ML17191B475
| ML17191B475 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 10/01/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17191B474 | List: |
| References | |
| NUDOCS 9910120319 | |
| Download: ML17191B475 (5) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.. 175 TO FACILITY OPERATING LICENSE NO. DPR-19 AND AMENDMENT NO. 171 TO FACILITY OPERATING LICENSE NO. DPR-25 COMMONWEAL TH EDISON COMPANY DRESDEN NUCLEAR POWER STATION. UNITS 2 AND 3 DOCKET NOS. 50-237 AND 50-249
1.0 INTRODUCTION
In a letter dated June 15, 1999, Commonwealth Edison Company (ComEd, the licensee) requested an amendment to their Technical Spe<:;ifications (TSs) for Dresden Nuclear Power Station, Units 2 and 3. The proposed amendment would change TS Section 3/4.7.D and the associated Bases to eliminate the individual leakage limits for each main steam isolation valve,
(MSIV). The removed limits would be replaced with a total limit for all four main steam lines combined. The current leakage limit is 11.5 standard cubic feet per hour (scfh) per valve. The proposed amendmentwould change the limit. to..46 scfh for all four* main steam lines combined.
The value chosen for the new total limit is equivalent to the sum of the current individual limits.
2.0 BACKGROUND
Compliance with Title 10, Part 50, Appendix J, of the Code of Federal Regulations ( 10 CFR Part 50, Appendix J) provides assurance that the primary containment, including those systems and components that penetrate the primary containment, do not exceed the allowable leakage rate values specified in the TSs and their bases. The allowable leakage rate is determined so that the leakage assumed in the safety analyses is not exceeded.
The Dresden primary containment system consists of a drywell, which encloses the reactor vessel and recirculation pumps, a pressure suppression chamber which stores a large amount of water, a connecting vent system between the drywell and the suppression chamber, and isolation valves. The four main steam lines that penetrate the primary containment boundary each have two 20-inch diameter i3olation valve;:; installed in series for a total of eight valves.
Type C leak rate testing of the MS IVs is performed in accordance with the requirements of 1 O CFR Part 50, Appendix J (as modified by an approved exemption). The purpose of the Type C testing is to verify that any leakage through the isolation valves would be within acceptable limits. Appendix J requir~s that the combined leakage of all containment 9910120319.991001 PDR
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r penetrations and valves that are subject to Type B and C tests shall be less than 0.6 times the maximum allowable containment leak rate (La). For Dresden, La is 0.5% (by volume) of the containment air per day at the calculated peak containment internal pressure (Pa> for a design-basis loss-of-coolant accident. Pa is 48 pounds per square inch gage (psig) for Dresden. The MSIVs are tested at a lower test pressure (PJ of 25 psig per a previous exemption. The allowable leakage through all main steam lines at P1 is 46 scfh. Furthermore, boiling-water reactor plants generally have additional leakage limits placed specifically on the.MSIVs, in recognition of their large size and historical tendency to leak excessively. In the case of Dresden, the total leakage limit is 11.5 scfh per valve.
ComEd stated in their letter of June 15, 1999, that use of the proposed combined steam line leakage rate would reduce unnecessary repair of the isolation valves. Dresden reviewed their last three refueling outages and concluded that, had the proposed limits been in effect, four MSIV overhauls could have been avoided while still maintaining the equivalent maximum leak rate. From this review, it can also be inferred that worker radiation exposure would have been reduced.
The Boiling Water Reactor Owners' Group (BWROG) issued a topical report on MSIV leakage limits, entitled NEDC-31858P, Revision 2, "BWROG Report for Increasing MSIV Leakage Rate Limits and ~limination of Leakage Control Systems," dated September 1993. In their report, the BWROG states that MSIV leakage could increase in excess of 200 scfh per valve without reducing the valve's ability to perform its safety function. Based on this, it can be seen that Dresden's current 11.5 scfh leakage limit doesn't provide indication that the valve's safety capability is reduced. The 11.5 scfh limit, therefore, causes Dresden to often perform unnecessary maintenance on the valves simply to maintain the low leakage rate. These unnecessary maintenance activities can reduce the valve life and lead to repeated failures and premature major repairs or valve replacements.
In a safety evaluation dated March 3, 1999, the NRC accepted the report for direct reference in future individual plant submittals on the MSIV leakage issue, subject to certain conditions. In the safety evaluation, the staff concurred with the conclusions stated in the paragraph above.
3.0 EVALUATION ComEd is proposing to change TS 3/4.7.D and the associated Bases to allow a combined maximum flow path leakage for all MSIVs of less than or equal to 46 scfh when tested at 25 psig. For Dresden, the MSIV leak rates are included in the Type B and C test totals for the plant, which are used for demonstrating compliance with the 0.6 La leakage limit. Therefore, the proposed amendment does not affect the total leakage through containment valves and penetrations subject to Type B and C test-requirements.
The effect of the proposed amendment woulrl nr:- to allow an individual MSIV to have a maximum leakage rate of up to 46 scfh (four times higher than previously), provided that the other three lines had no leakage. The original 1.1.5 scfh leakage limit value for the MSIV does not represent a limit which i_Ddicates significant valve degradation. As such, it does not indicate that the valve has degraded to the point where its ability to perform its safety function is.
reduced. Based on the BWROG report cited above, Dresden's proposed 46 scfh limit would
'.;..' not reduce the valve's ability to perform its safety function. As a result, the new limit would *not reduce overall plant safety.
Based on our review, we conclude that the proposed amendment does not increase Dresden's overall allowable leakage limit or reduce the ability of the MS IVs to perform their intended safety functions. The proposed amendment would also reduce worker radiation exposure which is consistent with the Commission's policy of keeping exposures as low as reasonably achievable.
Accordingly, we conclude that the proposed amendment is acceptable.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Illinois State official was notified of the proposed issuance of the amendments. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendments change a surveillance requirement. The NRC staff has determined that the amendments involve 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 expqsure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (64 FR 38024). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b}, no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
6.0 CONCLUSION
The Commission 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 Contributors:
Robert B. Elliott
- Jim Pulsipher Date:
October 1, 1999
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1UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 October 1, 1999 MEMORANDUM TO: Biweekly Notice Coordinator FROM:
SUBJECT:
Lawrence W. Rossbach, Project Manager, Section 2 Project Directorate Ill _.:;;;2 ~
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Division of Licensing PrQfect Management, NR~
REQUEST FOR PUBLICATION IN BIWEEKLY FR NOTICE -
NOTICE OF ISSUANCE OF AMENDMENTS TO FACILITY OPERATING LICENSES (TAC NOS. MA5892 AND MA5893)
Commonwealth Edison Company. Docket Nos. 50-237 arid 50-249, Dresden Nuclear Power Station. Units 2 and 3. Grundy County. Illinois Date of application for amendments: May 20, 1999, as supplemented by letters dated September 8, 1999, September 16, 1999, and September 20, 1999.
Brief description of amendments: The amendments revised Technical Specification (TS)
Section 3.8:A, "Containment Cooling Service Water System," (CCSW) to clarify that only one pump is required to support operability of the Control Room Emergency Ventilation System (CREVS).
Date of issuance: October 1, 1999 Effective date: Immediately, to be implemented wB fJJl.F !CfmJfR C@~\\f*
Amendment Nos.: 174 and 170 Facility Operating License Nos. DPR-19 and DPR-25: The amendments revised the Technical Specifications.
Date of initial notice in FEDERAL REGISTER: August 25, 1999 (64 FR 46426). The
- September 8, September 16, and Septemb~r 20, 1999, submittals provided additional clanfying information that did not change the initial proposed no significant hazards c.onsideration determination.
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I Biweekly Notice Coordinator The Commission's relate.d evaluation of the amendments is contained in a Safety Evaluation dated October 1, 1999.
No significant hazards consideration comments received: No.
Local Public Document Room location: Morris Area Public Library District, 604 Liberty Street, Morris, Illinois 60450 DISTRIBUTION:
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