ML20012E764

LER 90-005-00:on 900223,determined That Spent Fuel Pool Area Charcoal Filtration Unit VA-66 Was Outside Design Basis. Caused by Insufficient Airflow Into Unit.Affected Updated SAR Analysis Will Be updated.W/900326 Ltr

ML20012E764
Person / Time
Site:	Fort Calhoun
Issue date:	03/26/1990
From:	Gates W, Hollingsed M OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-005, LER-90-5, LIC-90-0234, LIC-90-234, NUDOCS 9004060261
Download: ML20012E764 (5)

Text

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Omaha PutWC Power D6 strict 1623 Hamey Omaha, Nt brena 68102 2247 402/536-4000 March 26, 1990 LIC-90-0234 l

U.S.NuclearRegulatorbCommission Attn Document Control sk l Mail Station P1-137  !

Washington, DC 20555 l

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Reference Docket No. 50 285 Gentlemen:

Subject:

Licensee Event Report 90-05 for the fort Calhoun Station Please find attached Licensee Event Report 90 05 dated March 26 Thisreportisbeingsubmittedpursuantto10CFR50.73(a)(2)(il)1990. (B).  !

If you should have any questions, ple6se contact me.

Sincerely, l

+. .a h l l W. G. Gates i

l Division Manager

Nuclear Operations WGEftes l

Attachment i c: R. D. Martin, NRC Regional Administrator ,

NRC Project Manager  :

A. Bournia,ll, P. H. Harre NRC Senior Resident Inspector j INPO Records Center 6 American Nuclear Insurers i

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At 1146 hours0.0133 days <br />0.318 hours <br />0.00189 weeks <br />4.36053e-4 months <br /> on February 23, 1990, plant management of Fort Calhoun Station determined that VA-66, the Spent Fuel Pool (SFP) area charcoal filtration unit, .

was outside its design basis due to insufficient airflow into the unit from the SFP area. For a fuel handling accident in the SFP, the Updated Safety Analysis -

Report (USAR)assumesthatallactivityreleasedfromadamagedfuelassembly will be filtered through VA-66. Recent testing has been unable to confirm that airflow in the SFP area will support this assumption.

At the time of the determination, the plant was in Mode 5, Refueling Shutdown, l for the 1990 Refueling and Maintenance outage.

An evaluation of the current configuration has confirmed that even with total bypass of VA-66 by )ost-accident gaseous releases, the radiological consequences would )e well within the limits of 10 CFR 100. Safety Analysis for Operability 90-02 has been approved to allow fuel handling in the SFP under the existing conditions. The affected USAR analysis will be updated and submitted to the NRC. An evaluation of other corrective actions will be completed.

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l for protection of the sublic in the event of a fuel handling accident (FHA) in  :

theSpentfuelPool(SrP) area,acharcoalfilterintheexhaustventilation l ductwork from the SFP is placed in service whenever irradiated fuel is handled in the SFP. The filter, VA-66, is designed to absorb gaseous iodines released during the FHA. The intake for SFP releases into the VA 66 ductwork is located i on the south wall of the Auxiliary Building, slightly above the level of the  ;

SFP walkway, and approximately 60 feet south of the pool.

The consequences of a FHA have been anal red in Section 14.18 of the Updated  !

! Safety Analysis Report (USAR). The anal sis determined that the outer row of F fuel pins (14 pins) of an assembly will e crushed during a FHA; however, for 1 added conservatism, failure of all pins (176 pins) was assumed in calculating '

the radiological consequences. In the analysis of a FHA in containment, no  !

credit is taken for the containment charcoal filtration unit. In the analysis of a FHA in the SFP, credit is taken for VA-66, and it is also assumed that all  ;

activity released to the airspace above the SFP will pass through VA-66 for filtration; therefore, the primary difference in these two evaluations is the charcoal filtration by YA-66 of gaseous iodines released from the SFP. i Surveillance Test ST-VA 4, Section F.8, was performed at a refueling frequency to verify that VA-66 was capable of passin a flowrate of 9 000 to 12,000 cubic  !

feetperminute,asrequiredbyTechnicalkpecificationTable35, item 10b.  :

Past performances of this test showed that, to achieve the required flowrate, bothAuxiliaryBuildingsupplyfans(VA-35AandVA-358)andall3 Auxiliary F Building exhaust fans (VA-40A B,andC)mustoperate. To ensure compliance withtheTechnicalSpecificat}onrequirements,OperationsMemorandum83-01was written in January, 1983, to require that both supply and all 3 exhaust fans be

placed in operation whenever fuel handling was in progress in the SFP. (In ,

January, 1989 the requirements of Operations Memorandum 83-01 were incorporated i into station procedures and the memorandum was cancelled.)

On December 17, 1988, during refueling operations of the 1988 Refuelin and Maintenance outage, it was discovered that only one supply fan and oni 2 exhaust fans were in service, in violation of Operations Memorandum 83 01.

Station Incident Report number 880521 was written at that time to document the violation, and to initiate an investigation of the potential radiological consequences in the event of a FHA. The investigation of the incident Report ,

concluded that the reduced airflow through VA-66 was a permissible condition and did not significantly reduce public safety. This conclusion was based on  ;

the Office of Nuclear Reactor Regulation's (NRR) safety evaluation of Technical Specification Amendment number 52, which states, *... the potential consequences of the postulated accidents without charcoal filtration of the '

radioactivity released from the spent fuel pool and to the safety injection t pump room are well within the exposure guidelines of 10 CFR Part 100.... <

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A secondary result of the incident Report investigation, however, was the i discovery of in leakage of air to the Auxiliary Building through a roll up l door, which could disrupt airflow patterns and prevent suction of radiological i releases from the SFP into VA-66. At that time administrative rettrictions l wereplacedonthehandlingofirradiatedfuelIntheSFPuntilfurther ,

investigation could determine the operabilit of VA-66. In March, 1989, the ~

OmahaPublicPowerDistrict(OPPD)DesignEnineeringdepartmentwasrequested to evaluate the ability of VA 66 to perform ts design function in light of the i discovery of Auxiliary Building in-leakage. Design t.ngineering responded in May, 1989, with an opinion that a FHA with VA 66 unavailable did not represent i an unanalyzed condition, since the radiological consequences of a FHA in the SFP with no credit for VA-66 would be identical to a FHA in containment, which has already been analyzed in USAR Section 14.18.

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Design Engineering did recommend, howevertheSFPareawithVA-66inserviceandallsu)est ply and exhaust fans in operation. Special Procedure SP-VA-AUX was t1erefore )erformed on January 19,  !

1990 to determine the air flowpath in the SFP area wit 1 the roll-up door sealed, and also with the seal removed. During the test, helium-filled ,

balloons tied to strings were used to detect air movement at the north and  :

south ends of the SFP, while all supply and exhaust fans were in operation.

The test demonstrated that with the roll-up door sealed, there was little, if any, indication of air movement at either end of the pool. With the seal i removed, airflow was in a northerly direction, away from the VA-66 intake for the SFP area.

Design Engineering was notified of these test results on January 22, 1990, and was re uested to evaluate their impact on the FHA anal sis and provide a Safety j Analys s for Operability (SAO) if it was shown that fi tration through VA-66 was not required to meet 10 CFR 100 requirements. On February 6, 1990, Design Engineering responded with a preliminary opinion that a lack of post-accident filtration could potentially place the plant outside one of its design bases, since the assumption of the USAR that all activity will be filtered through VA-66 was not satisfied. Design Engineering developed an SA0, supported b reanalysis of the FHA in the SFP using 14 failed fuel pins instead of 176,yand a assuming no charcoal filtration by VA-66. This reanalysis concluded that the ExclusionAreaBoundary(EAB)thyroiddosevaluewouldbe3.47 Rem,asopposed to the 6.54 Rem postulated in USAR Section 14.18.4.2.

These results and SAO-90-02 were presented to the Plant Review Committee (PRC) on February 23 1990. It was determined at 1146 hours0.0133 days <br />0.318 hours <br />0.00189 weeks <br />4.36053e-4 months <br /> on the same da that the inadequateairflowfromtheSFPtotheVA-66intakewascontrarytoteUSAR Section 14.18 assumption, and represented a condition outside of that design basis. A one-hour report was made to the NRC Operations Center at 1219 hours0.0141 days <br />0.339 hours <br />0.00202 weeks <br />4.638295e-4 months <br /> onthesameday,inaccordancewith10CFR50.72(b)(1)(ii)(B).

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To allow fuel handling operations to commence in the SFP with the existing  !

conditions, SAO 90 02 received final approval on February 27, 1990. The SA0 i was revised to assume failure of 176 pins, as opposed to the 14 originally i assumed by Design Engineering. The SAO recognizes that post-accident charcoal j filtration will likely be less than that assumed in the USAR, and therefore -

conservatively assumes that there will be no charcoal filtration after a FHA in j the SFP. These are the same assumptions made for the analysis of the FHA in t containment; therefore, the radiological consequences of the two' accidents l would be identical, and yield EAB doses of 43.6 Rem to the th roid and 0.751 Rem to the whole body. The10CFR100maximumdosesforthekxclusionAreaare 300 Rem to the thyroid and 25 Rem to the whole body. '

As defined by the NRC throughtheStandardReviewPlan(NUREG0800Section15.7.4),tobe*well ,

within" these limits, the )rojected doses must be less than 75 Rem to the ,

uences thyroid of a FHA and 6 Rem in the SFPtowill thebew1 olewithin well body;the therefore, 10 CFRthe 100radiological limits. The eff consec'ect on Control Room habitability was also evaluated; postulated dose was determined to be within the Standard Review Plan 6.4 limit of 30 Rem to the thyroid following e FHA in the SFP assuming no filtration through VA-66.

Although the SA0 has documented that fuel can be safely handled in the SFP with no flow through VA-66, the filter will continue to be whenever SFP fuel handling operations are in progress,placed as required byinOperati% service Procedure OP-11, Operating Instruction 01-fH-1, and Technical Specificatior.

2.8(8). l Long term corrective actions includes i (1) The FHA analysis in Section 14.18 of the USAR will be revised and submitted to the NRC as part of the annual USAR update in July, 1990.

(2)AnevaluationoffurthercorrectiveactionswillbecompletedbyMay31, i 1990.

Previous difficulties in achieving the required flowrate through VA-66 have l been reported in LER's77-033 and 78-041. Previous discoveries of the plant being outside the design basis have been reported in LER's88-009, 89-012, 89 015,89-016, 89-017, and 89-024.

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