ML20244C532
| ML20244C532 | |
| Person / Time | |
|---|---|
| Issue date: | 04/13/1989 |
| From: | Chilk S NRC OFFICE OF THE SECRETARY (SECY) |
| To: | Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| References | |
| REF-10CFR9.7 M890406B, NUDOCS 8904200256 | |
| Download: ML20244C532 (8) | |
Text
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I #' **'4 UNITED STATES IN RESPONSE, PLEASE c'
'j, NUCLEAR REGULATORY COMMISSION REFER TO:
M890406B j
W ASHIN GTON, D.C. 20555 j
J April 13, 1989
' OFFICE OF THE SECRETARY -
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l MEMORANDUM FOR:
Victor Stello, Jr.
Executive Director for Operations (bb -
l Samuel J.
Chilk, Secretary FROM:
SUBJECT:
STAFF REQUIREMENTS - AFFIRMATION / DISCUSSION AND VOTE, 11:30'A.M., THURSDAY, APRIL 6, 1989,, COMMISSIONERS' CONFERENCE ROOM, ONE' c.
WHITE FLINT NORTH, ROCKVILLE, MARYLAND (OPEN TO PUBLIC ATTENDANCE)
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SECY-88-325 - Policy Statement on Additional Acolications of Leak-Before-Break Technoloav The Commission, by a 5-0 vote, approved the attached policy statement indicating the Commission's position on extending the
. leak-before-break concept to emergency core cooling systems and i
equipment qualification.
Thel policy statement should be revised as noted and forwarded for signature and publication.
(. EDO)
(SECY Suspense:
5/12/89)
Attachment:
As stated cc:
Chairman Zech Commissioner Roberts Commissioner Carr Commissioner Rogers Commissioner Curtiss OGC j
GPA JDR - Advance vDCS - P1-24 D,DN
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8904200256 890413 PDR 10CFR
.PT9.7 F,DC w________-_-_____-__-__-_-.
[7590-01]
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NUCLEAR REGULATORY COMMISSION 10 CFR Part 50 g
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Policy Statement en Additional Applications of Leak-Before-Break Technology 5
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AGENCY: Nuclear Regulatory Commission.
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7 ACTION: r'olicy Statement.
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SUMMARY
- The Nuclear Regulatory Commission (NRC) has at this time decided not to undertake rulemaking which would extend the scope of application of Leak-Before-Break (LBB) technology to emergency core cooling r,ystems (ECCS) or environmental qualification (EQ) of safety-related electrical and mechanical equipment. IVse of exemptions with respect to the application of LBB to EQ continues to be permitted in accordance with the modification of General Design Criterion 4.
FOR FURTHER INFORMATION CONTACT:
John A. O'Brien, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Washington, DC 20555. Telephone (301)492-3894.
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[7590-01)
SUPPLEMENTARY INFORMATICH:
i EVALUATION OF PUBLIC COMMENT On April 6, 1988 the NRC solicited public comment nn the application of LBC to ECCS and E0 (53 FR 11311).
Twenty-one effective comment letters were received.
Twelve comment letters opposed the application of LBB to ECCS or EQ (from f
[privatecitizens,citizensgroups,regionalcoalitionsandenvironmental s'
groups)fwhile eight comment letters supported such an application}(from f
utilities, a nuclear steam supply system vendor, industry groups and a nuclear fuel vender). One nuclear steam supply system vendor took a neutral position.
Among those opposing, repeated citation was made to the Surry pipe rupture in December 1986, the March 1988 General Accounting Office ceport, " Action Needed pane-nTca to Ensure that Utilities Monitor and Repair Pipe Damage," the unreliability of T4.5 rt UC-To ultrasonic detection ef piping flaws and public statements made in August 1983 by the then Director of the Office of Nuclear Reactor Regulation (NRR) pertaining to intergranular stress corrosion cracking in BWR piping. The NRC has determined that none of these citations discredit either the present or proposed expanded scope of LBB.
This is explained as follows:
LBB acceptance criteria cannot be satisfied in the feedwater suction line which ruptured at Su rry. There is no reason to expect LBB behavior in this line. The cited GA0 l
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l report treated erosion /corrosior, of piping.
The factors which control i
erosion / corrosion are sufficiently understood so that the tTC can determine with confidence which piping systems are susceptible to erosion / corrosion. NRC acceptance criteria do not permit piping sub,iect to erosion / corrosion to qualify for LBE.
Difficulties with ultrasonic testing are irrelevant to LBR.
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Leakage detection with high margins is used instead to detect throughwall cracks in high energy piping during service.
The statements made in August 1983 to the Commissioners by the then Director of t;RR were made at a time when.
LBB had not advanced to its present state, and moreover were directed to BWR piping.. Unless special materials or measures are empicyed, LBB cannot be applied to BWR piping because of intergranular stress ' corrosion cracking.
The nuclear steam supply system vendor that took a neutral position with respect to the application of LBB to EQ and ECCS recognized that limited However, this -c(s.icamvendor-1 safety and operational benefits could result.
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(-for plads viih 1gi4sdesigr1}
3 concludedthatfcomparablebenefitscouldbeobtainedemployinganotherrecent-rule change (as described below), and that " economic benefit....does not appear to be major, and net safety benefits may not cutweigh the detriments."
Among those supporting the expanded use of LBB to EQ and ECCS, many economic, J
operating, testing, maintenance and design benefits were cited. The NRC remains firm in using) safety benefits as the prime measure in deciding (IWiled whethertodivertgresourcestotheresearchandrulemakingeffortsneededto apply LBB to EQ and ECCS. A few safety. benefits were identified in public comment. These are discussed as follows. The test and design requirement i
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for' fast. starting of emergency diesel generators is derived frca the double-ended guillotine rupture of reactnr coolant loop piping when analyzed in accordance with 10 CFR 50.a6 and Appendix K.
The test requirement degrades bearings, gears, the governor and power transmission such that the prospect of reliable service from the emergency diesel generators could be dininished if
. pipe ruptures actually occur.
Using LBB to postulate smaller pipe ruptures would lengthen the starting time and assist in preserving the reliability of the emergency diesel generators for some (but not all) plants. A second safety L
benefit deals with radiation embrittlement of the reactor pressure vessel. The
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.21< ce relatively low peaking limits for the fuel might be increased in so6e plants A
when smaller LOCAs replace the double-ended guillotine
- break requirement. With i
higher peaking limits the fuel configuration can be redesigned to yield less radial fluence leakage. This can mitigate concerns with vessel life extension and pressurized thermal shock of the vessel. An additional safety benefit can be achieved by equipment reliability improvements (other than for the emergency diesel generators) resulting from fewer plant scrams and challenges duc to lower ECCS set points and less harsh equipment qualification environments.
However, reliability improvement due to' lower ECCS set points and less harsh EPM 5 equipment qualification environments Atin be offset by safety degradations l
associated with such actions, particularly with respect to severe accident i
b performance. It is uncertain that overall safety would improve when less harsh i
EQ profiles are specified or ECCS set points are reduced.
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'[Llar$cParh f /he first two safety benefits cited above can be obtained{more expeditio and efficiently under the recent ECCS rule (53 FR 35996, September 16,1988) which permits best estimate methodology with quantified uncertainty for i
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evaluating LOCAs. The modr.ls needed for implementing the ECCS rule have
- undergone substantial development; however, research must be initiated to develop replacement design basis pipe ruptures when LBB is.. invoked for ECCS.
fioreover, whereas the ECCS rule already exists in final form, the rulemaking needed to expand'LP,B technology would censume at least two years and considerable NRC effort.
Finally, while the ECCS rule can be applied directly to all light water reactors (except one with stainless steel fuel cladding),
LBB can be applied only~ to qualifying reactors.
The scope of qualifying reactors is unclear; especially in cuestion are BWRs.
With respect to harsh environments inside the containment, unless LBB can be successfully applied to main steam lines, harsh environments will not substantially change.
Significant requirements will remain unless most of the large diameter piping inside the containment satisfy LBB, requirements.
Additionally, other breaches in the fluid system boundary, such as failed manways or valve bonnets, must be examined to determine whether they control EQ profiles. Reductions in EQ profiles are more readily achieved outside the containment because temperature, pressure and humidity do not build-up due to venting and blew out panels in some cases.
However, EQ profiles outside the containment attract lesser interest because the EQ profiles are usually less l
harsh and thus more easily satisfied. h ee"ar, there erm r.; current aeti"4 tier to pply Lam te ripf3 cut:idcth:<cetzient}
A few commenters noted difficulties with cable insulation, seals and valve seats resulting from materials selected to resist harsh environments associated 5
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with the postulated double-ended guillotine pipe rupture.
The NRC acknowledges these difficulties,'but is not certain that reducing harsh environments would, on balance, increase safety.
r d d f f i cu l i. i c > citeu s e s... te te.nr; rchud care +ycen:itrg,v,.;]
M r;'cze;knc.1. ;;;nc--i; cr -ai"+ananca factors than tn Additionally, it was suggested that the threat of pressurized thermal shock would be reduced by lower pumping set points for low pressure safety injection, k
The NRC does not accept this position because pressurized thermal shock is controlled by injection of. cold water at relatively high pressure during a small break LOCA.
POLICY STATEMENT Having considered all public comments received, the Commission has a4 tMs
$4me decided not to undertake any rulemaking to extend the applicability 4L' LBB of
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i o.f L %,p pny safety benefits associated with ECCS can be more readi y to ECCS or E obtained under the recent ECCS rule. The use of exemptions for applying LBB to environmental qualification was permitted in the revision to General Design Criterion 4 (52 FR 41288). This option continues to remain open.
IuSERT Dated at Rockville, Maryland this day of 1988.
For the Nuclear Regulatory Commission.
Samuel J. Chilk, Secretary of the Commission.
INSERT Nonetheless, the Commission has decided to keep open an avenue for future consideration of rulemaking which would permit the application of LBB to ECCS and EQ.
The Commission encourages industry to develop quantitative information that could justify the diversion of resources to the rulemaking efforts.
Primary attention should be given to establishing an appropriate substitute or replacement for the double-ended pipe rupture used in ECCS and EQ evaluations.
The Commission will consider modifying its current ECCS and SQ regulations when adequate technical justification support the feasibility and benefits of the proposed modifications.
In the interim, the Commission recognizes that situations may arise where justification can be developed by the industry for alternative ECCS and EQ requirements.
Such justifications, if accepted by the Commission pursuant to the existing exemption process, would allow a limited number of case-by-case modifications to ECCS and EQ requirements.
This could support future amendments to applicable requirements addressing ECCS and EQ.
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