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1、ANSVANS-8.3-1997; R2003 critically accident alarm system -,-,- -,-,- ANCANS-8.3-1997 American National Standard Criticality Accident Alarm System Secretariat American Nuclear Society Prepared by the American Nuclear Society Standards Committee Working Group ANS-8.3 Published by the American Nuclear
2、Society 555 North Kensington Avenue La Grange Park, Illinois 60526 USA Approved May 28,1997 by the American National Standards Institute, Inc. -,-,- American Standard Designation of this document as an American National Standard attests that the principles of openness and due process have been follo
3、wed in the approval procedure and that a consensus of those directly and materially affected by the standard has been achieved. National This standard was developed under.procedures of the Standards Committee of the American Nuclear Society; these procedures are accredited by the Amer- ican National
4、 Standards institute, Inc., as meeting the criteria for American National Standards. “he 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 indu
5、stry, 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 procedures not conforming to th
6、e 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 publication. Changes, if any, O
7、ccumng 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 It may be reaffirmed, revised, or withdrawn at any time in accordance with established procedures.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 to determine the valiity of
8、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 sent to the Standards Departm
9、ent 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 American Nuclear Society 555 No
10、rth Kensington Avenue La Grange Park, Illinois 60526 USA Copyright O 1997 by American Nuclear Society. All rights reserved. Any part of this standard may be quoted. Credit Lines should read “Extracted f r o m American National Standard ANSI/ANS-8.3-1997 with permission of the publisher, the Amencan
11、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 i s not part of Amencan National Standard Criticality Accident Alarm system, A“s 8.3-1997.)
12、 The usefulness and protective features of criticality accident alarm systems have been demonstrated,in instances of accidental criticality that have occurred duruig the processing of fissionable materials. This standard provides guidance for the establishment and main- tenance of an alarm system to
13、 initiate personnel protective actions in the event of inad- vertent criticality. Preparation of the standard, begun in 1966, resulted in the issuance of N16.2-1969, and an initial revision was issued in 1979. A second revision, issued in 1986, incorporated relevant features of American National Sta
14、ndard Immediate Evacuation Signal for U s e in Industrial Applications, ANSI N2.3-1979. The 1986 revision also deleted the section that addressed emergency planning such guidance is now provided in American National Standard Administrative Practices for Nuclear Criticality Safety, ANSI/ANs-8.19-1996
15、. Most of the changes incorporated into t h i s revision of ANS-8.3 are oriented towards clar- ifcation, rather than change, of existing standard requirements and recommendations. Where concern exists for accidents of smaller magnitude than alarm systems have tra- ditionally been designed to detect,
16、 additional guidance is now provided. Use of portable instruments to augment an installed accident alarm system is now more specifically addressed. The term “immediate evacuation“ has been replaced with “person- nel protective action“ since for some shielded facilities or locations, proper immediate
17、 re- sponse by some personnel may be to remain at their current location rather than to evac- uate. This standard i s compatible with IS0 7753, Nwlear energy - Performance and testing requirements for criticcrlity detection and alarm systems. IEC 860, Warning equipment for criticality accidents, con
18、tains useful information regarding electrical characteristics and testing procedures for alarm equipment. Appendix B has been extensively revised to provide analytical methods and example applications for determining detector placement. Working Group ANS-8.3, which revised this document, had the fol
19、lowing membership: D . A. Reed, Chairman, Oak Ridge N u f w d labor ato R. E. Anderson, Los Alumos National Laboratory W. A. Blyckert, Mohr however, this risk cannot be eliminated. Where a criticality accident may lead to an excessive radiation dose, it is important to provide a means of alerting pe
20、rsonnel and a procedure for their prompt evacuation, or other protective actions to limit their exposure to radiation. 2. scope This standard is applicable to all operations in- volving fissionable materials in which inadvert- ent criticality can occur and cause personnel to receive unacceptable exp
21、osure to radiation. This standard is not applicable to detection of criticality events where no excessive exposure to personnel is credible, nor to nuclear reactors or critical experiments. This standard does not include details of administrative actions or of emergency response actions that occur a
22、fter alarm activation. 3 . Dennitions 3 . 1 Limitations. The following definitions are of a restricted nature for the purpose of this standard. Other specialized terms are defined in the Glossary of Terms in Nuclear Science and Technology C 2 1 . 3 2 2 Shall, Shouid, and May. The word “shall is used
23、 to denote a requirement, the word “should to denote a recommendation, and the word “may“ to denote permission, neither a requirement nor a recommendation. To con- form w i t h this standard, all operations shall be performed in accordance with its requirements but not necessarily with its recommend
24、ations. 3 . 3 Glossary o f Terms criticality accident. The release of energy as a result of accidental production of a self-sus- taining or divergent neutron chain reaction. excessive radiation dose. Any dose to per- sonnel corresponding to an absorbed dose from neutrons and gamma rays equal to or g
25、reater than O . 12 Gy (E! rad) in free air. minimum accident of concern. The small- est accident, in terms of fission yield and dose rate, that a criticality alarm system is required to detect. 4. General Principles 4 . 1 General 4 . 1 . 1 . Installation of an alarm system im- plies a nontrivial ris
26、k of criticality. Where alarm systems are installed, emergency proce- dures shall be maintained. Guidance for the preparation of emergency plans is provided in American National Standard Administrative Practices for Nuclear Criticality Safety, ANSI/ ANS8.19-1996 31. 4 . 1 6 . Process equipment used
27、in areas from which immediate evacuation is required should be so designed that leaving the equipment will not introduce significant risk. 4 . 1 . 3 . The purpose of an alarm system is to reduce risk to personnel. Evaluation of the overall risk should recognize that hazards may result from false ala
28、rms and subsequent sud- den interruption of operations and relocation of personnel. 4.2 Coverage 4.2.1. The need for criticality alarm systems shall be evaluated for all activities in which the inventory of fissionable materials in individual unrelated areas exceeds 700 g of U-235, 500 g of U-233, 4
29、50 g of Pu-239, or 450 g of any com- Numbers i n brackets refer to corresponding numbers in Section 8, References. 1 -,-,- Amencan National Standard ANSUANS-8.3-1997 bination of these three isotopes2 For opera- tions involving significant quantities of other fissionable isotopes, this evaluation sha
30、ll be made whenever quantities exceed the subcriti- cal mass limits specified in American National Standard Nuclear Criticality Control of Spe- cial Actinide Elements, ANSUANS-8.15-1981 (R1995) 4. Also, this evaluation shall be made for all processes in which neutron moderators or reflectors more ef
31、fective than water are present, or unique material configurations exist such that critical mass requirements may be less than the typical subcritical mass limits noted above. For this evaluation, individual areas may be considered unrelated when the boundaries be- tween the areas are such that there
32、 can be no uncontrolled transfer of materials between areas, the minimum separation between mate- rial in adjacent areas is 10 cm, and the areal density of fissile material averaged over each individual area is less than 50 g/m2. This stip- ulation is applicable only to the three specifc isotopes no
33、ted above (U-235, U-233, and Pu- 2 3 9 ) . 4.2.2. A criticality alarm system meeting the requirements of in the other, beryllium. The spike yield in the first case has been estimated to have been about 2 x los fissions; in the second, a factor of ten less. Both spikes were followed by brief power pl
34、ateaus so that the total yields were 10l6 and 3 x loE fissions, respectively. Each assembly remained critical for about one second. The person nearest each of these assemblies received a lethal exposure but some uncertainly exists in the actual doses received. For the tungsten-carbide-reflected asse
35、mbly, data are quite sparse and are complicated by the presence of heavy shielding. Several studies have been made to determine the doses from the beryllium-reflected sphere. Hankins and Hansen (see Reference A33 derived a total absorbed dose of 11 Gy at a distance of about 40 cm, based on blood sod
36、ium activation data taken at the time of the accident. Another person, who was approximately 2 m from the excursion, received about 0.56 Gy. Although each of these accidents with plutonium was terminated by deliberate action of the individual involved, after he became aware of the occurrence, they a
37、lso represent a reasonable lower bound for accidents that are terminated by an inherent shutdown mechanism. Had the critical 6 -,-,- American National Standard A“S8.3-i997 configurations not been disassembled w i t h i n a few seconds the energy release in the first minute would have been about an o
38、rder of magnitude higher. Study of the behavior of the critical assemblies adds to our understanding of the characteristics of nuclear excursions. T w o of these assemblies at the Los Alamos Critical Experiments Facility are of particular interest. Godiva is an unreflected assembly of PsU-enriched u
39、ranium designed to be operated above prompt criticality in a fast pulse mode. The temperature coefficient of reactivity for this assembly is about -3.6 x loa dollarPC, so a temperature rise of about 300C is necessary to reduce the reactivity of the assembly from prompt criticality to delayed critica
40、lity, perhaps a reasonable minimum shutdown effect. “his energy would be supplied from about 5 x loE fissions which, in turn, would result in a dose, 2 m from the assembly, of approximately 7.5 Gy. Parka is a uranium-loaded graphite cylindrical core of 91 c m diameter and 137 c m length, with a 10-c
41、m-thick beryllium refledor. For such an assembly, criticality could inadvertently occur as a result of the introduction of a small quantity of water into the assembly. If this occurred slowly, the system could exceed delayed criticality by only a modest margin before the temperature would rise to th
42、e boiling point of water and equilibrium be established at a power which would maintain a constant water content. Neglecting the steady state condition, the initial temperature rise (70C) would correspond to about 2 x loie fissions and would result in a dose, 2 m from the assembly, in excess of 15 G
43、y. The Parka assembly, in size, Wei references cited in this Appendix but first cited earlier (such as MI) are listed at the end of Appendix A B . l Introduction Determining the adequacy of criticality alarm detector placement is far from an exact process. It involves many unknowns that require tech
44、nical judgments to be made on the part of the evaluator. The goal should be to provide technically reasonable assurance that credible criticality accidents posing a potential risk to personnel will be detected. This Appendix is intended to provide general guidance for assessing the adequacy of detec
45、tor place- ment. It is not intended to be inclusive with respect to all situations likely to be encountered, nor is it intended as a substitute for facility-specific analysis. Specific examples and discussion in this Appendix assume that the minimum accident of concern delivers the equivalent of an
46、absorbed dose rate to free air of 0.2 Gy/min at 2 meters from the reacting material. However, the techniques identified in this Appendix are equally applicable for situations where the minimum accident to be detected has a different fission yield. B.2 General Considerations Prior to a discussion on
47、the methods for assessing the adequacy of criticality alarm detector coverage, two general topics are addressed: operability characteristics of the detection system, and radiation field characterization of criticality accidents. B.2.l- Operability Characteristics of the Detection System. To meet the
48、 intent of ANS8.3, it is important to have knowledge of the detection systems characteristics, such as the type of radiation being detected, spectral dependencies, dead time, the potential for saturation, and whether the system is based on a rate or an integrated quantity, to name some of these Char
49、acteristics. Detector behavior in response to a rapid transient fission pulse should be understood. For rate detectors, the effects of needle or indicator inertia on the actual detectors response should either be measured or estimated, i.e., what fraction of the peak dose does the detector actually indicate (see R