TXX-8855, Comment Supporting Proposed Rule 10CFR50 Re Addl Applications of leak-before-break Technology.Util Strongly Endorses Proposal to Investigate Safety Benefits Associated w/leak-before-break Technology

Comment Supporting Proposed Rule 10CFR50 Re Addl Applications of leak-before-break Technology.Util Strongly Endorses Proposal to Investigate Safety Benefits Associated w/leak-before-break Technology

ML20151S717
Person / Time
Site:	Comanche Peak
Issue date:	08/05/1988
From:	Counsil W TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF THE SECRETARY (SECY)
References
FRN-53FR11311, RULE-PR-50 53FR11311-00019, 53FR11311-19, TXX-88557, NUDOCS 8808160079
Download: ML20151S717 (5)

Text

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Log # TXX-88557 L -File # 903.1 903.11 '88 AUG -8 P 5 :08 -

TUELECTRIC Ref. # 10CFR50.4(a) 0Fn - N 00Cni.i -

Wmism G. Coumil August 5, 1988 We becutive Vice Pressdent Mr. Samuel J. Chilk, Secretary of the Commission U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn: Docketing and Service Branch

SUBJECT:

COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)

COMMENTS ON ADDITIONAL APPLICATIONS OF LEAK-BEFORE-BREAK TECHNOLOGY (53 FED. REG. 11311, APRIL 6, 1988)

Dear Mr. Chilk:

In the subject Federal Register publication, the NRC stated that it is proposing to investigate the safety benefits associated with using leak-before-break technology to modify functional and performance requirements for emergency core cooling systems (ECCS) and environmental qualification (EQ) of safety-related electrical and mechanical equipment. The publication requested comments on this proposal, with particular emphasis on "documented evidence describing safety degradations and safety enhancements due to postulated pipe rupture requirements on EQ and ECCS...". It indicated that the priority which it "assigns to modifying functional and performance requirements for EQ and ECCS.will be determined in large measure from the balance between accrued safety benefits and detriments' believed to result (including impacts on severe accident performance)."

In response to this NRC request for comments, IV Electric strongly endorses the proposal to investigate the safety benefits associated with using leak-before-break (LBB) technology to modify functional and performance requirements for ECCS and EQ and urges the NRC to initiate a proposed rulemaking to implement such benefits.

The following comments describe the substantial safety benefits that would be derived from such additional applications of LBB technology. Although TV Electric cannot at this time provide documented data in support of such benefits it believes that the arguments are sufficiently convincing-that the NRC should assign high priority to a proposed rulemaking in this area.

l 8808160079 880805 PDR PR 50 53FR11311 PDR

,b5JO 400 North Olive Street iB 81 l>allas, Texas 7H01

TXX-88557 August 5, 1988 Page 2 of 5 EQ Related Comments (a) The current interpretation of accident criteria develops calculated l radiation exposures of 108 to 109 rads gamma plus beta for areas inside containment. Instruments gnd elegtrical penetrations in common ,

usage meet the requirements of 10/ to 100 rads gamma. The I application of leak-before-break (LBB) technology would reduce the level j of calculated radiation exposures inside containment under accident  !

criteria and thus-provide the follovfing significant safety benefits: '

(1) Elimination of Additional Qualification Testing Reduction in the qualification testing will make more types of instrumentation available to the designer at reasonable cost.

The system safety will be improved by the introduction of diverse safety equipment. For example, the AMSAC equipment utilized by CPSES has taken advantage of the availability of an alternative manufacturer (FSAR Section 7.8.1.9) . 3 (2) Utilization of Proven Equipment Standard equipment models represent the hulk of manufacturer operational experience and, in general, perform the best. If special adaptations are made to meet excessive radiation requirements, then the new material selection or design feature.

may not perform equivalently. This has many actual examples. A common one is the substitution of a more radiation resistant but i harder gasket material resulting in more repeated maintenance I than a resilient material would require. 1 (3) Improved Quality, Availability and Cost of Replacement Parts The discussion with respect to instrumentation availability as given in (1) is equally applicable to replacement parts. The discussion with respect to the use of proven equipment as given in (2) is equally applicable to the quality and capability of replacement parts.

(4) Elimination of Unnecessary Shielding If the equipment radiation resistance cannot be improved, the designer may elect to shield the equipment from the hypothetical radiation. This case is analogous to t':e additional supports eliminated by the original LBB interpretation. Elimination of the unnecessary shielding improves access for maintenance and testirig of the ECCS instruments.

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. 1 TXX-88557 August 5, 1988 Page 3 of 5 i

(5) Elimination of Unnecessary Surveillance and Maintenance in Radiation Areas '

Elimination of an unnecessarily high "reserve life" to accormnodate an accident will allow a longer qualified life, thcs reducing maintenance and replacement activity. This more 1

realistic approach will reduce the overall radiation exposure to {

plant workers. Less frequent maintenance activity will also improve plant availability. INP0 87-022 "Operational Performance of Reactor Protection Systems In U.S. Pressurized Water Reactors:

1981-1985" identifies trips while one channel is out for maintenance or surveillance, as a major cause of unplanned automatic scrams.

(b) Application of LB8 technology in determining the environmental requirements within containment will reduce the temperature and pressure parameters (as well as the radiation). This reduction would:

(1) Eliminate some additional qualification testing as in (a)(1) above.

(2) Enable more standard equipment to be applied as in (a)(2) above.

(3) Improve availability as in (a)(3) above.

(4) Extend qualified life and reduce surveillance and maintenance as in (a)(5) above.

(c) The nature of a large bore guillotine pipe break outside containment, e.g. main steam line break (MSLB), is to create harsh environmental conditions removed.

not only in the vicinity of the break, but in rooms far The application of LBB technology would:

(1)

Reduce EQ Requirements for Rooms Which Do Not Contain High Energy Piping Correspondingly, leak detection provisions outside containment will need to be supplemented and improved. The designer would be required to show that the leak detection capabilities are consistent with the reduction in the propagation of the environmental effects. Provision of radiation monitors for leak detection outside containment may have limited application.

However, area temperature and humidity monitors located in compartments where high energy piping failures are postulated should improve leak detection capability, w _-

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TXX-88557 August 5,11988 Page 4'of 5 (2) Improved Knowledge of Plant Condition An increased number of leak detection instruments distributed

-strategically throughout the plant would provide Control Room personnel with improved knowledge of pressure boundary performance. For the stme expenditure, the capability of the defense-in-depth is improved by investment in leak detection rather than by investment in qualifying equipment located in compartments that are remote from the postulated break area.

Use of various and appropriate. leak detection devices would represent a diversification of safeguard 5 as compared to the environmental qualification of existing equipment.

Equipment as presently specified is over-designed for the environment that it is likely to see throughout its lifetime.

The reduction of EQ requirements represents a more cost effective selection of equipment. An additional benefit of the extensive leak detection system will be better plant availability since operators will be able to respond earlier to a leat rather than ,

to the break that might ensue. Among the benefits of early response would be a reduction of drainage ano wastes.to treat.

I (d) Similarly to item (c), a postulated break in the letdown line creates an area of harsh chemical, temperature and dynamic effects. Under application of LBB technology:

If the harsh chemical environment br.s ruled out the use of some equipnient, benefits to diversit.v as described 'in (a)(1) will be possible; and If the harsh chemical environment has necessitated modifications to equipment, benefits to the quality of equipment'as described in (a)(2) will be possible.

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TXX-88557 August 5, 1988 Page 5 of 5 '

ECCS Related Comments '

(a) The designer can use LBB methodology to define a new "Design Maximum i 1.eak" as justified by the system components and piping employed, i defining a new "Design Maximum Leakage" may allow reduced capacity  !

requirements for the ECCS pumps. With a reduced capacity requirement, I the designer could improve pump reliability by lowering motor starting ,

torque, reducing required Net Positive Suction Head (NPSH), and improving l the NPSH available to the pumps. These factors would improve seal wear '

ring, and bearing wear and enhance equipment performance during testing and actual operation. I With reduced ECCS pump motor sizes, operational benefits will be accrued when loading the Emergency Diesel Generator (EDG). Assuming loss of offsite power, these pump motors will sequerce onto the safeguards hus more reliably because the load step with transient instability will be  !

lower. Mitigation of this transient may also be achieved by expanding '

the timing allowed for the EDG loading sequence.  ;

(b) The designer can use ti,e removal of the sudden large break case to revise the instrument setpoints for ECCS actuation. This would create a larger  !

margin to the normal operating range. This application of L8B technology l

would reduce the occurrences of inadvertent actuations of the ECCS systems due to the widening of margins'for normal instrumentation ,

readings. The occurrenco of spurious scrams amounted to 17% of the cases  !'

as reported in INPO 87-022.

l Once again, TV Electric strongly endorses the initiation of a proposed I rulcmaking to bring practical realism to modify functional and performance requirements for ECCS and EQ.

Very truly yours,

/ 7 W. G. Counsil HAM /grr c - Mr. R. D. Martin, Region IV Resident inspectors, CPSES (3)

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