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UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555November 22, 1988

NRC INFORMATION NOTICE NO. 88-92:" POTENTIAL FOR SPENT FUEL POOL DRAINDOWNAddressees:All holders of operating licenses or construction permits for nuclear powerreactors.Purpose:This information notice is eing provided to alert addressees to potentialproblems resulting from the failure of the fuel transfer canal door seal.It Is expected that recipients will review the information for applicabilityto their facilities and consider actions, as appropriate, to avoid similarproblems. However, suggestions contained in his information notice do notconstitute NRC requirements; therefore, no specific action or written responseis equired.Description of Circumstances:On October 2, 1988, with Surry Unit 1 in old shutdown, the licensee was pre-paring to test the fuel transfer system (see attached figure) before fueloff-load. The transfer canal door was in lace and the single door seal wasinflated. The fuel transfer canal was dry. The fuel transfer tube was open,the blind flange was removed on the containment side, and the gate valve wasopen on the spent fuel pool side. The refueling cavity seal was not in lace.An accidental pinhole puncture of the single air supply line to the transfercanal door pneumatic seal was promptly detected and the air leak quicklystopped before it could lead to a loss of seal integrity.Discussion:A review of this event by the licensee showed that, given the configuration ofthe transfer canal, the transfer tube, and the refueling cavity existing at thetime of the event, an inadvertent draindown of the spent fuel pool could occurto a height of only 13" above the top of the fuel assemblies (see attachedfigure). This postulated draindown assumes no operator action and a lossof instrument ai r or pneumatic seal failure. Increased radiation levels inthe spent fuel pool building would have limited stay time in he building andimpeded recovery. The licensee estimated that the dose rate, based on thespent fuel inventory at the time of the event, could have reached 50 R/houron the operating deck. The licensee also calculated that with the refuelingcavity seal assembly in lace, the spent fuel pool could only draindown to14 feet above the top of the fuel assemblies.

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In 88-92November 22, 1988Page 2 of 3If newly discharged fuel ha d been placed in he spent fuel pool, a postulateddraindown of the spent fuel pool could have led to even higher radiation levelsin he spent fuel pool building than the radiation levels postulated by thelicensee. If a seal failed and spent fuel pool water were lost while a fuelassembly was lifted, fuel could be uncovered and fuel cladding could fail.The licensee is considering several actions based on the review of this event.The short-term actions include: (1) revising procedures to require that therefueling cavity seal assembly be installed before opening the transfer tubegate valve for dry testing the fuel transfer system, (2) reviewing and up-grading a procedure for the loss of spent fuel pool inventory, (3) upgradingthe material of the plastic air hose inwhich the pinhole occurrede an d (4)providing an emergency escape system for personnel in the transfer canal. Thelong-term actions include: (1) evaluating the canal door and seal design in-cluding the need for a backup air supply, a low air pressure alarm, an d abackup seal, (2) evaluating other pneumatic seals used at Surry, (3) developinga procedure for installing, inspecting, an d testing the seals in accordancewith the manufacturer's recommendations, (4) revising procedures to ensurethe transfer tube blind flange is nstalled whenever the transfer canal isdrained for maintenance on the transfer tube gate valve, and (5) reviewingfurther the procedures for loss of spent fuel pool and refueling cavity waterlevel, after the short-term modifications to these procedures.In 1981, a related event occurred at Arkansas Nuclear One, Unit 2. At theend of a refueling outage with the transfer canal door closed and the doorseal inflated, the transfer canal was drained in preparation for performingmaintenance on the fuel upender. Concurrent maintenance on the air systemresulted in loss of air pressure to the seal, and water leaked from thespent fuel pool into the fuel upender pit. The transfer gate valve was closedand acted as a barrier to the flow. The leakage stopped when the water levelsequalized. The spent fuel pool level had decreased by 7 feet. If the sealha d leaked while the maintenance on the upender was in progress with the fueltransfer tube gate valve open and the fuel transfer tube blind flange removed,the spent fuel pool could have drained down to a level just above the top ofthe fuel assemblies.Pneumatic seals are also used in the refueling cavity seal assembly. In manycases, the failure modes of the refueling cavity seals (IE Bulletin 84-03,"Refueling Cavity Water Sealu an d Information Notice 84-93, "Potential forLoss of Water From the Refueling Cavity") apply to the spent fuel pool gateseals.These events show that a door equipped. with a single seal and/or a single airsupply is subject to complete loss of function from a single failure. There-fore, the seal must be properly installed, and the seal and air supply systemmust be carefully maintained. The scenarios discussed also point out the needfor carefully coordinating such activities as maintenance an d testing to avoidundesirable interactions between systems which could result in fuel uncovery,personnel injury, and personnel contamination.

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IN 88-92November 22, 1988Page 3 of 3

No specific action or written response is equired by this information notice.If you have any questions about this matter, please contact the technicalcontact listed below or the Regional Administrator of the appropriate regionaloffice.

4harlesE. oAii Dif/~tDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contact: Daniele Oudinot, NRR(301) 492-1174Attachments:1. Figure of Fuel Transfer System2. List of Recently Issued NRC Information Notices

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UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555November 29, 1991

NRC INFORMATION NOTICE 88-92, SUPPLEMENT I: POTENTIAL FOR SPENT FUEL POOLDRAINDOWN

AddresseesAll holders of operating licenses or construction permits for nuclear powerreactors.PurposeThe U.S. Nuclear Regulatory Commission (NRC) is issuing this supplement toInformation Notice (IN) 88-92 to inform addressees of additional informationregarding the potential for spent fuel pool draindown. 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 supplement are not NRCrequirements; therefore, no specific action or written response is required.BackgroundThe NRC issued IN 88-92 to alert addressees to problems that could result fromthe failure of pneumatic-type boot seals used to separate the spent fuel poo!(SFP) from other cavities such as the fuel transfer canal and the refuelingcavity. IN 88-92 described events involving the loss or potential loss of thistypt of seal that occurred at Surry Power Station, Unit 1, and Arkansas NuclearOne (ANO), Unit 2. A description of a recent event and two potential scenarioswith safety significance follows.Description of CircumstancesOn September 23, 1991, Wolf Creek Generating Station (WCGS) was in cold shut-down in preparation for refueling when it experienced a .SFP draindown. Thegate between the SFP and the fuel transfer canal was in place with the dualboot seals inflated (Figure 1). The fuel transfer canal was partially filled(about half full) with borated water and the fuel transfer tube which connectsto the refueling cavity was closed. The air supply for the SFP gate sealscomes from the nonsafety-related service air system. The event was initiatedby the loss of a nonsafety-related electrical bus which caused the service airto isolate from its source. Th e loss of this bu s also caused a loss of theinstrumentation that provided SFP level indication. The SFP gate seals subse-quently depressurized through leaks in the service air system (Figure 2). Th eleaks occurred at isolation valve packings, check valves, and at "Chicago"quick-connect fittings that were not in accordance with design drawings.

9111250106

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IN 88-92, Supplement 1November 29, 1991Page 3 of 3To mitigate the risk of the second scenario, the licensee committed to eitherhave all three fuel building cavities i.e. the SFP, the cask loading pool, andthe fuel transfer canal, full or to notify management and establish othercompensatory measures when performing fuel inspections or reconstitutions.This information notice supplement requires no specific action or writtenresponse. If you have any questions about the information in this supplement,please contact the technical contact listed below or the appropriate Officeof Nuclear Reactor Regulation (NRR) project manager.

4"harlesE. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contact: Dr. Dale A. Powers, RIV(817) 860-8195Attachments:1. Figure 1. Fuel Transfer System2 Figure 2. Spent Fuel Pool Gate Seal Air Supply Lines3. List of Recently Issued NRC Information Notices

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a

CONVE YO tEL TR9ANSFER TUBETRACKS - .

FUEL TRANSFER SYSTEM

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i" PIPE - CHICPOO FITTINGS NII ..F *,

SERVICE AIR FLEX HOSE

] ri i i iHBOOT SEALS

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SPENT FUEL POOL GATE SEAL AIR SUPPLY LINES

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Attachment 3IN 88-92, Supplement INovember 29, 1991Page I of ILIST OF RECENTLY ISSUEDNRC INFORMATION NOTICES

Information Date ofNotice No. Subject Issuance Issued to

91-78

90-57,Supp. I

91-77

91-76

91-75

Status Indication ofControl Power forCircuit Breakers Usedin Safety-Related Appli-cationsSubstandard, Refur-bished Potter & Brum-field Relays Repre-sented as NewShift Staffing atNuclear Power Plants10 CFR Parts 21 and50.55(e) Final Rules

Static Head CorrectionsMistakenly not Includedin Pressure TransmitterCalibration ProceduresChanges in PressurizerSafety Valve SetpointsBefore InstallationLoss of Shutdown CoolingDuring Disassenmly of HighPressure Safety InjectionSystem Check ValveIssuance of a Revision tothe EPA Manual of Protec-tive Action Guides andProtective Actions forNuclear IncidentsTraining and Supervisionof Individuals Supervisedby an Authorized User

11/28/91 All holders of OLs or CP sfor nuclear power reactors.

11/27/91 All holders of OLs or CPsfor nuclear power reactors.

11/26/91 All holders of OLs or CPsfor nuclear power reactors.

11/26/91 All holders of OLs or CPsand vendors for nuclearpower reactors.

11/25/91 All holders of OLs or CPsfor nuclear power reactors.

11/25/91 All holders of OLs or CPsfor nuclear power reactors.

11/21/91 All holders of OLs or CPsfor nuclear power reactors.

11/19/91 All holders of OLs or CPsfor nuclear power reactors.

11/12/91 All NRC medical licensees.

91-74

91-73

91-72

91-71

OL =Operating LicenseCP =Construction Permit

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UNITED STATESNUCLEAR RIGULATORY COMMISSIONWASHINGTON. D.C. 205M5AOUIqcALPUSE.1SSPEM4LTV FOR PRIVATE USE, $30D

POSIAGI 6 PlS asIDIUsta'

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IN 88-92, Supplement INovember 29, 1991Page 2 of 3

The SFP level decreased as water passed through the seals and into the fueltransfer canal. Finally, cooling to the SFP was lost when the SFP circulatingpump tripped on low level. The operators were not alerted to the loss of SFPwater in the early part of the event, because the SFP low-level alarm hadpreviously annunciated three days earlier indicating that the SFP level waslower than normal. however. it was still above technical specification (TS)requirements. At that time, the operators did not refill the SFP because ofthe need for adding makeup water to the reactor coolant system as cooldownprogressed. By tho time the operators recognized that the SFP-gate seals hadfailed and they rai completed actions to repressurize the seals, the SFP levelhad dropped about 44 inches. This was about 16 inches below the TS requiredlevel of 23 feet above the top of the spent fuel. An NRC Augmented InspectionTeam (AIT) was dispatched to WCGS to evaluate the event. The results of theinspection and further details of the event may be found in AIT InspectionReport 50-482/91-28.DiscussionDuring the AIT site visit, the NRC identified two additional scenarios ofsafety significance that applied to WCGS.The first scenario involved possible failure of the SFP gate seals whileperforming preventive maintenance on the fuel transfer system with the fueltransfer tube open. The licensee did not have established administrativecontrols over the refueling cavity drains or over the reactor vessel-to-cavityseal for this activity. Under the above conditions, the licensee estimatedthat, without oper~tor intervention, the failure of the SFP gate seals couldhave allowed the level in the SFP to drop to about I foot above the top of thespent fuel assemblies. The level in the SFP would have dropped to about 9 feetabove the spent fuel assemblies with the reactor vessel-to-cavity seal installedand the refueling cavity drains closed.The second scenario involved possible failure of the SFP gate seals during theperiodic inspection or reconstitution of fuel assemblies performed in the SFPor the cask loading pool with the fuel transfer canal drained. At WCGS, theSF F is connected to both the fuel transfer canal and the cask loading poolthrough removable gates with pneumatic-type seals. The licensee indicated tothe AIT that the gate between the SFP pool and the cask loading pool was seldomused. The licensee estimated that without operator intervention, the failureof the SFP gate seals could have allowed the level in the SFP and the caskloading pool to drop enough to uncover a fuel assembly held by the fuel hand-ling bridge crane or in the fuO! inspection stand.To mitigate the ri5k of the first scenario, the licensee committed to performthe followirng whos!ever *,e fuel transfer tube is open and the refueling cavityand the fuel trt fer (.aI are drained: fI) hdve a backup gas supply in placeto repressurize t-' omt, seakb if service air is lost, (2) have a dedicatedooerator in place to install the backup gas supply and close the fuel transfertube gate valve, and !3' have the reactor vessel-to-cavity seal in place andthe refueing cavity drains hlanked or sealed.

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