PY-CEI-NRR-2203, Forwards Responses to NRC Concerns Re ECCS Suction Strainer Mods
| ML20210L170 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 08/15/1997 |
| From: | Myers L CENTERIOR ENERGY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| PY-CEI-NRR-2203, NUDOCS 9708210012 | |
| Download: ML20210L170 (6) | |
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f Rower Generation Group Perry Nuclear Power Ptart.
Mail Aiiress-Pt 4280-6916 Lew W. Myers 10 Co'ter Road Ro. Don 97 FAk 21428080.9 Vre Presxtort Perry. Otw 44081 Perry.OH 44081 August 15,1997 PY CEl/NRR 2203L United States Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555 Perry Nuclear Power Plant Docket No. 50-440 Response to NRC Concerns on Emergency Core Cooling System Ouction Strainer hkxlifications Ladies and Gentlemen:
On July 9,1997, the NRC staff transmitted a letter discussing four concerns dealing with the
. proposed modification on the Emergency Core Cooling System suction strainers. The letter indicated that the NRC sf aff was not requiring a response to the concerns, but had included the concerns for consideration. Each of the four concerns and responses to the concerns were discussed during a telephone conference call conducted on August 1,1997. The Attachment summarizes the responses to each of the concerns.
If you have questions or require additional information, please contact hir. llenry L llegrat, hianager - Regulatory Affairs, at (216) 280 5606.
Very truly yours, M
Attachment
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NRC Project hianager NRC Resident inspector NRC Region ill 9700210012 970815
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l Atta6 hment PY CEl/NRR 22031.
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llACKGROUND l
In a letter from the NRC staff (llopkins) to the Centerior Service Company (Myers) dated l
July 9,1997," Emergency Core Cooling System Suction Strainer Program in Response to NRC llulletin 96-03, Perry Nuclear Power Plant, Unit 1 (TAC No. M96162)," the NRC staff discussed concerns dealing with the proposed modincation to the Emergency Core Cooling System (ECCS) suction strainers.
The enclosure to the referenced letter delineates concerns of the NRC staf f regarding proposed modifications to the ECCS suction strainers. The concerns were identined following the March 24,1997, Perry strainer design meeting with the staff, and a follow up telephone call on May 6,1997, Since that time, the analysis of the strainer design has evolved signincantly. At the time of the March 24,1997 meeting, acoustic methodology was planned to be used for a much greater portion of the analyses when dealing with the hydrodynamic loads on the strainers.11ased in part on the meeting with the NRC staff, and the questions that were raised by the NRC staff, the modincation analyses was re reviewed using methods prescribed in the GESSAR 11. The information presented in those earlier meetings has been augmented by the results of subsequent analyses and funher reviews of the license basis for Perry, such that the NRC concerns are considered to be adequately addressed. The following paragraphs detail each of the NRC concerns and provide a summary of the technical information w hich addresses each concern:
CONCERN (1):
In its meeting with the staffon Afarch N,1997, Perryprovideda handout entitled, "ECCS Suction Strainer Program and Design Review. " The handout discusses one of the advantages of the new Perrynirand Gulfstrainer design that it is "not conducive to air ingestion" assuming actuation ofone or more SRl"s. The staffis concerned about this statement because the new strainer design proposed by Perry and Grand Gulf would apparently infringe on an area conunonly called the " exclusion :one. " The exchtsion :one is a cylindrical:ane draan around and above every quencher. 7he
- one is a design rs quirement imposed by GE in the GESSAR 11. the GE standard FS4R for Afark 111, and BWR 6 designs. All Afark llPs referenced the GESSAR 11for the hpirodynamic loads portions of theirplant FS4R during plant licensing. In Appendix 3b ofthe GESSAR 11, GEprovidedguidancefor the de sign engineer stating that the ECCS suction pipir.g in the vicinity of the SR V quenchers should not penetrate the exclusion area. 7he exchtsion area was defined in Section 3B4.7 as a clearance :one around each quencher maintaining a minimum clearance of117 inchesfrom any ECCS suction inlet. The purpose of this clearance is not espressly discussed in the text of the GESSAR: however, the staff believes its purpose is to prevent impingement of thejet emanating at the quencher holes on piping or structures.
Ifa structure is nowplaced in thatjet path within the exclusion :one, the c((ccts of the jet impingement acting upon the strainer surface should be evaluatedfor local effects such as deformation. Thejet effect acting upon the nearfield strainer surface nury exert sufficientforce to damage the strainerperforated surface. An additional sta((
concern is related to the air plume discharge of the SR V becoming ingested into the l
Attachment PY Clil'NIW220.1L Page 2 of 5 ECCS suction piping. The plunse is createdfroin the initial air clearing of the SRI' tallpipe uhen Ihe vah'e opens.
Perry statedduring the Afarch 24,1997, inecting that their esisting strainers v olate this exchtsion :one in one location. This particular strainer, therefore, does noi ineet that design basis requirernent imposed by GE. The neseproposed toroidal shaped streer still not snect that design requircinent in inany locations around the strainer.
The licensee stated that schile they svere asvare cf the exchalon :one, they did not believe there tras an analysis to support the exclusion :one requirement, and have concluded that infringing on the zone with the nese strainer design is acceptable. 1he staffbelieves that hofringing upon the exchnion :one as described in the GESSAR 11 should be supported by analysis or test. Ifanalysis is provided they should addressJet load and the potentialfor air ingestion into the ECCS systems.
The sta[fis concerned that the engineering assessment described by Perry during the March 24,1997, meeting with the staffdoes not address these issues. The 1I7-inch minimum clearance as specified in the GESSAR llis not metfor the recently modified strainer design that is currently in place, and would not be metfor the new strainer design. Tids means that they would be infringing on many more quencher eschalon
- ones than their current design and, therefore, they nury have a higher likelihood of subjecting the strainer to localjet loads not previously evaluated and also ingesting noncondensables into the strainer.
ILESPONSE:
Loss of Coolant Accident (LOCA) vent clearing waterjet loads have been evaluated, and these pressure loads were subsequently evaluated for their effects on the strainer perforated plate and structure. The strainer is not in the SRV clearing waterjet zone of innuence based on GESSAR analysis methods. Con 0rmatory computational Guid dynamics analysis shows that waterjet loads on the strair.er are not significant.
The Perry specific SRV air clearing bubble properties have been determined based on GESSAR 11 methods for as built SRV discharge line con 0guration and Orst actuation and second pop events. There is no contact between the SRV bubble on any portion of the strainer, and therefore, no possibility for air ingestion into the suction pipe. The design of the strainer is conducive to air release if any air is ever ingested. The low approach and Dow velocities, internal ribs, and perforated plate on the center of the strainer at the suction tee all work to mitigate this phenomena.
The strainer design addresses the anticipated loads, such that there is no effect on the performance of the strainer. I'urther, since no air ingestion is expected to occur as the result of SRV actuations, and the strainer is conducive to air release if any air is ever ingested, the probability of air ingestion to the ECCS pumps is not increased.
Attoclunent PY CIl/NRR 2203L Pcge 3 of 5 CONCERN (2):
Also within the same harulout, the Perry licensee discusses the use of acoustic wave methodology as a s uitable methodfor calculating s ubmerged structure loads. 1(
reviewed, this inethod may befound suitable by the s ta[h however, both licensees believe this calculational change can be made under 10 CFR 50 59. The staffnotes that the GESSAR 11 specifically diu usses the calctdation ofsubmerged structure loads which are based on the Pressure Supturession Test Facility (PSTl] tests run 17 years ago. The GES&tR 11also discusses the snargin uhIch exists in the current method For example, GESSAR 11 states in Section 3BB.5 that expectedloadsfrom bulk pool swell (the air bubble phase ofIDCA) are at most 60 percent of the design loads with 10 inch pipes never exceeding 30 percent ofdesign valuefor drag loads, ll'ith the proposed method of acoustics, the licensees stated that an order of magnitude reduction in the calculatedloads on a submergedstructure nmy be obtained The staff believes that use of this alternative methodology appears to be reducing the safety margin and was not suty>orted or compared with existing test data to determine the available inargin that would exist using the proposed methodology. In addition, the staffis concerned that the use of acoustic wave methodology nwy not be an appropriate method u hen the originating event causes bull:J1uld displacement. Under a postulated i OCA or SRI' discharge, the initial air bubble generation causes large fluid displacement, and that subsequent motion generates dragforces on bodies restrained within thefluid The licensee's approach does not appear to model the water acceleration dragforces.
It is not clear to the sta((how the licensees concluded in their 10 CFR $0.59 eva,'uation that they are not reducing the margin to safety. Their discussion on March N,1997, did not address the subject ofinherent margin in their method and what they believe is adequate margin between calculatedloads versus design capability of the strainer device and its mounting.
RESPONSE
Acoustic methodology is the primary analytical method only for chugging loads in the current strainer hydrodynamic loads analysis. The NRC indicates the application of acoustic methodology to address chugging loads is "very conservative" in resolution of Ilumphrey concerns 19,1 and 19.2 (ref. Perry Nuclear Pow er Plant Supplemental Safety Evaluation Report 8, Appendix R). The acoustic method was not used for SRV air bubble loads or condensation oscillation loads as stated in the Perry NRC Bulletin 96 03 response. These loads are determined using the GESSAR 11 method ofimages.
Acoustic method calculations serse as independent verification of the GESSAR 11 method calculations for these loads. In these cases, the acoustic method calculations compare closely with the GESSAR 11 method analyses, and do not produce the order of magnitude load reductions indicated in the March 24 meeting. A confirmatory analysis has shown that the acoustic method with a GESSAR 11 based source provides conservative loads in the suppression pool as compared to Grand Gulf Nuclear Station SRV inplant test data, i
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Mtuhment l'Y.GlHRR 220E Page 4 of $
The acoustic method was not used for LOCA bubble loads, SI(V air clearing loads, or condensation oscillation loads. The acoustic method was only used for chugging loads, which have been determined to be an acoustic phenomena as documented in GESSAR and in documents related to closure ofllumphrey concerns 19.1 and 19.2.
The use of the GESSAR 11 inputs for acoustic methodology has been compared to GESSAR 11 bases and assumptions to ensure the applicability of the load source. A confirmatory analysis using the acoustic method, a GESSAR 11 based source; and Grand Gulf Nuclear Station SRV inplant test data show the conservatism in this method and that adequate safety margin exists.
CONCERN (3):
Use of the new methodologvfor calculating air clearing loads has led both licensees to conclude that uphft loads wouhl be insufficient to lift the strainer, and therefore, no attachment to thefloor or other vertical bracing is needed. The staffbelieves that a new event may need to be e on tidered because of the proposed design of the strainer.
Their proposed strainer is designed to have three hydraulically distinct regions within the torold: however, because of the physical arrangement, the strainer has all ECCS suction piping mechanically tied together at the strainer.
The asynnnetric load condition is an assumption used currently by the Mark Illplants in the LOCA air bubble event. If the proposed Perry methodfor calculating air bubble / air clearing loads should underestimate theforces or an asymmetricforce be generated, then the possibility exists that the strainer cmdd rotate or move. This cordd lead to the possibility of disabling or reducing the performance ofall of the ECCS systems ifa hinge isformed in the ECCSpiping. The reduction in ECCS performance may occur of the strainer rotates andpartially collapses the ECCS suction piping.
There was insufficient detail available at the meeting in order to address this potential issue in sufficient depth.
RESPONSE
Asymmetric loading is a design consideration for the LOCA bubble and other applicable load cases. The air clearing loads are calculated according to the existing plant license basis. The strainer is restrained froni movement by radial restraints symmetrically spaced around the strainer circumference. The strainer is additionally restrained from axial motion by bottom plate restraints that bear against the leak chase channels. No significant axial movement of the strainer is possible. Adequate margin exists between (conservatively) calculated uplift loads and weight of the strainer, considering buoyancy. The strainer design has been evaluated for common mode failure. The design has considered all applicable load combinations, such that the strainer design is structurally adequate to handle the applicable loads and load combinations.
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Attachment l'Y CElHRR 2203L Page5of$
CONCEltN (4):
From a technicalstandpoint, the staffnoted during the Afarch 2.I, I997. meeting that the methat which the licensees propose, which is described in NEDE 24822 entitled, "Afark ll Improved Chugging Afethodology, " and appros ed by the staffin NUREG 0808, does not cur-ently address the use of the acoustic wave methodologyfor the air clearing portion of the event. That method was intendedfor the analysis of chugging and condensation oscillations induced loads as described in the NEDE and NUREG. In addition, since staff approval was based in large part on a comparison of analysis with test data, the licensees needed to demonstrate that their "new method" of using acoustic wave methodologyfor calculating LOCA air bubble and cptencher air bubble loads will achieve a 93% 93% confidence level as was donefor the original licensing submittal.
ItESI'ONSE:
The acoustic method was never intended to be used and was not used for LOCA air bubble loads. The acoustic method was not used for SRV air bubble loads; GESSAR 11 methods were used appropriately, A confirmatory analysis using the acoustic method, a GESSAR 11 based source, and Grand Gulf Nuclear Station SRV inplant test data show the conservatism in this method and that adequate safety margin exists. The sources utilized as inputs to the acoustic method are from the GESSAR and have been reviewed for their applicability The GESSAR sources were previously reviewed and accepted by the staff as exhibiting the 95495% level of confidence.
CONCLUSION Ilased on the above evaluations of the NRC concerns and the discussion of these responses in the August I telephone conference call, it has been concluded that sufficient technical information exists to demonstrate the adequacy of the proposed ECCS suction strainer design, analytical methods, and margin of safety,
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