1、ANSI/ANS-8.21-1995use of fixed neutron absorbersin nuclear facilities outside reactorsANSI/ANS-8.21-1995REAFFIRMED May 19, 2011 ANSI/ANS-8.21-1995;R2001; R2011This standard has been reviewed and reaffirmed with the recognition that it may reference other standards and documents that may have been su
2、perseded or withdrawn. The requirements of this document will be met by using the version of the standards and documents referenced herein. It is the responsibility of the user to review each of the references and to determine whether the use of the original references or more recent versions is app
3、ropriate for the facility. Variations from the standards and documents referenced in this standard should be evaluated and documented. This standard does not necessarily reflect recent industry initiatives for risk informed decision-making or a graded approach to quality assurance. Users should cons
4、ider the use of these industry initiatives in the application of this standard. ANSI/ANS-8.21-1995American National Standardfor Use of Fixed Neutron Absorbersin Nuclear Facilities Outside ReactorsSecretariatAmerican Nuclear SocietyPrepared by theAmerican Nuclear SocietyStandards CommitteeWorking Gro
5、up ANS-8.21Published by theAmerican Nuclear Society555 North Kensington AvenueLa Grange Park, Illinois 60526 USAApproved June 12, 1995by theAmerican National Standards Institute, Inc.AmericanNationalStandardDesignation of this document as an American National Standard attests thatthe principles of o
6、penness and due process have been followed in the approvalprocedure and that a consensus of those directly and materially affected bythe standard has been achieved.This standard was developed under procedures of the Standards Committee ofthe American Nuclear Society; these procedures are accredited
7、by the Amer-ican National Standards Institute, Inc., as meeting the criteria for AmericanNational Standards. The consensus committee that approved the standardwas balanced to ensure that competent, concerned, and varied interests havehad an opportunity to participate.An American National Standard is
8、 intended to aid industry, consumers,governmental agencies, and general interest groups. Its use is entirely volun-tary. The existence of an American National Standard, in and of itself, doesnot preclude anyone from manufacturing, marketing, purchasing, or usingproducts, processes, or procedures not
9、 conforming to the standard.By publication of this standard, the American Nuclear Society does not insureanyone utilizing the standard against liability allegedly arising from or afterits use. The content of this standard reflects acceptable practice at the time ofits approval and publication. Chang
10、es, if any, occurring through develop-ments in the state of the art, may be considered at the time that the standardis subjected to periodic review. It may be reaffirmed, revised, or withdrawn atany time in accordance with established procedures. Users of this standardare cautioned to determine the
11、validity of copies in their possession and toestablish that they are of the latest issue.The American Nuclear Society accepts no responsibility for interpretations ofthis standard made by any individual or by any ad hoc group of individuals.Requests for interpretation should be sent to the Standards
12、 Department atSociety Headquarters. Action will be taken to provide appropriate response inaccordance with established procedures that ensure consensus on theinterpretation.Comments on this standard are encouraged and should be sent to SocietyHeadquarters.Published byAmerican Nuclear Society555 Nort
13、h Kensington AvenueLa Grange Park, Illinois 60526 USACopyright 1995 by American Nuclear Society. All rights reserved.Any part of this standard may be quoted. Credit lines should read “Extracted from Amer-ican National Standard ANSI0ANS-8.21-1995 with permission of the publisher, the Ameri-can Nuclea
14、r Society.” Reproduction prohibited under copyright convention unless writtenpermission is granted by the American Nuclear Society.Printed in the United States of AmericaForewordThis Foreword is not a part of American National Standard for Use of Fixed Neutron Absorbers inNuclear Facilities Outside
15、Reactors, ANSI0ANS-8.21-1995.!Nuclear criticality safety is an essential part of the safety assessment of a facility or anoperation involving fissionable material. Designers, operators, safety professionals, regula-tors, and standard writing groups dealing with non-reactor nuclear facilities need to
16、 ad-dress nuclear criticality safety. This standard provides guidance for the use of fixed neutronabsorbers as an integral part of nuclear facilities and fissionable material process equip-ment outside reactors, where such absorbers provide criticality control as required in asafety analysis.This st
17、andard was drafted by Working Group ANS-8.21 of Subcommittee ANS-8 of theAmerican Nuclear Society Standards Committee. The following members participated inthe preparation of the standard:H. Toffer, Chairman, Westinghouse HanfordCompanyR. D. Carter, Mohr and AssociatesA. S. Garcia, Argonne National
18、LaboratoryS. T. Huang, The Ralph M. Parsons CompanyN. Ketzlach, The Ralph M. Parsons Company(retired)R. A. Libby, Battelle Pacific Northwest LaboratoryR. E. Rothe, IndividualD. A. Reed, Martin Marietta Energy Systems, Inc.R. Tayloe, Battelle Memorial InstituteA. H. Wells, Science Applications Intern
19、ationalCorp.R. E. Wilson, U.S. Nuclear Regulatory CommissionThe membership of Subcommittee ANS-8, Fissionable Materials Outside Reactors, at thetime of its ballot for approval of this standard, was as follows:T. P. McLaughlin, Chairman, Los AlamosNational LaboratoryJ. C. Schlesser, Secretary, Los Al
20、amosNational LaboratoryF. M. Alcorn, Babcock have neutronabsorption properties; and are incorporated intodesigns to assure safety margins for sub-criticality as needed for normal and abnormaloperating conditions. The guidance applies tothe design, construction, and operation of fa-cilities used for
21、handling, processing, and stor-ing of fissionable materials. This guidance alsoapplies to equipment associated with the trans-portation of fissionable material.Use of fixed neutron absorbers may reduce theneed for reliance on administrative criticalitysafety controls. Such use may provide morecost-e
22、ffective utilization of the facility or equip-ment while maintaining adequate safetymargins. When fixed neutron absorbers arepresent but are not required to maintain sub-criticality under normal or credible abnormalconditions, compliance with the requirementsof this standard is not mandatory.2. Scop
23、eThis standard provides guidance for the useof fixed neutron absorbers as an integral partof nuclear facilities and fissionable materialprocess equipment outside reactors, where suchabsorbers provide criticality safety control.3. Definitions3.1 Limitations. The definitions given be-low are of a rest
24、ricted nature for the purposeof this standard. Other specialized terms aredefined in Glossary of Terms in Nuclear Sci-ence and Technology 4#.3.2 Shall, Should, and May. The word“shall” is used to denote a requirement, theword “should” to denote a recommendation,and the word “may” to denote permissio
25、n, nei-ther a requirement nor a recommendation. Inorder to conform with this standard, all oper-ations shall be performed in accordance withits requirements but not necessarily with itsrecommendations.3.3 Glossary of Termsbenchmark experiment. An experiment ap-propriate for the validation of calcula
26、tionalmethods applicable to the evaluation of theneutron absorber system.fixed moderator. A moderator with an es-tablished geometric relationship to the loca-tions occupied by the fixed neutron absorberand fissionable material.fixed neutron absorber. Neutron absorbersin solids with an established ge
27、ometric1Numbers in brackets refer to corresponding numbers in Section 6, References.1relationship to the locations occupied by fis-sionable material.in-service verification. Periodic verificationof the integrity of the neutron absorber systemsubsequent to installation.moderator. A material that redu
28、ces the en-ergy of neutrons by scattering them. Neutronabsorption is normally enhanced at lower neu-tron energies.!neutron absorber. A neutron-capture material.neutron absorber system. Any combinationof fixed neutron absorbers, fixed moderators,and other materials with an assigned nuclearcriticality
29、 safety function.nuclear criticality safety. Protection againstthe consequences of an inadvertent nuclearchain reaction, preferably by prevention of thereaction.validation. A process to demonstrate that theanalytical methods used to compute the effec-tiveness of the neutron absorber systems forcriti
30、cality control meet predetermined require-ments.verification. The establishment or confir-mation of the truth or accuracy of a fact byinvestigation, comparison with a standard, orreference to the facts.4. General Safety Considerations2The purpose of fixed neutron absorbers in crit-icality control ap
31、plications is to assure sub-criticality for normal and credible abnormaloperating conditions over the operating life ofthe facility or equipment. The nuclear critical-ity safety practices of ANSI0ANS-8.1-1983R1988!1# are applicable. Verification of theabsorbers and their effectiveness to captureneut
32、rons shall be required before the materialsare used. After the installation, there shall beverification to ensure that the neutron absorbersystem is in place as intended. The extent andfrequency of verification shall be dictated bythe impact of the environment in which theabsorbers are placed, on th
33、e absorber mate-rial properties, and on the configuration. Toestablish the effectiveness of neutron absorb-ers requires either use of applicable experi-mental data or use of analytical methods thathave been validated with suitable benchmarkexperiments. The material selection and pro-tection for spec
34、ific applications must beconsistent with the neutron absorption require-ments for the projected facility operationunder both normal and credible abnormal con-ditions. If moderator or structural materialsare needed for criticality safety in a neutronabsorber system, these materials are also sub-ject
35、to controls, analyses, and verifications asspecified in the succeeding sections.5. Requirements and GuidanceRequirements for the use of fixed neutron ab-sorbers for criticality safety control are groupedunder three topics: design, safety evaluations,and verification and inspection. These topicsshall
36、 be considered as part of the implemen-tation and application process during design,construction, testing, and operation. A qualityassurance program that meets the appropri-ate requirements of American National Stan-dard Quality Assurance Program Requirementsfor Nuclear Facilities, ANSI0ASME NQA-1-1
37、9895#, or equivalent, shall be established toimplement the activities specified in thisstandard.5.1 Design5.1.1 Fixed neutron absorbers shall be de-signed to maintain their required geometricalrelationship with fissionable materials dur-ing the intended operating life.5.1.1.1 A means of verification
38、 shall be pro-vided to determine that the design, safety, andoperating requirements are met for all neutronabsorber system components. Requirements forin-service verification shall be considered dur-ing the design of the neutron absorber system.5.1.1.2 The design shall include assess-ment of the ope
39、rating environment. Degrada-2The Appendix lists documents that contain experimental data, examples of applications, material properties, and verification ofneutron absorber characteristics.American National Standard ANSI0ANS-8.21-19952tion of the neutron absorber or materials usedto protect the neut
40、ron absorber due to chem-ical, physical, radiological, and mechanicalimpacts shall be protected against or allowedfor in the design process.5.1.1.2.1 The fixed neutron absorber shallbe designed to maintain its designed neutron ab-sorption capability during its intended operatinglife, including all c
41、redible conditions of neutronmoderation and reflection.5.1.1.2.2 Radiation effects on the neutronabsorber system over its expected life e.g., deple-tion by neutron absorption, embrittlement, andradiolysis! shall be evaluated.5.1.1.3 The design shall make allowances forprocess material variations, fo
42、r manufacturingtolerances, for uncertainties in the absorber den-sity and distribution, and for uncertainties in thenuclear properties such as the accuracy of neu-tron cross sections! of the neutron absorber.5.1.2 The neutron absorber system shall bedesigned such that the criticality safety func-tio
43、n is not compromised for all credible opera-tional and natural phenomena events for thefacility or equipment.5.1.3 The neutron absorber system shall bedesigned to prevent inadvertent removal, dis-placement, or alteration of its components.5.1.4 The design of equipment and facilitiesincorporating fix
44、ed neutron absorbers shall in-corporate human factors engineering practicesfor installation, operation, and maintenance offixed neutron absorbers.5.1.5 The requirements of operations, fission-able material accountability, and other safetydisciplines shall be considered in the design ofthe neutron ab
45、sorber system.5.2 Safety Evaluations5.2.1 The criticality safety practices of ANSI0ANS-8.1-1983 R1988!1# shall be applied.5.2.1.1 The potential for neutron absorberdegradation in the normal operating environ-ment due to physical or chemical actions andany material composition changes, and changesin
46、the material of the neutron absorber systemfor example, cladding!, shall be assessed.5.2.1.2 The impact of credible adverse envi-ronmental and operating conditions on the neu-tron absorber system, such as radiation damage,chemical reactions, fire, temperature varia-tions, pressure conditions, vibrat
47、ions, mechani-cal impacts, abrasion, corrosion, inadvertentremoval, depletion, and flooding, shall beevaluated.5.2.1.3 Any event that subjects the neutronabsorber system to physical or chemical condi-tions outside the design envelope shall requirethe reassessment of the system prior to restartof ope
48、rations.5.2.2 Safety analyses shall be based on re-sults obtained from validated calculationalmethods or results obtained from applicableexperiments. The calculational methods shallbe validated in accordance with ANSI0ANS-8.1-1983 R1988!1#.5.2.2.1 The calculational methods used shallreplicate the ef
49、fect of neutron flux depressionsassociated with localized neutron absorbers.5.2.2.2 The effect on criticality of in-homogeneity for example, neutron streamingthrough the neutron absorber material! of thefixed neutron absorbers shall be assessed.5.2.3 Evaluations shall consider manufac-turing tolerances, material substitutions, ge-ometry changes, corrosion allowance, modelingassumptions, process variables, and other rel-evant uncertainties.5.3 Verification and Inspection5.3.1 The inspection and verification planfor fixed neutron absorber systems shall con-form to the operating
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