296 (5) | |
Text
10 CFR 50.90 March 18.
U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Three Mile Island Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR-50
Subject:
Three Mile Island Unit 1 Response to Request for Additional Information Related to Technical Specification Change Request No. 351: "Maximum Allowable Power With Inoperable Main Steam Safety Valves"
References:
(1)
Letter from P. B. Cowan (Exelon Generation Company, LLC) to U.S. NRC, "Technical Specification Change Request No. 351: Maximum Allowable Power with Inoperable Main Steam Safety Valves" dated September 24, 2010 (2) from P. Bamford (U.S. Nuclear Regulatory Commission) to M. J. Pacilio (Exelon Generation Company, LLC), 'Three Mile Island, Unit 1 - Request for Additional Information Regarding License Amendment Request proposing changes to the number of required Operable Main Steam Safety Valves (TAC NO. ME4808)" dated February 14, 2011 By letter dated September 2010 (Reference 1), Exelon Generation Company, LLC (Exelon),
requested an amendment to the Technical Specifications (TS) for Three Mile Island Nuclear Station, Unit 1 (TMI, Unit 1) to revise TS 3.4.1.2.3 to allow up to two (2) Main Steam Safety Valves (MSSVs) per steam generator to be inoperable with no required reduction in power level, and to revise the required maximum overpower trip setpoints for any additional inoperable MSSVs.
The U.S. Nuclear Regulatory Commission (USNRC) staff has been reviewing the Reference 1 submittal and has determined that additional information is needed to complete the review. The USNRC staff formally requested additional information on February 14, 2011 (Reference 2).
Exelon's response to the USNRC question is provided in the attachment to this letter.
Exelon has determined that the information provided in response to this request for additional information does not impact the conclusions of the No Significant Hazards Consideration or Environmental Consideration as stated in Reference 1.
There are no regulatory commitments contained in this submittal.
U.S. Nuclear Regulatory Commission March 18, 2011 Page 2 In accordance with 10 CFR 50.91, "Notice for public comment; State consultation," paragraph (b), EGC is notifying the Commonwealth of Pennsylvania of this response by transmitting a copy of this letter and its attachment to the designated State Official.
Should you have any questions concerning this letter, please contact Wendy Croft at (610) 765-5726.
I declare under penalty of perjury that the foregoing is true and correct. Executed on the 18th day of March, 2011.
Respectfully, David P. Helker Manager - Licensing and Regulatory Affairs Exelon Generation Company, LLC
Attachment:
Response to Request for Additional Information Related to Technical Specification Change Request No. 351
U.S. Nuclear Regulatory Commission March 18, 2011 Page 3 cc:
Regional Administrator, USNRC Region I Project Manager, NRR, USNRC Three Mile Island, Unit 1 Senior Resident Inspector, USNRC Three Mile Island Director, Bureau of Radiation Protection Pennsylvania Department of Environmental Protection Chairman, Board of County Commissioners of Dauphin County, PA Chairman, Board of Supervisors of Londonderry Township, Dauphin County, PA R. R. Janati, Commonwealth of Pennsylvania
ATTACHMENT Response to Request for Additional Information Related to Technical Specification Change Request No. 351 Three Mile Island Generating Station, Unit 1 Renewed Facility Operating License No. DPR-50
Response to RAI Related to Technical Specification Change Request No. 351 Attachment Page 1 of 1 NRC Question to the submittal, document number 86-9054640-02, page 47, assigns a value of 6.9% full power (FP) uncertainty to the overpower trip setpoint, independent of power level.
Please provide justification that this uncertainty is applicable to all of the power levels analyzed.
TMI Unit 1 Response The 6.9% full power uncertainty applied to the overpower trip setpoint is more conservative than necessary. AREVA derived this value from the difference between the maximum reactor power (112% full power) and the Reactor Protection System (RPS) High Flux trip setpoint (105.1 %) for the limiting overpower design event. These are the design values for the RPS setpoint and maximum possible reactor power. The appropriate uncertainty applicable for the reactor power limit with limited Main Steam Safety Valve (MSSV) capacity is the difference between the indicated and actual reactor power. The approach that AREVA used in document number 86-9054640-02 to determine the uncertainty is not applicable, but results in a very conservative assumption. This discrepancy was recognized and discussed in Technical Evaluation No.
A2148778 E18.
The function of the 105.1 % overpower trip setpoint is to prevent core thermal power from exceeding 112% during a transient which causes an increase in reactor power. The bounding transient for determining the required MSSV capacity is a Turbine Trip without an anticipatory reactor trip or Integrated Control System (ICS) runback. In that event, there is no power escalation. Reactivity decreases as a result of the rising Reactor Coolant System (RCS) temperature and the reactor trips on high RCS pressure. The basis that AREVA used to determine uncertainty for overpower trip setpoints does not apply to the bounding MSSV capacity transient.
As applied in the proposed Technical Specification (TS), the modified RPS setpoint is used to ensure that the reactor power level used in the analysis is greater than the actual reactor power.
The appropriate uncertainty to apply is the 2% reactor power measurement uncertainty (Reference UFSAR Table 3.2-11). By setting the overpower trip at 2% below the analyzed power level, actual core power is ensured to be lower than the analyzed power levels where secondary side overpower protection is demonstrated to be adequate. The proposed TS satisfies this requirement by setting the overpower trip at 6.9% below the analyzed power level.
The AREVA recommended overpower setpoints are more conservative than necessary. The applicability of a 2% uncertainty is described in the Three Mile Island (TMI) Unit 1 acceptance of the AREVA analysis. However, financial consideration did not warrant a change to the AREVA analysis and Exelon has decided to accept the recommended overpower trip setpoints.