Information Notice 1993-39, Radiation Beams From Power Reactor Biological Shields

Radiation Beams From Power Reactor Biological Shields

ML031080043
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, 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:	05/25/1993
Revision:	0
From:	Grimes B K Office of Nuclear Reactor Regulation
To:
References
IN-93-039, NUDOCS 9305200025
Download: ML031080043 (10)

UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555May 25, 1993NRC INFORMATION NOTICE 93-39: RADIATION BEAMS FROM POWER REACTORBIOLOGICAL SHIELDSAddressesAll holders of operating licenses or construction permits for nuclear powerreactors,PAurpo leThis Information notice is to alert addressees to narrow, intense beams ofradiation that can stream Into accessible areas of a drywell throughpenetrations in the biological shield of a boiling-water reactor (BWR),potentially causing personnel exposures above regulatory limits and exposingenvironmentally qualified (EQ) equipment located In a drywell to high levelsof radiation. It is expected that recipients will review the information forapplicability to their facilities and consider actions, as appropriate, toavoid similar problems. However, suggestions contained in this informationnotice are not NRC requirements; therefore, no specific action or writtenresponse is required.eSrDi c dPI ofs CcUms~tamesDuring startup of the Philadelphia Electric Company (the licensee) LimerickGenerating Station, Unit 1, on July 7, 1992, operators could not properlyoperate a main steamline sample-flow isolation valve (HV-041-IF084) from thecontrol room. Members of the licensee Operations Group determined that thevalve was an inboard primary containment Isolation valve and generated anaction request to troubleshoot the valve. The valve is on the 303-footelevation of the drywell (at an azimuth of 280 degrees). The electricaljunction box for the valve is on the 296-foot elevation at about the sameazimuth in the drywell and is directly across from the reactor water-levelInstrument-line penetration in the biological shield.The licensee revised an existing radiation work permit, originally preparedfor the inspection of systems in the Unit I drywell, to include trouble-shooting of the valve. The licensee stated that it routinely performs suchinspections during startup from a refueling outage.From July 7 through 9, 1992, six separate work crews performed troubleshootingand repair work in the drywell with the reactor operating at a maximum ofabout 10 percent of its rated power.During the first and second entries into the drywell on July 7 and 8, 1992,personnel worked only on the 303-foot elevation of the drywell, where9305200025 1 4 a-P t o+;%t)

IN 93-39May 25, 1993 radiation levels were generally low and where there were no biological shieldpenetrations in the immediate work area. However, during the third and fourthentries on July 8 and 9, 1992, personnel went to the 296-foot elevation andeither passed in front of or worked in sight of tRe reactor water-levelinstrument-line penetration (Figures 1, 2, and 3) .Unknown to those workingon this elevation, a narrow, intense, beam of radiation passed from reactorwater-level instrumentation penetration N16-D directly across the drywell,striking the inner drywell wall in the immediate vicinity of the work area.The diameter of the beam ranged from about 0.15 meter [0.5 foot] at thepenetration to 0.3 to 0.6 meter (1 to 2 feet] at the drywell wall. The NRCdetermined that licensee radiological controls personnel did not know that thethird work crew had gone to the 296-foot elevation. Although a radiologicalcontrols technician (RCT) accompanied the fourth work crew, the beam was notdetected during this entry.During the fifth entry, on July 9, 1992, the work crew, accompanied by aradiological controls technician, entered the 296-foot elevation and worked insight of penetration N16-D. While working, one worker's dosimeter alarmed;apparently, the beam struck the dosimeter. The RCT conducted a radiationsurvey, detected the beam, and immediately evacuated the work area.The licensee detailed survey found, at the extremity of the work area,radiation levels of about 30 mSv per hour [3 rem per hour] (gamma); and, atthe point where the beam emerged from the penetration, levels of about150U mSv per hour [150 rem per hour) (gamma) and greater than 50 mSv per hour(5 rem per hour] (neutron). Radiation dose rates in the work area, readilyaccessible to personnel, and attributable to the beam, ranged from about 30 toabout 250 mSv per hour [about 3 to about 25 rem per hour] (gamma) while themaximum general area radiation dose rates were 10 mSv per hour [1 rem perhour] (gamma) and 5 mSv per hour [500 millirem per hour] (neutron). Theselast maximum general area dose rates were used as the basis for radiation workpermit requirements for work in the area. Figures 1, 2, and 3 show thelocation of the penetration, the approximate path of the beam, and the worklocation on the 296-foot elevation of the Unit I drywell. After the licenseedetected the beam and reviewed the situation, a sixth work crew entered the296-foot elevation to restore electrical connections to the isolation valvewhile remaining out of the path of the beam.Specific licensee actions in response to this event are described inAttachment 4.From the Philadelphia Electric Company's presentation to the NRCOctober 14, 1992 IN 93-39May 25, 1993 Upon reviewing this event, the NRC concluded that a significant potentialexisted for personnel to receive exposures i,. excess of regulatory limits onthe 296-foot elevation of the drywell. This conclusion is based on thefollowing: (1) personnel entered an area (the 296-foot elevation where thebeam was later found) without the knowledge of radiological controlspersonnel; (2) the licensee failed to detect the beam using its normalradiation survey p ocedures and techniques; and (3) the licensee did notanticipate such beams. The NRC also found that such beams may exist at otherfacilities, pr.ticularly at BWRs.The Limerick event Indicates that licensees may not be adequately consideringthe effects of radiation beams with respect to environmental qualification ofequipment exposed to such beams. The NRC established environmental designcriteria to ensure that all safety-related equipment is capable of performingits safety function or remaining in a safe mode under all conditionspotulated to occur during its Installed life. these criteria areIncorporated Into requirements such as Section 10 CFR 50.49 of Title 10 of theSQ.LELL~AJeit&R99eU141J~n1 (10 CFR Part 50).Worker entry intn a BWR drywell or pressurized-water reactor containment atpower involves a challenging environment for radiological controls andmonitoring. These include (1) the possibility of high levels of airborneradioactivity, (2) high gamma and neutron radiation dose rates, (3) thepotential for large radiation dose rate gradients, Including relatively small,Intense beams of radiation, which may change location as rod positions change,and (4) the difficulty of detecting and characterizing small beams ofradiation, using routine survey procedures and instruments. If appropriateradiation surveys inside containment at power have not been performed during aprevious reactor startup, the potential exists for significant undetected anduntharacterized radiation dose rates from radiation beams. Each of thesefdctors presents significant personnel exposure control problem IN 93-39May 25, 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.Brian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor RegulationTechnical contacts: R. L. Nimitz, RI(215) 337-5267J. M. Bell, NRR(301) 504-1083William Ruland, RI(215) 337-5227

Attachments:

I. Figure 1, 'Limerick Generating StationUnit I Drywell*2. figure 2, 'Limerick Generating Station,Unit 1, Drywell 296 Elevation Survey Data"3. Figure 3, 'Limerick Generating Station,Unit 1, Section Along Azimuth 2806*4. Licensee Actions5. Ist of Recently Issued Information Notices-

((Figure 1:Source:_ -i_-_Limerick Generating Station Unit I Drywell -Philadelphia Electric Company's Briefing of NRC, 10/14/92

.C3(7=r%e Z'E D r9-'0 iw 00 R/hr Gonrn0 = Renm/hr Neutron180Figure 2: Limerick Generating Station Unit I Drywell296' Elevation Survey DataSource: Philadelphia Electric Company's Briefing of IRC, 10/14/92

-fo IFe esIV Fn"LREL. 2M--9 --lNo OD AL robSCAVE -;I w-Figure 3:Limerick Generating Station Unit I DrywellSection Along Azimuth 280-Source: Philadelphia Electric Company's Briefing of NRC. 10/14/92 Attachment 4IN 93-39May 25, 1993Page I of 2LICENSEE ACTIONSAfter detecting and characterizing the beam, the licensee took the followingcorrective actions:1. Immediately evacuated the area and had radiation protection supervisorsand station managers evaluate the situation.2. Prevented personnel from entering the beam path.3. Sent personnel dosimeters for evaluation and performed dose assessments.4. Studied each individual's activities in the drywell to determineindividual exposures and which individuals may have been exposed to thebeam. The licensee believes that the maximum individual exposure fromthe beam was about 300 inillirem and that no one's radiation exposureexceeded regulatory limits.5. Prepared a radiological occurrence report.6. Had its Independent Safety Engineering Group (ISEG) perform a root-cause and barrier analysis of the event. The Group recommended that thelicensee review EQ concerns. The licensee concluded that reactor powerdid not increase while personnel were in the drywell.7. Had the ISEG evaluate the event during which it found that:* the beam should have been anticipated,* the beam probably resulted from the unique geometric arrangement ofthe low-pressure coolant injection (LPCI) piping, the shieldpenetration, and the core peak axial power location, and that* moving the rods downward to increase reactor power caused thelocation of peak axial power to move downward in the core,increasing the angle of the beam unward and causing the beam to passover the top of a LPCI line, located in front of the penetration,and Into the work area (see Figure 3). (Although operators changedthe reactor power level between entries, power level changes werecontrolled so that no changes occurred while personnel were in thedrywell.)8. Had the ISEG review the potential for beams at other biological shieldpenetrations. The ISEG:* concluded that, owing to the unusual circumstances, the subjectpenetration was the worst case for occupational radiationprotection, and Attachment 4IN 93.39May 25, 1993

• found that the recirculation inlet nozzle penetration had thehighest associated radiation dose rates for EQ considerations. (Thedose rates at this latter penetration were used for bounding EQcalculations).9. Confirmed previous EQ evaluations but found that more detailed reviewswere needed.10. Compared measured dose rates as a function of distance from penetrationN16-!) with dose rates calculated earlier by the architect-engineer,establishing that the measured dose rates associated with thepenetration did not decrease as rapidly as indicated by thecalculations.11. the licensee planned to complete the following long-term correctiveactions:* Prepare a special procedure for drywell entries at power.* Require a higher level of station management approval for work inthe drywell at power.* Prepare special guidance on survey techniques and Instruments forsurveying penetrations in the biological shield.* Emphasize work-area boundaries In preparing radidtion work permits,performing ALARA reviews, and performing pre-Job briefings.* Emphasize the need for the control of reactor power levels duringwork in the drywell.* Increase health physics coverage during at-power entries to thedrywell.* Improve shielding, access control, or both, for high-radiation areasresulting from radiation beams.* Include review of this event in the training of health physics,operations, and radiation worker ; Attachment 5IN 93-39May 25, 1993Page 1 of ILIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformatlonNotice No. Subject Issuance Issued to93- 30Inadeq~ute Testing ofEngineered SafetyFeatures ActuationSystemOS/24/93All holdersfor nuclearof OLs or CPspower reactors.93-3 793 -36Eyebolts with Indeter-minate Properties In-stalled in LimitorqueValve Operator HlousingNotifications, Reports,and Records of Misadmin-istrdtions05/19/9305/07/93All holders of OLs or CPsfor nuclear power reactors.All U.S. Nuclear RegulatoryCommission medicallicensees.93-3593 34,Supp. I93 -3493-33Insights from Common-Cause Failure EventsPotential for Loss ofEmergency CoolingFunction Due to ACombination ofOperational and Post-Loca Debris in Contain-mentPotential for Loss ofEmergency CoolingFunction Due to ACombination ofOperational and Post-Loca Debris in Contain-mentPotential Deficiencyof Certain Class IEInstrumentation andControl Cables05/12/9305/06/9304/26/9304/28/g3All holdersfor nuclear(NPPs).of OLs or CPspower plantsAll 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.Opera n gicse --- --CP -Construction Permit