ML20207B195
| ML20207B195 | |
| Person / Time | |
|---|---|
| Issue date: | 05/27/1999 |
| From: | Poslusny C NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Shankman S NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| NUDOCS 9905280140 | |
| Download: ML20207B195 (10) | |
Text
1 Pat gg.
UNITED STATES NUCLEAR REGULATORY COMMISSION O
E WASHINGTON, D.C. 30666-0001
\\*****/
May 27, 1999 MEMORANDUM TO:
Susan F. Shankman, Deputy Director Licensing and inspection Directorate
[
Spent Fuel Project Office, NMSS Chester Poslusny, Jr., Sr. Project Officeh i
FROM:
Transportation and Storage Safety and Inspection Section Licensing and inspection Directorate Spent Fuel Project Office, NMSS
SUBJECT:
SUMMARY
OF THE APRIL 26,1999 PUBLIC MEETING j
WITH THE NUCLEAR ENERGY INSTITUTE ON DECOMMISSIONING ISSUES 4
On April 26,1999, representatives of the Nuclear Energy Institute (NEI) and the U.S. Nuclear Regulatory Commission (NRC) met at the NRC office in Rockville, Maryland. Representatives 1
of utilities and Electric Power Research Institute (EPRI) also attended the meeting. NRC j
offices represented included Office of Research (RES), Office of Nuclear Material Safety and i
Safeguards (NMSS), and Office of Nuclear Reactor Regulation. Attachment 1 is a list of attendees. Attachment 2 is a copy of NEl'a Talking Points. The meeting was noticed on April 21,1999.
The purpose of the meeting was to discuss decommissioning issues which included risk informing Part 72, probabilistic risk assessments (PRAs), the licensing process for dry cask storage designs, fuel burnup credit, and materials release. The highlights for each issue are discussed below:
Risk Informina Part 72. PRAs for Soent Fuel Storace Systems NEl discussed the need to risk inform Part 72 or interpretations thereof. Specifically, NEl recommended that risk insights be incorporated into fuel storage regulations. This revision would narrow the scope and oversight of regulatory reviews to those areas with the highest safety significance and risk for accidents and releases. NEl discussed the recent Calvert Cliffs PRA for its dry cask storage system. NEl noted that overly conservative initiating event and design criteria assumptions were used, resulting in a wcrst case dose of only about 31 mrem.
Further, NEl suggested that given the extremely low potential doses from storage systems, it might be cost effective to avoid conducting a complex PRA evaluation for the designs and, instead, require a simpler and less costly methodology or evaluation.
t Regarding excessive conservatism in the Calvert Cliffs PRA, on a case-by-case basis and with sufficient justification, the staff considers reductions in conservatism regarding interpretations of regulatory requirements. The staff noted that the interim staff guidance (ISG) process is y
continually redefining the level of conservatism in a number of areas. Regarding new PRA O Nud %l work, an in house PRA effort is underway by RES to evaluate the potential risk of fuel M
glp
[gd3 M
,,osaeono 9,0327
[pf!l/fd f
f PDR REVGP ERGN C
2 gv3
S. Shankman storage systems. The staff acknowledged NEl's comments and indicated that although the scope and depth of this effort is in the developmental stages, the staff would not rule out identifying the need to do less than a full PRA if Justified. The staff committed to keeping NEl informed about its progress in addressing the PRA.
Licensina Process for Drv Cask Da= Ions NEl raised a concem that in the reactor program, a licensee can propose complex technical changes to its license or technical specifications using the amendment process that is streamlined and timely. It was suggested that Part 72 be revised to adopt an easier and less-resource intensive process to reduce the burden for both licensees and the regulator. Further, NEl offered to develop suggestions for the revisions.
NRC staff commented that any revision to the regulations must include public participation and that steps are currently being taken to revise 10 CFR 50.59 and 72.48 to reduce the regulatory burden on licensees and mandatory staff review of changes to licenses, technical i
specifications, and certificates of compliance.
Bumuo Credit NEl discussed its frustration with the staff's current position on bumup credit that can be used in the design of spent fuel storage and transportation systems. Specifically, the suggested value of approximately 50% credit does not appear to be an attractive option for licensees if the x
required supporting analysis is extensive and expensive from a cost / benefit and timeliness perspective. Further, it was noted that the work completed by Department of Energy (DOE) did not provide significant insight for licensees because of limited applicability and attractiveness.
NEl requested that the staff provide advance copies of proposed revisions to the bumup credit ISG to foster early industry participation in the development process, enhance understanding of those issues considered most difficult by the staff, and provide an understanding of those conservatisms which are sensitive.
The staff suggested that industry take advantage of the upcoming workehop in May on bumup credit. Prior to the meeting, the staff is planning to issue an ISG revis;on to facilitate industry participation in the revision process. Further, the staff stated that it welcomes industry to provide information on benchmarking codes, since DOE was unable to identify the sources of 4
information to support its work on burnup credit. During this discussion, RES staff noted that it would be developing priority ranking for issues supporting burnup credit. NEl was invited to participate in a teleconference, prior to the May workshop, to discuss the RES Work Plan. NEl agreed to participate in such a call to be setup by RES staff.
Materials Release The staff discussed the proposed clearance rulemaking, which has not received Commission endorsement, and the recently issued NUREG-1640 which deals with dose contributions. A number of public workshops are being scheduled from August to November 1999 in locations across the country to obtain input from industry and citizens.<
S. Shankman l NEl stated that a task force is following this rulemaking. NEl is particularly interested in the l
Issue of release of materials by reactor licensees in that it is being considered i
as a performance indicator'under the new performance evaluation program being developsd for reactor licensees. Some comments on NUREG-1640 were provided regarding modeling assumptions and conservatism. NEl committed to attend each of the planned rulemaking workshops to facilitate industry input and understanding of the potential changes being developed.
Sionificant Aareements and Commitments 1.
The staff agreed to keep NEl informed of RES support for a PRA for spent fuel storage facilities and acknowledged NEl's comments on the Calvert Cliffs PRA.
2.
NMSS plans to issue a revised ISG on burnup credit and will conduct a public workshop on May 17,1999, which will be supported by NEl and interested utilities.
3.
RES will setup a teleconference, with support from NMSS, to discuss the RES Work Plan supporting burnup credit prior to the May 17,1999, meeting.
4.
NEl will support the upcoming public workshops on the clearance rulemaking.
No proprietary information was disseminated or presented at this meeting. No regulatory decisions were requested or made.
Please contact me if you wish to further discuss these issues.
Docket 72-1016 l
Attachments: 1. Attendance List
- 2. NEl Talking Points l
1 1
1 l
1
)
l l
l
Attendance List l
1 Attendance List NRC Public Meeting with Nuclear Energy institute On Decommissioning lasues April 26,1999 Name Oraanization Phone Number John Zwolinski NRR 301-415-1453 M. Wayne Hodges NMSS/SFPO 301-415-2398 Margaret Federline RES 301-415-6637 Lawrence Kokajko NMSS/SFPO 301-415-1309 Stuar1 Richards NRR 301-415-1395 Farouk Eltawila NRC/RES 301-415-5741 Aby Mohseni NMSS 301-415-6409 l
Tom King NMSS/SFPO 301-415-5790 Chet Postusny NMSS/SFPO 301-415-1341 Marty Virgilio NMSS 301-415-7358 Bill Brach NMSS/SFPO 301-415-8500 John Greeves NMSS/DWM 301-415-7437 Don Cool NMSS/IMNS 301-415-7197 Steve Redeker SMUD 916-732-4827 A.E. Scherer SCE 949-368-7501 Mike Meisner MYAPC 207-882-5700 Lynnette Hendricks NEl 202-739-8109 Albert Machiels EPRI 650-855-2054-Greg Withrow Consumers Energy 616-547 8176 l
Paul H. Genova NEl 202-739-8034 Elaine Hirou Nuclear Fuel 202-383-2163 Sidney Crawford Self 301-515-6398 Alan Nelson NEl 202-739-8110
NEl Talking Points
~
l Talking Points (Prepared by NEl)
"Bumuo Credit": Term used to define desired reductions in conservatism in the calculations e
of critical arrays of spent fuel assemblies. Bumup credit accounts for the reduced reactivity of the fuel due to the depletion of U235 and the buildup of actinide nuclides and non-gaseous fission products.
Current regulations and regulatory practice for criticality safety for spent fuel storage and transportation systems require a demonstration of subcriticality under prescribed conditions:
Subcriticality is assured when k,, < 1.
The allowable k., is then reduced from 1 to account for such things as modeling and calculational biases and uncertainties.
Additionally, the allowable k,is further reduced by applying an arbitrary criticality safety margin of 5% (i.e., Dk = -0.05).
Fuel can only achieve criticality when immersed in water. In situations where the water e
cannot be precluded (e.g., loading of the fuel into a cask or canister in unborated water and/or accident scenarios), the water is assumed present.
Finally, the actual state of the spent fuelis ignored. It is assumed to be in its most reactive condition. That is, the fuel is assumed to be fr.gph fuel.
it is only the factor that burnup credit seeks to change.
e 1
NRC concems that are delaying acceptance of burnup credit for design of storage and e
transportation systems involve uncertainties in the characteristics of spent fuel and the possibility of misloading.
Without BUC, there is a capital cost and safety penalty resulting from the need for more storage or transportation devices and facilities:
Increased exposure and risk to operators and the public, due to more handling and e
transportation for a given amount of spent fuel could be about 30%.
Overall cost to the US economy, resulting from the conservative designs that use the fresh fuel assumption has been estimated at about $1 billion.
NRC regulates SNF in pools according to 10CFR50; independent dry storage is regulated by 10CFR72; transportation of spent fuel is regulated by 10CFR71 and disposal of HLW is regulated by 10CFR60 and 10CFR63.
Approval of bumup credit will not be an unprecedented action, its acceptance and use is becoming common worldwide for spent fuel transport. It is common in other spent fuel management applications such as storage in pools and reprocessing. Although these other approvals and applications may differ from what we're discussing here, their approval sends a clear message. Examples include:
BUC has been permitted in France for reprocessing and for transportation of spent fuel, in the UK, BNFL intends to use BUC in shipment of fuel. BNFL has submitted a Trial e
Safety Assessment to their regulatory authorities.
2 BUC is used in the US for design of PWR spent fuel pools, with consideration of e
accidental loading of one new assembly in the most critical position (Reg. Guide 1.13).
There are additional requirements for boron concentration in the pool water DOE OCRWM has developed two different BUC approaches, one by the Washington DC Headquarters, for PWR spent fuel packages (storage and transportation), and one by the Yucca Mountain Site Characterization Office, for the post-closure phase of the spent fuel disposal. Key differences between the two are:
PWR only vs. all fuel Actinides only (9 or 10 isotopes) vs. a larger subset (29) of isotopes present in e
commercial SNF, including fission products.
The DOE Actinide-Only Topical Report (DOE /RW-0472) has two key versions: Rev.1 (May 1997) and Rev. 2 (September 1998). The major differences between these two revisions are:
Maximum burnup used for BUC reduced from 50 GWD/MTU to 40 GWD/MTU Fuel with enrichments above 4.05 (nominal 4) weight percent U-235 not considered e
(was 5%)
Statement added to the report that "the cask user must verify each candidate e
assembly's burnup and reduce that verified burnup by the amount of burnup uncertainty." The earlier revision discussed verification, but avoided making it mandatory.
A draft interim Staff Guidance (ISG) for BUC appears to include the following points:
Only x% of actual burnup will be credited (x = 50 has been mentioned)
Verification of burnup for each assembly may be mandated contrary to some early e
statement made at the March 2-3 Workshop Actinide-only isotopic content to be considered e
initial enrichment may or may not be limited (TBD) e The proposed draft iSG, if implemented, will negate any potential advantage of using BUC.
e It will require significant costs in terms of experimental verification and need for sophisticated analysis. The additional effort for industry and NRC might not be justified.
Given the large safety margin introduced by choosing x = 50%, the NRC approach may be acceptable if this approach is kept simple:
Assume value of burnup provided by reactor records No restriction on the value of initial enrichment up to 5%
Accept verification of bumup by simple means, such as radiation measurement (to eliminate erroneous inclusion of fresh fuel)
Risk Informing Dry Cask Storage Regulatory Process Goal: Risk inform Part 72 or interpretations deriving from Part 72 per Commission's objectives:
3 1.
Enhance Safety (Optimize design trade offs, e.g., shielding vs. heat removal; reduce complexity of designs and permutations of designs that would otherwise be necessary to accommodate different fuels; easier to fabricate) 2.
Reduce unnecessary regulatory burden. (Overly conservative designs mean casks cost more to build and/or store / ship less fuel per cask, 3.
Enhance public confidence 4.
Improve efficiency and effectiveness of regulatory process. (Not addressing generic issues up front in a risk informed manner causes licensees to have to come back for multiple amendments which take additional NRC review and licensing resources.)
Immediate Needs:
1.
Reasonable implementation of Part 72 2.
Stability 3.
Draft ISGs offer immediate opportunities to use risk insights for generic issues.
Regulatory approach should be risk informed:
1.
Does not necessarily mean need for extersive analysis 2.
Goals and methods should be consistent with safety goals and reasonable consideration of risk insights.
3.
Metrics employed should be consistent with those for operating reactors and NRC's regulatory mandate, i.e., Part 72, public exposure of 5 rem.
Program Plan for PRA:
1.
Extensive and complete PRA performed by Calvert Cliffs concluded only two events have any offsite consequences; worst case was 31 mrom whole body dose.
2.
Significant releases are not credible because accident generating enough energy to pulverize fuel to 1 micron size particles have not been identified.
3.
NRC doubts few if any scenarios could lead to 5 rem dose consequence for hazardous condition defined in 72.106(b).
4.
Cask breach is extremely unlikely and not likely to lead to significant in appreciable offiste consequences.
5.
Reducing the hazardous condition as proposed in the plan, e.g., to 100 mrem at the site boundary, looking for water contamination from a 500 year flood, changing the metric is not appropriate. One of the goal of the white paper on risk informed and performance based regulations is to ensure a consistent and coherent framework for regulatory decisionmaking. End points proposed for dry cask PRA are not in synch with approaches for other parts of NRC regulations.
6.
Potential for added insights gained for 4FTEs and 2 years of work is not a reasonable use of resources. Apply limited resources to determine if Calvert Cliffs PRA is likely to bound analyses for other sites and cask designs.
General Conservatisms in NRC Licensing of Dry Storage Systems:
Operational Conservatisms Spent fuel bundles / assemblies with limiting characteristics (maximum burnup, minimum e
cooling time, etc.) are assumed to be loaded into every location. This is never
c-4 approached in actuality. It would be rare to have even one such bundle / assembly loaded.
From both shielding and thermal standpoints, the point of loading is the most e
demanding. As time goes by, radiation fluxes and temperatures decrease away from the initial conditions.
{
For criticality control, an appropriate amount of conservatism is justifiable. The e
assumption of optimum moderation, however: is very conservative once a cask is j
loaded and sealed. Likewise, the no burnup credit assumption is extremely conservative (There must a good reason why nuclear plant operators do not continue to use these bundles / assemblies to generate power!).
From the standpoint of violating shielding and thermal limits, the consequences in terms e
of health and safety are relatively benign and would virtually be undetectable unless grossly violated. This fact, under the risk-informed regulatory approach, makes it inappropriate to include excessive levels of conservatism in the licensing approach.
Licensing Methodologies e
Thermal Limits and Models Uses single peak clad temperature point as limit, which means that all other clad e
temperatures will be below limit.
Nominal 380*C is conservative, at least for today's moderate burnups (40-45 GWdfr)
Temperature-induced failure modes are such that should the cladding fall, the fuel rod e
internal pressure (i.e., the driving force) is relieved and the failure mechanism ceases to operate. Gross degradation of the fuel does not occur.
Current regulations ignore convection, which makes the results of the analysis e
conservative in some situations.
Criticality Full credit for poisons not given (generally -75%)
e Assumes optimum moderation by water, even for sealed canister e
e No burnup credit in Parts 71 and 72 e
Shielding This area tends to have the least conservatism (actually, there have been a few non-e l
conservative surprises!
l