Information Notice 2006-07, Inappropriate Use of a Single Parameter Limit As a Nuclear Criticality Safety Limit at Fuel Cycle Facilities
| ML060580510 | |
| Person / Time | |
|---|---|
| Issue date: | 03/31/2006 |
| Revision: | 0 |
| From: | Pierson R C NRC/NMSS/FCSS |
| To: | |
| References | |
| IN-06-007 | |
| Download: ML060580510 (6) | |
UNITED STATES NUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDSWASHINGTON, D.C. 20555March 31, 2006 NRC INFORMATION NOTICE 2006-07:INAPPROPRIATE USE OF A SINGLE-PARAMETER LIMIT AS A NUCLEAR CRITICALITY SAFETY LIMIT
ADDRESSEES
All licensees authorized to possess a critical mass of special nuclear material.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alertaddressees to a concern arising from the inappropriate use of single-parameter limits as nuclear criticality safety limits at fuel cycle facilitie It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoidsimilar problem However, suggestions contained in this IN are not new NRC requirements;therefore, no specific action nor written response is required.
DESCRIPTION OF CIRCUMSTANCES
Under 10 CFR Parts 70 and 76, certain licensees processing, storing, or handling criticalmasses of fissile material are required to analyze accident scenarios leading to criticality and provide safety limits that bound potential criticality event A fuel cycle licensee relied on asingle-parameter limit from a national consensus standard as the safety limit for the concentration of fissile material in a nonuniform aqueous solution stored in unsafe-geometry tank The licensee took the single-parameter limit for concentration of uranium-235 in uranyl nitrate solution from Table 1 of ANSI/ANS-8.1, "Nuclear Criticality Safety in Operations with Fissionable Materials Outside Reactors," and applied it as the concentration limit for a set of large unsafe-geometry tanks used to store waste wate The value chosen is considered to be always subcritical for a uniform solution and wasdesignated in the consensus standard as applying to "uniform aqueous solutions." The waste water solution was mixed and uniform on discharge to storage, but settled into solids on arrival in the storage tanks, in a verifiable manner such that the solution was nonuniform while actually in storag Although the licensee had referred to the concentration limit in parameter studies, the limit was not discussed nor justified in criticality analyses for the systems and processesinvolved.Fuel cycle facilities licensed under Parts 70 and 76 have specific limits on subcritical marginspecified in their licenses or certificate These limits on subcritical margin are typically specified in terms of effective neutron multiplication or kef The single-parameter limits in ML060580510 1Nuclear Science and Engineering: 81, 371 (1982), Subcritical Limits for Uranium-235Systems, "...three [calculational] methods were used to compute limits...a margin as small as 0.01 was occasionally considered acceptable, even though with no method was the margin asgreat as 0.02." Table 1 of ANSI/ANS-8.1 were based on a subcritical margin of between 1 and 2% k1 asnoted in technical documentation of the standar The minimum subcritical margin allowed by the license was 2% k, and the licensee did not otherwise specifically commit to this consensusstandard application in the facility licens As a result, the safety limit relied on by the licenseefor concentration control in this case exceeded the license limit on minimum subcritical margin for normal and credible abnormal condition
DISCUSSION
NRC Regulatory Guide 3.71, "Nuclear Criticality Safety Standards for Fuels and MaterialFacilities," describes methods that the NRC staff considers generally acceptable for complying with regulation This regulatory guide endorses specific nuclear criticality safety standards developed by the American Nuclear Society's Standards Subcommittee 8 (ANS-8), "Operations with Fissionable Materials Outside Reactors." NRC endorsement of a consensus standardapplies to the use of information and methodology from the standard in licensing applications.
NRC endorsement of consensus standards does not supersede approved license condition The NRC is concerned that licensees clearly understand the relationship of consensusstandards to the approved facility licens The facility license in this situation allowed the use ofexperimental data to establish safety limit Data from ANSI/ANS-8 series nuclear criticality safety standards are typically calculated by computer methods and should, in most cases, be considered analytical data.In addition, NRC is concerned about the application of limits from consensus standards withoutregard to their applicabilit In this case, the standard required aqueous solutions to be uniformfor the limits to be applicable and the underlying basis for the standard noted that subcriticalmargin may be as low as 0.0 Inappropriate use of a single-parameter limit exposes fuel cyclelicensees to the possibility of implementing inadequate nuclear criticality safety controls which,in this case, resulted in inadequate subcritical margin in an unfavorable geometry tank. NRC criticality safety inspections typically include the review of the adequacy and applicabilityof single-parameter limits used as safety limits, including the completeness and adequacy of nuclear criticality safety analyses, to ensure that controlled parameters and their associated limits are adequate to maintain fissile material operations within subcritical limit This IN requires no specific action nor written respons If you have any questions about theinformation in this notice, please contact the technical contact listed below./RA/ Robert C. Pierson, Director Division of Fuel Cycle Safety and Safeguards Office of Nuclear Material Safety and Safeguards
Technical Contact:
Tamara D. Powell, NMSS301-415-5095 E-mail: tdp@nrc.gov
Attachments:
1. Referenced Codes and Standards 2. "List of Recently Issued NMSS Generic Communications" This IN requires no specific action nor written respons If you have any questions about theinformation in this notice, please contact the technical contact listed below. /RA/ Robert C. Pierson, Director Division of Fuel Cycle Safety and Safeguards Office of Nuclear Material Safety and Safeguards
Technical Contact:
Tamara D. Powell, NMSS301-415-5095 E-mail: tdp@nrc.gov
Attachments:
1. Referenced Codes and Standards 2. "List of Recently Issued NMSS Generic Communications" ADAMS ACCESSION #: ML060580510OFCFCSS/TSGTech EDIMNSFCSS/TSGFCSSNAMETPowellEkraus by faxAMcIntoshMGallowayRPiersonDATE 3/ 3 /06 3/ 07 /063/ 09 /063/ 29 /063/ 31 /06 Attachment 1 Referenced Codes and StandardsAmerican National Standards Institute/American Nuclear Society, ANSI/ANS 8.1-1998, "NuclearCriticality Safety in Operations With Fissionable Materials Outside Reactors," ANS, LaGrange Park, Illinois Attachment 2 Recently Issued NMSS Generic CommunicationsDateGC No.Subject
Addressees
01/26/06RIS-02-15,Rev. 1NRC Approval ofCommercial Data Encryption Products For the Electronic Transmission Of Safeguards InformationAll authorized recipients andholders of sensitive unclassified safeguards information (SGI).01/24/06RIS-06-01Expiration Date for NRC-Approved Spent Fuel Transportation RoutesThe U.S. Nuclear RegulatoryCommission (NRC) licensees who transport, or deliver to a carrier for transport, irradiated reactor fuel (spent nuclear fuel (SNF)).01/13/06RIS-05-27,Rev. 1NRC Regulatory IssueSummary 2005-27, Rev. 1, NRC Timeliness Goals, Prioritization of Incoming License Applications and Voluntary Submittal of Schedule for Future Actions for NRC ReviewAll 10 CFR Parts 71 and 72licensees and certificate holders.01/19/06IN-06-02Use of Galvanized Supportsand Cable Trays with Meggitt Si 2400 Stainless- Steel-jacketed Electrical CablesAll holders of operating licensesfor nuclear reactors except those who have permanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel; and fuel cycle licensees andcertificate holders.Note: NRC generic communications may be found on the NRC public website,http://www.nrc.gov, under Electronic Reading Room/Document Collections.