ML20249A189

SER on Moderate Energy Line Pipe Break Criteria for Perry Nuclear Power Plant,Unit 1 & Requests Addl Info to Demonstrate That Plant & FSAR in Compliance W/Staff Position & GDC as Discussed in SER

ML20249A189
Person / Time
Site:	Perry
Issue date:	06/11/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20249A182	List: ML20249A181 ML20249A189
References
NUDOCS 9806160157
Download: ML20249A189 (4)

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k UNITED STATES

[m j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 2006H001

\...,..l2 SAFETY ASSESSMENT l

OFFICE OF NUCLEAR REACTOR REGULATION MODERATE ENERGY LINE PIPE BREAK CRITERIA PERRY NUCLEAR POWER PLANT. UNIT 1 DOCKET NO. 50-440

1. INTRODUCTION By letter dated August 11,1997, Centerior Energy, the licenses, provided a response to NRC Inspection Report 50-440/97-201, dated June 10,1997, which discussed the NRC Design l i

Inspection conducted at the Perry Nuclear Power Plant (PNPP) by the Office of Nuclear f Reactor Regulation between February 17 and March 27,1997. One of the unresolved issues identified in the inspection report concerns the pipe break / crack criteria for nonseismic Category 1, moderate energy piping systems (URI 97-201-10). The August 11,1997, response, as well as the information provided to the inspectors during the associated inspection, describes the licensee's position that nonseismic, moderate energy piping is considered to have the same failure modes as seismic Category I moderate energy piping, and thus, is subject only to the postulation of " controlled cracks"in piping and branch runs, even in the event of a design basis earthquake. However, as described below, it is the staffs position that as a result of a design basis earthquake, nonseismic Category I moderate energy piping could fail catastrophically and the ability to achieve and maintain safe reactor shutdown following such failures must be demonstrated in order to be in compliance with General Design Criterion (GDC) 2 " Design Bases for Protection Against Natural Phenomena." ,

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2. DISCUSS!ON in its letter of August 11,1997, the licensee referenced Updated Safety Analysis Report (USAR) Section 3.6.2.1.3 which states that "For moderate energy fluid systems, pipe breaks '

are confined to postulated controlled cracks in piping and branch runs." This statement does not distinguish between the postulated pipe failure modes of seismic and nonseismic moderate ,

energy fluid systems. This statement was also contained in the Final Safety Analysis Report  !

(FSAR) at the time of licensing review (May 1982). Based on a review of the histoiical l information, the staff determined that it had discussed this issue in detail with the licensee prior to the submittal of the FSAR and informed the licensee that the staff required the complete severance of nonseismic moderate energy piping to be considered in the licensee's flooding analysis.

I in the May 1982 time frame, the licensee revised the then current pipe rupture analyses that assumed full circumferential breaks in moderate-energy, nonsafety-related, nonseismic ENCLOSURE I

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Category I piping outside containment. In its letter of August 11,1997, the licensee states that I it considered this approach acceptable under current and past Standard Review Plan (SRP)

J criteria of SRP Sections 3.6.1 and 3.6.2. The licensee's justification to postulate only cracks in these nonseismic moderate-energy systems was based on their interpretation of the 1981 revisions to the SRP. The licenses concluded that the published criteria in the SRP for postulating breaks in moderate-energy piping outside containment do not require, and have not required, full-size breaks whether in seismic or nonseismic piping.

The licensee's letter of August 11,1997, concludes that the design and licensing basis for moderate energy line cracks was reviewed and accepted during the original plant licensing. As previously stated, USAR Section 3.6.1.3,

• Postulated Pipe Breaks and Cracks," states that ,

"For moderate energy fluid systems, pipe breaks are confined to postulated controlled cracks in piping and branch runs." The staff's Safety Evaluation Report (SER, NUREG-0887) issued in May 1982 stated, "Tt e plant design accommodates the effects of postulated cracks b moderated energy fluid systems outside containment with respect to jet impingement, flooding, l and other environmental effects." The SER also stated, "The design will be of a nature to mitigate the consequences of pipe ruptures so that the reactor can be safely shutdown and rr.:!ntained in a safe shutdown condition in the event of a pos.tulated rupture of a high- or moderate-energy piping rystem inside or outside of containment."

The review for adequate protection from the failure of nonseismic moderate energy fluid systems was performed by the Plant Systems Branch (SPLB) (the Auxiliary Systems Branch

[ASB) at the time of Perry licensing review) under Branch Technical Position (BTP) ASB 3-1

" Plant Design for Protection Against Postulated Piping System Failures in Fluid Systems j Outside Containment." The staff issued the SER approving the pipe break analyses in May 1982. It is apparent from the dates of the licensee's revised pipe break analyses and the I issuance of the SER (both in May 1982), that the staff was unaware of the change to the Perry nonseismic, moderate energy p!pe break criteria. From a review of the historicalinformation, it is also apparent that the staff assumed the licensee's moderate-energy analysis included full-sized ruptures in nonseismic moderate-energy piping systems when it prepared the SER for licensing of the plant.

I It is the staff's position that the licensee's interpretation of SRP Sections 3.6.1 and 3.6.2 and I their attached BTPs ASB 3-1 and MEB 3-1 is incorrect. As discussed in the background sections of SRP Sections 3.6.1 and 3.6.2, BTPs ASB 3-1 and MEB 3-1 were developed to provide an acceptabl6 method of meeting the requirements of GDC 4, " Environmental and Dynamic Effects Design Bases," as it relates to protection from the effects of postulated pipe I break accidents or events. Position B.2.c.(2) of BTP MEB 3-1 identifies the criteria for postulating cracks in nonseismic moderate-energy piping. As stated in Position B.3.a of BTP ASB 3-1, these cracks are postulated to occur as an initiating event occurring under normal plant operation (not under seismic conditions). BTP MEB 3-1 does not address the failure j mode of piping during seismic events (for seismically or nonseismically designed piping).

1 Regulatory Guide (RG) 1.29 provides the guidance for meeting the requirements of GDC 2 as it relates to protection against earthquake. Without analytical evaluations, the staff does not accept the assertion that nonseismically supported piping cannot rupture as a result of a design basis earthquake. It should be noted that Perry FSAR Section 3.7.3.13 refers to Position C.2 of I

. Regulatory Guide (RG) 1.29 " Seismic Design Classification." That specific provision of RG 1.29 recommends that a postulated failure of piping systems not designed to seismic Category I standards should not result in any loss of capability of any system important to safety, i.e.,

seismic Category I systems. Therefore, in order to meet the requirement of GDC 2, an assessment of the potentialimpact on safety-related piping systems and components as a result of a postulated failure of the nonseismic piping system during a seismic event should be performed.

In the 1981 revision (Rev.1) to SRP Section 3.6.1, the staff revised Position B.3.d of BTP ASB 3-1 in an attempt to decouple oostulated oioina failures (as defined in BTP ASB 3-1) occurring during nomial plant conditions from failures in nonseismic piping systems during a reismic event. It was intended to make clear that complete failures in nonseismic piping systems during a seismic event would be assumed in lieu of cracks or longitudinal .

breaks. The revised Position B.3.d specifies that "The functional capability of essential systems and components should be maintained after a failure of piping not designed to seismic Category I standards, assuming a single active fa: lure." In order to determine that the failure of these nonsafety-related, nonseismic systems would not affect safe shutdown systems, analyses must be performed to show that the non-seismic piping will not catastrophically fail during an SSE or that the consequences (flooding, spray, missiles) from a catastrophic failure are acceptable. At Perry, these nonsafety-related, nonseismic piping systems are apparently not seismically supported, nor have they been analyzed to show that they would not fait during an SSE event. Therefore, flooding analyses should be based on an SSE causing the complete severance (full circumferential break) of the piping in the system being analyzed. Past staff practice has typically accepted that flooding analyses for each area be based on the complete failure of only one nonseismic moderate energy line that produces the most limiting results (usually the largest nonseismic pipe). The catastrophic simultaneous failure of all nonseismic piping is not expected to occur and it is not iequired to be assumed for flooding analysis purposes.

The staff agrees with the licensee's position that pipe break effects are only required to be analyzed for pipe breaks as initiating events and do not have to be analyzed as an independent event following an accident, including a loss-of-coolant accident (LOCA). However, for j nonseismic Category I piping, a seismic event is considered an initiating event that can cause i pipe breaks (ruptures) of nonseismic Category I piping (both moderate energy and high energy piping systems) in accordance with RG 1.29. Therefore, reliance on nonseismic Category I

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equipment, including offsite power, to mitigate the consequences of such piping failures cannot i.,e assumed. Also, when evaluating the environmental effects (such as flooding) from the rupture of a nonseismic pipe, only singular ruptures, in lieu of simultaneous multiple ruptures, need to be evalua+ed for a given event. However, the staff does not agree with the licensee's assumption that credit can be taken for nonseismic Category I piping maintaining its integrity as a fission product boundary (or containment boundary) following a design basis LOCA. Such credit would be contrary to Paragraph VI.(a) of Appendix A to 10 CFR Part 100 which requires that equipment necessary to mitigate the consequences of a loss-of-coolant accident (LOCA) t'e designed to remain functional following a safe shutdown earthquake (SSE).

It should be noted that in some instances piping cracks could be more limiting than a complete rupture of the same pipe caused by a seismic event. Fluid flow from a complete rupture is often

. immediately detectable while fluid flow from a critical crack may continue undetected for some period of time. Also, an SSE is assumed to result in a loss of offsite power and the source of water may be interrupted limiting the amount of water that could be discharged from a ruptured piping system. A loss of offsite power does not need to be assumed along with a crack during normal plant operation unless the postulated piping crack results in a plant trip. If a plant trip is a direct result of a postulated piping crack then the event should be analyzed both with and without offsite power to determine which is the most limiting case. It follows that in order to l

meet both the ASB and MEB BTPs, unless it is demonstrated that a complete rupture analysis bounds the analysis from a postulated crack, both a rupture and a postulated crack analysis would have to be performed. if a nonseismic moderate-energy piping system is seismically supported, then only postulated piping cracks would have to be assumed in any hazard analysis (flooding and spray effects) associated with failure of that piping even in the event of a design basis earthquake.

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3. CONCLUSION Based on the above evaluation, the staff concludes that the revised criteria for nonseismic moderate-energy lines at Perry is not consistent with Position B.3.d of BTP ASB 3-1 attached to SRP Section 3.6.1, Revision 1. The staff further concludes that the revised criteria were not considered in the conclusions reached in the staff's 1982 SER. The licensee is requested to provide information to demonstrate that the plant and FSAR are in compliance with the staff's position and GDC 2 as discussed above.

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