ML20150G042
| ML20150G042 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 07/12/1988 |
| From: | Craig Harbuck Office of Nuclear Reactor Regulation |
| To: | Tison Campbell ARKANSAS POWER & LIGHT CO. |
| References | |
| NUDOCS 8807190187 | |
| Download: ML20150G042 (5) | |
Text
._
July 12,1988 m
Docket No. 50-313' Mr. T. Gene Campbell Vice President Nuclear Operations Arkansas Power and Light Company Post Office Box 551 Little. Rock, Arkansas 72203
Dear Mr. Campbell:
SUBJECT:
PROPOSED CHANGE TO TECHNICAL SPECIFICATIONS FOR ARKANSAS NUCLEAR ONE, UNIT 1 (ANO-1) REGARDING PRIMARY TO SECONDARY LEAKAGE RATE LIMITS The. staff's request to incorporate a 1.0 gpm primary to secondary leak rate limit into the AN0-1 Technical Specifications was discussed by telephone on February 5, 1988 between Messrs. Dale James and Richard Thornton of your staff and Messrs. George Dick and Emett Murphy of the NRC staff.
In this discussion you comitted to submit such a license amendment to revise your Technical Specifications.
On July 6, 1988, you verbally requested background information to aid in your preparation of the submittal for the license amendment. ~.nclosed is a sunwrary of tha background information which lead to the staff's conclusions and request.
Should you have any questions concerning the information in the enclosures, please contact me.
Sincerely,
/s/
C. Craig Harbuck, Project Manager Project Directorate - IV Division of Reactor Projects - III, IV, V and Special Projects Office of Nuclear Reactor Regulation
Enclosure:
As stated cc:
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July 12,1988 Docket No. 50-3 0 Mr. T. Gene Campbell Vice President Nuclear Operations Arkansas Power and Light Company Post Office Box 551 Little Rock, Arkansas 72203
Dear Mr. Campbell:
SUBJECT:
PROPCSED CHANGE TO TECHNICAL SPECIFICATIONS FOR ARKANS/S NUCLEAR ONE, UNIT I (ANO-1) REGARDING PRIMARY TO SECONDARY LEAKAGE RATE LIMITS The staff's request to incorporate J 1.0 gpm primary to secondary leak rate limit into the ANO-1 Technical Specifications was discussed by telephor.e.
on February 5,1988 between Messrs. Dale James and Richard Thornton of your staff and Messrs. George Dick and Emett Purphy of the NRC staff.
In this discussion you comitted to submit such a license amendment to revise your Technical Specifications.
On July 6, 1988, you verbally requested background information to aid in your preparation of the submittal for the license amendment.
Enclosed is a sumary of the background information which lead to the staff's conclusions and request.
Should you have any questions concerning the information in the enclosures, please contact me.
Sincerely.
Y C. Craig Harbuck, Project Manager Project Directorate - IV Division of Reactor Projects - III.
IV, V and Special Projects Office of Nuclear Reactor Regulation
Enclosure:
As stated s
cc:
See next page
4 e-Mr. T. Gene Campbell Arkar.sas Power & Light Company
-Arkansas Nuclear One, Unit I cc:
Mr. Dan R. Howard, Manager Licensing Arkansas Nuclear One P. O. Box 608 Russellville, Arkansas 72801 Mr. James M. Levine, Executive Director Nuclear Operations Arkansas Nuclear One P. O. Box 608 Russellville, Arkansas 72801 Mr. Nicholas S. Reynolds Bishop, Cook, Purcell & Reynolds 1400 L Street, N.W.
Washington, D.C.
20005-3502 Mr. Robert B. Borsum Babcock & Wilcox Nuclear Power Generation Division 1700 Rockville Pike, Suite 525 Rockville, Maryland 20852 Resident Inspector U.S. Nuclear Regulatory Commission 1 Nuclear Plant Road Russellville Arkansas 72861 Regional Administrator, Region IV U.S. Nuclear Regulstory Commission Office of Executive Director for Operations 611 Ryan Plaza Drive. Suite 1000 Arlington, Texas 76011 Mr. Frank Wilson, Director Division of Environmental Health Prciection Department of Health Arkansas Department of Health 4815 West Markham Street Little Rock, Arkansas 72231 Honorable William Abernathy County Judge of Pope County Pope County Courthouse Russellville, Arkansas 72801
O a.
Enclosure BACKGROUND INFORMATION FOP THE PROPOSED P_R_IMARY TO SECONDARY LEAK RATE TECHNICAL SPECIFICATION LIMIT Steam generator tube integrity was designated as an Unresolved Safety Issue (USI) in 1978 after it became apparent that steam generator tubes were subject to wicispread degradation, frequent leaks, and occasional ruptures. For the interim period pending resolution of these USIs, the staff concluded that there was adequate basis, > assure continued safe operation of Pk'Rs. The staff's basis for continued operation was formally documented in NUREG-510 and e
NUREG-0571 and included primary to secondary leakage limits as an important element. This was expressed in NUREG-0571 a,s folicws:
Primary-to-secondary leakage rate limits, and associated surveillance requirements have been established to provide assurance that the occurrence of tube cracking during operation will be detected and that appropriate corrective action will be taken expeditiously. Early experience with leaks in B&W steam generators indicates that if a crack occurs it will propagate around the circumference of the tube in a short period of time (several hours) provided that there is flow of sufficient energy to drive it. However, the crack formed will produce an identifiable leak, the detection of which will result in prompt corrective action (i.e., plant shutdown).
In citing this basis, it was implicitly assumed by the staff that all PWRs had Technical Specification limits on allowable primary to secondary leakage rate limits of 1.0 gpm or less. The basis for this assumption was based in part on a survey conducted by the NRC staff by letter dated December 9, 1977, to which APLL responded on June 15, Ir78 indicating the existence of a 1.0 gpm leak rate limit. However, ANO-1 did not and still does not have a specific TS limit on primary to secondary leak rate.
As a result of the staff's USI effort (NUREG-0844), the staff issued a number of staff-recommended actions concerning steam generators in NRC Generic Letter 85-02. These reconnendations included a reconnendation that PWRs with less restrictive limits than the Standard Technical Specification (STS) limits on allowable primary to secondary leakage adopt the STS limits; namely, a 1.0 gpm limit on total primary to secondary leakage and a 500 gpd (i.e., a.35 gpm) limit for leakage from any one steam generator. The 1.0 gpm limit is intended to ensure that the dosage contribution from tube leakage will be limited to a small function of 10 CFR Part 100 limits in the event of a steam generator tube rupture (SGTR) or main steam line break (MSLB) event. The 500 gpd limit was derived from test data & Westinghouse steam generator tubes and corresponds to the expected leakage for the eximum sized crack length which would not be expected to fail under worst case pressure differential loadings associated with a design basis MSLB or feed line break (FLB) (
Reference:
Westinghouse Report No. WTD-SM-77-058, dated in July 1977, which was submitted by Carolina Power and Light Company in a letter to the NRC dated July 17, 1977). Although the test data was developed for Westinghouse SG Model 51 tubes, the staff believes that this data can reasonably be applied to B&W tube geometries as a
i
.. first order approximation since the radius / thickness ratios and the burst strength of the BW tubes are within 5% of those for the Westinghouse tubes.
To the staff's knowledge, the Westinghouse data is unique it that it is based upon test specimens containing actual cracks induced by fatigue rather than simulated cracks produced with an electro discharge machining (EDM) procedure which would tend to produce less conservative results.
Approximately two-thirds of operating PWRs have Technical Specification leak rate limits which are at least equally restrictive as the STS limits and which are therefore consistent with the staff's recomendation in Generic letter 85-02. As a minimum, all plants with the exception of Oconee Units 2 and 3 and ANO-1 have Technical Specifications or license conditions which limit total primary to secondary leakage to 1.0 gpm.
In addition to assuring that site boundary dose will be within the Part 100 guidelines during design basis accidents, the 1 gpm limit has proven effective in minimizing the potential for tube ruptures under nomal operating conditions as evidenced by the fact that only four of several hundred primary to secondary leaks to date have involved a gross tube ruptura. The I gpm limit on total primary to secondary leakage also serves to minimize periods during whi.h tubes may be vulnerable to rupture, given a postulated accident such as a main steamline or feedline break, although the 500 gpd (.35 gpm) limit per steam generctor in the STS provides an even more effective limit in this regard.
(As previously noted, the staff has recomended (but not required) that plants with less restrictive limits than the STS limits adopt the more effective STS limits.)
In the absence of specific limits regarding allowable primary to secondary leakage in the ANO-1 Te-hnical Specifications, primary to secondary leakage is limited in the Technical Specifications for this unit only by the 10 gpm limit on total RCS leakage. Continued plant operation beyond 1.0 gpm to 10 gpm wculd represent an order of magnitude departure from industry practice to date.
It would pemit further crack extension beyond what the staff has long considered to be prudent from the standpoint of maintaining tube integrity.
No,upporting evidence has been provided to the staff to demonstrate that the t' oes have been designed to accomodate flaws leaking at the rate of 10 gpm while maintaining (1) an extremely low probability of abnomal leakage in accordance with GDC-14, and (2) sufficient margin to assure that when stressed r
under postulated cccident conditions, the probability of rapidly propagating fracture is minimized in accordance with GDC-31.
In addition to tube integrity considerations, primary to secondary leakage rates exceeding 1.0 gpm would be in excess of what was assumed in the ANO-1 FSAR safety analyses, which was reviewed by the staff, for purposes of demonstrating that offsite boundary doses during design basis accidents do not exceed the 10 CFR Part 100 guideline limits.
A 1.0 gpm limit on total primary to secondary leakage should be incorporated into the ANO-1 Technical Specifications to co W nue to assure that this unit will continue to be in compliance with GDC 14 and 31. This change will bring i
the primary to secondary leak rate limit for ANO-1 to within the envelope of limits which (1) have been established for other PWRs, (2) were assumed to exist for all PWRs when establishing the bases for continued safe operation pending USI resolution, and (3) were assumed in the FSAR safety analyses for design basis accidents.
.