1、rO)., iH f f) u-u DEC 08 2006 lbV AN SI/ANS ANSIiANs-B.22-1997 nuclear criticality safety based on limiting and controlling moderators This standard has been reviewed and reaffirmed with the recognition that it may reference other standards and documents that may have been superceded or withdrawn. T
2、he 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 appropriate for the faCilit
3、y. 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 conSider the use of these in
4、dustry initiatives in the application of this standard. Secretariat American Nuclear Society Prepared by the American Nuclear Society Standards Committee Working Group ANS8.22 Published by the American Nuclear Society 555 North Kensington Avenue La Grange Park, Dlinois 60526 USA Approved October 31,
5、 1997 by the ANSVANs-8.221997 American National Standard for Nuclear Criticality Safety Based on Limiting and ContrOlling Moderators American National Standards Institute, Inc. American National Standard Designation of this document as an American National Standard attests that the principles of ope
6、nness and due process have been followed in the approval procedure and that a consensus of those directly and materially affected by the standard has been achieved. This standard was developed under procedures of the Standards Committee of the American Nuclear Society; these procedures are accredite
7、d by the Amer ican National Standards Institute, Inc., as 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 Stand
8、ard is 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, does not preclude anyone from manufacturing, marketing, purchasing, or using products, processes, or proce
9、dures not conforming to the standard. By publication of this 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 publi
10、cation. Changes, if any, occurring through develop ments in 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 t
11、o determine the validity of copies in their possession and to 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. Requests for interpretation should be s
12、ent to the Standards Department at Society Headquarters. Action will be taken to provide appropriate response in accordance with established procedures that ensure consensus on the inter pretation. Comments on this standard are encouraged and should be sent to Society Headquarters. Published by Amer
13、ican Nuclear Society 555 North Kensington Avenue La Grange Park, Dlinois 60526 USA Copyright 1997 by American Nuclear Society. All rights reserved. Any part of this standard may be quoted. Credit lines should read “Extracted from American National Standard ANSIIANS-8.22-1997 with permission of the p
14、ublisher, 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 America Foreword (This Foreword is not a part of American National Standard for Nuclear Criticality Safety
15、Based on Limiting and Controlling Moderators, ANSIIANS-8.22-1997.) This standard has been in the draft stage for more than two decades with several different chairmen and several different working groups. The continuing effort over many years illustrates the consistent desire for a standard for mode
16、ration control. Diversity in the individuals in the working group and diversity in the organizations that the individuals represent have made this standard a tool that can be used throughout the complex. The interest in this standard is consistently demonstrated by the large attendance at the workin
17、g group meetings and by the large membership of the current Working Group ANS-8.22. Many ideas have been brought before the working group ranging from publication of definitive limits to a standard for general guidance specific to limiting and controlling moderators. This new standard was prepared b
18、y Working Group ANS-B.22 of Subcommittee B of the Stand ards Committee of the American Nuclear Society. This working group was composed of: J. S. Bullington, Chairman, Westinghouse Safety Management Solutions J. J. Bazley, Parallax, Inc. G. H. Bidinger, Individual C. L. Brown, Individual W. E. Cox,
19、Individual M. J. Crouse, Westinghouse Safety Management Solutions L. C. Davenport, Individual E. P. Elliot, Individual I. E. Fergus, U.S. Department of Energy A. L. Hess, Westinghouse Hanford Company J. E. Hicks, Safe Sites of Colorado, LLC. B. O. Kidd, Babcock the word “should“ to denote a recommen
20、dation; and the word “may“ to denote permission, neither a re quirement nor a recommendation. 3.3 Glossary of Terms moderation. The process of decreasing the en ergy of neutrons through successive collisions with moderator nuclei without appreciable com peting capture. moderator. A material that red
21、uces neutron energy by scattering without appreciable cap ture. Materials of prime concern are those con taining light nuclei with large scattering cross sections and relatively low absorption cross sections.2 moderator control area. An area defined by the process evaluation in which moderators are
22、limited and controlled for nuclear criticality safety. moderator control engineered barrier. A physical feature of a system specifically identified and used to limit or control the introduction of moderators for nuclear criticality safety.3 process evaluation. A document that identi ties and defines
23、 all known criticality safety con cerns; documents criticality safety assumptions, requirements, limits, and controls; and demon strates subcriticality. The process evaluation is often referred to as a Nuclear Criticality Safety Evaluation (NCSE). 4. Nuclear Criticality Safety Prac tices 4.1 Admjnis
24、trative Practices for Limitation and Control of Moderators 4.1.1. Written procedures shall include the nuclear criticality safety limits and controls for operation. These procedures should address any steps to be taken if a moderator control fails. I Examples of typical moderators are provided in Ap
25、pendix A. 1 Numbers in brackets refer to corresponding numbers in I Ezamples of typical moderator control engineered barriers Section 6, References. are provided in Appendix D. 1 American National Standard ANSI/ANS8.221997 4.1.2. Written procedures shall be provided for monitoring, testing, and main
26、tenance to ensure that the limits and controls specified in process evaluations are maintained. 4.1.3. Written procedures shall be provided for moderator sampling and analysis as required by the process evaluation. 4.1.4. Moderator control areas shall be identi fied to personnel in accordance with f
27、acility specific practices. 4.1.5. Appropriate limits and other means for moderator control shall be posted. 4.1.6. Moderator control requirements shall be included in the fire-fighting plans. 4.1.7. Combustible materials in moderator con trol areas should be minimized. 4.1.8. Training in understand
28、ing and comply ing with moderator limits and controls shall be provided to appropriate personnel as part of nu clear criticality safety training. Additional guid ance can be found in American National Stand ard for Nuclear Criticality Safety Training, ANSIIANS-B.20-1991 3. 4.1.9. Additional guidance
29、 for administrative practices can be found in American National Standard Administrative Practices for Nuclear Criticality Safety, ANSIIANS-B.19-1996 4. 4.2 Process Evaluations for Limitation and Control of Moderators 4.2.1. The process evaluation shall define the moderator control area. 4.2.2. The p
30、rocess evaluation shall demon strate that the operation will be subcritical under both normal and credible abnormal conditions. 4.2.3. The process evaluation shall explicitly identify the limits, controls, and engineered bar riers for moderator control areas. The limits shall be based on experimenta
31、l data or derived through the use of calculational methods which are vali dated as required by ANS-B.l l. 4.2.4. The process evaluation shall address properties of all materials present that could change the moderator content. Examples of properties of interest include hygroscopic, hydric, 2 absorpt
32、ive, adsorptive, and radiolytic natures of the materials. 4.2.5. The process evaluation shall address moderators present in, introduced to, or accum ulated in a moderator control area, either by design or by accident.4 4.2.6. The process evaluation shall address the distribution of the moderators wi
33、thin the fissile material and between discrete fissile material units. Nonuniform. distribution of moderators that might occur during mechanical (e.g., mix ing), thermal, or chemical processes shall also be addressed. 4.2.7. The process evaluation should address tolerances and changes in the appropr
34、iate chem ical and physical properties of the moderator. 4.2.8. The process evaluation should address the adequacy and integrity of containers used to transfer and store moderators or moderator con trolled materials in a moderator control area. 4.2.9. The process evaluation shall address moderators
35、that might be encountered during maintenance, decontamination, construction, and non-operational activities. 4.2.10. The process evaluation shall address the need for special controls involving fire pre vention and suppression. The impact of fire fighting in adjacent areas should also be con sidered
36、. 4.2.11. The process evaluation shall establish the requirements for moderator measurement necessary to ensure specified limits and controls are maintained. II 4.2.12. The process evaluation shall address the double contingency principle as stated in ANS-B.l 1. 5. Engineered Practices for Moder ato
37、r Control Areas 5.1 Moderator Control Area Barriers. Mod erator control areas shall be provided with en-4 Examples of moderators are provided in Appendix A and examples of sources of moderators are provided in Appendix B. 5 Appendix C provides an example of some aspects and con siderations to assure
38、 integrity of moderator content meas urements. gineered barriers as required by the process eval uation.6 Consideration should be given to poten tial hazards external to the moderator control areas that could compromise the integrity of the engineered barriers. 5.2 Equipment and Containers. Fissile
39、ma terial processing equipment and containers used in moderator controlled areas shall be designed, constructed, and maintained to limit and control moderators in accordance with the process eval uation. 5.3 Penetrations 5.3.1. Penetrations into a moderator control area should be minimized. 5.3.2. S
40、ystems that penetrate a moderator control area and normally contain moderators shall have limits and controls as required by the process evaluation. 5.3.3. Systems (such as ventilation ducts, com pressed gas lines, electrical conduits, and drains) that penetrate a moderator control area, but which d
41、o not normally contain moderators, shall have controls as required by the process eval uation. 5.4 Fire Prevention and Suppression 5.4.1. Fire control in moderator control areas shall incorporate the design features identified by the process evaluation. The use of non-moder ating fire suppressant me
42、dia should be con sidered. 5.4.2. Preference should be given to the use of non-combustible or fire-resistant building com ponents, equipment, and materials to reduce the probability of introducing moderator material in fire fighting activities. Examples of these barriers are provided in Appendix D.
43、American National Standard ANSIIANS.8.221997 5.4.3. Combustible materials should be min imized in moderator control areas to reduce the probability of introducing moderator material during fire fighting activities. Necessary mate rials that are combustible or not fire resistant should be maintained
44、in a manner to minimize the risk of fire. 5.5 Instrumentation and Controls. Instru mentation and controls may be used to detect or prevent the presence of moderators. Instru mentation and controls identified in the process evaluation shall be designed, installed, operated, and maintained in accordan
45、ce with site require ments. 6. References 1 American National Standard for Nuclear Criticality Safety in Operations with Fis sionable Materials Outside Reactors, ANSI! ANS-8.1-1983 (R1988). 2 Glossary of Terms in Nuclear Science and Technology. 3 American National Standard for Nuclear Criticality Sa
46、fety Training, ANSI!ANS-8.20-1991. 4 American National Standard Administra tive Practices for Nuclear Criticality Safety, ANSI!ANS-8.19-1996. When one of the standards referred to in this document is superseded by a revision, the revision shall apply. All of the references listed above are available
47、 from: American Nuclear Society 555 North Kensington Avenue La Grange Park, n. 60526 3 American National Standard ANSIIANS-8.22-1997 Appendix A (This Appendix is not a part of American National Standard for Nuclear Criticality Safety Based on Limiting and Controlling Moderators, ANSIIANS-8.22-1997,
48、but is included for information only.) Typical Moderating Materials Many materials routinely encountered in nuclear facilities can be neutron moderators. Some of these materials may be more effective moderators than water. The following list, while not complete, is intended to promote the considerat
49、ion of the possible moderating properties of materials that could be encountered. Alcohol Ammonium or other hydrated radicals Antifreeze Benelex Beryllium Biological materials Butvar Carbon (e.g., graphite, charcoal) Cane fiber board (Cellotex ) Cleaning agents Concrete Construction materials Deuterium compounds Environmental or atmospheric moisture Fire suppressants Fuel pellet binders and pore-formers Gasoline, kerosene Gloves Hands Heavy water Hydraulic fluid Hydrides Hydrocarbons and other organic materials Lubricants Oils Paint Paper and paper
