Information Notice 1993-70, Degradation of Boraflex Neutron Absorber Coupons

Degradation of Boraflex Neutron Absorber Coupons

ML031070107
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, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	09/10/1993
From:	Grimes B K Office of Nuclear Reactor Regulation
To:
References
-nr IN-93-070, NUDOCS 9309070206
Download: ML031070107 (9)

IUNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON D.C. 20555September 10, 1993NRC INFORMATION NOTICE 93-70: DEGRADATION OF BORAFLEX NEUTRON ABSORBERCOUPONS

Addressees

All holders of operating licenses or construction permits for nuclear powerreactors.PurDoseThe U.S. Nuclear Regulatory Commission (NRC) is issuing this informationnotice to alert recipients to a potentially significant problem pertaining todegradation of Boraflex neutron absorber coupons. It is expected thatrecipients will review the information for applicability to their facilitiesand consider actions, as appropriate, to avoid similar problems. However,suggestions contained in this information notice are not NRC requirements;therefore, no specific action or written response is required.BackgroundPalisades has high-density fuel storage racks installed in the spent fuelpoolthat use Boraflex, a proprietary neutron absorbing material that wasmanufactured by Brand Industrial Services, Incorporated (BISCO). The storageracks are supplied by Westinghouse. The Boraflex is attached to the walls ofeach canister and is held in place by a stainless steel wrapper, which is spotwelded to the walls.The licensee has a surveillance program using Boraflex coupons to indicate thestatus of the Boraflex contained in the high density storage racks in thespent fuel pool. Recently observed degradation of several of these coupons,which may be due to exposure to high level gamma radiation in conjunction withinteraction with pool water, raised questions about the integrity of theBoraflex contained in the storage racks. Significant loss of Boraflex in thehigh-density fuel racks could result in loss of the subcriticality margin inthe spent fuel pool. 'Through a commitment to the NRC, Palisades was required to test and inspectthe Boraflex coupons after 5 years of use. The tests include opening thecoupons for visual observation, neutron attenuation determination, and aBoraflex hardness test.DescriDtion of CircumstancesDuring a period from August 17 through 19, 1993, 5 of the existing 10 Boraflexcoupons were removed from the spent fuel pool, 4 being full-length coupons9309070206Phi tE funt 3- O7G O1~

IN 93-70September 10, 1993 and 1 a short-set coupon (see Figure 1). During removal of the full-lengthcoupons a powdery substance and a grey debris cloud were observed emanatingfrom the coupons. Further investigation of the full-length coupons revealedthat one coupon had lost an estimated 90 percent of its Boraflex, two others50 percent, and one 38 percent. Investigation of the short-set coupon showedthat it had retained 100 percent of its Boraflex. The licensee has determinedthat the Boraflex in the 4 full-length coupons and the short-set coupon camefrom different lots of material.A principal difference between the short-set and the full-length coupons istheir geometrical design. The short-set coupon consists of eight compartmentsencapsulating the Boraflex with pool water accessing only the edges of thecoupons. However, in the full-length coupon Boraflex is sandwiched axiallyover the entire length of coupon and bolted between two 0.51-mm [0.020-inch]stainless steel metal strips. The licensee postulated that a much larger areaof the full-length coupon was exposed to the pool water environment and flow.In addition, the full-length coupon has a 12.7-mm [0.5-inch] hole through themetal strip on the top portion of the coupon, which contributes to the poolwater flow around the Boraflex. The licensee has no immediate plans forremoval or testing of the remaining five coupons in the spent fuel pool, butdoes intend to conduct neutron "blackness" testing in the spring of 1994.The licensee also had initiated measurements of the silica content of thespent fuel pool water. No increase in silica above normal 1-4 ppm levels havebeen observed except in instances when the pool boron concentration wasincreased. Because silica filler material is a constituent of Boraflex, thepresence of silica in the water may be an indication of degradation of theBoraflex in the fuel pool.DiscussionPotential degradation mechanisms for Boraflex include (1) gamma flux, whichchanges the material characteristics of the base polymer, and (2) chemicalenvironment, namely the accessibility of water to the Boraflex. The licenseehas not drawn firm conclusions as to (1) the root cause of the observeddegradation of Boraflex in the coupons, or (2) the correlation of the behaviorof Boraflex in the coupons to that in the storage racks.Degradation of the Boraflex in fuel storage racks could reduce thesubcriticality margin in the spent fuel pool. The design basis assumes a5 percent subcriticality margin on the basis of lowest pool temperature, noboron concentration in the pool water, and minimum spacing between fuelassemblies. In its preliminary analysis, the licensee assumed no boron in thepool water and a complete loss of Boraflex from the fuel storage racks. Thisreduced the subcriticality margin from greater than 5 percent to about2 percent. However, the licensee used the burnup for the currently storedfuel in the criticality calculation. This is higher than the design burnupvalue, implying less reactive fuel in the fuel pool than assumed in the designcalcul ation.The licensee took several compensatory measures, including (1) making theoperating staff aware not to dilute the spent fuel pool, (2) increasing the

IN 93-70September 10, 1993 spent fuel pool chemistry sampling frequency to daily, and (3) keeping theboron concentration in the spent fuel pool above 1800 ppm, which exceeds thetechnical specification requirement for boron concentration. With theseprecautions a subcriticality margin greater than 5 percent would bemaintained.Degradation of Boraflex has been previously addressed by NRC in InformationNotice 87-43, "Gaps in Neutron-Absorbing Material in High-Density Spent FuelStorage Racks," September 8, 1987. The Electric Power Research Institute,which has been studying this phenomenon for several years, has recentlypublished an interim report, "Boraflex Test Results and Evaluation,"TR-101986, February 1993.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.(~/'Bran Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Regulatory RegulationTechnical contacts: Kombiz Salehi, RIII(708) 790-5782K. I Parczewski, NRR(301) 504-2705Larry Kopp, NRR(301) 504-2879Vern Hodge, NRR(301) 504-1861Attachments:1. Figure 1, Palisades Boraflex Coupon Types2. List of Recently Issued NRC Information Notices

IN 93-70.- tSeptember 10, 1993 spent fuel pool chemistry sampling frequency to daily, and (3) keeping theboron concentration in the spent fuel pool above 1800 ppm, which exceeds thetechnical specification requirement for boron concentration. With theseprecautions a subcriticality margin greater than 5 percent would bemaintained.Degradation of Boraflex has been previously addressed by NRC in InformationNotice 87-43, "Gaps in Neutron-Absorbing Material in High-Density Spent FuelStorage Racks," September 8, 1987. The Electric Power Research Institute,which has been studying this phenomenon for several years, has recentlypublished an interim report, "Boraflex Test Results and Evaluation,"TR-101986, February 1993.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Original signed UyMaian K. Grime$Brian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Regulatory RegulationTechnical contacts: Kombiz Salehi, RIII(708) 790-5782K. I Parczewski, NRR(301) 504-2705Larry Kopp, NRR(301) 504-2879Vern Hodge, NRR(301) 504-1861Attachments:1. Figure 1, Palisades Boraflex Coupon Types2. List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFFICE OGCB:DORS:NRR DRS:RIII DD:DRS:RIII SRXB:DSSA:NRR C:SRXB:DSSA:NRRNAME *CVHodge *KSalehi *WLForney *LIKopp *RCJonesDATE 09/02/93 09/02/93 09/02/93 09/03/93 09/03/93Tech Ed D:DSSA EMCB:DE:NRR EMCB:DE:NRR C:EMCB:DE:NRR C:OEAB:DORS*DGable *ACThadani *JStrosnider *KlParczewski *RAHermann *AEChaffee09/01/93 09/04/93 01J0 M22 09/03/93 09/03/93 09/03/9311 _ _ _ _ ,_C:OGCB:DORS:NRR*GHMarcus j I09/03/93 09/7 /93DOCUMENI NAME: 93-/U.IN

K>IN 93-xx ISeptember xx, 993This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate Office of !Nuclear Reactor Regulation (NRR) project manager. IBrian K. Grimes, DirectorDivision of Operating Reactor SupiOffice of Nuclear Regulatory Regul0ortat on

Technical Contact:

Kombiz Salehi,(708) 790-5782RIIIK. I Parczewski, NRR(301) 504-2705Larry Kopp, NRR(301) 504-2879Vern Hodge, NRR(301) 504-1861Attachments:1. Figure 1, Palisades Boraflex Coupon Types2. List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCE... ..... -..' at .-law. 1OFFICEOGCB:DORS:NRRDRS: RI I¢ .RPDD DR4:RIIIrSRXB:DSSA:NRR: L/C:SRXB:DSSA:NRRLNAME CVHodge KSalehi WLForney LIKop RC ones,DATE O /l2/93 CO/72/93 £ /O2I93 7/3 /93 /3 /93*Tech Ed D:DSS r EMCB:DE:NRR _MCB:DE:NRS C: 7 U D NRR IOEAB:DORSACThada i Strosnider XParczewski RAHermann j 0aef ffee/9 / /9 /3 /93 '1 /,3/93 § /3 /93 ___________.. _.93C:OGCB:DORS:NR4D:DORS:NRRGHMarcus OI M BKGrimesq/13 /93 / /93DOCUMENT NAME: PALN0902.CVH4Adr of ads? >.4 A 42XsK 4-ct-M etO 4 vJIN 93-xxSeptember xx, 993The licensee took several compensatory measures, including (1) making theoperating staff aware to not dilute the spent fuel pool, (2) increasing thespent fuel pool chemistry sampling frequency to daily, and (3) keeping theboron concentration in the spent fuel pool above 1800 ppm, which exceeds thetechnical specification requirement for boron concentration.Degradation of Boraflex has been previously addressed by NRC in InformationNotice 87-43, "Gaps in Neutron-Absorbing Material in High-Density Spent FuelStorage Racks," September 8, 1987. The Electric Power Research Institute, whohas been studying this phenomenon for several years, has recently published aninterim report, "Boraflex Test Results and Evaluation," TR-101986, February1993.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactthe technical contact listed below or the appropriate Office of NuclearReactor Regulation (NRR) project manager.Brian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Regulatory Regulation

Technical Contact:

Kombiz Salehi, RIII(708)790-5782K. I Parczewski, NRR Larry Kopp, NRR Vern Hodge, NRR(301) 504-2705 (301) 504-2879 (301) 504-1861Attachments:1. Figure 1, Palisades Boraflex Coupon Types2. List of Recently Issued NRC Information NoticesrnmriIDDrrr*CFF DDVITNIC.3c LL. VUL J UVIRUURAJWOFFICE lOGCB:DORS:NRR DRS:RIII D:DRS:RIII SRXB:DSSA:NRR C:SRXB:DSSA:NRRNAME CVHodge Ug KSalehi TOMartin LIKopp RCJonesDATE Oq/ol0/93 / /93 / /93 /93 /93Tech Ed D:DSSA EMCB:DE:NRR EMCB:DE:ND C:EMCB:DE:NRR C:OEAB:DORSq j ACTHADANI JStrosnider KIParczews'ki RAHermann AEChaffee____ /93 /_/93 /_/93 9 /l/93 /L/93 / /93C:OGCB:DORS:NRRD:DORS:NRRGHMarcus [BKGrimes/ /93 J / /93DOCUMENT NAME: PALNOFIG.CVH

K-IAttachment 1IN 93-70September 10, 1993 Figure 1_Palisades Boraflex aCoupon TypesaBodfes mate wboned bloom twoI3Shoet M Paf kn*QIi..I I3i i3_..I:I --I39r Iale i ! 2III4 i..4I.IIE Li

Axtachment 2IN 93-70September 10, 1993Page 1 of ILIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to93-6993-6892-16,Supp. 293-6793-6693-6593-6493-63Radiography Events atOperating Power ReactorsFailure of Pump ShaftCoupling Caused byTemper Embrittlementduring ManufactureLoss of Flow from theResidual Heat RemovalPump during RefuelingCavity DraindownBursting of HighPressure CoolantInjection Steam LineRupture Discs InjuresPlant PersonnelSwitchover to Hot-LegInjection FollowingA Loss-of-CoolantAccident in Pres-surized Water ReactorsReactor Trips Causedby Breaker Testingwith Fault ProtectionBypassedPeriodic Testing andPreventive Maintenanceof Molded Case CircuitBreakersImproper Use of SolubleWeld Purge Dam Material09/02/9309/01/9308/23/9308/16/9308/16/9308/13/93All holders of OLs or CPsfor nuclear power reactorsand all radiographylicensees.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor pressurized waterreactors.Al 1forholders of OLs or CPsnuclear power reactors.08/12/9308/11/93All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.* OL = Operating LicenseCP = Construction Permit