NRC Generic Letter 1985-22

NRC Generic Letter 1985-022: Potential for Loss of Post-LOCA Recirculation Capability Due to Insulation Debris Blockage

ML031150731
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Skagit, Marble Hill
Issue date:	12/03/1985
From:	Thompson H L Office of Nuclear Reactor Regulation
To:
References
GL-85-022, NUDOCS 8511270253
Download: ML031150731 (3)

-.Iv ."I, -we .. ....I an, a; *.._A ..7,i0IxDecember 3, 1985TO ALL LICENSEES OF OPERATING REACTORS, APPLICANTS FOR OPERATING LICENSEES,AND HOLDERS OF CONSTRUCTION PERMITS.Gentlemen:SUBJECT: POTENTIAL FOR LOSS OF POST-LOCA RECIRCULATION CAPABILITY DUE TOINSULATION DEBRIS BLOCKAGE (Generic Letter 85-22 )This letter is to inform you about a generic safety concern regarding LOCA -generated debris that could block PWR containment emergency sump screens orBWR RHR suction strainers, thus resulting in a loss of recirculation orcontainment spray pump net positive suction head (NPSH) margin.The potential exists for a primary coolant pipe break to damage thermalInsulation on the piping as well as that on nearby components. Insulationdebris could be transported to water sources used for long-term post-LOCArecirculation and containment sprays (i.e., PWR containment emergency sumpsand BWR suction intakes in the suppression pools) and deposited on debrisscreens or suction strainers. This could reduce the NPSH margin below thatrequired for recirculation pumps to maintain long-term cooling.This concern has been addressed as part of the efforts undertaken to resolveUSI A-43, "Containment Emergency Sump Performance." The staff's technicalfindings contain the following main points.0 Plant insulation surveys, development of methods for estimating debrisgeneration and transport, debris transport experiments, and informationprovided as public comments on the findings have shown that debrisblockage effects are dependent on the types and quantities ofinsulation employed, the primary system layout within containment,post-LOCA recirculation patterns and velocities, and the post-LOCArecirculation flow rates. It was concluded that a single genericsolution is not possible, but rather that debris blockage effects aregoverned by plant specific design features and post-loca recirculationflow requirement.O The current 50% screen blockage assumption identified in RegulatoryGuide (RG) 1.82, "Sumps for Emergency Core Cooling and ContainmentSpray Systems," should be replaced with a more comprehensiverequirement to assess debris effects on a plant-specific basis. The50% screen blockage assumption does not require a plant-specificevaluation of the debris-blockage potential and usually will result ina non-conservative analysis for screen blockage effects. _The staff has revised Regulatory GuideFmarn rnev C rs nalinn and Containment(RG) 1.82, Revision 0, "Sumps forSprav Systems" and the StandardJLO --L577/ra:pj: I7tVQReview PICTI- edilf;w G.. ', 1intIM"~l l latRjv FW11 VCLI l" de vMnlei s -N A ~~~~i @ * * * * * * * * * * * *

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2above technical findings. However, the staff's regulatory analysis-(NUREG-0869, Revision 1, "USI A-43 Regulatory Analysis") evaluated (1)containment designs and their survivability should loss of recirculationoccur, (2) alternate means to remove decay heat, (3) release consequences(which were based on pipe break probabilities which did not incorporateinsights gained from recent pipe fracture mechanics analyses), and (4) costestimates for backfits considered (i.e., reinsulating). This regulatoryanalysis did not support a generic backfit action and resulted in thedecision that this revised regulatory guidance will not be applied to anyplant now licensed to operate or that is under construction. The revisedguidance will be used on Construction Permit Applications, Preliminary DesignApproval (PDA) applications, and applications for licenses to manufacturethat are docketed after six (6) months following issuance of RG 1.82,Revision 1, and Final Design Approval (FDA) applications, for standardizeddesigns which are intended for referencing in future Construction PermitApplications, that have not received approval at six (6) months followingissuance of the RG 1.82, Revision 1.Although the staff has concluded that no new requirements need be imposed onlicensees and construction permit holders as a result of our concludinganalyses dealing with the resolution of USI A-43, we do recommend that RG1.82, Revision 1 be used as guidance for the conduct of 10 CFR 50.59 reviewsdealing with the changeout and/or modification of thermal insulationinstalled on primary coolant system piping and components. RG 1.82,Revision 1 provides guidance for estimating potential debris blockageeffects. If, as a result of NRC staff review of licensee actions associatedwith the changeout or modification of thermal insulation, the staff decidesthat Standard Review Plan Section 6.2.2, Revision 4 and/or RG 1.82, Revision1 should be (or should have been) applied to the rework by the licensee, andthe staff seeks to impose these criteria, then the NRC will treat such anaction as a plant-specific backfit pursuant to 10 CFR 50.109. It is expectedthat those plants with small debris screen areas (less than 100 ft2), highECCS recirculation pumping requirements (greater than 8000 gpm), and smallNPSH margins (less than 1 to 2 ft of water) would benefit the most from thistype of assessment in the event of a future insulation change. RG 1.82,Revision 0 with its 50% blockage criteria does not adequately address thisissue and is inconsistent with the technical findings developed for theresolution of USI A-43.This information letter along with enclosed copies of NUREG-0897, Revision1, RG 1.82, Revision 1 and SRP Section 6.2.2, Revision 4 should be directedto the appropriate groups within your organization who are responsible forconducting 10 CFR 50.59 reviews.OFFICEO ........................ ........................ ........................ ........................ ........................ ........................ ............SURN"UIE i ... ........................ ................................ ........................................ ........................ ............ ............... ......... ............... ........................DATE j ............. ........................I.....................-t ............. ............. ..........NRC FORM 319 (10 60) NFICM 0240O FFICIA L Rt6CCJKru %WTr-Ivans .,-... -..,

' io- *kg -3No written response or specific action is required by this letter.Therefore, no clearance from the Office of Management and Budget isrequired. If you have any questions on this matter, please contact yourproject manager._Urll1nal signed byHu'h L.ThomPSOfnJr.Hugh L. Thompson, Jr., DirectorDivision of LicensingEnclosure:NUREG-0897, Revision 1RG 1.82, Revision 1SRP Section 6.2.2, Revision 4*See previous sheet for concurrenceORAB:DL* SL:ORAB:DL* C:ORAB:DL* AD:SA:DL'l:D 4li-iOFIC ............ ..... ............... ......... ............. ........ ................. .,.......... ........................i PTremblay/t JHannon GHolahan DCrutchfiel r HThoII son................ .......... ........................ ............................... ............................... ............ .................. ..................................... ........................DATa.7-./1l.85 ... .. ..3l/85.... .8.l.I./.85.l.lt/.5.l .. ........ .. ........... .. .1 I.. .. ........ ....NRC FOAM 3tJ (10 60) NRCMt 0240O FFICIA L R EC O RD C OPYUSGPO 1N3-315-960