ML20217K128
| ML20217K128 | |
| Person / Time | |
|---|---|
| Issue date: | 07/15/1997 |
| From: | Callan L NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | |
| References | |
| SECY-97-148, SECY-97-148-01, SECY-97-148-1, SECY-97-148-R, NUDOCS 9708150147 | |
| Download: ML20217K128 (11) | |
Text
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RELEASED TO THE PDR lp(, D, / i l
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RULEMAKING ISSUE (Notation Vote) 1 E
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July 15. 1997 SECY-97-148 n
FOR:
The Commissioners y
y FROM:
L. Joseph Callan Executive Director for Operations
SUBJECT:
RECOMMENDATION ON NEED FOR RULE ON ADVANCED LIGHT WATER REACTOR SEVERE ACCIDENT PERFORMANCE PURPOSE:
To provide the Commission with a recommendation on the need for generic rulemaking on Advanced Light Water ReSctor (ALWR) severe accident performance.
BACKGROUND:
The staff proposed, in SECY 90-341. " Staff Study on Source Term Update and Decoupling Siting From Design." dated October 4, 1990, an integrated set of activities to address regulatory implementation of updated source term information and plant design requirements related to severe accidents.
in that paper the staff outlined a two phased approach to decou and plant design via rulemaking changes to Parts 50 and 100.ple reactor siting In Phase 1 the staff proposed a rulemaking to revise reactor site criteria under 10 CFR 100 based on siting criteria described in Regulatory Guide 4.7.
Under Ph'ase*II, a
~
rulemaking would revise Part 100 to delete the dose calculation requirement and revise Part 50 to include a revised source term or plant design requirements based upon revised source term insights.
Contacts:
Charles G. Tinkler, RES 415-6770 SECY NOTE:
TO BE MADE PUBLICLY AVAILABLE WHEN THE FINAL SRM IS hikWilson,NRR gg gy3733tg 970815o147 970715
-14 PDR
The Comissioners 2
An advance notice of proposed rulemaking was published (57 FR 44513) on September 28. 1992, outlining alternative approaches to generi: regulation addressing the challenges from severe accidents for future lig1t water reactors.
In SECY 93 226. "Public Coments on 57 FR 44513 Pro >osed Rule on ALWR Severe Accident Performance." dated Seatember 14, 1993, tie staff provided a sumary and discussion of the pu)lic coments received on the proposed rule on advanced light water reactor (ALWR) severe accident' performance and recomended delaying a final decision to issue a rule.
In an SRM dated September 14. 1993, the Comission approved the staff recomendation to delay a decision on generic rulemaking at least until after the Final Safety Evaluation Reports (FSER) are issued for the evolutionary designs, the ABWR and the System 80+.
The Comission also expressed the view that a staff l
l recomendation on generic rulemaking should await and reflect some further experience with plant-specific design certification rulemaking proceedings.
Additionally the Comission directed that the generic rulemaking, if needed, should follow completion of the revisions to 10 CFR 50 and 10 CFR 100 which address siting and source terms.
DISCUSS 10th The staff believes that the status of the reviews of the evolutionary and passive designs and related certification rulemakings has reached the point where our experience allows us to offer a reccmendation on generic rulemaking.
The staff believes that the value in pursuing generic severe accident rulemaking does not warrant the resource expenditure.
Therefore, the staff recomends withdrawal of the advance notice of proposed rulemaking.
The design certification for the ABWR design was completed on May 19. 1997.
(62 FR 25800) and the design certification of the System 80+ design was completed on May 21. 1997 (62 FR 27840).
Further, on December 11. 1996. the Comission published the final revisions to 10 CFR 50 and 10 CFR 100.
These activities, the oncoing review of the AP600 and the numerous interactions with the Comission relative to the review and design certification of future reactors have provided us with the necessary experience to recommend action on rulemaking.
The advance notice of proposed rulemaking )ublished in 1992 (attached) outlined three olternative approaches to tie specification of recuirsments addressing severe accident performance.
The first alternative, cescribed as a hardware oriented rule, would specify reasonable design features or design characteristics directed towards prevention or mitigation of explicitly identified risk significant phenomena.
The risk significant phenomena identified were:
tydrogen generation, transport and combustion: high pressure melt ejection: core concrete interactions and basemat ablation: long term containment overpressurization: steam ex)losions from fuel-coolant interactions: and containment bypass.
Tlese phenomena represent the potential contributors to cortainment failure or bypass and thus the mechanisms for large offsite radic. active release. Alternative 2. described as a phenomena oriented rule, is a modification of the first alternative wherein an overall containment perforrance goal would be specified along with the phenomena to be considered, as ider.tified above.
The designer would then be required'to
The Commissioners 3
perform analysis of the impact of those phenomena and develop and propose the design features to meet the goal.
Regulatory guides would add'ess analytical methods, acceptance criteria and design criteria for hardware. L This approach, similar to Alternative 1, would be an overlay on the existing design basis s)ecified in 10 CFR Part 50 and justified on an enhanced safety basis.
The t11rd alternative, described as a general design criteria (GDC) oriented rule, involved development of a set of new design requirements to address specific challenges and issued as changes to Appendix A. " General Design Criteria" to '
Each new design criterion would describe the nature of the challenge as well as the, success criterion.
This approach, which was proposed by the ACRS in a letter to Chairman Carr, dated May 17, 1991, also involved the development of Regulatory Guides to provide additional guidance on analysis methods and assumptions.
This approach is similar to the other alternatives, es etially Alternative 2 but differs in that the existing 10 CFR Part 50 desi n basis would be modified to include severe accidents, As discussed in the Supplementary Information of the advance notice of proposed rulemaking,d consistency and standardization to the resolution of a primary purpose for the generic severe accident rulemaking-was to ad severe accident issues for future designs based on current technical information. Further, in SECY-93 226, the staff expressed the view that the current requirements regarding severe accidents addressed in 10 CFR 50.34(f) do not completely reflect current technical information (10 CFR 50.34(f) was issued as a final rule on January 15, 1982).
For example, while 10 CFR 50.34(f) contains reauirements addressing the severe accident challenge associated with hydrogen generation and combustion, there were no provisions dealing with other phenomena that imp 4ct containment performance, e.g., high pressure melt ejection with direct containment heating and core concrete interactions and ex vessel debris coolability. However, in addition to the requirements of 10 CFR 50.34 (f), 10 CFR 52,47 (a) requires an applicant to perform a design-specific PRA. - The discussion and interactions on severe accident provisions, which served as the basis for the approval in the FSERs for System 80+ and ABWR, reflect an updated status of our understanding of severe accident challenges, including technical insights on high pressure melt ejection and ex vessel debris coolability. While the staff's original technical recommendations were outlined in SECY-90-016. " Evolutionary Light Water Reactor (LWR) Certification Issues and Their Relationship to Current Regulatory Requirements," dated January 12, 1990, numerous subsequent papers including SECY-93-087, " Policy Technical, and Licensing Issues SECY Pertaining to Evolutionary and Advanced Light Water Reactor (ALWR) Designs,"
dated April 2,1993, outlined the evolution of staff positions for the evolutionary and advanced passive reactors considering: 1) information from the review of current operating reactor designs, evolutionary designs and advanced passive ALWR designs, 2) insights from probabilistic risk assessments, 3) Commission guidance, 4) the review of the EPRI Utility Requirements for evolutionary and passive ALWR designs, and 5) insights from the severe accident research program. While, in general, the staff believes consistency among many design reviews is best achieved through generic rules, i
as-a practical matter, since the number of new applicants is likely to remain quite limited, it is more efficient-to proceed with design specific reviews.
In fact, the staff is not aware of any new applicants in the foreseeable
- future, 4
The Comissioners 4
Another purpose of the generic severe accident rulemaking. i.e.. facilitation of design certification rulemaking, has been rendered moot by ;he experience gained in design certification rulemakings.
Furthe7more, now that the design certification rulemakings are completed for the General Electric Advanced Boiling Water Reactor and ABB-CE System 80+. the only design currently under staff review is the Westinghouse AP600. This review is evaluating the AP600 design against the selected technical and severe accident. -
requirements given in SECY 90 016 and SECY-93 087.
The resolution of severe accident design specific requirements would be set forth in the AP600 design control document and approved in the AP600 design certification rulemaking.
The Comission could ensure its expectations for standardization and enhanced safety are maintained by imposing a restrictive change process, as the Comission did in the certifications of the two evolutionary designs, While certain arguments in favor of generic rulemaking (i.e.. promoting i
consistency and standardization in the resolution of severe accident issues i
and providing guidance to future LWR designers and applicants) continue to apply in varying degrees, practical aspects limit the need for such an activity. At this point, given the lack of any new potential plant or design applicants, the staff believes that the benefits of generic rulemaking do not justify the allocation of staff resources to proceed with the development of l
new regulations addressing severe accidents. While severe accident research has made substantial Mark I liner failure, progress % resolving specific technical issues (e.g.,
i direct containment heating, in vessel steam explosions, hydrogen combustion) much of the issue resolution research has focussed on the consideration of these issues relative to current plant designs.
Additional substantial effort would be required., depending on the approach taken, to develop generic regulatory requirements independent of plant design.
While considerable effort went into developing the advance notice of rulemaking and addressing the public comments received on the three alternatives, there was no clear consensus on either the need for rulemaking or on a preferred regulatory approach.
it is anticipated that considerable effort would be required to develop a preferred regulatory approach, Finally, development over the next several years of a comprehensive integrated set of regulations addressing severe accident issues, with the accompanying regulatory guides.
would be competing with other resource needs.
Upon consideration of the potential value of a generic rule, the status Qf the review and design certification of future reactors, and the potential resource requirements, the staff believes that the value in pursuing generic severe accident rulemaking does not warrant the resource expenditure. While the staff does not perceive the need for generic rulemaking in the foreseeable future, should conditions change regarding potential applicants, the staff would reassess the merits of rulemaking and advise the Comission at that
- time, OGC has reviewed this paper and has no legal objection.
The ACRS was briefed on the recomendation contained in this paper.
)
The Comissioners 5
RECOMMENDATION:
That the Comission approve the staff's plans to withdraw the hdvance notice of proposed rulemaking on severe accident performance for future light water reactors.
s
'A L
.. Joseph Calla
_ ecutive Dir or for Operations Commissioners' comments or consent should be provided directly to the Office of the Secretary-by c.o.b. Wednesday, July -30, 199J.
Commission staff office. comments, if any, should be submitted to the Commissioners NLT July 23, 1997, with an information copy to SECY.
If the paper is of such a nature that it requires additional review and comment, the Commissioners and the Secretariat should be apprised of when comments may be expected.
DISTRIBUTION:
Commissioners OGC i
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i' PWtf 50 o PROPOND RULE MMONG l
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14 CFR port et m_
m Nuclear Reguleter (NRC)le eenendering 1.y Commleolon i,' ;
Asseptabuny of plant portermones for Seeme Assisentes scope of reguletiene andw to CpR part so for Considerssonin telety Regulatione future LWRe to addreas the ability of the i
plant to withetend che from asesesv: Nuclear Reguletory
- nosociaudwl sev e core Comml/elon.
'demage occidente, severe sore damage acner s Advance notice ofH:;:_:,
occidente m low probebility evente
,rvie. eking.
heyond the doelpn basis established in eusseenem%e Nuclear Reguletory 10 CFR part to that een lood to -
Commiselon (NRC)le conohlweg en signifteent oore damage end redioactive murht rehm from h reactwIW emendment to its latione for future light water reactore 1.WRs).%e ph.N NRC h ht wh amendment would prevlolone for W M"on &e signancent eeva 6t event
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the design of the plant structures to g g m agg, to withetend enteln ohellenges from
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damage accident beyed se emnet "doelen boele sooidente."De NRC le plant have sufnetent melured a
w enew Nd leeuing this notice to invite advloe and I
krfwmanos artu,rk for fahre DVRe.
moommodenone from 6mtemwd
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,,wmakhs ANpRM)e from to incorporate these prevlolone into rthe advloe and eefety Ngulanone.
hkmbd p:tiene on the proper scope safse: Comment period empires and mothed wincorporate these December as.tsetDe NRC will sonalderatione into the NRC's consider commente received after thle repletions.
dele only if it is practical to do so but ihle ANpRM mfloots consideration of the Comunteolonis able to esem b exhnelve wwk ::
Y Min the considwetion only for comumente severe socident eres. Spes'encelly, the received on er before this date.
NRC has already taken verlene estions aossesses: Send written commente to:
in weponse to severe socident eeneerns.
De Secreteer of the t'=='aalas U. S.
On October 3.1se0, the Commleenon d
Nuclear Regulatory Commission, leeuedles FR e6474)en ANpRM that Weehtngton.DC 30665. Attention:
Invited advlos and reeemmendations on Docketing and Service Bronch. Deliver the conaldwetion of degreded or molten commente to:118e8 Rockville p6ke.
cores in oefety regulation.Baeed on Rockville. MD. between FAS em and 4:18 receenmendetiene received from that pm on poderal workdays. Copies of ANpRM. the Commleelen developed e commente received may be==amined at pol summent that addroceed severe the NRC public Deownent Room,also L acci t eeneWerettens and withdrew Street NW (14wer level). Weahlaston.
the ANpRM(
t a, teen; 30 FR ~
DC.
32181). In its Stelement on pen puemeenIescenhaneet eterfact:
Severe Reactor Accidente Regarding homas Kin $. Ofhoe of Nuclear puture Designe and Existing plante" Reguletory Research U.S. Nuclear published August 8,1986 (80 FR 32133).
/
J 50-PR 13 September te,1995
PART 50 o PROPOSED RULE MAKING the Commission stated its intentions for sought and received Commission results. and the Commission's Safet) rulemakmgs and other regulatory guidance on the appbcation of these Goal pobey ( August 4,1986. 51 FR telions for resolung sesere accident proposed ses ere accident and 2a044) In addition. this rule could safety issues for esisting plants. the containment criteria to the evolutionar) complement and support the review of Commission conduded that these plants LWR designs now undct review.
Sesere Accident Design Mitigation posed no undue risk to pubbc health and Guidance from the Commission was Alternatives (SAMD As) on future LWRs safety Therefore. it did not see a need provided in a Staff Requirements as part of the epvironmentai review for immediate action on genene Memorandum. S. Chilk to L Ts) lor.
carned out under 10 CFR Part 51.
rulemaking for these plants liccause of dated June 26.1990 The entena the low severe accident risk. The disevsted in this ANPRM would codify Basis for the Rule Commission has continued to take all much of the Commission's guidance for This rule would reflect the NRC's reasonable steps to further reduce the general application to all future LWRs.
curtent understanding of severe risk frorn seiere accidents at existing Additionally, the NRC plans to accident issues from its research:
plants through its regulatory programs.. improve its regulations for future plants esperience with light water reactors for example, the Cornmission completed by separating (dece9pling) the now in operation. and resiew of fuiure rulemakings on several key issues acceptance criteria for a reactor site designs. Accordingly, this rule would tstated to severe accidents (i.e., station from the acceptance enteria for the ly tolight water reactor designs blackout. ant cipated transients without design of vanous en ineered safety opfy, but could possibly provide on scram, hydrogen genershon and features (LSF) via ru emaking changes guidance for establishing criteria for control). has implemented a to 10 CTR parts $0 and 100. The first other reactor types.The development of containment performance improvement phase of this decoupling of siting criteria this rule relies on the major factors program based upon insights regardmg fro.n design criteria focuses on updating deed below contamment performance under sever, and revising siung critena. The sec.ond mlot d 1
mi 10 C part 50 f fu te f.WRs 1sland i ens 1d a e ea un hr e
nati n (IpE) for severe occident 0 g
.R source term This research has explored the in ormauon phenomena associated with in. vessel For future plants, the 5escre Accident Policy Statement established the critena (2) s >ecify erformance criteria for and ex vessel severe accident processes, h drogen generation and lent esign estures based onimproged controh the form. quantity, and timing of and procedural steps under which a new [nowledge of the release of radioactive design for a nuclear power plant could materialinto containment (i.e new radioacuve material release into the i
be acceptable for meeting severe source term), and containment; challenges to containment accident concerna.ne NRC recognized (3) specify cnteria for plant integrity; and the consequences to the the need to strike a balance between performance under severe accident pubhc.This research has led to the i
a:cident prevenuon and consequence conditions.The criteria discussed in this development of data and analytical mitigation in emploring the need for ANPRM are associated with a portion of tools to analyse severe accidents for additional desi n features in se neat this second phase namely item (3) current and future designs. assess generation of p ants. Also the NRC above'
' severe accident risk. and evaluate expected that these new planta would potential risk. reduction improvements in schieve a higher standard of severe Purposa of the Rule design and operation. -
accident safety performance than prior he NRC believes that adopting a rule Application of these research results designs.The Commission stated that a to specify acceptable plant perfonnance has occurred in many areas. One clanfication of containment in response to severe accidents would comprehensive application has been the performance will be made including a accomplish the following-development of NUREG-1150 8." Severe decision on whether to establish new
- 1. Codify the Commission's guidance Accident Risk: An Assessment for Five performance criseria los containment on severe accident and containment U.S. Nuclear Power Plants? NUREG-systems and. if so, what these should issues that resulted from the review of 1150 used probabilistic techniques to be.
advanced light m ater reactors.
analyze five operating plante from a The NRC staff has been reviewmg
- 2. Provide assurance that the severe accident risk perspective.This proposed critena for future LWRs performance of future LWRs under analysis provided the NRC staff with submitted by Elettric Power Research severe accident conditions is consistent basic insights into the important event institute (EPRI) and several new LWR with assumptions about severe accident sequences that can lead to severe designs with respect to the per'ormance used in developing new accidents and the mechanisms that can Commission's severe accident pohcy source term informauork lead to a loss of contamment function and the design certification aspects of to
- 3. Provide guidance to future LWR during severe accidents.These basic CFR part 52. In pedorming these designers and potential applicants, insights identified challenges to reviews. the NRC staff has proposed
- 4. Add consisteney and containment integrity that can be enteria to address severe accident and standardization to the resolution of divided into two groups: energetic or containment issues that depart from the severe accident issues based on the rapid energy releases and slower.
existing regulatiora For the current technical information.
evolutionary LWR designs tnany of
- 5. Facilitate design certification
,, g these proposed enterLa are contained in rulemakings.
gn,,,,,,,,,, o,,,,,,,a v s c vanmeni a paper provided to the NRC nie rule would then help assure that e, mima orree. e o non sma:. w.emnsives uc Commissioners on january 12.19%
the risk to the pubhc from severe axns-ros: cesnee m steo sie. latae from the SECY404n6. "Evolutmaary LWR accidents in future LWRs is maintuined wannat To-aatormanen sam s:ss Pon Certification issues and itcir at very low levels in accordance with
[',8 @ d[j" M, M E,,^,, $,'wac Rel.thonship to Current Regulatory espenence from existing plants, current poimc o,cu ot Room. riso L $treet NW. flower Requiremente? He NRC staff has insights from risk studies and research tmit we Mosta oc.
i Septernber 29,1995 50-PR 14 l
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- 1 PMT 50 o PROPOSED RULE MAKING peduelly evolving relmees to the closed System 30+).1t le likely ht the phonemenon. thne alternative would esoteinment eyelem. Exeroples of resolution of severe socident issues for require that the applicant provide en sentelement loadings in the intet group these designs will occur vie the evolustion of the phenomenon with leanede high pressere core melt election individual de '5n certificetions before rupect to the overall contelament with dinct contelament heating.
completio-Als rulemaking. De NRC performance objecun specified in the hydrogen combustion. and the inittel emper*
.osolution of severe accident twie. nle alternatiqe le derived from the senseee of stored energy Irem b reactor lowes.or the evolutionary LWRs and contelament performance criterle sostent systeen. Deosy heat and the resente of thle rule to be opentially developed as part of the Commission's sencondensible ses generation from the same.
advanced reactor reviewe and eere.eeecew Amtetecdone typify the ne NRC stelfis eleo mysewi future essentially codilles those criteria.
peup of slow energy roleeses to the LWR designs that we e puolve sign in this approach. those features of ti e e*w Further insights from this seneept. in osotreet to the evolutionerY design needed for sente accident
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eeslysis W=ahad major ossertbutore to designe. the IstC etsff has revkwed prevention and mitigation wouW be shk to the pubhc and potesteldesign only aseseptual doelgn information from specified directly in the rule.Deee selseless.
Ik pesolve plant endore. Die nquiresments would be en "overley" on Alas, the ISIC bas imguently prelisminary wview has not identifled h existing design bula requiremente in ietseested over the poet several years or y unique foetures that would prevent to CFR part 30 for nuclear power plants.
with spRI and verloos reacher designore the evaluation of these designe under De requiresnents would be considered q regulatory enterte for the the rule dieesesed in thle ANpRM.
and luet!!ied en en enhanced eefety lotu m a _ _^. - i and pesolve LWRe. - Derefore. thne rule would be generally bula (l.a. using eefety goal. cost. benefit game of these laterections have applicable to possive LWR designs.
enelyoh and othet appropriate addmesed both prohobilieuc and -
However. es detailed design information coneWerets such a delenee.in. depth deterehdeus eriterie seessisted with beconnes ovellable and review of the ed unewktnues) and would plant pestermanos under severe passive systems le completed, further
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EpRI Adveneed Light Water Reactor perfonnenes cetteria for severe y,,,,pg g g, g,gpeeved i_
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.. accidente foto the regulations' ady for wvm aceWat shipuu Alsernet/w J:Hordware OrientedJfule would not be sub to the some petC h
e proved by en - - 'ot study of his alternative (es em the other enwnun ene yeis and daign
"****'Y I" "9"i""**".O*h*"* "7 sentelement deoisa criterie enade by the alternettves discussed in this ANpRM)
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' y' *pm,g g " Igg 8,"g Advisory Comenettee on Reactor is bened upon ensuring that h risk g
gefaguards (Acts). In a letter to the t severe accident A:- r:;.e.
e-m en May 17. seek the ACRS ich may eeuse a less of contanament propeeed a set of cetterie addressing the function in en LWR are considered in ag o De a m i.
speedfle challengee peeed by severe future LWR deoipe. Bened upon divmity.eyelem ceP* 'F,.yy socidente to the coatelasnent design for currently evellable inferimetion, suP y.
- Pmen a
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futwo light water ructor nuclear power including h rumits of risk studies and plante. in SECY-es-We, dated February sevm accident resserch progreme.
An example of this almenettve an.1ges, the NRC staff enelysed these these risk significant sevm accident ICII" ACRS setterie with respect to EPRI phenomene are:
50.XX Prevention and snitigation of design requiremente for evolutionary
- 1. Hydrogen generetion and transport. eev m acc W nu and pesolve LWRe, evolutionary vendor includug burning and/or detonation.
- designe, we vendor designe, and the woulting irse seetel.weter and core (a) Applicobility.ne cetterte of this enieues neolon guWnce for the concrete reec6ons, section apply to the design of light water patC staff's review of severe accident L High preneure election of anotten nuclear power reactoes being considered tueuse for evole LWRe.%is core snatorial from the nector vessel; for e constroodon t or opmung AIWRM refloats tion of the
- 3. Interections between molten cor, 16cenes under to part as er.
epthe eGecen dem est this rule.htions unde to CFR part 52 o regehe of this emelyene and the ACRS debria and reacter beoemet material, o
proposed ernerte, containment well and structurel e,ogagg; criterie of this section eleo may prov6de AppheebetyeN We
- 4. Containment overpressure and guidance in establishing the he NRChas Wulated on ovatesaperature from decay heet. non, requiremente for other types of ructor
" of the evolueenery light eendensible see pnastion, meld.wewt designs.
water reacter' designs to semplement its react 6 ens.
(b) Conesiament J%rformance enderstanding of severe nacident leemos
- s. Steam explosione from fwl. coolant 06/ectiw.%e design shallinclude a Lee operating reacters. Bened on this inweections; and containment system that providee a understanding, it le expected that the
- s. Costelament bypnes, barrier egelnet the release of radioactive artnerie developed in als rule would be Aherneuve 1 would specify material for a period of approximately enesistent and onenpatible whh the rusomebbe sioeip feetwee or attrhtes 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following the onset of core =
criterte being i 'M and applied in of doeng festeres direemd toward desiege under the more likely sevm evolutionary LWR reviews.However, preventies er mitigation of the above accident challenges. Following this 24 due to the advanced stage of the phenomene.Where doelen featurse hour pedod the containment should cannot be p's severe accidentesadeely specified to prevent continee to melitteln a barrier aga reviews of the current nM_ry
- designe (CE ABWR and AM/CE or sitigste the uncontrolled release oflarge 50-PM.16 September 20,1996
PART 50 o PROPOSED MULE MAKING quantities of fiuion products his shall located outalde containment and dherse containment heat removal be accomplished by:
connected to the RCS to an ultimers optems or rely on the restoration of (1) including plant design features rupture strength at least equal to the full normal containment best remoial that:
RCS pressure, espsbility if enough time is asallable for (il Provide the reactor coolant systern (tl Not creditma use of containment maior recovery actions.
(RCS) with the capability to rapidly and ienting during the 24 hout period The advargtages of this approach reliably reduce RCS pressm, following the ouet of core damage in include prestnbing those design (Hl Provide a reactor cavity design evaluating the design for compliance features to reduce the risk from severe that restricts as much as practical the with the containment performance accidents. thus promoting a more amount of elected core debris that objective in paragraph (b) above, standardized resolution to severe reaches the ypper containment or (cl Equipment Sury/ rob /hty. Fee tures accident issues. In effect this implages directly on the containment provided for severe accident prevention alternative is also prescripuve regardinf walt ne cavity deelen. as a mitigatins or mitigation shall be designed to the severe accident phenomens that a feature, should not unduly interfere with operate for the tirne period needed la the future LWR design must address since operetions including refueling, environment (eg, pressure, temperoture, the design features specified are a direct maintenance, or surveillance acuvities.
radiation)in which the equipment is result of the phenomena considered.The (111) Provide a reactor vessel support rehed upon to function including prescriptive nature of this alternatise structure sufficient to retain the reactor consideration of the circumstances of will also tend to facilitate the NRC noselin place under the loads appl cable initiating evente (e ga review and dulgn certification process generated by a high prusure core melt trenelents. lose of AC power. loss of by focueln the review on the severe l
election.
coolant accidente)-
accident enomena which must be (iv) Provide for containment wide Maintaining containment integrity for conside and the basic features which hydrogen control (e g., igniters, large a period of apptcximately 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> the design must incorporate to address volume), that accommodates the following the onset of core damage those phenomena, thus enhancing hydrogen roeulting from a 100 percent provides time for the remaining altborne regulatory efficiency. in addition. this i
enetal weler reaction of the active fuel activity in the containment (principally approach euentially codifies cladding. sad limite containment noble gases and iodine) to decay to a Commission guidance on severe hydrogen concentration to no greeter level that, when analysed realistically, accident and contelnment issues from than to percent: or provides that the would be unlikely to cause prompt the advanced LWR reviews.This 1
post-accident atmosphere will not health effects !! containment failure or approach doce not require the applicant oupport h n combustion.
controlled unting were to occur after to perform extenelve severe accident of(interactions with molten core debrispotential for and effect that time. !n addi*n. It represents a analysis to show compliance with the vlReduce lev'el of ufety s a.lcantly below the quantitative heapth objective for prompt rule. m applicant could primarily rely uPon design features which. through l
by(:A) Providing reactor cavity floorfatalities defined in the Comrnission's dh epsoe to promote core debris spreading Safety Coal Policy. However.
[,I"[,8",*I@,$,dcE,',]n re' dub
, g and cootabilityt consideri%the uncertainties involved in* the riek from the mom like (B) Providing a means to flood the analysing e udare accident t
"P e t
ructor cavity to anlet in the cooling phenomena and progresolon and "dg*yg"*,
t ceftrm that g
procoes and scrubbing of fiselon emphasle on defense-in. depth,it is not the containment pe ormance objective products.
unreasonable to include some is met.
(C) Protecting the containment liner conservatism in the criteria. This time ne dindvantage to this option is that and other structural members from period would also enhance the time It could discourage designere of future direct contact by molten core debrie; available for offette protective actions.
LWRs from ceveloping other deeltn (D) Employing baumat materials To the utent practical during this which reduce the production of non.
period, the passive capability of the approaches that might be more cost.
e!!ective, innovative, or asfer.
madaaalble goes when in contact with containment and any related design enehen coes debris: and features (e4 suppresolon pool) should Alternouve 2:Phenomeno Orientedilule (El Ensuring that containment hrovide for containment integrity, ollowing this period, the containment This alternative le a modified wrelon tesaperature and prosaure incroues or the generetion of miselles resulting from should continue to provide a barrier of the first attemstive.It,like the first decer best, fuel coolant interections.
against the uncontrolled release of attemative, states an,overall wa gas generation and control, finton producta. However, in keeping containment performance s'oal and is and esee bassenat material lateractions ' with the concept of allowing for based upon preventing or mitigating the invol a tense of ennt o 4 wacee internation in coping with long. term or same seven accident phenomena as which coes debris in'.e the aredual energy release, controlled, dweribed in Alternative 1. However.
e== sala-aat do not came containment elevated wating (if provided in the instead of specifylag hardware stroeees to escoed ASME service level C design) may be ginn credit la the dulgn requirements to the rule to meet the limita for steel containments, or analysts after the initial 34 hout period goal, this allemative specifies the severv equivalent for concrete contatrunents, or to reduce the chance of containment accident phenomena that need to be signifloaat datloa of the failure.no intent of specifying in the addrawd la the design. Based upon eestainsneat ign luk rate.
dulgn analyste no reliance on analyele of thee serem accident (vt) Rodeos the pcssibility of contalrunent ventins during the tattlal 34 phenomena, the dealaner would develop containsment bypus and a loss of.
hour period to to achieve the design and propose the actual daign featums coolant soddent outside containment by objectin of high containment integrity necewary to swet ttw goal. Regulatory designing, to the extent practical, all but not to constrain use of venting guides would address items such as elemente of eyetems and subsyttems during operationif for some reason analytical methods, assumptions.
(eg. piples,lastrument lines. pump venting were the desired course of acceptance criteria and guidance on seals, best exchanger tubes, and valves) action. Alternatinly, a dwign may use dulga criteria for severe accident September 29,1995 50-P M 6
w-PART 50 o PROPOSED RULE MAKING hardware. An example of this design. nis alternative could be made This alternata e would differ from the ettemative follows:
more prescriptive by specifpng. for other alternetwes m that the esisting to CXX prevention and mitigation of example, the amount of hydrogen or Cf'5t part 50 design basis would be severe attidents molten core debns which must be modified to includt sesere accidents.
conaldered but, nevertheless. would Accordingly, the dpign requirements for (s) Ap',cobihty. The enteria of this provide designers with considerably the severe accidert equipment (e g.
section apply to the design of bght water more design flealbahty to address severe quehty assurance, equipment raclest power reactors beitig considered accident issues than Alternative 1.
s urvivabihty, redunda ncy / diversity )
for a construct on permit or operating Apphcants would be required to provide would need to be determined in relation license under 10 CFR part r:0 or analyses showing Lhet their proposed to those for traditional design basis applications undir 10 CFR part 52 on or design meets the tenteinment equipment. Different destgn-
~
after the effective date of this rule.De performance ob}ective. However, this
,cquirements may be appropriate for criteria of this section also may provide attemativa would place a heavy reliance severe accident equipment becluse of guidance in establishing the on analytical codes to predict me the low probability asecciated with requinments for other types of reactor likelrhood of severe accidents and their seven accident scenarios. This deeigns.
behavior accurately, umitations of these (b) Containment Performance analyucal codes and gaps in knowledge attemative would give the designer Objecthe. The design shallinclude a of the phenomenological progrenion of flexibility in devising proposed solutions containment system that provides a severe accidents may make such a to severe accident phenomena. Uke einst the release of radioactive heavy reliance unacceptable, unless shemative 2. this attemative would barrier a!or a period of apprealmstely sisterial bounding parameters are used. Uke nqutM apphcants k submH analysn 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following the onset of core Altematwe 1, this attemative would showing that the criteria are met. Ulte damage hnder the more hkely severe facilitate the NRC review and design alternative 2, this would place a heavy accident challenges. Following this 24 certihcation process by focusing the reliance on analytical codes to predict hour perjod, the containment should review and limiting litigation on the severe accident behavior securately and continue to maintain a barrier against severe acc6 dent phenomena which must would leave open to review and the uncontrolled release ollarge be considered; however,it would leave litigstion in a licensing hearing or design quantities of fission products. This aball open to review and litigation whether certification rulemaking whether the be accomplished by: likelihood or effects the designer has adequately addnseed designer has adequately addressed the (1) Mirumir.ing the the severe accident phenomena.
severe accident phenomena.
on containment integrity of the following Accordingly, this alternettve could plans and Schedulu severe accident phenomena:
potentially require considerable NRC (l) Uncontrolled hydrogen buming and r, view eflori prior to accepting an The plant performance requirements detonation; applicant's analytical results. Similar to described in this ANpRM are part of the hi) Interactions between molten com debns and the reactor basemat material Altemative 1, this attemative would be second phase of a program to decouple in the form of an overley on the existing siting and design criteria,in this phase.
reactor venel support structure, design basis specified in to Cf'R part 50 plarit performanca requirements for containment wall, and other structural j
materials; and justified on an enhanced safety severe accidenta,in combination with besis.
l (iii) High pressure melt ejection:
other necenary changes toto CI'R part will result in a rule that would (iv) Containment bypass and loss of Alternative 3: GeneralDesign Criterio 50'mplete the decouplire of siting and interfacing system integrity; (GDC) OnentedRule design. Currently, the Commission plans (v) Steam explosions due to fuel, in this attemative, the NRC would coolant interaction: and to publish the proposed rule for develop a set of new design comment in mid tw3 and to pubbsh the (2) Not crediting use of containment requirements that would include final rule in mid.1W4.
venting during the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period defintilon of specific challenges posed following the oneet of core damage in bv severe acc6 dents and issue them as Spedfic Considerations evaluating the design for compliance e..fianges or additions to appendix A.
1%e NRC invites comments and with the containment performance Ceneral Design Criteria" (GDC), to 10 objective in paregraph (b) abose.
CFR part 50. Each new GDC would recommendations from interested (c) Equipment Survivob//ity. Features describe the nature of the severe pmm on se m aI a " for th' providedfor uvere accident prevention accident challenge or containment losd proposeMma ing or a d al and mitigation shall be designed to alternatives. lf desired. Furthermore, the operste for the time period needed in the as well as a euccen criterion. Usually, success would be defined simply as NRC requests comments and supporting environment (e g., pressure, tempersture* maintenance of the containment I'{ lowing quuum al and technicalinformation on the radiation)in which the equipment is to relied upon to function, including function for an appropriate period conalderation of the circumstances of following the particular chauenge.
- 1. Is a rulemaking addressing severe apphenble initiating events (e.g.,
Regulatory Culdes would be developed accident plant performance criteria to provide additional guidance on items desirsble? If so, why? If not, why nott transients. loss of AC power. loss of coolant accidents)-
such as analysis methods and Would a rule provide better cobenoce assumptions.The ACRS outlined tus and predictabihty to the destgn review The approach in this phenomena.
oriented themative would be similar to approech in more detailin a letter to and certification procenes for future the hardwart oriented alternative in NRC Chairman K. Cert, dated May 17 reactor designs or is rulemaking on g gg'a thana issues via individual design that it is prescriptive regarding the certification sufficient?
severe accide it phenomena which must be addressed in the design: however, it ne gae p.6ne om.ent a, esm swet, ww.
pes.wy ammhMs Nudm seestewr a
doee provide flexibthty Ior the destgnet gtm ime,m htr. Thomes Kms. Ofta of Nudm washineten,tc ameeeorw m commm.as we.hy.n. oc ms, s*phee n
b propose solutions specific for the
...aetae tr 120**bwea 50 PR47 September 29,1995
3
,s RMtT 50 e PROPOSED RULA MMONG
-1. Would a now rule in 10 CFR part 30 generation) or le e generel etewment of and 2 (i.e., co,ntainment shall provW a
'a plant performance for severe the challenge enor, useitablef barriet agelnet the release of radioactive eeddente, ao discuand in b three
- 7. For what reason ma.e'kllot period of apprealmetely alterneuvea, provide a basis for revising significant;S-- :n(ed not a risk note oest 24 heure foi las the eneet of core ne reguleomente on lanersency erective solution) would any of the damage) represente a level of ofety for planning F.enes for future LWRef if so, crHerta proposed in the tiuse e agge Mwt plant sitedin scoordence why? If not, why nott ellerneuves not be luuy appl 6 cable to with10 CPR pett100 approalmetely 8.One opuen for an overall
- Passin deetped LWRet three ordere of magniques below the easteinment y.L, 3 criterion that
- 8. What featume sound an advenood rww quanutduve health e
bee been eensidered is that the LWR design include that would prevent eenetienet fedwe buityof the et mitigste fuel coolant laterecuenot obiootive for presept fatakties,as dennedin de rww SoldyGod e
sentainment beless than
- p. U e design includes the espebelHy le es eyews, policy Statement. It osund be segued thet ahnstely one in ten.Two of the git sh.
ovos use e determinieuc be to how e a future LWR design moeues this surngels that states that the soecese sevHy design and/or a reactot obinun andyen and b sentainment should remain leak tight for wesel support Mrustum capable of.
inocepereum delen feMuem ned
,j Weg a @
not consider the addition of othet d *ppo se feetwee, since these othw feetwee g,
after that tasse, remain a barrier egelnet
- 10. Should future LWR designe include would be directed at even more highly the uncontrolled release of radioactivity ; en m-line lastrumentation system that - unkholy seven aceident, m-when faced with shouence from b monitore containment atmeephere fee and esquences whieb seuld be see,e bly seem accidem "- ~ _ pas leakage le mduce the elsk hem an considered " remote end speculative" --
le this einerton a cultable eukeutete for
- Mm byenes of eenteinment undw de NeuenelEnvimamentalPolicy the eenesional eentainawat failure fumouent Would application of this Act (NEPA St.
probability of one in lent if os, explain system be sufholent beels to mesfy leek herefore, w) and 10 CPR ould the hostion and why. U not, emplain why not le a period rate tuting mquimmente under 10 CFR - cosapilense with euch a containsment -
of approalmstely 34 houre en put to, appenas i " primary Reactor performance objective be sufficient to appropriate une freaw? le its degen of Containment Leakage Teeung for eles defnm o point of truncation and conserveuses appropriate considering Water Cooled power Reacters" serve so the beste lot u amendment to uncertannues and defense in depth? If
- 11. What design critetta should be not, what alternative would be dmloped that swovide anwence that 10 CFR poet $1 eliminaung the need for further review of SAMDAs for future I
appropriew? What other criteria tie containewet e lategrity eeund easily LWRe under10 CFR part 31f tw durisis certain shutdows:
(probe or determinieuc) might be yta
'fk v6ews empened in
- 4. Alternetin a would requin g,,,,e ano m,u. meni,,ov
,. eb u=u -,.6a e aa-subouw e at prewauen or
~ h ama8**u mesiwd la entenetw mHane a map""i tools mitigetion be subhto (a)the same any esse 1NRC wulpeevide m 8* "3*"'*" 8" '8""
1 mguiraneau a baie equipmeni opputunity for aldhknelpublic
^ " * * *
(es., adundancy/divmay, comment on my propmod nde MNM*,,",'$dr yuppl on, dmloped H e ruult d this estia.
$g,f euch e, Specificatione, maintenanos priority.
IM of Sublestein to CFR post og o
y.
they, and fee what phenomene could 988 888"'**8 4 8' N I#88' Anutrust, Classined information, 4,
e ed design maagine Criminal penslues. Fire protocuen, they be used? How would altweetive a he 8 rb---a-df For saample, abound
" de E
Inompereuen by h,
,.,g,n.e.gseA,,e,,,,,',T.gitoryCuide b esdes and pa, emete,o be ppe e
- FP'md by gShould soseptance i.e.g nmenia,eiem Neae.,
u,,
artterte be scened or put in a regulatory standania, what standards would be pe*wr pianu and mecton, Rassum gg g::t _ Reester el'.ups criteria, Suidet 8.
tornative 1 discusses not R*Pormigand u # M 5.Should futwe LWR containement eacoeding ASME service level C strose
'*luimawate, deigns include feetwet twyond those limits for steel containmente under described in alterneuve 1 to yevent/
certeln severe accident eenditione. Am
.fk embrh d****"a,*u em# duum tw ese mi le severs accidente? !! so, what these limite a to for severe I"let pub a M,to em f
accident tionet if not, what 14alu Stat. se ended (42 U.S.C. satt);
tree its be loads nw aan se e a at kW'*t0l d**cllllr";'ol" c"S"e""""':ht e, g,: e'r, r + m e =d der ve is the same; there other severe soc / challenges. An mr equivalent ihmite appropriate ident ;"- -/ for concrete containmentet
- 14. What infonnation le evallable FwumNabu ' '-- " -
ehe that abooid be esoswidwedf What be b criterie for deciding - - regarding the coste (oepital and whether a severe accident mene oPeretional/ maintenance) of design Samuel B.thek, et ehelleeg le likely and be featume that would be required undw seenwy e/she Conunisien.
1
'- " a Should the challenges be -
these thermativeef aposined la moet detail (for example, 18.De contelament performance f
spoeilytag the asnount of hydrogen obloctin discussed in Alwrneuves 1 98Plember 29,1995 50 PR 18
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