L-PI-09-059, Supplemental Information Regarding Application for Renewed Operating Licenses
| ML091180327 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 04/17/2009 |
| From: | Wadley M Northern States Power Co, Xcel Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-PI-09-059 | |
| Download: ML091180327 (4) | |
Text
XcelEnergy-April 17, 2009 L-PI-09-059 10 CFR 54 U S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Units 1 and 2 Dockets 50-282 and 50-306 License Nos. DPR-42 and DPR-60 Supplemental Information Regarding Application for Renewed Operating Licenses By letter dated April 11, 2008, Northern States Power Company, a Minnesota Corporation, (NSPM) submitted an Application for Renewed Operating Licenses (LRA) for the Prairie Island Nuclear Generating Plant (PINGP) Units 1 and 2. In a letter dated April 6, 2009, NSPM provided its conclusion that the analysis of the probability of damage to safeguards equipment from turbine missiles discussed in LRA Section 4.7.5 need not be classified as a Time-Limited Aging Analysis (TLAA), and withdrew that LRA section. In a conference call on April 15, 2009, the NRC raised a follow up question related to inspections of the turbine rotors. Enclosure 1 provides additional information that responds to the follow up question.
If there are any questions or if additional information is needed, please contact Mr. Eugene Eckholt, License Renewal Project Manager.
Summary of Commitments This letter contains no new commitments or changes to existing commitments.
I declare under penalty of perjury that the foregoing is true and correct.
Executed on April 17, 2009.
Michael D. Wadley Site Vice President, Prairie Island Nuclear Generating Plant Units 1 and 2 Northern States Power Company - Minnesota 1717 Wakonade Drive East
- Welch, Minnesota 55089-9642 Telephone: 651.388.1121 A :33
Document Control Desk Page 2 Enclosure (1) cc:
Administrator, Region III;USNRC License Renewal Project Manager, Prairie Island, USNRC Resident Inspector, Prairie Island, USNRC Prairie Island Indian Community ATTN: Phil Mahowald Minnesota Department of Commerce Supplemental Information Related to Turbine Rotor Inspections In a letter dated April 6, 2009, NSPM provided its conclusion that the analysis of the probability of damage to safeguards equipment from turbine missiles, discussed in LRA Section 4.7.5, was not a TLAA. Jn a conference call onApril 15, 2009, the NRC requested clarification about how the Current Licensing Basis (CLB) for turbine missiles addresses the turbine rotorinspection interval. NSPM agreed to provide clarifying information to supplement the discussion in the April 6 letter.
The CLB for turbine valve testing is encompassed by the PINGP Technical Requirements Manual (TRM), Section 3.7.3, Turbine Overspeed Protection. The TRM is a licensee-controlled document that is maintained consistent with the USAR. A licensee's TRM is recognized by the NRC as an element of a plant's licensing bases in NRR Office Instruction LIC-1 00, Control of Licensing Bases for Operating Reactors.
The TRM surveillance requirement for turbine valve stroke testing states, "Frequency of testing shall be consistent with the methodology presented in WCAP-1 1525, "Probabilistic Evaluation of Reduction in Turbine Valve test Frequency", and in accordance with the established NRC acceptance criteria for the probability of a turbine missile ejection incident of 1.0 x 10-5 per year. In no case shall the turbine valve test interval exceed one year." The NRC approved the use of WCAP-1 1525 methodology to determine turbine valve test frequency in PINGP License Amendments 86 (Unit 1) and 79 (Unit 2) issued by an NRC letter dated February 7, 1989.
WCAP-1 1525 was prepared to provide a probabilistic basis for selecting a turbine valve testing interval. The WCAP methodology is used to define a valve test interval that, in conjunction with other factors, maintains the overall probability of turbine missile ejection less than 1 E-5/year. The valve test interval, in conjunction with the design configuration and valve failure rates, determines the probability that a design, intermediate or destructive overspeed event could occur. However, the valve test interval, in itself, is only one of the factors which contribute to the overall probability of missile ejection. At PINGP, turbine valve stroke tests are currently performed at a nominal interval of six months.
While the PINGP CLB does not specify a required turbine rotor inspection frequency, WCAP-1 1525 recognizes that the probability of a missile ejection at any speed is a function of the type and condition of the rotor. The probability that a missile would be ejected at normal operating speed or overspeed is directly dependent'on the elapsed operating time since the last rotor inspection. Each performance of a rotor inspection reduces the probability of missile ejection from rotor failure. After each rotor inspection, the probability of a missile ejection from a rotor failure increases with time until the next inspection. The rotor inspection interval selected in WCAP-1 1525 for evaluation of the fully integral turbine rotors installed at PINGP is ten years, even though Westinghouse evaluations resulted in very low failure probabilities after 30 years of continuous operation with no inspection. The WCAP analysis did not establish this ten operating year interval as a limiting requirement; it was simply one of the variables that had to be specified along with the applicable rotor type as an input to the analysis. At PINGP, turbine rotor inspections are performed at a nominal interval of 100,000 operating hours (approximately 11.4 operating years). Low pressure turbine rotor inspections are currently planned during the next refueling outages (1 R26 and 2R26) of both Units 1 1
Supplemental Information Related to Turbine Rotor Inspections and 2. The curve that appears as USAR Figure 12.2-38 is not used to determine a rotor inspection interval.
In summary, in order to satisfy the TRM requirement to maintain the overall probability of turbine missile ejection below 1 E-5/year, PINGP must utilize both an appropriate turbine valve test interval and an appropriate turbine rotor inspection interval to assure that the assumptions used in the WCAP-1 1525 analysis methodology continue to be met. Neither the turbine valve test interval nor the rotor inspection interval involves a time-limited assumption defined by the current operating term of the plant. Therefore, the analysis of the probability of damage to safeguards equipment from turbine missiles is not a TLAA.
2