View source for Information Notice 1990-78, Previously Unidentified Release Path From Boiling Water Reactor Control Rod Hydraulic Units

{{Adams
| number = ML031130145
| issue date = 12/18/1990
| title = Previously Unidentified Release Path From Boiling Water Reactor Control Rod Hydraulic Units
| author name = Rossi C E
| author affiliation = NRC/NRR
| addressee name = 
| addressee affiliation = 
| docket = 05000003, 05000010, 05000029, 05000133, 05000155, 05000171, 05000206, 05000213, 05000219, 05000220, 05000237, 05000244, 05000245, 05000247, 05000249, 05000250, 05000251, 05000254, 05000255, 05000259, 05000260, 05000261, 05000263, 05000265, 05000266, 05000267, 05000269, 05000270, 05000271, 05000272, 05000275, 05000277, 05000278, 05000280, 05000281, 05000282, 05000285, 05000286, 05000287, 05000289, 05000293, 05000295, 05000296, 05000298, 05000301, 05000302, 05000304, 05000305, 05000306, 05000309, 05000311, 05000312, 05000313, 05000315, 05000316, 05000317, 05000318, 05000320, 05000321, 05000322, 05000323, 05000324, 05000325, 05000327, 05000328, 05000329, 05000330, 05000331, 05000333, 05000334, 05000335, 05000336, 05000338, 05000339, 05000341, 05000344, 05000346, 05000348, 05000352, 05000353, 05000354, 05000361, 05000362, 05000364, 05000366, 05000368, 05000369, 05000370, 05000373, 05000374, 05000382, 05000387, 05000388, 05000389, 05000390, 05000391, 05000395, 05000397, 05000400, 05000409, 05000410, 05000412, 05000413, 05000414, 05000416, 05000417, 05000423, 05000424, 05000425, 05000437, 05000438, 05000439, 05000440, 05000441, 05000443, 05000444, 05000445, 05000446, 05000454, 05000455, 05000456, 05000457, 05000458, 05000461, 05000482, 05000483, 05000498, 05000499, 05000508, 05000528, 05000529, 05000530
| license number = 
| contact person = 
| document report number = IN-90-078, NUDOCS 9012120148
| document type = NRC Information Notice
| page count = 11
| revision = 0
}}
{{#Wiki_filter:UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555December 18, 1990NRC INFORMATION NOTICE NO. 90-78: PREVIOUSLY UNIDENTIFIED RELEASE PATH FROMBOILING WATER REACTOR CONTROL ROD HYDRAULICUNITS

==Addressees==
:All holders of operating licenses or construction permits for boiling waterreactors (BWRs).

==Purpose==
:This information notice is intended to alert addressees to potential problemspertaining to a previously unidentified release path from the control rod drivehydraulic systems in boiling water reactors that may lead to design basisaccident radiation doses significantly exceeding the values specified in theFinal Safety Analysis Report. It is expected that recipients will review theinformation for applicability to their facilities and consider actions, asappropriate, to avoid similar problems. However, suggestions contained in thisinformation notice do not constitute NRC requirements; therefore, no specificaction or written response is required.

==Description of Circumstances==
:In June 1989, a design review for unmonitored release paths at WashingtonNuclear Power Plant Unit 2 resulted in the discovery of a previously unidenti-fied radiation release path in the control rod drive hydraulic system. Thispath is postulated to result from the following sequence of conditions. Thetwo control rod drive pumps are shut down following a design basis accident.There is a break outside of the reactor building (secondary containment) inthe non-seismically qualified piping or tankage to which the control rodhydraulic system is connected (see Figure 1). Reactor coolant leaks past thedouble seals in any of the 185 control rod drives and the valves in theirassociated hydraulic control units. The leakage flows back through one ormore of the four headers connecting each of the 185 hydraulic control units tothe common control rod drive (CRD) pump header. The leakage then flows throughthe CRD pump header and the control rod drive pumps to the break or the conden-sate storage tank located outside of the reactor building.Much of the pathway to the condensate storage tank lies outside of the reactorbuilding and includes piping that is not seismically qualified. In addition,this piping passes close to the air intakes for the control room ventilationsystem. Consequently, a failure of the supply piping for the drive pumpss3 -1D8W- /'C IN 90-78December 18, 1990 during an accident would not only greatly increase the potential externalrelease, but could increase the radiation dose to the control room operators.General Electric-Nuclear Energy performed calculations for the newly postulatedrelease path for a design basis accident with concurrent failure of thenon-seismically qualified supply piping for the control rod drive system atWashington Nuclear Power Plant Unit 2. The calculations incorporated thesource terms specified in Regulatory Guide 1.3 and assumed that 10% of theiodine would escape as a gas from the liquid release. These calculationsproduced a 30-day thyroid dose for control room operators of 121 rem per gpm ofleakage, a 30-day thyroid dose at the outer boundary of the low-population zoneof 86 rem per gpm of leakage, and a 2-hour thyroid dose at the exclusion zoneboundary of 36 rem per gpm of leakage. A generic communication discussing thisconcern was sent by General Electric-Nuclear Energy to each BWR utility inJuly 1989.Discussion:For the control rod hydraulic systems at General Electric boiling water reac-tors, the inboard isolation for the primary containment is provided by thedouble seals in the control rod drives, and the outboard isolation for theprimary containment is provided by valves within the hydraulic control units.However, past leak tests of the rod drive seals that were performed by GeneralElectric produced a maximum of 5 gpm per drive. Leakage from the hydrauliccontrol units can also be significant.As shown in Figure 1, four paths lead from each of the 185 hydraulic controlunits to the common CRD pump header. Three of these paths, the accumulatorcharging header, the drive header and the cooling header include check valvesto prevent the return of water from the hydraulic units. In addition, waterescaping through the accumulator charging header must leak through the insertside scram valve, and water escaping through the drive header must leak throughone of the directional control valves. However, the check valve in the exhaustheader is oriented so as to permit the flow of water back to the CRD pump header.The exhaust water then flows via the CRD pump header back to the reactor vessel(or, as at Washington Nuclear Power Plant Unit 2, to the reactor water cleanupsystem) along with the excess pump flow. Therefore, only one normally closedvalve prevents water that is leaking out of each of the 185 control rod drivesfrom returning through the associated exhaust header to the CRD pump header.During startup testing at Limerick Unit 1, and at Susquehanna Unit 1, the totalleakage from all of the hydraulic control units combined was measured at 5 gpmand 11 gpm, respectively. Both of these reactors include additional check valvesat the discharge of the control'rod drive pump (area A in Figure 1). A partialaudit by the NRC staff indicates that many of the newer BWR plants have checkvalves installed in the discharge pipe of the control rod drive pumps. However,this audit also showed that other BWR plants, mostly the earlier ones, did nothave such check valves. The control rod drive system for BWR/6 plants is de-signed with a testable check valve and a motor-operated isolation valve. There-fore, this pathway is applicable to pre-BWR/6 plants onl IeIN 90-78December 18, 1990 Combining the General Electric dose calculations for the postulated path withthe leak rates measured from the hydraulic units at either Limerick orSusquehanna produces dose rates significantly in excess of the values in theFinal Safety Analysis Report. Independent calculations by the NRC staff pro-duced offsite dose values that were comparable to the General Electric results.Radiation release by this path is not possible as long as the control rod drivepumps are kept running. However, continued operation of these pumps followingan accident cannot be assured, particularly if the non-seismically qualifiedsuction piping were to fail.This problem was resolved at Washington Nuclear Power Plant Unit 2 by theinstallation of two check valves in series in the common discharge pipe fromthe control rod drive pumps (at area A in Figure 1) to prevent backflow out ofthe reactor building (secondary containment). The Washington Nuclear PowerPlant Unit 2 installation includes provisions for leak testing the valves anda leak rate criterion of 0.01 gpm was established for these valves.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact oneof the technical contacts listed below or the appropriate NRR project manager.Division of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts: Charles R. Nichols, NRR(301) 492-0854Donald C. Kirkpatrick, NRR(301) 492-1849

===Attachments:===
1. Figure 1. BWR Control Rod Drive System2. List of Recently Issued NRC Information Notices Note: At Washington Nuclear PowerPlant, Unit 2, the control rod drivereturn water Is piped to the reactor wwater cleanup systemSvITE..t. .... \SECONDONDARYOAin4Z( EXHAUST CWHIOL VALV(S CONTAINMENT~I ~>*PCV "(ES CUOUTSIDE OF DRVBUILDINGA-HAREAA SCIM VALVIE6TaLQUT1 COTROL4MmuMRGRMOO140MIX RODTo OTHECONTARNEN R-OD I.-AJ___ -. CrIDRIVEPUMPSM ~j0 cFigure 1. BWR CONTROL ROD DRIVE SYSTEM Attachment 2IN 90-78December 18, 1990 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to90-7788-23,Supp. 390-7690-7590-7490-7390-7290-7190-7090-38,Supp. 1Inadvertent Removal of FuelAssemblies from the ReactorCorePotential for Gas Binding ofHigh-Pressure Safety InjectionPumps During A Loss-Of-CoolantAccidentFailure Of Turbine OverspeedTrip Mechanism Because OfInadequate Spring TensionDenial Of Access To CurrentLow-Level Radioactive WasteDisposal FacilitiesInformation on Precursors ToSevere AccidentsCorrosion Of Valve-To-Torque Tube Keys InSpray Pond Cross ConnectValvesTesting of Parallel DiscGate Valves In EuropeEffective Use of Radi-ation Safety Committeesto Exercise Control OverMedical Use ProgramsPump Explosions InvolvingAmmonium NitrateLicense and Fee Require-ments for Processing Fin-ancial Assurance Submittalsfor Decommissioning12/12/9012/10/9012/7/9012/5/9012/4/9011/29/9011/28/9011/6/9011/6/9011/6/90All holders of OLs orCPs for pressurized-water reactors (PWRS).All holders of OLs orCPs for pressurized-water reactors (PWRs).All holders of OLs orCPs for nuclear powerreactors.All Michigan holdersof NRC licenses.All holders of OLs orCPs for nuclear powerreactors.All holders of OLs orCPs for nuclear powerreactors.All holders of OLs orCPs for nuclear powerreactors.All NRC licenseesauthorized to use by-product material formedical purposes.All uranium fuelfabrication andconversion facilities.All fuel facility andmaterials licensees.OL = Operating LicenseCP = Construction Permit IN 90-78December 18, 1990 Combining the General Electric dose calculations for the postulated path withthe leak rates measured from the hydraulic units at either Limerick orSusquehanna produces dose rates significantly in excess of the values in theFinal Safety Analysis Report. Independent calculations by the NRC staff pro-duced offsite dose values that were comparable to the General Electric results.Radiation release by this path is not possible as long as the control rod drivepumps are kept running. However, continued operation of these pumps followingan accident cannot be assured, particularly if the non-seismically qualifiedsuction piping were to fail.This problem was resolved at Washington Nuclear Power Plant Unit 2 by theinstallation of two check valves in series in the common discharge pipe fromthe control rod drive pumps (at area A in Figure 1) to prevent backflow out ofthe reactor building (secondary containment). The Washington Nuclear PowerPlant Unit 2 installation includes provisions for leak testing the valves anda leak rate criterion of 0.01 gpm was established for these valves.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact oneof the technical contacts listed below or the appropriate NRR project manager.Origina Signkd INCharles E RossiCharles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts: Charles R. Nichols, NRR(301) 492-0854Donald C. Kirkpatrick, NRR(301) 492-1849

===Attachments:===
1. Figure 1. BWR Control Rod Drive System2. List of Recently Issued NRC Information Notices*12/11/90NJDi *C/OGCB:DOEA:NRRCHBerlinger12/L~/jW 111/09/90*OGCB:DOEA:NRR *SPLB:DST:NRR *C/SPLB:DST:NRR *D/U ST:NRR *RPB:ADMDCKirkpatrick CRNichols CMcCracken AThadani TechEd08/17/90 08/20/90 09/24/90 10/30/90 08/06/90DOCUMENT NAME: IN 90-78 IN 90-XXAugust xx, 1990 for these and other plants produced offsite dose values that were comparableto the General Electric results and that could also significantly exceed thevalues specified in the Final Safety Analysis Report. Radiation release bythis path is not possible as long as the control rod drive pumps are keptrunning. However, continued operation of these pumps following an accidentcannot be ensured, particularly if the non-seismically qualified suction pipingwere to fall.This problem was resolved at Washington Nuclear Power Plant Unit 2 by theinstallation of two check valves in series in the common discharge pipe fromthe control rod drive pumps to prevent back flow out of the secondary contain-ment. The Washington Nuclear Power Plant Unit 2 installation includes provisionsfor leak testing the valves. Washington Nuclear Power Plant Unit 2 planned toestablish a leak rate criterion for these valves of 0.01 gpm.The control rod drive system for BWR/6 plants is designed with a testablecheck valve and a motor-operated isolation valve, therefore this pathway isapplicable to only pre-BWR/6 plants.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact thetechnical contact listed below or the appropriate NRR project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts: Charles R. Nichols, NRR(301) 492-0856Donald C. Kirkpatrick, NRR(301) 492-1849

===Attachments:===
1. Figure of Control Rod Hydraulic System2. List of Recently Issued NRC Information NoticesDocument Name: UNIDENTIFIED RELEASE PATH IN*SEE PREVIOUS CONCURRENCESD/DOEA:NRR C/OGCB:DOEA:NRRCERossi CHBerlinger10/ /90 10/ /90OGCB:DOEA:NRR SPLB:DST:NRR C/SPLB:DST:NRR D/DST:NRRK4 RPB:ADMDCKirkpatrick* CRNichols* CMcCracken* AThadani TechEd*08/17/90 08/20/90 09/24/90 10M /90 08/06/90 1990Page 3 f 3Combining the General Electric dose calculations for the postulated path withthe leak rates measured from the hydraulic units at either Limerick orSusquehanna produces dose rates significantly in excess of the values specifiedin the Final Safety Analysis Report. Independent calculations by the NRC staffproduced offsite dose values that were comparable to the General Electricresults and that could also significantly exceed the values specified in theFinal Safety Analysis Report. Radiation release by this path is not possibleas long as the control rod drive pumps are kept running. However, continuedoperation of these pumps following an accident cannot be assured, particularlyif the non-seismically qualified suction piping were to fail.This problem was resolved at Washington Nuclear Power Plant Unit 2 by theinstallation of two check valves in series in the common discharge pipe fromthe control rod drive pumps (at area A) to prevent backflow out of the reactorbuilding secondary containment. The Washington Nuclear Power Plant Unit 2installation includes provisions for leak testing the valves and a leak ratecriterion of 0.01 gpm was established for these valves.This information notice requiresyou have any questions about theof the technical contacts listedno specific action or written response. Ifinformation in this notice, please contact onebelow or the appropriate NRR project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:Charles R. Nichols, NRR(301) 492-0854Donald C. Kirkpatrick, NRR(301) 492-1849

===Attachments:===
1. Figure 1. BWR Control Rod Drive System2. List of Recently Issued NRC Information NoticesDocument Name:RELEASE PATH NOTICED/DOEA:NRRCERossi11/ /90*D/DST:NRRAThadani10/30/90ok 1vko .*C/OGCB:DOEA:NRRCHBerlinger11/09/90*RPB:ADMTechEd08/06/90*OGCB:DOEA:NRRDCKirkpatrick08/17/90*SPLB:DST:NRRCRNichols08/20/90*C/SPLB:DST:NRRCMcCracken09/24/90 IN 90-XXAugust xx, 1990 this path is not possible as long as the control rod drive pumps are keptrunning. However, continued operation of these pumps following an accidentcannot be ensured, particularly if the non-seismically qualified suction pipingwere to fail.This problem was resolved at Washington Nuclear Power Plant Unit 2 by theinstallation of two check valves in series in the common discharge pipe fromthe control rod drive pumps to prevent back flow out of the secondary contain-ment. The Washington Nuclear Power Plant Unit 2 installation includes provisionsfor leak testing the valves. Washington Nuclear Power Plant Unit 2 planned toestablish a leak rate criterion for these valves of 0.01 gpm.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact thetechnical contact listed below or the appropriate NRR project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:Charles R. Nichols, NRR(301) 492-0856Donald C. Kirkpatrick, NRR(301) 492-1849

===Attachments:===
1. Figure of Control Rod Hydraulic System2. List of Recently Issued NRC Information NoticesDocument Name:UNIDENTIFIED RELEASE PATH IN*SEE PREVIOUS CONCURRENCESOGCB:W EA:NRRDOrirkpathick08/e 9/90 VC<SPLB:DST:NRRCRNichols08AV2/9M;*^CISPLB:DST:NRRCMcCrackenOF/p/90D/DOEA:NRRCERossi08/ /90D/DST:NRRAThadani408/ /90V1C/OGCB:DOEA:NRRCHBerlinger08/ /90*RPB:ADMTechEd08/06/90 IN 90-XXAugust xx, 1990 The Washington Nuclear power installation includes provisions for leak testingthe valves. Washington Nuclear Power has established a very low leak ratecriterion for these valves (.01 gpm was indicated). A partial check by the NRCstaff indicates that many of the newer BWR plants already have check valvesinstalled in the control rod drive pump discharge pipe. However, this checkalso showed that other BWR plants, mainly the earlier ones, did not have suchcheck valves.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact thetechnical contact listed below or the appropriate NRR project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor Regulation

===Technical Contact:===
Charles R. Nichols, NRR(301) 492-0854

===Attachments:===
1. Figure of Control Rod Hydraulic System2. List of Recently Issued NRC Information NoticesDocument Name:UNIDENTIFIED RELEASE PATH IND/DOEA:NRRCERossi08/ /90D/DST:NRRAThadani08/ /90C/OGCB:DOEA:NRRCHBerlinger08/ /90RPB:ADMTechEd J ai P08/C /90OGCB:DOEA:NRR SPLB:DST:NRRDCKirkpatyi .- CRNichols08/' /9 xF 08/ /goC/SPLB:DST:NRRCMcCracken08/ /90}}

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