1、11American National Standard ANSI/ANS-8.15-2014ANSI/ANS-8.15-2014American National Standard Nuclear Criticality Safety Control of Selected Actinide NuclidesSecretariatAmerican Nuclear SocietyPrepared by theAmerican Nuclear SocietyStandards CommitteeWorking Group ANS-8.15Published by theAmerican Nucl
2、ear Society555 North Kensington AvenueLa Grange Park, Illinois 60526 USAApproved October 10, 2014by theAmerican National Standards Institute, Inc.Designation of this document as an American National Standard attests that the principles of openness and due process have been followed in the approval p
3、rocedure and that a consensus of those directly and materially affected by the standard has been achieved.This standard was developed under the procedures of the Standards Committee of the American Nuclear Society; these procedures are accredited by the American National Standards Institute, Inc., a
4、s meeting the criteria for American National Standards. The consensus committee that approved the standard was balanced to ensure that competent, concerned, and varied interests have had an opportunity to participate.An American National Standard is intended to aid industry, consumers, governmental
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6、s standard, the American Nuclear Society does not insure anyone utilizing the standard against liability allegedly arising from or after its use. The content of this standard reflects acceptable practice at the time of its approval and publication. Changes, if any, occurring through developments in
7、the state of the art, may be considered at the time that the standard is subjected to periodic review. It may be reaffirmed, revised, or withdrawn at any time in accordance with established procedures. Users of this standard are cautioned to determine the validity of copies in their possession and t
8、o establish that they are of the latest issue.The American Nuclear Society accepts no responsibility for interpretations of this standard made by any individual or by any ad hoc group of individuals. Responses to inquiries about requirements, recommendations, and/or permissive statements (i.e., “sha
9、ll,” “should,” and “may,” respectively) should be sent to the Standards Department at Society Headquarters. Action will be taken to provide appropriate response in accordance with established procedures that ensure consensus.Comments on this standard are encouraged and should be sent to Society Head
10、quarters.Published byAmerican Nuclear Society555 North Kensington AvenueLa Grange Park, Illinois 60526 USAThis document is copyright protected.Copyright 2014 by American Nuclear Society. All rights reserved.Any part of this standard may be quoted. Credit lines should read “Extracted from American Na
11、tional Standard ANSI/ANS-8.15-2014 with permission of the publisher, the American Nuclear Society.” Reproduction prohibited under copyright convention unless written permission is granted by the American Nuclear Society.Printed in the United States of AmericaAmerican National StandardAmerican Nation
12、al Standard ANSI/ANS-8.15-2014The American Nuclear Society (ANS) Standards Committee will provide responses to inquiries about requirements, recommendations, and/or permissive statements (i.e., “shall,” “should,” and “may,” respectively) in American National Standards that are developed and approved
13、 by ANS. Responses to inquiries will be provided according to the Policy Manual for the ANS Standards Committee. Nonrelevant inquiries or those concerning unrelated subjects will be returned with appropriate explanation. ANS does not develop case interpretations of requirements in a standard that ar
14、e applicable to a specific design, operation, facility, or other unique situation only and therefore is not intended for generic application.Responses to inquiries on standards are published in ANSs magazine, Nuclear News, and are available publicly on the ANS Web site or by contacting the ANS Stand
15、ards Administrator.Inquiry requests shall include the following:(1) the name, company name if applicable, mailing address, and telephone number of the inquirer;(2) reference to the applicable standard edition, section, paragraph, figure, and/or table;(3) the purpose(s) of the inquiry;(4) the inquiry
16、 stated in a clear, concise manner;(5) a proposed reply, if the inquirer is in a position to offer one.Inquiries should be addressed toAmerican Nuclear SocietyATTN: Standards Administrator555 N. Kensington AvenueLa Grange Park, IL 60526or standardsans.orgInquiry RequestsAmerican National Standard AN
17、SI/ANS-8.15-2014Inquiry FormatAmerican National Standard ANSI/ANS-8.15-2014-i-American National Standard ANSI/ANS-8.15-2014(This Foreword is not a part of American National Standard “Nuclear Criticality Safety Control of Selected Actinide Nuclides,” ANSI/ANS-8.15-2014.)This standard provides guidanc
18、e for the prevention of criticality accidents in the handling, storing, processing, and transportation of nineteen selected actinide nuclides. The revision revises most of the subcritical limits for the original fourteen nuclides in the 1981 standard and adds five additional nuclides, bringing the t
19、otal number of nuclides to nineteen. The nuclides were selected on the basis that they have half-lives greater than 45 days and it is judged there is sufficient knowledge of their physical properties to support evaluation of subcritical mass limits. The working group has elected to change the title
20、of the standard by referring to “selected actinide nuclides” rather than “special actinide elements.” This is the first revision of ANS-8.15 since its publication in 1981. ANS-8.15 is intended to be complementary to ANSI/ANS-8.1-2014 by providing technical nuclear criticality safety guidance for nuc
21、lides other than 233U, 235U, and 239Pu.In Footnote 5, the 1981 standard speculates that 232U and 236Pu may be “exceptions” to the correlation of critical mass with the even-number and odd-number neutron of the nuclide. Both nuclides are included in the scope of this revision with 236Pu appearing in
22、Table 2, clearly breaking the correlation. No significant advancement in understanding the criticality of californium isotopes has occurred since 1981. Consequently, the water-reflected subcritical limits for the californium isotopes 249Cf and 251Cf are brought forward to this revision unmodified fr
23、om the original standard. In addition, isotopic mixtures of plutonium, americium, and curium are not addressed in this revision. Instead, this topic has been moved from Section 6.1 of the 1981 version to an Appendix (called Appendix A). The revised standard urges users to calculate subcritical limit
24、s for mixtures using modern methods rather than use the 1981 tables. Currently, the usage of the words fissionable and fissile within the community is not consistent (see “The Heritage and Usage of the Words Fissionable and Fissile in Criticality,” Norman L. Pruvost, J. Eric Lynn and Charles D. Harm
25、on, II, LA-UR-04-6514, Los Alamos National Laboratory, September 2004). Since ANS standards can be viewed as models of proper usage, the working group has chosen to omit these words from the revision. “Modern Fission Theory for Criticality,” J. Eric Lynn, LA-14098, Los Alamos National Laboratory, Fe
26、bruary 2004, examines the understanding gained during the forty-five years since the formulation of the structure underlying the original 1981 Appendix A (primarily from “Considerations on the Probability of Nuclear Fission,” R. Vandenbosch and G. T. Seaborg, The Physical Review, 110 (2), 507-513, A
27、pril 1958) and concludes that its basis is empirical, unexplained, and “totally outmoded” (LA-14098) thus, the original 1981 Appendix A has been removed. Appendix B of the original standard was mostly composed of technical reference material and is reproduced from the original standard with no attem
28、pt to update any of the information.This standard might reference documents and other standards that have been superseded or withdrawn at the time the standard is applied. A statement has been included in the references section that provides guidance on the use of references.This standard does not i
29、ncorporate the concepts of generating risk-informed insights or a graded approach to quality assurance. The user is advised that one or more of these techniques could enhance the application of this standard.This standard was prepared by the ANS-8.15 Working Group of the American Nuclear Society. Th
30、e following members contributed to the development of this standard:Foreword-ii-American National Standard ANSI/ANS-8.15-2014C. T. Rombough, (Chair), CTR Technical Services, Inc.J. Anno, Institute of Radioprotection and Nuclear Surete-France (retired)R. Brewer, Los Alamos National Laboratory A. Clay
31、ton, Atomic Weapons Establishment-United KingdomH. Okuno, Japan Atomic Energy AgencyN. L. Pruvost (former Chair), deceasedV. Sviridov, IPPE-RussiaR. M. Westfall, Oak Ridge National LaboratoryK. R. Yates, Westinghouse Savannah River CompanyThe membership of the ANS-8 Subcommittee at the time of its a
32、pproval of this standard was as follows:L. Paulson (Chair), GE Hitachi Nuclear EnergyB. O. Kidd (Vice Chair), Babcock however, there are also other isotopes of uranium, pluto-nium, and other elements within the actinide group that are capable of supporting a chain re-action and that may be encounter
33、ed in sufficient quantities to cause concern. In many practical conditions, these nuclides may be dispersed with an effective concentration smaller than that re-quired to achieve criticality for a homogeneous metal-water mixture of infinite dimensions. This revision provides guidance for such condit
34、ions in Table 3 by tabulating subcritical concentration limits (and the associated minimum hydrogen to fissile atom ratios), which are about one-half the estimated critical concentration limit. The experimental data for nuclides other than 233U, 235U, and 239Pu are dramatically fewer. Consequently,
35、calculation results based on eval-uated neutron cross sections play a major role in providing the basis for guidance in this stan-dard. The subcritical limits in the standard are in some cases substantially less than the esti-mated minimum critical values. No experimen-tal systems containing the nuc
36、lides in the scope of this standard have achieved criticality based solely on the neutronic properties of the nuclide. Some experimental data are available for esti-mating the critical mass of 237Np and 242Pu where critical experiments have been performed with substantial fractions of these two nucl
37、ides.For the purpose of this standard, the nuclides selected are actinides having half-lives greater than 45 days.2 ScopeThis standard is applicable to operations with the following nuclides:232U, 234U, 237Np, 236Pu, 238Pu, 240Pu, 241Pu, 242Pu, 241Am, 242mAm, 243Am, 242Cm , 243Cm, 244Cm, 245Cm, 246C
38、m, 247Cm, 249Cf, and 251Cf.Subcritical mass limits are presented for isolat-ed units. These limits are not applicable to inter-acting units.3 Definitions3.1 LimitationsThe definitions given below are of a restricted nature for the purposes of this standard. Other specialized terms are defined in Glo
39、ssary of Nu-clear Criticality Terms 2.3.2 Shall, should, mayThe word “shall” is used to denote a requirement, the word “should” to denote a recommendation, and the word “may” to denote permission, nei-ther a requirement nor a recommendation.3.3 Glossary of termsnuclear criticality safety: Protection
40、 against the consequences of a criticality accident, prefer-ably by prevention of the accident.subcritical limit: The limiting value assigned to a controlled parameter that results in a sub-critical system under specified conditions. The parameter limit allows for uncertainties in the calculation an
41、d experimental data used in its derivation, but not for contingencies, e.g., dou-ble batching or failure of analytical techniques to yield accurate values.1)Numbers in brackets refer to corresponding numbers in Sec. 6, “References.”32American National Standard ANSI/ANS-8.15-20144 Nuclear criticality
42、 safety practices4.1 Administrative and technical practicesOperations within the scope of this standard shall be conducted in accordance with ANSI/ANS-8.1-2014 1, except that the subcritical limits given herein may be utilized.5 Single parameter limits for selected actinide nuclidesOperations may be
43、 performed safely by com-plying with safety limits and controls based on the appropriate subcritical mass limits given in Tables 1, 2, and 4 or the appropriate subcritical concentration limits given in Table 3.5.1 The appropriate subcritical mass limits of Table 1 are applicable only when the surrou
44、nding ma-terials can be shown to be no more effective at in-creasing neutron multiplication than enclosing the unit in a contiguous layer of the reflector to which the limit corresponds. For example, to ap-ply the water-reflected mass limit to a reflector other than water, it must be demonstrated th
45、at the system is less reactive with the surrounding material than with a water reflector.Table 1 Subcritical mass limits for unreflected, water-reflected, and steel-reflected spherical metal systems (kilograms)NuclideCrystallographic density (g/cm3)1)Subcritical mass limit (kg)Unreflected Water-refl
46、ected2)Steel-reflected3)232U 18.681 1.7 1.0 0.9234U 18.842 64. 59. 34.237Np 20.476 39. 35. 21.236Pu 19.601 3.3 1.7 1.6238Pu 19.768 6.3 5.1 3.3240Pu 19.934 27. 20. 15.241Pu 20.017 8.9 3.7 3.7242Pu 20.101 60. 55. 40.241Am 13.660 30. 24. 16.242mAm 13.717 4.5 1.6 1.7243Am 13.774 70. 65. 45.242Cm 13.407
47、8. 6. 4.243Cm 13.463 3.7 1.4 1.4244Cm 13.518 14. 11. 7.245Cm 13.574 3.4 1.3 1.3246Cm 13.629 19. 16. 10.247Cm 13.685 3.5 1.5 1.4249Cf 15.110 3.1 1.2 1.4251Cf 15.232 1.3 0.6 0.61)For practical purposes, crystallographic density is the maximum density of the nuclide under conditions of standard tempera
48、ture and pressure (see Ref 3). 2)The water reflector is 15 cm of water.3)The steel reflector is 20 cm of SS304.32American National Standard ANSI/ANS-8.15-2014Table 2 Subcritical mass limits for nuclides in metal-water mixtures (grams)*NuclideNuclide concentration at minimum critical mass (g/cm3)Subc
49、ritical mass limit (Grams)Unreflected (g)Water-reflected1)(g)Steel-reflected2)(g)236Pu 0.150 1100. 600. 450.241Pu 0.022 360. 185. 140.242mAm 0.0025 21. 11. 9.243Cm 0.028 190. 90. 80.245Cm 0.009 58. 23. 22.247Cm 0.180 1,000. 500. 350.249Cf 0.014 20. 10. 10.251Cf 0.004 10. 5. 5.1)The water reflector is 15 cm of water.2)The steel reflector is 20 cm of SS304.* These metal-water mixtures have minimum critical masses that are smaller than the metal critical mass.Table 3 Subcritical concentration limits and corresponding atomic ratios for homogeneous metal-water mixturesNuclideMax su
