Information Notice 2006-10, Use of Concentration Control For Criticality Safety
| ML060880311 | |
| Person / Time | |
|---|---|
| Issue date: | 04/23/2006 |
| Revision: | 0 |
| From: | Pierson R C NRC/NMSS/FCSS |
| To: | |
| References | |
| IN-06-010 | |
| Download: ML060880311 (5) | |
April 23, 2006
NRC INFORMATION NOTICE 2006-10:USE OF CONCENTRATION CONTROL FOR CRITICALITY SAFETY
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 informaddressees of a concern about the use of concentration control for criticality safety as the primary nuclear criticality safety (NCS) control for unsafe-geometry vessel It is expected that licensees will review this information and consider actions, as appropriate, to avoid similarproblem Suggestions contained in this IN are not NRC requirements; therefore, no specificaction 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 identify accident scenarios leading to criticality and develop, implement, and maintain reliable controls to ensure that inadvertent criticality is highly unlikel Typical criticality safety analyses identify credible accident sequences leading to criticality; identify bounding assumptions related to the processes, equipment, or material being analyzed; and establish limits or boundaries of processes, equipment, or material that comply with corresponding bounding assumption Criticality may be deemed not credible when inherent features of the process, equipment, or material in a specific accident sequence leading to criticality can be shown to constrain the reactivity of fissile material within subcritical limit The safety concern arises when accident scenarios leading to criticality are deemed not credible, based on bounding assumptions that are less than optimal for the system involve During a recent review of criticality safety analyses at a fuel cycle licensee facility, NRCinspectors noted routine sampling results showing concentrations near a licensee-proposed bounding concentration value in an unsafe-geometry tan The fuel cycle licensee relied solelyon concentration control to maintain safety in an unsafe geometry tan The licensee asserted that the NCS method for controlling concentration in the tank was by limiting the concentrationin the waste stream leading into the tan The licensee stated that the waste stream solutionwas uniform on entry to the tank, and that settling could not result in an unsafe concentration. The analysis demonstrated that by regulating the waste stream concentration to 0.06 gramsuranium-235 (U235)/liter (0.227 grams U235/gallon), the overall concentration in the tank wasguaranteed to remain below the maximum-assumed concentration of 8 grams U235/liter (30.28 grams U235/gallon). However, the licensee performed chemical analysis on settled solids in the tank and determinedthat the solids contained fissile material near 8 grams U235/lite As part of routine sampling, thelicensee found a sample with a concentration of 7.74 grams U235/liter (29.30 grams U235/gallon). The licensee sparged the tank, but only in instances where a sample was to be extracted fromthe waste solutio The sparging was not credited with, nor used to maintain uniformity in, the tan
DISCUSSION
The effective use of concentration control requires a system in which concentration changesare well-understood and controlle NRC is concerned that, in this instance, the licenseemaintained the use of concentration control as the single parameter for assuring criticality safety without adequately maintaining a uniform solution and without treating settling in the tankas an upset conditio In this case, the U235 concentration limit was chosen from expectedconcentrations in the tank as a result of limiting inlet waste stream concentration The licensee determined that 8 grams U235/liter (30.28 grams U235/gallon) would bound all knownU235 concentrations in the unfavorable tank Without ensuring uniformity within the tanks, it iscredible for settling to occur in the solutio The idea of settling within the tank was not considered as an upset condition in this cas Had possible accumulations of settled solids been further evaluated, it may have been shown to be credible for fissile material concentrations in settled solids to exceed the 8-gram (0.018-pound) limit. An inappropriate use of concentration control was highlighted in an earlier notice (IN-2004-14),on use of a limit on uranium concentration that was less than bounding for the process in which it was applie A licensee determined that mass controls would limit the uranium concentrationin the incinerator ash to less than 21.6 percent throughout the incinerator syste However,material control and accountability (MC&A) sampling data showed concentration levels above21.6 percent uranium in some parts of the incinerator syste Although the IN focused on theneed to establish appropriate interactions between criticality safety and MC&A staff, it also provides another case which exemplifies the need, when using concentration control, for licensees to ensure that they adequately capture all credible bounding scenarios which could potentially impact their syste Licensee NCS staff should fully understand their systems and all changes that could upsetconcentration control in the syste Staff should also ensure that all credible scenarios areaddressed, and that analyses governing the process bound all such scenario During future inspections, NRC inspectors will review systems using this control to ensure that propercontrols are in place and that they are properly implemente
CONTACT
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:
Natreon Jordan, NMSS301-415-7648 E-mail: njj@nrc.gov
Enclosure:
List of Recently Issued NMSS Generic Communications
CONTACT
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:
Natreon Jordan, NMSS301-415-7648 E-mail: njj@nrc.gov
Enclosure:
List of Recently Issued NMSS Generic CommunicationsADAMS ACCESSION #: ML060880311OFCFCSS/TSGTech EDIMNSFCSS/TSGFCSSNAMENJordanEkraus by faxAMcIntoshMGallowayRPiersonDATE3/ 30 /06 4/ 09 /064/ 20 /064/ 20 /064/ 23 /06 EnclosureIN 2006-10Recently Issued NMSS Generic Communications DateGC No.Subject
Addressees
01/26/06RIS-02-15,Rev. 1NRC Approval of Commercial DataEncryption Products For theElectronic Transmission OfSafeguards InformationAll authorized recipients and holders ofsensitive unclassified safeguardsinformation (SGI).01/24/06RIS-06-01Expiration Date for NRC-ApprovedSpent Fuel Transportation RoutesThe U.S. Nuclear Regulatory Commission(NRC) licensees who transport, or deliverto a carrier for transport, irradiatedreactor fuel (spent nuclear fuel (SNF)).01/13/06RIS-05-27,Rev. 1NRC Regulatory Issue Summary2005-27, Rev. 1, NRC TimelinessGoals, Prioritization of IncomingLicense Applications andVoluntary Submittal of Schedulefor Future Actions for NRC ReviewAll 10 CFR Parts 71 and 72 licenseesand certificate holders.03/21/06IN-02-23,Supl. 1Unauthorized Administration ofByproduct Material for Medical UseAll medical licensees.01/19/06IN-06-02Use of Galvanized Supports andCable Trays with Meggitt Si 2400Stainless- Steel-jacketed ElectricalCablesAll holders of operating licenses fornuclear reactors except those who havepermanently ceased operations and havecertified that fuel has been permanentlyremoved from the reactor vessel; and fuelcycle licensees and certificate holders.Note: NRC generic communications may be found on the NRC public website athttp://www.nrc.gov, under Electronic Reading Room/Document Collections.