ML061280517

NRC Generic Letter 2006-XX: Post-fire Safe-shutdown Circuit Analysis Spurious Actuations

ML061280517
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Issue date:	05/10/2006
From:	Office of Nuclear Reactor Regulation
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Wolfgang R, NRR/DRA, 415-1624
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ML061280515	List: ML061280517
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OMB-3150-0011
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ML061280517 ENCLOSURE 1 OMB Contro l No.: 3150

-0011 UNITED STATES NUCLE AR RE GULATOR Y COM MISS ION OFFICE OF NUC LEAR REAC TOR REGU LATION WASHINGTON, DC 20555 NRC GE NERIC LETTER 2006-XX: POST-FIR E SAF E-SHU TDOWN CIRCUIT ANALY SIS SPURIOUS ACTUATIONS ADDRESSEES All holders of oper ating lic enses f or nuclea r power rea ctors , except t hose who have permanently ceased operati ons and hav e certified that fuel has been p ermanently re moved from the react or vessel.

PURPOSE The U.S. Nucle ar Regulatory Commission (N RC) is iss uing this generi c letter (GL) to:

(1)Reques t addre ssees to rev iew their fire pr otecti on pro gram to c onfirm c ompli ance w ith applicabl e regulatory re quirements regarding thei r interpretation of multiple sp urious actuations caused by hot shorts, in light of the information provided in this GL and, if approp riate, take ad ditio nal a ction s to re turn to compl iance. Spec ifical ly, a lthou gh some licensees have performed the ir post-fire safe-shutdo wn circui t analyse s based on a n assumption of onl y a single spurious ac tuation per fire event or tha t spurious ac tuations will occur with sufficient time betw een them for operators to take correctiv e actions, (commonly referr ed to by the NRC and industry as "one-at-a-time")

recent industry cable fire tes t resul ts demo nstrate d that these assump tions are no t val id. (2)Require addressees to subm it a written response to the NRC in accordance with NRC regulations i n Title 10 of the Code of Fede ral Regula tions (10 CF R), Se ction 50.54 (f). The reason for this request is to reaffirm the N RC positio n that multipl e spurious a ctuations caused by hot shorts must be considered and eval uated per 10 CFR 50.48 a nd 10 CFR Part 50, Appendi x A, General Design Crite rion (GDC) 3.

This positio n was con firmed by th e resu lts of th e Ele ctric P ower Resea rch Ins titute (EPRI)/Nucl ear En ergy In stitut e (NEI)cable fire tests, which sh owed a re lativel y high proba bility of multiple spu rious actuati ons occurring simultaneous ly, or in rapid succession, during or afte r a fire (see EPRI Report No. 100 6961, "Spurio us Actuation of Electrical Circuits Du e to Cable Fires: Resu lts of an Expert E licitation

," dated Ma y 2002 an d NUREG/CR-67 76, "Cable In sulation R esistance Measurem ents Made Du ring Cab le Fire Te sts," dated Jun e 2002). Some licens ees have GL 2006-XX Page 2 of 12 assumed a single spurious actuation per fire event, and others have assumed that multiple spuri ous ac tuatio ns can only occur with sufficien t time betwe en actuations to allow for mitigat ion. The EPR I/NEI t est da ta cle arly show that th e assu mption that th ere is suffici ent ti me between a ctuations to a llow for mi tigation betw een multipl e spurious a ctuations is not appropriate. If l icensees ha ve not con sidered multi ple spuriou s actuations occurring simu ltan eous ly or in rapid succ essi on dur ing o r af ter a fir e in th eir po st-fir e saf e-sh utdo wn circuit anal ysis, they may not be in complia nce with 10 CFR 50.4 8 and 10 CF R Part 50, Appen dix A, GDC 3, w hich require that s tructur es, sy stems, a nd comp onents impor tant to safety shall be designed and located to minimiz e, consistent w ith other safety requirements, the probabili ty and effect of fires and explosi ons. Licens ees who conclude tha t they are n o longer in complia nce with 10 CFR 50.4 8 and 10 CF R Part 50, Ap pendix A , GDC 3, based on the in form ati on pro vi ded in thi s GL , sh oul d i mpl eme nt c omp ens ato ry mea sur es a nd in form the sta ff of their planne d corrective actions to re turn to compli ance wi th 10 CFR 5 0.48 and 10 CFR Part 50, Appendi x A, GDC 3

.BACKGROUND The regulatory re quirements for post-fire safe shu tdown are given in 10 CFR 50.4 8 and 10 CFR Part 5 0, App endix A, GDC 3. Ad ditio nall y, al l nuc lear p ower plan ts (NP Ps) li censed to operate before Janua ry 1, 1979, are required to comply with 10 CFR Part 50, Appendix R, Section III.G, "Fire Protection o f Safe Shutdown Capabili ty." All NPPs lic ensed to opera te after January 1, 1 979, were evaluated against Secti on 9.5.1 of NURE G-0800, the Stand ard Revie w Plan. The fir e prote ction plan (FPP) and th e asso ciate d safety eval uatio n repo rt (SER) are specifically incorporated into those plants' licensing bases. All NPP licensees are responsible for meeting fire protection and lice nse conditi on commitments made during the establ ishment of their fire pro tectio n progra m.The objective of the fire protection requirements and guidance is to ensure that o ne train of systems necess ary to achi eve and mai ntain safe shutdo wn remains free of fire damage. To do so, license es must protect ci rcuits who se fire-induced failure could prevent the operation, or cause malope ration , of equi pment n ecessa ry to achie ve an d main tain p ost-fire safe sh utdow n. As part of its fire p rotection program, eac h licensee performs a circuit analysi s to identify these circuits and to provid e adequate protecti on against fire-in duced failures.

Beginning in 1997, the NRC staff noticed that a s eries of lice nsee even t reports (LERs) identified pl ant-specific prob lems related to potential fire-induced el ectrical ci rcuit failures th at could prev ent operation, or cause malop eration, of equipment necessary to achieve and maintain safe sh utdown. The staff documented these pro blems in Informatio n Notice (IN) 99-17, "Probl ems Associated With Post-Fire Safe-Shutdow n Circuit A nalyses."

Based on the nu mbe r of si mil ar L ERs , th e N RC tre ate d th e i ssu e ge ner ica ll y. In 19 98, the NR C s taff started to intera ct with i nterested stakehold ers in an a ttempt to understand the problem a nd develop an effective risk-in formed solution to the circuit analysi s issue. NR C also is sued Enforcement Guidance Memorandum 98-002, Rev ision 2 (A gencywid e Documents Ac cess and Management Sy stem (ADAMS) Accession No. ML003 710123), to prov ide a proces s for treating inspe ction findi ngs wh ile t he is sues w ere be ing cl arifie d. Bec ause d ifferent s takehol ders interpreted the regulations di fferently, the NRC decided to te mporarily s uspend the as sociated circuit part o f fire protection in spections. Thi s decision is documented in an NR C memorandum GL 2006-XX Page 3 of 12 from John Hanno n (Chi ef, Pla nt Sy stems B ranch, Office of N uclea r Reac tor Regu latio n (NRR))to Gary Hol ahan (Directo r, Divisi on of Safety Sy stems, NRR) dated November 2 9, 2000 (ADAM S Acce ssion No. M L0037 73142).In 2001, EPR I and NEI performed a series of cabl e functionali ty fire tests to further the nuclear industry's understandin g of fire-induced circ uit failures, p articularly spurious equi pment actuat ions initi ated b y hot shorts. EPR I coord inate d this effort and issue d the fi nal re port (EPRI Report No. 1006961). Additional analysis of the EPRI/

NEI test results can be found in NUREG/CR-6776. Based on the test results, the NRC staff and N EI concluded that the probability of fire-induced circu it failures can be relatively high and that there can be a relatively high probabil ity of multip le spurious actuations o ccurring simultan eously o r in rapid succession.

DISCU SSION Although both th e NRC and the industry have use d the phrase "o ne-at-a-time" in connection with post-fire spurious actua tions caused by hot sh orts, it is no t defined in 1 0 CFR Part 5 0 reg ulat ions or f ire pr otec tion guid ance docu ment s. Th e phr ase h as be en us ed in a t leas t two different senses. Some licensees have use d "one-at-a-time" to mean that only one spuriou s actuat ion n eed be postu lated for any singl e fire e vent. Other l icens ees ha ve us ed the phras e to mean that multip le spurious actuations d o not occur si multaneously and that there is sufficient time betwee n spurious a ctuations for opera tors to take correctiv e actions. N RC has iss ued SERs that ac cepted both i nterpre tation s for spe cific s ituati ons i n spec ific pl ants (e.g., NUREG-0876, S upplement No.

6, "Safety Ev aluation R eport Related to the Operatio n of Byron Sta tio n, U ni ts 1 an d 2 ," A DAM S L ega cy Ac ces sio n N o. 8 411 200 507). H ow ev er, the NR C s taff has interpreted the regulation s to mean that the se interpretati ons are only allow ed with respect to the design of alterna te shutdown capability. The EPRI/NEI cable fire test ing conducted in 2001 demonstrated that neither i nterpretation co nforms with the likely effects of a fire in an area con tai ni ng s afe-sh utd ow n ca bl es. The refo re, the se i nte rpr eta tio ns d o n ot e nsu re s afe shutdo wn. In the S. J. Co llins (NR C) letter to R.

E. Beedle (NEI) dated M arch 11, 1997 (ADAMS Accession No. ML003 716454), the N RC reiterated its positio n that multipl e spurious a ctuations caus ed by hot shorts must be considered and eval uated. Subseque nt to the Col lins letter, the 2001 EPRI/NEI fire testing demonstrated that m ultiple spurious actuations can occur with a relatively high probabil ity and th at they can occur simultan eously o r in rapid succession w ithout sufficient time for mitigat ion b etwe en act uatio ns. One of th e key o bserv ation s of the EPRI t est rep ort (EP RI Rep ort No. 10069 61) w as tha t,"give n that a hot s hort oc curs i n a mul ti-con ductor cabl e, it i s highl y pro bable (ove r 80 pe rcent)that multiple target conductors w ill be a ffected (i.e., multiple simultaneou s dependent h ot shorts)." The testin g covered most o f the types of cabl e insulati on and jacketing materi als and the types of race ways co mmonly used in nuclea r power pl ants. During the testing, numerous variable s were i ntroduced to i nvestigate the impact of vari ous factors on cabl e performance and failure characteri stics.

GL 2006-XX Page 4 of 12 While the staff has maintained th at post-fire multip le spurious actuations s hould be c onsidered, the nu mber of a ctuati ons th at must be con sider ed has not be en defi ned. Since the determi nisti c appr oach t o post-fire sa fe-shutd own analy ses as sumes t hat al l cab les i n a fire area are damaged by the fire except where prot ection described in 10 CFR 50, Appendix R, paragraph III.G.2 is pro vided (se paration of cabl es with a 3-hour fire barri er, physica l separation of cables of redund ant trains by 20 feet, or separati on of cables w ith a 1-hour fire barrier and fire suppression and detectio n), it follow s that all possible s purious actua tions, as w ell as the cumula tive effect of th e actu ation s, shou ld be consi dered. The SERs inc orporated into the licensi ng bases of Byron Station, Uni ts 1 and 2 a nd Braidwoo d Station, Un its 1 and 2 , specificall y allow a design assu mption of a singl e spurious actuat ion p er fire even t in th e post-fire sa fe-shutd own circui t anal ysis. How ever, most pl ants postul ated i n thei r lic ensin g basis that mu ltipl e spur ious actuat ions occur w ith su fficient time betw een sp uriou s actua tions for ope rators to take c orrecti ve ac tions. All li censees should review their circuits analysis to verify that it assumes the possibility of simultaneous m ultiple spurious actua tions during a fire. Dependi ng on the resul ts of this revi ew, lic ensees may conclude tha t they are n o longer in c ompliance w ith the fire prote ction regulati ons. Licens ees who so d etermine shoul d implement co mpensatory measu res and inform the staff of their plan of corrective ac tions to return to compliance with 10 CFR 50.48 and 10 CFR Part 50, Appendix A, GDC 3. One acceptable corrective a ction is to make plant modificati ons to protect agains t possib le multip le spurio us actua tions. Another is to just ify an exemptio n (or licen se amendment, as app licable) as described in the "M ethods of Compli ance" section of this GL.

The NE I lette r of Ma y 30, 1997, prese nts the indu stry's posi tion o n the p hrase "one-a t-a-tim e." The industry' s position is that "possi ble functional failure states from a single hot sh ort in the compon ent's contro l cir cuitry shoul d be a naly zed 'one-at-a-time' (not sequen tiall y nor wit h cumulative consequences) for a fire in a certai n fire area." As one basis for thi s position, the letter referen ces the respo nse to Questi on 5.3.10 in GL 86-1 0, "Impl ementat ion o f Fire Protec tion R equire ments." Altho ugh thi s respo nse sta tes tha t "the s afe shut down capab ilit y should not be adversely affected by any one spurious actuation or sig nal resulting from a fire in any plan t area," per Questi on 5.3.10, the re sponse appl ies only to Appendi x R, Secti on III.L,"Alternativ e and Dedi cated Shutdow n Capabil ity." The NR C emphasiz ed this posi tion in an April 30, 1 982, letter from Denn is M. Cru tchfield (Chie f, Operating Reactors Bra nch #5, Divisi on of Licen sing) to P. B. F iedle r (Vi ce Pr esid ent & Direc tor , Oys ter Cree k) (ADAMS Accessi on No. ML011 150521) by stating that "it is essent ial to rem ember that th ese alter native requirements (i.e., III.G.3 a nd III.L) are not d eemed to be equi valent" to protection require d by 10 CFR Part 5 0, App endix R, par agraph III.G.2. As not ed in the att ach men t to a F ebr uar y 6 , 19 97, mem ora ndu m fro m L. B. Ma rsh (Ch ie f, Plant Systems Branch, NRR) to J. F. Stolz (Director , Project Directorat e I-2) regarding the NRC interpretation of the GL 86-10 guid ance on spuri ous valv e actuation, th e reference to "any one spurious actua tion" in the response to Que stion 5.3.10 i s intended to provide a design basi s for determining the c apacity a nd capabil ity of the al ternative o r dedicated s hutdown trai n (e.g., the size of the p ump and the su pport systems n eeded to main tain reactor co olant inv entory, the scope of onsite electrical power di stribution an d power n eeds, and an operational baseline and set of pl ant co nditi ons to define the sc ope of i nitia l manu al ac tions to res tore sy stems GL 2006-XX Page 5 of 12 necessa ry to acco mplish t he requ ired rea ctor pe rfor mance g oals). Again, t hese alte rnative requirements do no t provide the same lev el of protection as required by 10 CFR Pa rt 50, Appen dix R, para graph II I.G.2. NEI also sta ted in the M ay 30 , 1997 , lette r that "any othe r interpretation leads to co mplex and costly ana lysis w hich is no t justified for the v ery small safety benefit." The N EI letter offered no assess ment of th e safety signi ficance of multi ple s equenti al an d cumul ativ e fail ures. It is import ant to note th at the NEI l etter o f May 30, 19 97, pre ceded the 20 01 EP RI/NEI fire te sting. As noted abo ve, the cabl e functionali ty fire testing de monstrated that multi ple spuriou s actuations can occur and tha t they can occur in rapi d succession without sufficient time for mitigat ion. Therefore , if a l icens ee doe s not a ccount for mult iple spuri ous ac tuatio ns in its circuits ana lysis, the licensee may not be i n compliance with 10 CFR 50.48 and 10 CFR Part 50, Appendi x A, GDC 3 , which require that a l icensee prov ide and mai ntain free of fire da mage one train of sys tems ne cessar y to a chiev e and mainta in sa fe shutd own. A boun ding analys is on t he pot enti al fi re ri sk in term s of core dama ge f req uenc y (ADA MS Accession N

o. ML0608 30212) indi cates that, despi te some likely conservati ve assumptio ns, multiple sp urious actuati ons caused b y hot shorts can be risk si gnificant. METHODS OF COMPLIANCE Based on the information provided in this GL, if a licensee concludes that it is no longer in compli ance w ith th e fire p rotecti on regu latio ns, the re are seve ral ac ceptab le meth ods to rees tabl ish f ull re gula tor y comp lianc e. On e way is t o rep erf orm the po st-fir e saf e-sh utdo wn circui t anal ysis based on gui dance prov ided in thi s GL an d make th e nece ssary modifi catio ns. Anothe r way to add ress th is is sue i s to pe rform eit her a r isk-in formed ev aluat ion th at con sider s defense-in-depth a nd safety margins o r a determinis tic eval uation.If a licensee proposes to use a risk-informed appro ach to justify a n exemption or license amendment in ac cordance w ith 10 CFR 50.12, the l icensee sho uld follow the guidance of Regulatory Guide 1.174, "An Approac h for Using Probabilistic Risk Assess ment in Risk-In formed D ecisi ons on Plan t-Spec ific C hanges to the Licen sing B asis."Licensees w ho have a dopted the stan dard fire protectio n license condition i n GL 86-10 can make changes to the a pproved fire p rotection program w ithout prior staff approval if the changes woul d not adve rsely affect the ab ility to achieve and maintai n safe shutdow n in the event of a fire.

GL 86-10, "Implementa tion of Fire P rotection Requi rements," provid es guidance on performing and do cumenting these ch anges. Plants licensed a fter January 1, 1 979, that use a risk-i nformed a pproac h must s ubmit a lice nse ame ndment in ac cordan ce wi th 10 C FR 50.90. The exceptio n to 10 CFR 50.90, prov ided in th e standard li cense condi tion and i n 10 CFR 5 0.48(f)(3), does not ap ply becau se the risk as sessme nt app roache s used by th ese pl ants deviate from the approved d eterministic a pproaches used in their l icensing basi

s. Furthermore, the li censee s' ri sk asse ssment tools have not be en rev iew ed or i nspect ed agai nst qual ity standards found ac ceptable to th e NRC staff. Conseque ntly, the sta ff believes that the use of risk informe d approaches should receive prior NRC approval.

GL 2006-XX Page 6 of 12 An add ition al meth od to a chiev e compl iance is th e adop tion o f a perfor mance-b ased fi re protection program i n accordance with 10 CFR 50.48(c), "N ational Fi re Protection A ssociation Standa rd NFP A 805." Regul atory Guide 1.205 , "Ris k-Informed , Perform ance-B ased F ire Prot ecti on f or Exis ting Ligh t-W ater Nucle ar Po wer Pla nts," dat ed Sep tem ber 2 004 (ADAMS Accession N

o. ML0427 40308), and N EI 04-02, "Guida nce for Implementing a Risk-Informed, Performance-Based Fi re Protection P rogram Under 10 CF R 50.48(c)," Rev ision 0, d ated March 200 6 (ADAMS Accession No. ML060 600183), prov ide additi onal guidanc e to licen sees who pla n to use this option.APPLICABLE REGULATORY REQUI REMENTS NRC regulatio ns in 10 C FR 50.48 and 10 CFR Pa rt 50, Appendi x A, GDC 3 , require each operat ing NP P (li censed before or after issua nce of GD C 3) to have an FP P prov idin g post-fi re safe-shutdown c apability. That is, a mean s must be prov ided of ensuri ng that one of the redundant trains of saf e-shutdown structures, systems, and components is prote cted so that it remains free of fire damage, allowing saf e shutdown of the plant. The reg ulation in 10 CFR 50.9 0 requires a l icensee w ho desires to amend its l icense, to su bmit an amendment request to the NRC. An NPP licensed to operate before Jan uary 1, 197 9, may submit an exemp tion r equest i n acco rdance wit h 10 C FR 50.12. All NPPs licensed to operate before January 1, 1979 (pre-1979 plants), are require d to comply with 10 CFR Pa rt 50 , App endix R, par agr aph I II.G, "Fire Prot ecti on of Saf e Shut down Capab ilit y." Paragraph III.G states, in part, that "on e train of sys tems necessary to achiev e and maintain hot shutdown c onditions from ei ther the control room or emergency control statio n(s)is free of fire da mage." P aragrap h III.G.2 states , in p art, tha t "wh ere ca bles or equi pment, includin g associated no n-safety circui ts that could prevent ope ration or caus e maloperatio n due to hot shorts, open circui ts, or s horts t o groun d, of red undan t train s of sy stems n ecessa ry to achieve and maintain hot shutdow n condition s are located within the same fire area outside of primary containment, one of the following means of ensuring that one of the redundant t rains is free of fire damage shall be pro vide d." Al l NPP s lic ensed to ope rate afte r Janu ary 1 , 1979 , are required to comply with 10 CFR 50.48(a), which requires that each operating NPP have an FPP that satisfies GDC 3. Th e FPP is in corpor ated i nto the opera ting l icens e for po st-197 9 pla nts as a license condition. This license condition specifically cites the staf f SER in the licensee's FPP to d emo nst rat e th at t he li cen se c ond iti on has be en met (al tho ugh li cen see s ma y m odi fy their FPP as lo ng as th ere is no ad verse effect on safe sh utdow n).Based on the regulations th at state that cabl es or equipment th at could prev ent operation or cause malopera tion of a safe shutd own train of equipment due to hot shorts, ope n circuits, o r shorts to ground mu st be protected, and the new inform ation provided by the EPRI/NEI cable fire tests, appr oved fire protection prog rams that do not include protect ion against possible simul taneou s occu rrence of multi ple s purio us actu ation s (inc ludi ng progra ms for pl ants w ith SERs that sp ecific ally appro ve th e assu mption of a si ngle sp uriou s actua tion p er fire even t)may no t compl y w ith th ese re gulato ry requ iremen ts.

GL 2006-XX Page 7 of 12 APPLICA BLE REGULATORY GUIDA NCE Fire-ind uced hot s hort s tha t cau se sp urio us ac tuat ions can pr event a tra in of saf e shu tdown equipme nt from pe rforming i ts post-fire sa fe-shutd own functio n. NRC regulations do not limit the nu mber of s purio us actu ation s that must be consi dered. In ad ditio n, NRC regulatio ns do not state wh ether multipl e spurious a ctuations shou ld be assumed to occur simul taneously or sequentially. Licensees should ad equately justi fy any li mits or assumptio ns used in performing the post-fire safe-shutdow n circuit an alysis.In or der t o dem onst rat e com plian ce with the r egu lato ry req uire ment that one sa fe-shut down train remain free o f fire damage, licensee s should an alyze the potential for multiple, co ncurrent or in rapid succession spurious actua tions and pro vide ade quate protection w here required.

Fire m odeli ng techn iques a nd ris k analy sis te chniqu es wh ich th e staff ha s found accept able are provi ded i n Sect ion 4.0 of Re gulato ry Gui de 1.2 05, "Ri sk-Informed , Perform ance-B ased F ire Prot ecti on f or Exis ting Ligh t-W ater Nucle ar Po wer Pla nts," dat ed Mar ch 20 06 (A DAMS Accession N

o. ML0606 00183) and may be used i n the eval uations.The det ermini stic me thodol ogy i n NEI 00-01, Rev. 1 (Jan uary 2005), "Guida nce for P ost-Fi re Safe Shutdown Circuit Analysis," Chapter 3 (including the ass ociated appendices), for analysis of post-fire safe-shutdow n circuits, i n conjunction with the guidance prov ided in th is GL, is on e acceptable approach to achieving reg ulatory compliance with post-fire saf e-shutdown circuit protec tion r equire ments for multi ple s purio us actu ation s. Licen sees s hould assume that th e fire may affect all un protected cabl es and equipmen t within the fire area simultaneou sly and address all c able and equ ipment impac ts affecti ng the r equire d safe-s hutdow n path in th e fire area. All potential i mpacts withi n the fire area s hould be a ddressed.The risk significance analysi s methodology provided in Chapter 4 of NEI 00-01 sh ould not be applied a s a basis for regul atory compli ance excep t where a National F ire Protection Association (NFPA) 805 licensing b asis has be en adopted i n accordance with 10 CFR 50.48(c) or it is use d to support ex emption and l icense amendme nt requests for plants that have n ot adopted an N FPA licen sing basis. F urthermore, regardless of the plant li censing basis , the NRC a grees w ith th e NEI 00-01 guidan ce tha t "all failu res de emed to be ri sk signi ficant, whether they are clearl y complia nce issues or not, should be placed in the Corre ctive Acti on Program with a n appropriate priority for ac tion." The remain ing sections o f NEI 00-01 prov ide acceptable c ircuit anal ysis guida nce on both th e deterministi c approach an d the risk-informed, performance-based app roach.REQUESTED ACT IONS All addres sees are requested to take the follow ing actions:

(1)W ithin 90 days of the date of this letter, all addressees are requested to evaluate their lice nsing b asis r egardi ng multi ple s purio us pos t-fire s afe-shut down circu it ana lyse s. Speci ficall y, the y are request ed to c ompare the pl ant li censi ng basi s to th e regul atory requirement for protectin g redundant safe-shutdo wn trains from multiple simu ltaneous spuri ous ac tuatio ns and mainta inin g one tr ain fre e of fire damage.

GL 2006-XX Page 8 of 12 (2)Based on the plant li censing basis and the in formation provid ed in this GL, addressees should reach a conclusion, within 90 days of the date of this GL, on whether the NPP is in complia nce with regulatory require ments.(3)If addre ssees concl ude th at thei r plan ts are not in compl iance wit h regul atory require ments, t hey s hould , in a ccorda nce w ith th eir FP P, imp lement compen satory actions and prepare correcti ve action plans. These addressees sh ould make plan s within 6 months of the date of this letter for pl ant modification s, license amendments, exemption requests, or other means to meet reg ulatory requirements and th e plant's licensing b asis.REQUE STED INFORM AT ION All addres sees are requested to provid e the follow ing information:

(1)W ithin 90 days of the date of this GL subm it a description of their licensing basis regarding multipl e spurious p ost-fire safe-shutdow n circuit an alyses. S pecifically , they shou ld c ompa re th e pl ant l ice nsi ng ba sis to th e reg ula tory requ irem ent fo r pro tect ing redundant safe-shutd own train s from multiple si multaneous spu rious actuati ons and mainta inin g one tr ain fre e of fire damage. (2)Within 90 days of the date of this GL submit a conclusi on based on the plant l icensing basis and th e information prov ided in th is GL as to w hether the NPP is in co mpliance with regula tory requirements.

a.If addre ssees concl ude th eir pl ants a re not in co mplia nce w ith re gulato ry requirements, they should sub mit an assessmen t of the functionali ty of affected structures, systems, and components that addresses th e ability to achiev e and mai nta in saf e sh utd ow n i n l igh t of mul tip le spu rio us h ot s hor ts a s a res ul t of a fire. A n asse ssment consi stent w ith an eval uatio n perfor med for R egulat ory Information Summary (R IS) 2005-20 w ill be a cceptable.

b.Addres sees th at con clude they are no t in c ompli ance w ith re gulato ry requirements shou ld also submit a description of the compen satory measures in place to maintain the safe-sh utdown function of af fected areas of the plant in accord ance w ith th e appr oved fire pr otecti on pro gram.(3)Within 6 months of the date of this GL, submit the p lan to return each of the affected structures, systems, and components to compliance with regul atory requirements

.REQUIRED RESPONSE In accordance w ith 10 CFR 50.54(f), an address ee is required to respond as described b elow so that the NR C can determin e whether a facility license sh ould be modi fied, suspended, or revoked, or w hether other acti on should be taken.

GL 2006-XX Page 9 of 12 W ithin 30 days of the date of this GL, an addr essee is required to submit a written respo nse if the ad dresse e cann ot prov ide th e infor mation or can not mee t the re quested compl etion date. The add ressee must ad dress i n its respon se any alter nativ e cour se of ac tion t hat it propo ses to take, includin g the basis for the acceptabili ty of the propos ed alternativ e course of actio n.The requ ired w ritten respo nses s hould be ad dresse d to th e U.S. Nucl ear Re gulato ry Commission, ATTN:

Document Control Desk, 11555 Ro ckville P ike, Rockvill e, Maryl and 20852, under o ath or affirmation unde r the provi sions of Sectio n 182a of the Ato mic Energy Ac t of 1954, as amende d, and 10 CF R 50.54(f). In addi tion, a copy of the response s hould be submit ted to the ap propri ate regi onal admini strator.REASON FOR INFORMAT ION REQUEST As discussed above, the NRC posi tion has bee n that all multiple sp urious actuati ons caused b y hot shorts hav e to be consi dered in a post-fire safe-shutdow n circuits a nalysis. The EPRI/NEI-performed cab le fire testing i n 2001 demons trated that multip le spurious actuations can occur with relatively high likelihood and that they can occur simultaneously or in rapid succes sion with out su fficient time for mitiga tion b etwe en act uatio ns. M any l icens ees' circui ts analy sis an d/or sa fe-shutd own analy sis di d not c onsid er thi s rela tive ly h igh pro babil ity. The NRC staff will review the responses to this GL and will notify affec ted addressees if concerns are i dentified regardin g compliance w ith NRC regul ations. The staff may also conduct insp ections to de termine addresse es' effectiveness in addressi ng the GL.

RELATED GENERIC COMMUNICATIONS GL 86-10, "Implementa tion of Fire P rotection Requi rements," April 24, 1986.GL 91-18, Rev. 1, "Information to Li censees Regardi ng NRC Inspecti on Manua l Section on Resolution of Degraded and N onconforming Condi tions," October 8, 1997.IN 92-1 8, "Pot entia l for Lo ss of Re mote Sh utdow n Capa bili ty Du ring a Contro l Roo m Fire ,"February 28 , 1992.IN 99-17, "Probl ems Associated With Post-Fire Safe-Shutdow n Circuit A nalyses," J une 3, 1999.

RIS 2004-03, "Risk-I nformed Approac h for Post-Fire Saf e-Shutdown Associated Circuit Inspections

," March 2, 2 004.RIS 2004-03, Rev. 1, "Risk-Inf ormed Approach for Post-Fire Safe Shutdown Circuit Inspec tions ," Dece mber 29 , 2004. RIS 20 05-030 , "Cla rificat ion o f Post-F ire Sa fe-Shutd own Circu it Regu latory Requi rements ,"December 20, 20

05.

GL 2006-XX Page 10 of 12 BA CKFIT DISCU SSION Under the prov isions of Sec tion 182a o f the Atomic Energy Act of 1954, as amended, 10 CFR 50.109(a)(4)(i), and 10 CFR 50.54(f), this GL req uests addressees to evaluate their facilities to confirm complianc e with th e existi ng applicabl e regulatory re quirements as discussed i n this GL. The N RC positio n has been that all mul tiple spuri ous actuation s caused by ho t short s hav e to be consi dered in a p ost-fire safe-sh utdow n circ uits a naly sis. A lso, the 2001 EPRI/NE I fire test program demonstra ted that the prev ious assumpti ons regarding spurious actua tions do not adequately a ddress the pote ntial risk to safe shutdown.

The EPRI/NEI cabl e fire tests clea rly show ed, during and after a fire, a relati vely h igh probabil ity that multiple sp urious actuati ons wil l occur simul taneously or in rapid succession.

Fire-induce d hot shorts that ca use sp uriou s actua tions can p reven t a trai n from pe rforming i ts post-fire safe-shutdown functi on. The regulati ons require that spurious actua tions must be c onsidered.

Although both th e NRC and the industry have use d the phrase "o ne-at-a-time" in connection with post-fire spurious actua tions caused by hot sh orts, it is no t defined in 1 0 CFR Part 5 0 reg ulat ions or f ire pr otec tion guid ance docu ment s. Th e phr ase h as be en us ed in a t leas t two different senses. Some licensees have use d "one-at-a-time" to mean that only one spuriou s actuat ion n eed be postu lated for any singl e fire e vent. Other l icens ees ha ve us ed the phras e to mean that multip le spurious actuations d o not occur si multaneously and that there is sufficient time betwee n spurious a ctuations for opera tors to take correctiv e actions. N RC has iss ued SERs that acc epted both i nterpretations for sp ecific situati ons in spec ific plants (e.g., NUREG-0876, S upplement No.

6, "Safety Ev aluation R eport Related to the Operatio n of Byron Stati on, Units 1 and 2," ADAM S Legacy Ac cession No.

8411200507). How ever, the NRC staff has interpreted the regulations to mean that these interpretations are only allow ed with respect to the d esign of alternate shutdown c apability. The EPRI/NEI cable fire testi ng con duc ted in 20 01 dem ons tra ted tha t ne ith er i nte rpr eta tio n co nfo rms wi th t he li kel y e ffec ts o f a fire in an area containing saf e-shutdown cables. Accordingly, the NRR staf f's positions in this GL with res pect to current fire protection require ments do not con stitute backfitting as d efined in 10 CFR 50.10 9(a)(1). How ev er, for By ron Sta tio n, U ni ts 1 an d 2 an d B rai dw ood Sta tio n, U ni ts 1 an d 2 , th e st aff positions w ith respect to one spurious actuation pe r fire represents a change in staff positi on, and if appli ed to the li censees of these plants, wo uld constitu te backfits under 10 CFR 50.10 9(a)(4)(i). A s disc ussed in thi s GL, th e impo sitio n of the posi tion w ith re spect t o multiple sp urious actuati ons is nece ssary to compl y with the (unchanged) staff interpretation of 10 CFR 50.4 8 and 10 CF R Part 50, Ap pendix A , GDC 3. Staff approv al of the "single spurious actuation per fire event" for By ron Station, U nits 1 and 2 and Braid wood Stati on, Units 1 and 2 constituted staff incon sistencies w ith respect to the necessary prerequisites for d emonstrating compliance w ith 10 CFR 50.48 and 1 0 CFR Part 5 0, Appendix A, GDC 3. If nece ssary, the inconsisten cies wou ld be rectifie d by any backfitting imposed b y the NRC in accordan ce with 10 CFR 50.1 09(a)(4)(i) and 1 0 CFR Part 5 0, Appendix A, GDC 3.

The NRC staff has determi ned, in acco rdance wi th 10 CFR 5 0.54(f), that the informatio n sought in this GL is necessary to verify licensee compliance with existing regulatory requir ements in 10 CFR 50.4 8 and 10 CF R Part 50, Ap pendix A , GDC 3.

GL 2006-XX Page 11 of 12 FEDERAL REGISTER NOTIF ICA TION A notice of opp ortunity for pub lic comment on this GL w as publish ed in the Federal Reg ister (FR) (70 FR 60859) on October 19, 2005.

At the request of the indust ry, a notice that the public comment period for thi s GL was reo pened wa s publishe d in the Federal Reg ister (70 FR 7608 3)on December 22 , 2005.SMALL BUSINESS REGULA TORY ENFORCEMENT FAIRNESS A CT The NR C has determi ned th at thi s acti on is subjec t to the Small Busi ness R egulat ory Enforcement Fairnes s Act of 1996. The Office of Management and Budget (OMB) ha s declared the letter not to be a major rule.

PAPERWORK REDUCTION A CT STA TEMENT This GL contain s information col lections tha t are subject to th e Paperwo rk Reduction Ac t of 1995 (44 U.S.C. 3501 e t seq.). Thes e inf orm atio n coll ecti ons wer e appr oved b y OMB clearance no. 3150-0011, w hich exp ires on Feb ruary 28, 20 07.The b urde n to the p ubl ic fo r the se ma ndat ory info rmati on c oll ecti ons is e stim ated to a ver age 709 ho urs pe r respo nse, i nclud ing the time for revi ewi ng inst ructio ns, sea rchin g exi sting d ata sources, gathering an d maintaini ng the data need ed, and compl eting and rev iewing the information coll ection. This burden does n ot include the hours that w ill be re quired to be expended by lice nsees to return to compliance with the regulations i f they are determi ned to be not in compl iance w ith the regulati ons. Send co mments on any aspect of these i nformation collection s, includi ng suggestions for reduci ng the burden, to the Records an d Freedom of Information Act/Priv acy Serv ices Branch (T5-F52), U.S. Nucl ear Regulatory Commission, Washington, DC 20555-0001, or by Interne t electronic mail to INFOCOL LECTS@NRC.GOV;and to the De sk Officer, Office of Information and Regulatory Affairs, NEOB-10202 (3150-0011), Office of M anageme nt and Budget , Washington, DC 2 0503. Public Pro tection Noti ce The NRC may not conduct no r sponsor, and a person is not required to re spond to, an information coll ection unle ss the requesting do cument displa ys a currentl y vali d OMB con trol number.

GL 2006-XX Page 12 of 12 CONTACT Please di rect any questi ons about thi s matter to the tech nical conta ct or the Lead Project Manager li sted below or to the app ropriate Office of Nucle ar Reactor Regul ation NRR project manager.Christopher I. Gri mes, Director Div isi on o f Pol icy and Rul emaki ng Office of Nuclear Reacto r Regulation Techni cal C ontact: Robert W olfgang, NRR 301-415-1624 E-mail: rjw1@nrc.gov Lead P roject M anager: Quynh Nguyen, NRR 301-415-8123 E-mail: qtn@nrc.gov Note: NRC generic communica tions may b e found on the N RC publi c Web site, http://www.nrc.

gov, under Elec tronic Readi ng Room/Docum ent Co llec tions.