ML20217K177
| ML20217K177 | |
| Person / Time | |
|---|---|
| Issue date: | 10/10/1997 |
| From: | Seale R Advisory Committee on Reactor Safeguards |
| To: | Callan L NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| References | |
| ACRS-R-1726, GL-95-05, GL-95-5, NUDOCS 9710230308 | |
| Download: ML20217K177 (3) | |
Text
.
a-ACRSR-1726 UNITED STATES PDR
/
NUCLEAR REGULATORY COMMISSION
{
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS -
WASHWGTON,o C.20888 October 10,1997 Mr. L Joseph Callan Executive Director for Operations U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001
Dear Mr. Callan:
SUBJECT:
RESOLUTION OF THE DIFFERING PROFESSIONAL OPINION RELATED TO STEAM GENERATOR TUBE INTEGRITY During the 445th meeting of the Advisory Committee on Reactor Safeguards, October 2-3,1997, we reviewed the proposed resolution of the subject differing professional opinion (DPO). On several previous occasions,we have reviewed the issues raised in the DPO and related matters.
During these reviews, we had the benefR of discussionswith representatives of the NRC staff and the author of the DPO. We also had the benefit of the documents referenced.
' The DPO initially arose during the development of Generic Letter (GL) 91H)5 " Voltage-Based Repair Criterie for Westinghouse Steam Generator Tubes Affected by Outside-Diameter Stress.
Corrosion Cracking." The staff recognizes that the use of altemate repair criteria such as the voltage-basedlimit for outside diameterstress corrosion crackirm (ODSCC)in tube support p'ates might permit operations with the presence of short throughwval; cracks. The issues raised in the DPO focus on concems that arise when steam generators are permitted to operate with such degradation.- The concems raisad in the DPO bear upon GL 97-xx, "Stsam Generator Tube Integrity," and the draft regulatory guides DG-1074, " Steam Generator Tube Integrity," and DG-1073, "An Approach for Plant-Specific, Risk-informed Decision Making; induced Steam Generator Tube Rupture," only insofar as to whether they provide sdequate guidance for the development of altamate repair criteria.
- We believe that the DPO-issues-response document prepared by the staff accurately summarizes the issues associated with the DPO. The staff grouped the issues into five related areas and noted they are not independent.These areas are: nondestructive examination (NDE) reliability; leakage under design-basis accdont (DBA) conditions,i.yluding main steamline break (MSLB); increased frequency of core damage with containment bypass; nonconservative estimates of lodine spiking during depressurizationtransients, such as an MSLB; and increases in the frequency of thermally induced tube failures unoer certain severe-accident scenarios.
In his recent presentationto us, the DPO author agreed that two of these issues, iodine spiking and thermally induced tube failure, had been resolved adequately by the staff. He felt that the remaining three issues noted belcw were properly stated by the staff, but he did not concur with the proposed resolution of these issues: NDE reliability; leakage under DBA conditions including MSLB; the increased frequency of core damage with containment D
are closely linked.
p } rn. ] N V.h 9710230308 971010
- 726 PDRL h
Aas J
'e r The higher frequency of core damage with containment bypass estimated by the author of the DPO is largely due to the much higher levels of leakage that he projects to occur during DBAs. The DPO-lesues-response document notes that leakage through degraded tubes under DBAs was addressed in GL 95-05 for voltage-based repair criteria for ODSCC at tube support plates, in GL 95-05, an empirical correlation relating leakage to eddy-current voltage is used to estimate leakage under DBAs. Recognizing that such empirical correlationsinvolve large uncertainties, the
~ taff proposed that these uncertainties be addressed through performance monitoring and s
statistical analyses, and the staff provided guidelines for such analyses and monitoring.
The author of the DPO argues that such an approach does not adequately assess tim uncertainties in the leakage estimates. As discussed in draft NUREG-1477, " Voltage-Based Interim Plugging Criteria for Steam GeneratorTubes," such empirical conelations am !n much better agreement with existing laboratory data and field experience on leakage than estimates based on the fracture mechanics cited by the author of the DPO.
We believe the DPO-issues-response document provides a good statement of tne issues and represents a serious attempt by the staff to resolve them. We believe that the staff should issue this document for public comment.
[
Dr. William J. Shack did not participate in the Committee's deliberations regarding this matter.
L Sincerely, i
l R. L Seale i
Chairman
References:
l 1.
Memorandum dated May 23,1997, from L Joseph Callan, Executive Director for l
Operations, NRC, to NRC Commissioners,
Subject:
Steam Generator Rulemaking, F
2.
Letter dated November 20,1996, from v S. Kress, Chairman, ACRS, to James M.
j Taylor, Executive Director for Operat.m, NRC,
Subject:
Proposed Rule on Steam j
Generator Integrity.
3.
Memorandum dated June 27,1997, from L Joseph Callan, Executive Director for Operations,NRC,to NRCCommissioners,
Subject:
J. Hopenfeld's Differing Professional Opinion Concoming Voltage-Based Repair Criteria for Star.m Generator Tubes: Steam Generator Rulemaking.
l 4.
Memorandum dated September 19,1997, from Brian W. Sheron, Office of Nuclear i
Reactor Regulation, NRC, to John Larkins, ACRS,
Subject:
ACRS Reviewof the Differing l
Professional Opinion Related to Steam Generator Tube Integrity (Predecisional).
5.
Memorandum dated August 12, 1997, from T. T.
Martin, Office of Nuclear Reactor Regulation, NRC, to John s.arkins, ACRS,
Subject:
ACRS Review of the Proposed '
Steam Generator Generic Letter (Predecisional).
l 6.
U. S. Nuclear Regulatory Commission, Draft Regulatory Guide DG-1073, "An Approach for Plant-Specific, Risk informed Decision Making: Induced Steam Generator Tube l_
Rupture,* Revised August 26,1997,.
l 1
.o i
to 3
7.
U. S. ~ Nuclear Regulatory Commission, NUREG-1477, " Voltage Based interim Plugging Criteria for Steam Generator Tubes,' June 1993.
8.
U. S. NuclearRegulatory Commission, NRC Generic Letter 95-05: Voltage Based Repair i
Criteda for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress j )
Corrosion Cracking, August 3,1995 i
4 i
i
+
i c
s 4
)
L.
N
~
I a
e m
.