ML061090627

of Regulatory Guide 1.201, Guidelines for Categorizing Structures, Systems, and Components in Nuclear Power Plants According to Their Safety Significance (for Trial Use)

ML061090627
Person / Time
Issue date:	04/28/2006
From:	Harrison D G NRC/NRR/ADRA/DRA
To:
Harrisson D G
References
DG-1121 RG-1.201, Rev 1
Download: ML061090627 (11)

Text

1 Comm ission paper s cited in t his trial r egulatory guide are availa ble through the NRC's public Web site at http://www.nrc.gov/reading-rm/doc-collections/commission/secy s/, and the re lated Federal Register notices are available through the Federal Register Web site sponsored by the Governm ent Printing Office (GPO) at http://www.gpoa ccess.gov/fr/ind ex.ht ml.Th e U.S. N ucle ar R egu latory C om m ission (NR C) iss ues regu latory gu ides to descr ibe and make avail able t o the p ubli c methods t hat t he NRC staff consi ders ac ceptabl e for use in i mplementing s pecif ic par ts of the ag ency's regul ati ons, t echniq ues that the staf f uses i n evaluati ng specifi c problems or postul ated accident s, and dat a that the s taf f need in reviewi ng applicat ions for permits and l icenses.

Regulatory guides are not substit utes for regulat ions, and compli ance wit h them is not r equir ed. Met hods and sol uti ons that dif fer fr om those set for th i n regul ator y gui des wil l be deemed acceptab le i f t hey pr ovide a basis f or the f indings r equired f or the i ssuance or conti nuance of a permit or li cense by t he Comm issi on.Th is guide was issue d after c ons idera tion of c om m ents rece ived from the pu blic. The NR C st aff enc oura ges and welc om es c om m ents and sug ges tions in con nec tion w ith im prov em ents to publi shed regulat ory gui des, as well as it ems for incl usion in regulat ory gui des that ar e current ly being developed.

The NR C staff will revise ex isti ng guides, as appropr iat e, t o accommodate comm ents a nd to r efl ect ne w inf ormati on or ex peri ence. W ri tt en comments may be submit ted to t he Rules an d Dire cti ves Branch, Offi ce of Administ rat ion, U.S. Nucl ear Regul ator y Commission, W ashing ton, DC 20555-0001.

Re gula tory guides are i ssued in 10 broad di visi ons: 1, Power Reactors; 2, Research and Test Reactors; 3, Fuels and Mat erial s Facili ties; 4, E nv iron m en tal an d S iting; 5, M ate rials an d P lan t Pro tec tion; 6, P rod uc ts; 7, T ran sp orta tion; 8, O ccu pa tion al H ea lth; 9, An titrus t and Fina nc ial R ev iew; and 10, G en era l.Re que sts for si ngle copies of draft or acti ve regul ator y gui des (whi ch may be r eproduce d) shou ld be made to th e U.S. Nucl ear Regul ator y Commission, W ashing ton, DC 20555, Atten ti on: Reproduct ion an d Dist ri buti on Servi ces Secti on, or by f ax t o (301) 415-228 9; or by email to Distr ibut ion@nrc.gov. Ele ctro nic c op ies o f this g uid e an d oth er re ce ntly issue d guid es are ava il able thr ough th e NRC's publi c W eb sit e under the Regul ator y Gui des document co ll ecti on of t he NRC's Elect roni c Reading Room at http://www.nr c.gov/r eading-r m/doc-co ll ections/ and th rough t he NRC's Agencywi de Documents Access and Manag ement Sys te m (ADAMS)at http://ww w.nrc.gov/read ing-rm/ada m s.htm l , under Accessio n No. ML06109062 7.U.S. NUCLEA R REGULA TORY COMMISSION May 2006 Revi si on 1 REGULATO RY GUIDE OFFICE OF NUCLEAR REGULA TORY RESEARCH REGU LATORY GUIDE 1.201 (For Trial Use)(Previ ously i ssued for tr ial use, Janua ry 2006)GUI DELI NES FOR C A TEGORI ZI NG STRUC TURES, SYS TEMS, AND COM PONE NTS IN NUCLEAR POW ER PLANTS A CCORDI NG TO T HEI R SA FETY SI GNI FI CA NCE A. INTRODUC TION The U.S. Nuclear R egulatory Co mmission (NRC) has prom ulgated regulation s to permit pow er reactor licensees and license applica nts to implement an alter native regula tory frame work with respect to "special treatment,"

where special treatme nt refers to those requirem ents that provide incre ased assurance beyo nd normal indus trial practices that structures, systems, and comp onents (SSCs) perform their design-bas is functions.

Under this framewo rk, licen sees us ing a ris k-informed proces s for ca tegori zing SSCs a ccord ing to th eir sa fety si gnific ance ca n remove SSCs of low safety significance from the scope of certain iden tified special treatment req uirements.

The genes is of this frame work ste ms from Option 2 of SECY-98-300, "Options for Risk-I nformed Revisions to 10 CFR Part 5 0, 'Domestic L icensing of Productio n and Utilization F acilities'," dated Decem ber 23, 1998.

1 In that Com mission paper, th e NRC staff recom mended dev eloping risk-informed approache s to the application of special treatment requirem ents to reduce unneces sary regula tory burden related to SSCs of low safety significance by removing such SSCs from the scope of special treatment requirements.

The Commis sion subsequ ently approved the NRC staff's rulemaking plan and issuance of an Advanced Notice of Proposed Rulemaking (ANPR) as outlined in SECY-99-256, "Rulemakin g Plan for Risk-I nforming Special Treatment Requirements,"

dated October 29, 1999.

2 NEI 00-04, "10 C FR 50.69 SSC Cat egoriza tion Guideli ne," is a vailable through the N RC's Ag encyw ide Docum ents Acces s and Manag ement S ystem (ADA MS), http://www.nrc.gov/r eadin g-rm/ad ams/web-base d.h tml , under Acces sion #ML052910035.

RG 1.201, Re

v. 1, Pag e 2 The Comm ission published the AN PR in the Federal Register (65 FR 11488) o n March 3, 2000, and subsequently published a proposed ru le for public com ment (68 FR 26511) on May 1 6, 2003. Then, on Nove mber 22, 20 04, the Com missi on adop ted a ne w sectio n, refe rred to as §50.69, wi thin Title 10, Part 50, of the Code of Federal Re gulations , on risk-informed categ orization and treatm ent of SSC s for nu clear po wer pla nts (69 FR 680 08).This trial regulatory g uide describes a m ethod that the NRC staff considers acceptable for u se in complying with the Commission's requi rements in §50.69 with re spect to the cate gorization of SSCs that are considered in risk-informin g special treatm ent requirements.

This categorization m ethod uses the process that the Nuc lear Energy I nstitute (NEI) d escribed in Revision 0 of its guidance document NEI 00-04, "10 CFR 5 0.69 SSC Categ orization Guideline,"

dated July 2005.

2 Specifically, this process determines the safety significance of SS Cs and categoriz es them into on e of four risk-informed safety class (RI SC) categories.

The NRC issued a draft of this guide, D raft Regulatory Guide DG-1121, for public rev iew and comm ent as part of the §50.

69 rulemak ing packag e in May 2003.

The staff subsequently received and addressed public com ments in dev eloping the prev ious revision of this guide, which th e agency published in January 20 06, and has since in corporated additional stak eholder comm ents in preparing the current revision. Howev er, since this is a new regula tory approach to categorizing SSCs, and to ensure that the final guidance adequatel y addresses lessons learned from the init ial applicat ions, the NRC decided to issue this g uide for trial use. Therefore, this trial regulatory guide does not e stablish any final staff positions for purpose s of the Backfit R ule, 10 CFR 50

.109, and m ay continue to be revised in response to experience with its use. As su ch, any chang es to this trial guide prior to staff adoption in final form will no t be con sidered to be b ackfit s as def ined in 10 CFR 50.10 9(a)(1). This wi ll ensur e that the final regulatory guide adequately addresses lessons learned from regulatory review of pilot and follow-on applications, and that the guidance is sufficient to enhance regula tory stability in the review, approv al, and implementatio n of probabi listic risk assessm ents (PRAs) and their results in the risk-inform ed categorization pro cess required by § 50.69.The NRC issues regula tory g uides to describ e to the public metho ds that the staf f consid ers acceptable for use in im plementing s pecific parts of the ag ency's regulation s, to explain techniques that the staff uses in ev aluating specific problem s or postulated accidents, and to provide g uidance to applicants.

Regul atory guides are not substitutes for regulations, and compliance with regula tory guides is not required.

This reg ulatory guide contain s inform ation co llection s that a re cov ered by the req uirem ents of 10 CFR Part 5 0 which the Office of Management a nd Budget (OMB) approved under OMB control number 3150-0011.

The NRC may neither conduct nor sponso r, and a person is not required to respond to, an information collection request or requirement unless the requesting document displ ays a currentl y valid OMB co ntrol nu mber.

3 NEI 00-04 uses the term "high-sa fety-signif icant (HSS)

" to ref er to SSCs t hat perfor m saf ety-s ignific ant functi ons. The NRC understands H SS to have t he sam e mea ning as "s afety-signif icant" (i.e., SSCs tha t are ca tegorize d as RISC-1 or RISC-2), a s used in §50.69.

RG 1.201, Re

v. 1, Pag e 3 B. DISCUSSION This trial regula tory guide provides interim guidance for complying with the NRC's requirem ents in §50.69, by using the process described in Revisio n 0 of NEI 00-04 to determine the safety significance of SSCs and place them into the appropr iate RISC categories.

The safety significance of SSCs is determined using an integ rated decision-m aking process, which incorporates both risk and traditional en gineering insigh ts. Th e safe ty funct ions of SSCs inc lude bo th the d esign-bas is func tions (deri ved from th e safe ty-related definition) and functions credited for preventing and/or mitig ating severe ac cidents. Treatment requi rements are the n commensur ately ap plied for the categor ized SSCs to mainta in thei r funct ional ity.Figur e 1 provides a conceptual understanding of the new risk-inform ed SSC categorization scheme. The fig ure dep icts the current safety-rela ted ve rsus no nsafety-rela ted SSC categ orizat ion sch eme w ith an overlay o f the new safety-significance catego rization. I n the traditional determ inistic approach, SSCs were gener ally categorized as either "safety-related" (as defined in 10 CFR 50.2) or "nonsafety-related." This div ision is shown by th e vert ical line in the f igure. Risk insig hts, in cluding consid eration of sev ere accidents, can be used to identify SSCs as being either safety-significant 3 or low-safety-significant (L SS)(as shown by the horizontal line in the figure). This results in SSCs being grouped into one of four categories, as represen ted by the four b oxes in Figure 1

.Figure 1. §50.69 R ISC Categories RG 1.201, Re

v. 1, Pag e 4 RISC-1 SSCs are safety-related SSCs that the risk-informed categ orization process determ ines to be significant contributors to plant safety. Licen sees must continue to en sure that RISC-1 SSCs perform their safety-significant fu nctions consistent with the categorization pro cess, including tho se safety-sig nificant functions that go beyond the functions defined as safety-related for which credit is taken in the categoriza tion process.

RISC-2 SSCs are those th at are defined as nonsafety-related, althoug h the risk-informed categorization process determines that they are significant contrib utors to plant safety on an individual basis. The NRC staff recognizes that some RISC-2 SSCs may not have existing special treatment requirements.

As a result, the focus for RISC-2 SSCs is on the safety-sig nificant functions for which credit is taken in the categoriza tion process.

RISC-3 SSCs are those that are defined as safety-related, altho ugh the risk-inform ed categorization process determines that they are not significant contrib utors to plant safet y. Special treatment requirem ents are rem oved for RI SC-3 SSCs and rep laced w ith hig h-le vel re quirem ents. Th ese hig h-le vel re quirem ents are inte nded to provi de suffi cient re gulato ry trea tment , such that the se SSC s are sti ll expec ted to p erform their safety-rela ted functions under desig n-basis condition s, albeit at a reduced lev el of assurance compa red t o the curr ent spec ial trea tment requ ire ments. Howe ver, §50.69 do es no t all ow th ese R ISC-3 SSCs to l ose the ir fun ction al capa bilit y or be remove d from the facil ity.Finally, RI SC-4 SS Cs are those that are de fined as nonsafety-related, and that the risk-informed categorization process determines are not significant contrib utors to plant safet y. Section 50.69 does not impose alternativ e treatment requirem ents for these RI SC-4 SS Cs. Howev er, as with the RI SC-3 SS Cs, changes to the design bases of RISC-4 SSCs must be made in accordance with current applica ble design change control requ irements (if any

), such as those set fo rth in 10 CFR 50

.59.The NRC staff believ es that the guidance in NEI 00-04 prov ides an acceptable approach for use in categorizing SSCs to support th e impleme ntation of §50.69.

Section C of this trial reg ulatory guide provides the NR C staff's regulatory positions on NEI 00-04.

4 The Com mission's Final Policy Statem ent on Use of PRA Methods i n Nuclear Regulator y Ac tivities , SP-95-146, announced in the Federal Register (60 FR 42622) on August 16, 1995, is availabl e throu gh the NRC's public Web site at http://ww w.nrc.g ov/reading-rm/doc-collections

/comm ission/policy

/60fr42622.pdf

.5 Copies of NUMARC 91-06, "Guidelines for Industry Actions to Assess Shu tdown Managem ent," dated December 1991, may be obtained f rom the N uclear Ene rgy I nstitute, A ttention: Ms.

Tonya Camer on, 1776 I Street , NW, Suite 400, Washingt on, DC 20006-3708 (phone

202-739-8148).

RG 1.201, Re

v. 1, Pag e 5 C. REGULATO RY POSITION This trial regul atory guide provi des inte rim g uidance for tria l use of the pro cess an d criter ia for determining the safety sig nificance of SSCs using the categorization process described in R evision 0 of NEI 00-04, "10 CFR 50.69 SS C Categoriza tion Guideline," dated July 2005.1.Other Documents Referenced in Revision 0 of NEI 00-04 Revision 0 of N EI 00-04 references num erous other docum ents, but the NRC

's endorsement of Revision 0 o f NEI 00-04 does not constitute an endorsement of those other referenced docu ments.2.Use of Examples in Revision 0 of NEI 00-04 Revis ion 0 o f NEI 00-04 inclu des exa mples to supp lemen t the g uidance. How ever, the NR C's endorsement of Revision 0 of NEI 00-04 does not constitu te a determination that the examples are applica ble for all licensees. A licen see or applicant m ust ensure that a g iven examp le is applicable to its particular circumstances before implementing the guidance as described in that exam ple.3.Use of Methods Other Than Revision 0 of NEI 00-04 To meet the requirem ents of §50.69 for ca tegorization of S SCs, licensees m ay use m ethods other th an thos e set fo rth in R evisio n 0 of N EI 0 0-04. The N RC staf f will d eterm ine the accepta bility of such other m ethods by ev aluating them against the requirem ents of §50.69.

4.Limitations of Types of Analyses Used in Implementing Revision 0 of NEI 00-04 In its Final Policy Statement on Use of PRA Methods in Nuclear Regul atory Activities, SP-95-146, dated August 16, 1995, the Commis sion determined that the use of PRA techn ology should be increased in all regulatory m atters, to the extent suppo rted by state-of-the-art PRA meth ods and data.

4 Im plementation of risk-info rmed regulatio n is possible because the developmen t and use of a quantitativ e PRA requires a systematic and integrated ev aluation. Develo pment of a techn ically defensible quantitativ e PRA also requires sufficient and structured documentation to allow investigatio ns of all aspects of the e valuation.

To meet the requirem ents of §50.69 for ca tegorization of S SCs, licensees m ust use risk ev aluations and insights that cov er the full spectrum of potential events (i.e

., internal and external in itiating events) and the range of plan t operat ing m odes (i.e., ful l-po wer, lo w-p ower, a nd shut down o peration s).Revision 0 of N EI 00-04 allows the use of non-PRA-type ev aluations (e.g., fire-induced vulne rability evaluation (FIVE), seism ic margins analy sis (SMA), and NEI guidance in NUMARC 91-06,"Guidelines for I ndustry Actions to Assess Shutdown Mana gement,"5 to addr ess shu tdown o peration s), when PRAs have not b een per formed. Such non-PR A-type evalu ation s will r esult in more co nserva tive catego rizatio n, in th at speci al treatm ent requ ireme nts will not be allowed to be re laxed fo r SSCs that are relied upon in suc h evaluations. The degree of relief th at the NRC will accept under §50.69 (i.e., SSCs subject to relaxation of special treatm ent requirements) w ill be comm ensurate with the assurance provided by the evaluation.

6 Copies of NEI 00-02, "Probabilistic Risk Asses sment Peer Review Process Guidance ," Rev. A3, dated March 20, 2000, may be obtained f rom the N uclear Ene rgy I nstitute, A ttention: Mr.

Biff B radley , 1776 I Street , NW, Suite 400, Washingt on, DC 20006-3708 (phone

202-739-8083).

7 The lett er from Cynthia A. Car penter (NR C) to Anthony R. Pietrang elo (NEI), dated Apr il 2, 2002, conce rns NRC staff review guidance for PRA results used to support Option 2 based upon NEI 00-04, supported by NEI 00-02. This lett er is av ailable e lectronica lly throug h the NRC's public Web site at http://adamswebsearch 2.nrc.gov/idmws/doccontent.dll?ID=00406606 5:&LogonId=b1d7d05 0903b9714 e6861221ea531aab , and through the NRC's Agenc ywide Docume nts Acc ess and Ma nagem ent Sys tem (A DAMS), http://www.nrc.gov/reading-rm/adams/

web-b ased.html , under Ac cession #ML 020930632.

8 Single copies of regulator y guides, both active and draft, and draft NUREG documents may be obtained free of charge by wr iting the R eproduction and D istribution Ser vices Se ction, OCIO , USNRC, W ashington, D C 20555-0001, or by fax to (301)415-2289, or by email to DISTRIB UTION@nrc.gov. Activ e guides m ay al so be purchas ed from the National T echnical I nforma tion Servic e (NTIS)on a standing order basis. Details on this serv ice ma y be obta ined by contacting NTIS at 5285 Port Royal Road, Springf ield, Virgini a 22161, online at http://ww w.ntis.g ov , or by te lephone at (703) 487-4650. C opies are also ava ilable f or inspection or copying for a f ee from the NRC's Public Docum ent Room (PDR), which is located at 11555 Rockville Pike, Rockville, Maryland; the PDR's mailing address is USNRC PDR, Washing ton, DC 20555-0001. T he PDR can a lso be rea ched by t elephone at (301) 415-4737 or (800) 397-4205, by fa x at (301) 415-3548, and by e mail to PDR@nrc.gov. Copies of certain g uides and m any othe r NRC docum ents are available electronically through the Public Electronic Reading Room on the NRC's public Web site, http://ww w.nrc.g ov , and through the NRC's A gency wide Doc uments A ccess a nd Managem ent Sys tem (A DAMS)at http://www.nrc.gov/r eadin g-rm/ad ams.ht ml.9 ASME RA-S-2002, "Standa rd for Probabili stic Risk Asses sments for Nucl ear Power Plant Applic ations," is availa ble through the W eb-based pr oduct catal og sponsored by the Am erican Soc iety f or Mechanic al Enginee rs at http://cata log.asm e.org/Code s/PrintBook/RA S_2002_Probabilistic_R isk.cf m?CA TEGOR Y=CS&Sta rtRow=101.RG 1.201, Re

v. 1, Pag e 6 5.Technical Adequacy Attributes of Analyses Implem enting Revision 0 of NEI 00-04 The peer review process described in NEI 00-02, "Probabilistic Risk A ssessment Peer R eview Process Guidance,"

6 as ame nded to in corp orat e NRC c omment s pro vide d in t he NRC's le tte r to N EI, dated April 2, 2002, 7 and as endorsed in Regulatory G uide (RG) 1.200, "An Approach for D etermining the Technical Adequacy of Probabilistic Risk Assessments,"

provides a m echanism for licensee s to determine if their internal event s PRA meets the attributes required for this application.

8 An alter native to NEI 00-02 is the A merican Society for Mechanical Engin eers (ASME) Standard A SME RA-S-2002,"Standard for Probabilistic R isk Assessm ents for Nuclear Power Plant Applications,"

9 as amended to incor porate N RC com ments and as endorse d in RG 1.200. Both NEI 00-02 and the ASM E Stand ard are endorsed for trial use b y the NRC in RG 1.200, w ith appropriate clarifications and e xceptions.

The license e or applicant is expected to document the technical adeq uacy of their inter nal events PRA for this application, in acco rdance with the docum ents mentioned ab ove, as endorsed in RG 1.200.

However, the documents m entioned above cu rrently cover on ly internal even ts at full power.

There is not currently a s imilarly endorse d standard for the external events, internal fires, and low-po wer and shutdown PRAs, or for non-PRA-type analyses (e.g., FIVE, SMA, NUMARC 91-0 6), and Section 3.3 of Revision 0 of NEI 00-04 provides only limited guidance for determining the technical adequacy attributes required for these types of analyses for this specific application.

Therefore, for §50.69 subm ittals that are received before the NRC endorses standards for external events, internal fires, and low-power and shutdown PRAs, as well as non-PRA-type an alyses, the NRC staff expects the licensee or applicant to docum ent the bases for why the method em ployed is technically adequate for this application. Toward that end, as part of the plant-specific application requesting to implem ent §50.69, the licens ee or applicant will provide the ba ses supporting the technical adequacy o f its external events, internal fires, and low-po wer and shutdown PRAs, and non-PRA-ty pe analyses for this application.

10 SECY-04-0118, "Pla n for the I mplem entation of the Comm ission's Phase d Approach to Probabilistic Risk A ssessm ent Quality ," dated J uly 13, 2004, is availa ble through the NRC's public Web site at http://www.nrc.gov/r eadin g-rm/doc-coll ectio ns/c ommissi on/s ecys/2 004/secy2 004-011 8/20 04-0 118 scy.ht ml or http://www.nrc.gov/r eadin g-rm/doc-col lection s/commission

/secys/200 4/secy200 4-011 8/200 4-011 8scy.pdf#p agemode=boo kmarks.11 Single copies of regulator y guides, both active and draft, and draft NUREG documents may be obtained free of charge by wr iting the R eproduction and D istribution Ser vices Se ction, OCIO , USNRC, W ashington, D C 20555-0001, or by fax to (301)415-2289, or by email to DISTRIB UTION@nrc.gov. Activ e guides m ay al so be purchas ed from the National T echnical I nforma tion Servic e (NTIS)on a standing order basis. Details on this serv ice ma y be obta ined by contacting NTIS at 5285 Port Royal Road, Springf ield, Virgini a 22161, online at http://ww w.ntis.g ov , or by te lephone at (703) 487-4650. C opies are also ava ilable f or inspection or copying for a f ee from the NRC's Public Docum ent Room (PDR), which is located at 11555 Rockville Pike, Rockville, Maryland; the PDR's mailing address is USNRC PDR, Washing ton, DC 20555-0001. T he PDR can a lso be rea ched by t elephone at (301) 415-4737 or (800) 397-4205, by fa x at (301) 415-3548, and by e mail to PDR@nrc.gov. Copies of certain g uides and m any othe r NRC docum ents are available electronically through the Public Electronic Reading Room on the NRC's public Web site, http://ww w.nrc.g ov , and through the NRC's A gency wide Doc uments A ccess a nd Managem ent Sys tem (A DAMS)at http://www.nrc.gov/r eadin g-rm/ad ams.ht ml.RG 1.201, Re

v. 1, Pag e 7 Indu stry standards have been or are being prepared for external events, internal fires, and low-power and shutdown PRA

s. For §50.69 submittals receive d after a standard is dev eloped by the ind ustry and endorsed by the NRC via rev isions to RG 1.200 , the NRC expe cts the licensee or applicant to use that standard to demo nstrate the technical adequacy of the corresponding aspect of the PRA, if it is used to support the categorization.

This is consistent with the Comm ission's phased approach to PRA quali ty.10 The licensee or applicant should provide, as part of the plant-specific application requesting to implement§50.69, the bases s upporting the technica l adequacy of their PRAs for this application per the standards as endorsed by R G 1.200.6.Uncertainty Considerations in Revision 0 of NEI 00-04 The staff notes that the purpose of the sensitiv ity studies performed as part of the risk categorization process is to ad dress th e imp act of p arame ter and mode l uncert ainties on the c atego rizatio n. The s taff understands the phrase "applic able sensitiv ity studies identified in the characterization of PRA adequa cy"(in Tables 5.2 through 5.5 of Revisio n 0 of NEI 00-04), a s meaning those uncertainties not address ed by the other sensitiv ity studies in Tables 5.2 through 5.5.

These uncertainties are typ ically identified via PRA peer reviews or self-assessm ents that are associated with the licensee's choice of specific mode ls and assumptions, as discussed in Section 2.2.5.5 of Reg ulatory Guide 1.

174, "An Approa ch for Using Probabilistic Risk A ssessment in Risk-In formed Decisions on Plant-Spe cific Changes to th e Licensing Basis."11 7.Comm on-Cause F ailure and D egradat ion Mecha nism Cons ideratio ns in Revisio n 0 of NEI 00-04 The NRC staff notes that mecha nis ms that could lead to large increases in core damage frequency (CDF) and large early release frequency (LERF), which could potentially inv alidate the assumption s underl ying the ca tegori zation proces s, incl uding th e risk se nsiti vity stud y, are th e emergenc e of ext ensive common-cause failures (C CFs) impacting multiple sys tems and sig nificant unmitiga ted degradation.

However, for th ese types of im pacts to occur, the m echanisms that lead to failure, in the absence or relaxation of treatm ent, would have to be sufficie ntly rapidly developing or not self-re vealin g, such that there would be few opportunities for early d etection and corrective action. Section 12.4 of NEI 00-04 describes an acceptable perfo rmance-based approach to addre ss these concerns.

RG 1.201, Re

v. 1, Pag e 8 Alter native ly, those aspects of treatment that are necessa ry to prevent significant SSC degradation or failure from k nown mechan isms, to the ex tent that the results of the risk sensitivity study would be invalidated, could be identified by the licensee or applica nt, and such aspects of treatment would be retained. This alte rnativ e appro ach wo uld requ ire an u ndersta nding of the d egrad ation an d com mon-cause fa ilure mechanism s and the elemen ts of treatment that a re sufficient to prevent them. As a n example of h ow thi s alt erna tive appr oach might b e impl ement ed, t he kno wn ex ist ence of ce rta in de grad ati on mec hani sms affectin g pres sure bo undary SSC in tegrity could b e used t o suppo rt retain ing th e curren t requir emen ts regarding inspec tions or examination s or use of the risk-informed ASME Code Cas es, as accepted by the NRC's regulatory proc ess. As another example, cha nging levels of treatment on severa l similar SSCs that might b e sensitive to potential CCF would require consideration of whether th e planned mon itoring and cor recti ve actio n progra m, or othe r aspec ts of tr eatment , would b e effe ctive t o suffi cient ly minimize the potential for CCFs impacting m ultiple systems, such that the categ orization process (includin g the risk sensitivity study) rem ains valid.

8.Import ance of, and I nterre lationships wit hin, the P rocesse s Descr ibed in Revi sion 0 of NEI 00-04 The NRC staff notes that the implem entation of all processes desc ribed in NEI 00-04 (i.e., Sections 2 throu gh 12) is integ ral to providing reasonable confidence in the evaluations required by §50.69(c)(1)(iv

). All aspects of the guidance are im portant and interrelated. S ections 2 through 7 and Section 10 of N EI 00-04 describe the processes used to determine the set of SSCs, for which unreliab ility i s adjuste d in the risk s ensitiv ity stu dy de scribed in Sect ion 8, which i s used t o confir m that the categorization process results in accepta bly small increases to CDF and LERF. Section 9 describes the integrated decisionm aking panel (IDP) function of reviewing and ensuring tha t the system functions and operating expe rience have been a ppropriately considered in the process. Finally , Sections 11 and 1 2 describe the processes that p rovide reasonable con fidence that the validity of the categoriz ation process (including the risk sensitivity study) is maintained.

Thus, all aspects of NEI 00-04 m ust be followed to achie ve rea sonable confide nce in t he eva luation s requir ed by §50.6 9(c)(1)(iv).9.NRC Endors ement of Revision 0 of NEI 00-04

Specific C larificat ions Revision 0 of N EI 00-04 presents an approach that the NRC staff c onsiders acceptable for use in meeting the categorization requirements set forth in §50.69, subject to the above regulato ry positions and the following specific clarifications.

Section 1.2 The second paragraph of Section 1.2 discusse s a third set of equipm ent referred to as "import ant-to-sa fety" an d its re latio n to saf ety-rela ted and nonsaf ety-rela ted equ ipment. This us age is inconsistent with the N RC's regulatory usage. The NR C staff's general end orsement of NE I 00-04 does not constitute an en dorsement of this usage of the term "important-to-safety."

In the con text of this guidance, the NRC staff understands this term as referring to nonsafety-related SSCs that hav e been determined to be impor tant. These nonsafety-related SSCs will be categorized as either RISC-2 or RISC-4, as determined by their safety sign ificance, in accordance w ith the §50.69 categ orization process.

The fourth paragraph of Section 1.2 states that the integrated decision-making process"-blend s risk insig hts, ne w techn ical info rmatio n and o peration al feedb ack-." The NR C staff understands this phrase, a nd similar phrases (e.g., the third guiding princip le in Section 1.3), as meaning that t he inte grated decisi on-making pro cess must systemat icall y consid er the quanti tative and qual itati ve information av ailable regarding the various m odes of plant operation an d initiating even ts, including PRA quantitative risk results and insig hts (e.g., CD F, LERF, and importance m easures); deterministic, traditional engineering factors and insigh ts (e.g., defense-in-depth, safety margins, and containment integr ity);

12 Code Cases associated with the ASME Boiler and Pressure Vessel Code are available through the Web-based ASME Dig ital Store sponsored by the Am erican Soc iety f or Mechanic al Enginee rs at http://store.

asme.org/cate gory.asp?catalog%5Fname=Codes+and+Standards&category%5Fname=

Boilers+and+Pressure+Vessels&Page=1

.RG 1.201, Re

v. 1, Pag e 9 and any other pertinent information (e.g., industr y and plant-specific operational and performance experience, feedback, and co rrective actions prog ram) in the categ orization of SSCs.

Section 1.3 The second guiding principle in Section 1.3 states that deterministic or qualitative inform ation should be used if no PRA information exists related to a particular hazard or operating mode. This princip le is not to be understood to mean that dete rministic or qualitativ e information shou ld be used only when no PRA inform ation exists. The NRC staff believes that the integrated decision-making process must system atically consider the quant itati ve and quali tative information availa ble regarding the various modes of operation and initiating events, including PRA, quantitativ e risk results and ins ights; deterministic, traditional engineering factors and insights, and any other pertinent information in the categorization of SSCs.Section 4.0 In Section 4

.0 and Section 5.1 , NEI 0 0-04 references ASME Code Case N-660, "R isk-I nformed Safety Classification for Use in Risk-Informe d Repair/Replacem ent Activities," as an approach for addressing the pressu re-retaining function or passive function of active co mponents.12 The version of ASME Code C ase N-660 that is acceptable to the N RC staff for use in this application is the versio n identified in RG 1.14 7, "Inserv ice Inspection C ode Case Acceptability , ASME Section XI , Division 1,"

subject to any conditions or limitations specified therein. Alternatives to this Code Case may be submitted for NRC review and approval as part of a specific §50.69 application.

Section 6.2 In Section 6

.2, the NEI 00-04 g uidance contains criteria for co nfirming that an SSC is LSS (or recategorizing it as safety-sig nificant) based on defense-in-depth considerations, which include criteria related to containmen t bypass, containm ent isolation, early h ydrogen bu rns, and long-term containm ent integr ity. The cont ainme nt isola tion cri teria lis ted in t his sect ion of N EI 0 0-04 are app licable to containment penetration

s. The NRC staff un derstands the use of the phrase "containmen t penetration" as including electrical pe netrations, air locks, equipment hatches, and piping pen etrations (including containment isolation valv es). Further , the staff notes that the containment isolation criteria in this section of NEI 00-04 are separate and distinct from those set forth in §50.69 (b)(1)(x). The criteria in §50.69(b)(1)(x) are to be used in determ ining which conta inment penetrations and valves m ay be exem pted from the Type B and Ty pe C leakag e testing requirem ents in both Options A and B of Appen dix J to 10 C FR Par t 50, b ut the §50.69(b)(1)(x) criteria are not used to determ ine the proper RIS C categ ory for containment isolatio n valves or penetrations.

RG 1.201, Re

v. 1, Pag e 10 Section 8 The risk sensiti vity study addres ses the impac t of pot ential in creases in the f ailure r ates of all RISC-3 SSCs resulting from the chang e in treatment.

Section 8 of NEI 00-04 inclu des comm entary on the consideration of known degradation mecha nis ms and common-cause interactions and failures in PRAs, which includes the obse rvation that intersy stem com mon-c ause failures are not ty pically mode led because factors such as desig n dive rsity a nd diffe rent ser vice e nviron ments ensure they are neg ligibl e contrib utors to risk. The NR C staff notes th at becau se inter system comm on-c ause fai lures ar e typi cally not included in PRA models and, therefore, are not addressed by the risk sensitivity study. Therefore, the licensee or applicant relies upon the alternative tre atment and feedba ck requireme nts, including correcti ve act ion pro vision s, estab lished i n §50.69 and discuss ed in S ection 1 2 of NE I 00-04, to ensu re that any significa nt intersystem common-cause failure m echanisms would be identified and corrected so that the assum ptions underlying the categorization are not invalidated.

Section 9.2 Section 9.2 of NE I 00-04 limits the I DP review of risk information to active functions and SSCs.

The NRC staff believ es that this limitation in review scope is attributable to the reliance of N EI 00-04 on ASME Code C ase N-660 to address passive fu nctions, which is perform ed by an expert panel. The expert pan el used in perfor ming ASME Code Case N-660 may be the same panel as the IDP used in the §50.69 categorization pro cess; however, it is not required to be the same panel.

As such, the IDP rev iew of risk inform ation should address both active and passiv e functions and SSC s.Section 11.2 The NEI 00-04 guidance allow s licensees to implem ent different approaches, de pending on the scope of their PRA (e.g., the ap proach if a seismic margins ana lyses is relied upon is different and more limiting than the approach if a seism ic PRA is used). As part of the NRC's review and approval of a licensee's or applica nt's application requesting to implement §50.69, the NRC staff intends to impose a licens e condi tion tha t will e xplicitl y add ress the scope o f the PR A and n on-P RA m ethods used in the licensee's categorization approach. If a licensee or applicant wishes to change its categorization approach and the change is outside the bounds o f the NRC's license c ondition (e.g., switch from a se ismic marg ins analy sis to a seism ic PRA), the licensee or applicant will need to seek NRC approv al, via a license amen dmen t, of the i mplem entation of the n ew app roach in their ca tegori zation proces s. The f ocus of the NR C staff's review and appro val will be on th e technical adequacy of the methodo logy and a nalyses relied upon for this application.

Section 12.1 The guidance in Section 12 of NEI 00-04 refers to the need to update the risk inform ation and categorization pr ocess if the cat egorization result s are "-more than minimally affect ed." The NRC staff un derstan ds that being "mor e than m inima lly aff ected" w ould in clude a situatio n in wh ich ther e is indication that an SSC that is categorized as low safety significant would be changed to safety-sig nificant. The NRC staff also recognizes that the licensee or applicant may change the categorization and/or treatment aspects of SSCs so that there is reasonable confid ence that the cum ulative risk increas e from imple menti ng §5 0.69 is main tained a cceptab ly sm all.

RG 1.201, Re

v. 1, Pag e 11 Section 12.4 The gui dance i n Sectio n 12.4 of NEI 00-04 defin es CCF as "-th e sim ultaneo us failu re of more than o ne SSC to perform its function, due to th e same cause-,"

and Appendix B to NEI 00-04 provides a sim ilar definition, but with "sim ultaneous" replaced by "during a short p eriod of time."

These de finition s are de rived from their us e in a P RA con text, w here the emph asis is o n failur e of mo re than one SS C durin g a sp ecified missi on tim e. The s taff not es that the lice nsee's o r applic ant's corrective action program associated with the implementatio n of §50.69 should address the potential for SSC failures at different times resulting from a common cause, even if they are revealed at different times.In addition, the staff notes that the g uidance in Section 12.

4 that potential advers e trends need not be evaluated until the number of ex pected failures for a g roup of SSCs dou bles may not be practical for SSCs with low fail ure rates assumed in th e PRA.D. IMPLEMEN TATION The purpose of this section is to provide inform ation to applicants and licen sees regarding the NRC staff's plans for using this trial reg ulatory guide.

No backfitting is intended or approv ed in connection with the issuance of this guid e.Except in those cases in which an applicant o r licensee proposes or has previously estab lished an acceptable alternative method for com plying with the categorization portion of §50.69, the methods described and/or endorsed in this guide will be used in evaluating licensee compliance with the requirem ents of §50.69 for the categ orization of SSCs.

REGUL ATORY ANAL YSIS The NRC staff did not prepare a separate reg ulatory analysis for this trial regulatory guide. The regulatory analy sis that was prepared for the rulemakin g is still applicable, a s is its value/im pact statem ent. The regula tory analy sis is availa ble in the NRC's Agencywid e Docum ents Access and Management Syste m (AD AMS) at htt p://www.nrc.gov/rea ding-rm/ad ams.h tml , under Accession #ML 022630028.