ML20086A040
| ML20086A040 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 10/16/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20086A037 | List: |
| References | |
| NUDOCS 9111180201 | |
| Download: ML20086A040 (6) | |
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UNITED STATES o
!" 3 m I,j NUCLEAR REGULATORY COMMISSION r,,
.y WASHINGTON, D. C. 20555
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N05. IPJ AND 143 TO FACILITY OPERATING LICENSE N05. DPR-24 AND DPR-27 WISCONSIN ELECTRIC POWER COMPANY POINT BEACH NUCLEAR PLANT, UNIT NOS. 1 AND 2 DOCKET N05. 50-266 AND 50-301 1
1.0 INTRODUCTION
By letter dated September 7,1989 (NRC-89-107), Wisconsin Electric Power Company (the licensee) requested amendments to Technical Specifications appended to Facility Operating Licenses DPR-24 and DPR-27 for the Point Beach Nuclear Plant Units 1 and 2.
The proposed amendments would change the specifications related to two subjects. First, the amendments would revise the frequency of the surveillance testing of the turbine stop and gov 1rnor valves associated with turbine overspeed protection. Specifically, Technical Specification 15.4.1, " Operational Safety Review," would be revised by changing the test requirements in Table 15.4.1-2, " Minimum Frequencies for Equipment and Sampling Tests."
Item 18 in that table currently specifies that turbine stop and governor valves shall be tested monthly.
Footnote 10 in the table waives this requirement during end-of-cycle operation when boron concentration may present a practical limitation. The licensee would amend Item 13 to show that this test is done annually (11) and (12) would be instead of monthly.
Existing footnote 10 would be eliminated.
Footnotes renumbered as (10) and (11) and changes would be made in the table to correct the references to the new footnote numbers.
The second proposed change is to Technical Specification Section 15.7.8.4.A.5,
" Administrative Controls, RETS Reporting Requirement, Semiannual Monitoring Report, Meteorological Data." The current specification requires maintenance of data on wind speed, wind direction, atmospheric stability, and precipitation (if measured). The specification gives three options for maintaining the data: strip charts, magnetic tape, or joint frequency distributions.
The proposed amendment would delete the requirement for maintaining rainfall records and would delete the option of maintaining the data in the form of joint frequency distributions. The amendment would authorize the licensee to keep the data either in the form of strip charts or as hour-by-hour averages stored in electronic form.
2.0 EVALUATION 2.1 Reduction in turbine stop valve test frequency.
In a letter to Mr. James A. Martin, Westinghouse Electric Corporation Generation Technology Systems Division, dated February 2, 1987, the NRC 9111180201 911016 PDR ADOCK 05000266 P
. staff presented its views on precluding turbine missiles and consequential damage to safety-related structures, systems, and components. Utilizing testing and inspection to maintain an initial small value of the probability of a turbine failure resulting in the ejection of fragments through the turbine casing simplifies and improves procedures for evaluation of turbine missile risks and ensures that the public health and safety is maintained.
In its letter, the staff provided generic turbine failure guidelines for total turbine missile generation probabilities to be used for determining (1) frequencies for turbine disc ultrasonic inspections, and (2) maintenance and testing schedules for turbine control and overspeed protection systems.
Subsequent to the NRC guidance letter, Westinghouse Electric Corporation prepared a report for the Turbine Valve Test Frequency Evaluation Subgroup of the Westinghouse Owners Group. That report, published as Westinghouse Electric Corporation Topicai Report WCAP-11525, "Probabilistic Evaluation of -
Reduction in Turbine Valve Test Frequency," June 1987, provides a detailed probabilistic basis for extending the testing intervals of turbine valves.
In a supplement to o safety evaluation dated February 7,1989 for Northern States Power Company, Prairie Island Nuclear Generating Plant, Unit Nos.
1 and 2, the staff found the methodology described in Westinghouse Topical Report WCAP-11525 acceptable.
A letter dated November 2,1989, to the Chairman of the Turbine Valve Test Frequency Evaluation Subgroup, Mr. D.M. Musolf, Manager, Nuclear Support Services, Northern States Power Company, provided the NRC staff's generic conclusions regarding license amendment requests for changes in the surveillance intervals for turbine valve tests and the applicability of WCAP-11525 to support these requi.sts. The letter to Mr. Musolf included a model technical specification for turbine overspeed protection to guide licensees in preparing an amendment application. The letter also set forth the following plant-specific infonnation which the staff would need to review license amendment requests proposing changes in turbine valve test frequencies:
(1) If applicable, provide a justification for us total turbine missile generation probability other than less than 10~g ofy r' (2) Provide a commitment to work with the turbine vendor to maintain a turbine valve data base for the purpose of tracking changes in valve component failure rates.
1 (3) Provide a commitment to accumulate valve f ailure rate information in a manner accessible for staff audit, and that this information will be reviewed by the licensee at least once every 3 years and updated when more than minor changes occur in the data.
(4) Provide a connitment to review and reevaluate the turbine valve test frequency probabilistic analysis (by the Methodology of WCAP-11525-A) when any major changes to the turbine system are made in accordance with I
l 10 CFR 50.59 or when a significant upward trend in the valve failure rate data is identified.
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-~- - The WEPCo application, dated September 7, 1989, was submitted prior to the issuance of the guidance to the owners subgroup. Nevertheless, the standard represented by the guidance to the owners subgroup is applied in this evaluation.
It is also noted that the Technical Specifications for the Point Beach Nuclear Plant were published before the development of the Standard Westinghouse Technical Specifications. The difference in format precludes direct adoption of the model supplied to the owners subgroup.
However, the technical specifications at Point Beach should include the substantive requirements of the model provided to the owners subgroup.
The information provided by WEPCo is evaluated relative to the information requirements set forth in the November 2, 1989, letter to the owners group as follows:
(1) The testing frequency proposed by WEPCo is consistent with staff criteria. The licensee states that "WCAP-11525 demonstrates that the mean annual probabilities of turbine missile ejection for PBNP Units 1 and 2 for turbine valve test intervals of up to one year remain well below the NRC criterion for turbine valve missile generation probability." Therefore, there is no need for justification of an alternate probability. The proposed testing frequency of once per year is therefore acceptable.
(2)
In its application, WEPCo stated that " Westinghouse currently maintains a turbine valve failure data base and is developing a method to assist licensees in the review of failure-rate data and turbine valve test frequency changes, when required." The staff accepts this as a commitment on the part of WEPCo to work with the turbine vendor (Westinghouse).
(3) WEPCo states in their application: "Since changes in failure rates would affect these probabilities, and thus the periodicity at which turbine valve testing is required, Wisconsin Electric will review, at least once every three years, turbine valve failure-rate data to determine if the testing frequency requires modification." This commitment meets the information requirement with the understanding that the data will be subject to staff audit.
(4) In their application WEPCo stated: " Additionally, anytime that major changes to the turbine system are made or a significant upward trend in turbine valve failure rate is identified, we will review the turbine valve test frequency." The staff believes that this commitment meets the information requirement.
Overspeed is a potential cause of turbine failure. Governor valves and stop valves are central to the turbine overspeed protection system, and thus to the probability of a turbir,e missile.
Point Beach has experienced a sub-stantial improvement in valve failure rate since the original technical specifications were issued.
Prior to the use of All-Volatile-Treatment (AVT) for secondary chemistry, the periodic cycling of the turbine valves associated with overspeed protection provided assurance that the buildup of chemical deposits did not
. cause mechanical binding of the valves. The AVT type of secondary plant chemistry control reduced the specific failure mode of chemical deposit binding to a negligible value.
In establishing a valve failure rate, the WCAP-11525 evaluation uses the fact that valve failure due to chemical deposit binding is now virtually non-existent.
WEPCo provided information to show that the Point Beach turbine stop and governor valves have been very reliable, especially since early 1975 af ter both units switched to all volatile secondary chemistry control. Since January 1975, Unit I has undergone 174 surveillance tests and the Unit 2 valves have been tested 182 times. There were three instances where the Unit 1 turbine valves did not fully close.
In each of these instances, the appropriate governor valve fully closed and no threat of tuttine overspeed existed.
It is significant to note that the tests have not resulted in a failure to close since March 1978.
In the same time period, Unit 2 experienced no turbine stop valve failures but two instances where a governor valve did not fully close. With the turbine stop valves closed, there was no threat of turbine overspeed.
The licensee claims that the testing itself results in an increment of risk.
Existing Technical Specification Table 15.4.1-2, " Minimum Frequencies for Equipment and Sampling Tests," requires that turbine stop and governor valves be functionally tested monthly except during periods of refueling shutdown and during end-of-cycle operations when the primary coolant boron concentration is less than 100 ppm. The licensee conducts these functional tests by cycling each valve to the full closed position and returning it to the original position. Although not in the technical specifications, the licensee advised that the Plant Procedure for the tests requires direct observation of the valve movement.
To conduct this test, reactor power must be reduced to about 50 to 60 percent of full power. This-pawer level corresponds to the maximum steam flow which one set of one stop and two governor valves can provide.
The reactor power level reduction is achieved by adding boron to the reactor coolant system and by inserting control rods. When both sets of stop and governor valves have been tested, reactor power is returned to pretest conditions by withdrawing control rods and by removing the added boron by processing the reactor coolant in the chemical and volume control system.
Each valve test with the prerequisite power swing places an additional thermal and pressure cycle on plant equipment, increases the amount of radioactive waste from reactor coolant processing to remove the added boron, and places the plant in a condition more vulnerable to an inadvertent reactor trip. Additionally, later in core life, these power swings cause p
axial power fluctuations and divergent xenon oscillations during which core-power stabilization becomes more difficult.
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. Using the WCAP methodology, the licensee found that the mean annual probabi-lities of turbine missile ejection for turbine valve test intervals of up to 1 year remain well below the NRC criterion for turbine valve missile genera-tion probability.
Because new experience with valve failure rates could alter the ' probabilities of turbine missiles calculated using the WCAP methodology, the licensee has committed to review turbine valve failure rate data once every 3 years to determine whether the valve testing frequency should be modified. WEPCo has also committed to review the turbine valve
-testing frequency any time that major changes are made to the turbine system, or anytime a significant upward trend in turbine valve failure rate is identified.
The staff concludes that a reduction in frequency (using WCAP-11525 methodology) for turbine valve testing will reduce (1) the amount of time the reactor plant is placed in a vulnerable position; (2) unnecessary stress due to the number of thermal cycles for piping, valves, and other equipment; and (3) the amount of radioactive waste generated along with the resultant man-rem exposure.
Based on the Point Beach Nuclear Plant operating experience, the benefits mentioned above, and the assurance by the licensee that they will meet the NRC guidelines for turbine missile generation probabilities and reduction of power transients, the staff finds the proposed changes in testing frequency acceptable.
The proposed change in the frequency of valve testing from monthly to annually is found acceptable as stated above.
2.2 Meteorological data record keeping requirements.
WEPCo proposes to delete the requirement that " precipitation data be main-i tained if measured."
The basis for their request is that indeed they do not measure precipitation. The existing wording was not included as a result of a concern over precipitation at the Point Beach -site. The existing wording is consistent with the Westinghouse Standard Technical specification which would be applicable to those licensees which-do measure precipitation as well as to those, like WEPCo, that do not.. Removing the superfluous wording does not alter the intent.of the technical specifications nor does it introduce the possibility for any different it,terpretation.
7 Therefore, this change is considered to be administrative and has no safety significance.
WEPCo proposes to delete the option of storing certain meteorological data in the form of joint frequency distributions rather than as hour-by-hour listings. The existing wording does not require that joint frequency distributions be computed and is not included as the result of a saf ety analysis _of meteorological phenomena. The wording is consistent with the standard technical specifications which would apply to licensees who calculate joint frequency distributions as well as to those, like Point Beach, who do not. The licensee is not proposing changing any of its practices regarding the collection or maintenance of meteorological amendment nor would this amendment authorize any change in such practices.
Furthermore, the amendment l
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. does not introduce the possibility of any different interpretation of the technical specifications. Therefore, this change is considered to be administrative and has no safety significance.
Finally WEPCo has proposed changing the technical specification option of storing meteorological data in the form of " hour-by-hour averages listed on magnetic tape" to read " hour-by-hour averages stored in electronic form."
This proposed revision would allow the licensee to take advantage of tech-nological advances in data handling. Although the change does authorize a change in procedures, it is confined to data maintenance and is not considered to be substantive. Therefore this change has no safety significance.
The proposed changes to the meteorological data recordkeeping requirements are found acceptable as stated above.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Wisconsin State official was notified of the proposed issuance of the amendment. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
This amendment involves a change to a requirement with respect to the instal-lation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 or a change to a surveillance requirement. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration and there has been no public comment on such finding (54 FR 49140).
Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
This amendment also involves changes in recordkeeping, reporting or administrative procedures or requirements.
Accordingly, with respect to these items, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(10).
Pursuant to 10 LFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
5.0 CONCLUSION
The staff has concluded, based on the considerations discussed above, that (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
Robert B. Samworth Date:
October 16, 1991