NRC Generic Letter 1984-21

NRC Generic Letter 1984-021: Long Term Low Power Operation in Pressurized Water Reactors

ML031180064
Person / Time
Site:	Beaver Valley, Millstone, Calvert Cliffs, Davis Besse, Salem, Oconee, Mcguire, Palisades, Palo Verde, Indian Point, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Watts Bar, Sequoyah, Byron, Arkansas Nuclear, Three Mile Island, Braidwood, Summer, Prairie Island, Surry, Limerick, North Anna, Turkey Point, Crystal River, Haddam Neck, Ginna, Callaway, Vogtle, Waterford, Farley, Robinson, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, McGuire, 05000000, Washington Public Power Supply System, Trojan, Marble Hill
Issue date:	10/16/1984
From:	Eisenhut D G Office of Nuclear Reactor Regulation
To:
References
GL-84-021, NUDOCS 8410160115
Download: ML031180064 (3)

Ot REO'aUNITED STATESNUCLEAR REGULATORY COMMISSIONWASHINGTON, D. C. 20555October 16, 1984TO ALL PRESSURIZED WATER REACTOR LICENSEES AND APPLICANTS FOR ANOPERATING LICENSEGentlemen:SUBJECT: LONG TERM LOW POWER OPERATION IN PRESSURIZED WATER REACTORS(Generic Letter 84-21)In June 1983, the NRC staff received a Licensee Event Report from a PressurizedWater Reactor (PWR) licensee concerning extended operation at low power followedby a return to full power operation. The licensee had not contemplated thistype of plant operation in performing their safety analysis for the cycle ofoperation in question. Based on the results of a subsequent reanalysis, thelicensee concluded that load follow operations in conjunction with this type ofplant operation and with a return to full power could result in core peakingfactors being greater than those resulting from the original safety analysis.This unanticipated increase in the core peaking factors was caused by a burnupdistribution produced by the extended low power operation which was differentthan the full power burnup distribution. Upon return to full power, this burnupdistribution, now representative of the low power operation and interacting withthe moderator temperature coefficient and the moderator density variation, wouldproduce this unanticipated increase in the core peaking factor. Consequently,this type of plant operation could result in a potential unreviewed safetyquestion and would be reportable under the provisions of 10 CFR Part 50.59.The fuel supplier for this particular licensee has performed an evaluation ofextended, low power operation followed by a return to full power. They haveevaluated first and reload cycle cores as a function of time in cycle. Theyhave also evaluated, parametrically, the effect of reduced power, time at reducedpower, and a control rod bank insertion strategy and worth on the core totalpeaking factor and radial peaking factor. The outcome of this analysis is aset of procedures that the plant, using this fuel supplier's safety analysis,should follow when extended, low power operation occurs.All other PWR fuel suppliers have provided responses to an NRC request forinformation on how extended, low power operation is treated in their safetyanalyses. Each of these fuel suppliers has provided an adequate response interms of either directly including extended, low power operation in theirsafety analysis; using incore measurements; or providing plant operationinstructions for a given fuel cycle.Accordingly, PWR licensees and applicants for an operating license are remindedthat core safety analyses involve a number of assumptions concerning plantoperation throughout a given fuel cycle. If, for any reason, a plant is notoperated as planned (e.g., extended, low power operation as described above),the licensee should review the cycle safety analysis to verify its applicability. (If parts of the safety analysis are not applicable, these should be reanalyzedand the applicability of the Technical Specifications should be confirmed. /841016 011e Ao5009c V

-2 -This letter is provided for information purposes only. Actions based on therecommendations provided herein are voluntary and no response to the NRC orreview by the NRC is required. Therefore, no clearance from the Office ofManagement and Budget is required.Division o icensing01ta, S(CO iv7- Phi The Generic Letter Assigned this Number Was Never Issued / Index I Site MaD I FAl HelD l Glossary l Contact Us Search Advanced SearchU.S. Nuclear Regulatory Commissionl Home ll Who We Are What We Do ll Nuclear Reactors ll Nuclear Materials ll Radioactive Waste ll Public Involvement ElectrnicReadingooHome > Electronic Reading Room > Document Collections > Generic Communications > Generic Letters > 1984 > GL84022GL 84-22THE GENERIC LETTER ASSIGNED THIS NUMBER WAS NEVER ISSUEDENDENDhttp://www.nrc.govlreading-rmldoc-collectionslgen-conmmngen-letters/1984/gl84022.htmI 2122002/12/2003