1、 ISO 2013 Nuclear criticality safety Estimation of the number of fissions of a postulated criticality accident Scurit de criticit nuclaire valuation du nombre de fissions en cas dun hypothtique accident de criticit INTERNATIONAL STANDARD ISO 16117 First edition 2013-10-01 Reference number ISO 16117:
2、2013(E) ISO 16117:2013(E)ii ISO 2013 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2013 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or postin
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4、htiso.org Web www.iso.org Published in Switzerland ISO 16117:2013(E) ISO 2013 All rights reserved iii Contents Page Foreword iv Introduction v 1 Scope . 1 2 Terms and definitions . 1 3 General principles . 2 4 Fissions number estimate . 3 4.1 General . 3 4.2 Input data 3 4.3 Use of simplified models
5、. 3 4.4 Use of calculation tools 4 Annex A (informative) Flow diagram of a criticality accident analysis(from ISO 27467:2009) .5 Annex B (informative) Characteristics of criticality accidents that occurred during process operation 7 Annex C (informative) Experimental results 12 Annex D (informative)
6、 Simplified formulae.18 Bibliography .24 ISO 16117:2013(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committ
7、ees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the Int
8、ernational Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the d
9、ifferent types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2. www.iso.org/directives Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall
10、not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received. www.iso.org/patents Any trade name used in this document is inform
11、ation given for the convenience of users and does not constitute an endorsement. The committee responsible for this document is ISO/TC 85, Nuclear energy, nuclear technologies, and radiological protection, Subcommittee SC 5, Nuclear fuel cycle.iv ISO 2013 All rights reserved ISO 16117:2013(E) Introd
12、uction In activities involving fissile materials, the potential for a criticality accident occurrence cannot be totally excluded. Therefore, in order to prepare emergency responses in case of such an occurrence, ISO 27467 specifies areas to be studied (Annex A) to perform the analysis of potential c
13、onsequences whenever a credible criticality accident may occur. This International Standard deals with one of these areas and is devoted to the estimate of number of fissions (also commonly named “fission yield”) for a postulated criticality accident. This topic is essential because most of the othe
14、r issues of the criticality accident analysis depend on a suitable estimate of this number of fissions. ISO 2013 All rights reserved v Nuclear criticality safety Estimation of the number of fissions of a postulated criticality accident 1 Scope This International Standard provides a methodology to es
15、timate a reasonably maximal value of the number of fissions of a postulated criticality accident. The fission number estimate, associated with its postulated criticality accident, impacts the accident emergency planning and response because it is used for the estimation of radiation doses and of rad
16、ioactive materials release. This International Standard does not provide a methodology and guidance to determine bounding accident scenarios. This International Standard does not cover criticality accident detection which is dealt with by ISO 7753. This International Standard does apply to nuclear f
17、acilities, plants, laboratories, storage, and transportation of fissile material (but not to nuclear power reactor cores) where a credible criticality accident may occur. 2 Terms and definitions For the purposes of this document, the following terms and definitions apply. 2.1 postulated criticality
18、accident postulated association of one accident scenario and one accident evolution Note 1 to entry: One postulated criticality accident is associated with one estimated number of fissions. 2.2 accident scenario set of credible, postulated conditions under which a fissile material-containing facilit
19、y/process develops one or more fault conditions such that it is likely to exceed the critical state and thus to result in a criticality accident Note 1 to entry: This definition is drawn from ISO 27467. 2.3 accident evolution progress of the criticality accident (after the critical state is exceeded
20、), taking into account physical phenomena (for example, temperature and void effects) and possible human interventions to stop it 2.4 area of applicability set of parameters (for example, environment, geometrical characteristics, fissile material, accident duration) within which a tool/model is inte
21、nded to be used Note 1 to entry: In Annex D, the last columns of the tables summarize the area of applicability of some simplified formulae. INTERNATIONAL ST ANDARD ISO 16117:2013(E) ISO 2013 All rights reserved 1 ISO 16117:2013(E) 3 General principles PREREQUISITES Once the objectives of the critic
22、ality accident analysis (analysis based, for example, on ISO 27467) are defined, one or several criticality accident(s) may be postulated. The assumptions of the postulated criticality accident, and therefore the potential consequences, are to be related with the objectives of the criticality accide
23、nt analysis (for example, design of evacuation routes, dose mapping, assembly station(s) choice). EXAMPLE 1 Because bounding assumptions may be different for radiation dose estimates and for radioactive materials release estimates, it is possible to choose a set of assumptions adapted for each estim
24、ate. EXAMPLE 2 The design of evacuation routes may be performed with an arbitrary number of fissions; the goal is to optimize the operators evacuation routes, whatever the value of the dose is. In this case, the location of the postulated criticality accident is the most important parameter. 3.1 For
25、 the estimation of the number of fissions, the following assumptions, as well as their variations, should be considered: description of the equipment (geometric configuration, reflector, etc.); degree of confinement and environment (vessel open or closed, pressure, cooling, etc.); fissile material (
26、quantity, enrichment, media, physical shape, chemical form, etc.); total reactivity addition; rate of reactivity addition; time delay before the first persistent chain reaction (function of the initial neutron source, i.e. spontaneous fissions, (alpha, n)-reactions, etc.); duration of the criticalit
27、y accident (calculated/estimated with and without intervention, where applicable). 3.1.1 The determination of these assumptions should be drawn from the accident scenario and the accident evolution of the postulated criticality accident. 3.1.2 The chosen assumptions shall be within the domain physic
28、ally possible according to the characteristics of the considered activity (characteristics of the facility, of the transportation, etc.). WARNING The estimation of the number of fissions is only the first part of the determination of the consequences of the postulated criticality accident (see, for
29、example, the flow diagram from ISO 27467 in Annex A). The overall estimation of the consequences shall take into account all the aspects of the criticality accident and iterations between estimation of the number of fissions and subsequent actions (for example, doses estimation) should be performed.
30、 For example, in case of different possible locations for a criticality accident, the postulated criticality accident leading to the highest number of fissions may not necessarily lead to the maximum doses for workers and the public because of its location. Other assumptions affecting the consequenc
31、es of the postulated criticality accident should then be considered, such as: location of the equipment, place of the criticality accident; building description; location of people; criticality accident alarm system presence/absence. 3.2 Each fissions number estimate shall be associated with an appr
32、oximated duration. Account should be made of any anticipated human interventions in the accident evolution.2 ISO 2013 All rights reserved ISO 16117:2013(E) 3.3 Number of fissions shall be determined by using simplified models (4.3 and notably 4.3.2) or calculation tools (4.4) or both. 4 Fissions num
33、ber estimate 4.1 General 4.1.1 For the estimate of the number of fissions, the use of the simplified models route (4.3) should be firstly considered. 4.1.2 The use of the calculation tools route (4.4) may then be considered, according to the objectives of the criticality accident analysis (for examp
34、le, design of evacuation routes, dose mapping, and assembly station(s) choice). This route requires: the availability of a calculation tool able to simulate the criticality accident, and the determination of all input data needed for the calculation tool. 4.1.3 In the case where the two routes of es
35、timate are used, the origin of a different order of magnitude between the two results should be understood and documented. 4.2 Input data 4.2.1 The input data needed for the simplified models or the calculation tools (geometry, external environment, media characteristics, etc.) shall be taken from a
36、ssumptions considered for the accident scenario and the accident evolution. When the accident scenario and the accident evolution do not set necessary input data, these should be measured or calculated or estimated from the international literature. NOTE Depending on the way estimates are made, the
37、type and the number of input data needed may vary. 4.2.2 The selected input data sensitivities (linked to uncertainties and possible variations pointed out in 3.1) should be studied for the chosen route(s) of estimate (4.3 and/or 4.4). This study will provide a better understanding of the uncertaint
38、ies associated with the estimated number of fissions. This study may be one possible basis for the nuclear criticality safety specialist to appropriately select a maximal estimate. Otherwise, further justifications should be made as to the applicability of the result. 4.2.3 Account shall be made for
39、 parameters that could vary significantly for the criticality accident duration. 4.3 Use of simplified models 4.3.1 The estimate of number of fissions should be based on simplified options providing “order-of- magnitude” values. 4.3.2 This estimate should rely on the collective experiences from past
40、 criticality accidents (Annex B) and criticality experiment results (Annex C) and the possible use of simplified formulae (Annex D). 4.3.3 When a simplified model is used, the consistency of its area of applicability with the chosen assumptions of the postulated criticality accident shall be justifi
41、ed and documented. NOTE The duration of the criticality accident has a significant impact on the evaluation. Actually, simplified models are mainly based on criticality experiments and past criticality accidents stopped after human intervention. ISO 2013 All rights reserved 3 ISO 16117:2013(E) 4.3.4
42、 To estimate the number of fissions, the simplified models results should be associated with the sensitivity study performed (4.2.2). 4.4 Use of calculation tools WARNING Care should be taken when using the criticality accident calculation tool results for the estimation of the number of fissions. I
43、n particular, a complete validation of a criticality accident calculation tool is presently difficult, mainly due to the complexity of models and paucity of criticality experiment and precise information from past criticality accidents. 4.4.1 The calculation tool used shall be documented, including
44、the verification of the adequate implementation of the different models (for example, neutron physics, thermal transfer, bubbles behaviour). 4.4.2 When it is possible, comparison between the calculation tool results and experiments/accidents close to the chosen assumptions of the postulated critical
45、ity accident should be documented. 4.4.3 When a calculation tool is used, the consistency of its area of applicability with the chosen assumptions of the postulated criticality accident shall be justified and documented. In case of inconsistency, the calculation tools may still be used; however, jus
46、tification for its use shall be documented. 4.4.4 Free evolution of the system during the accident duration shall be accounted for. Resulting assumptions used in the calculation should lead to a maximal evaluation of the number of fissions. 4.4.5 To estimate the number of fissions, the calculation t
47、ool results should be associated with the sensitivity study performed (4.2.2) and with other available elements (for example, results obtained from comparison with experiments, complexity of models, possible penalizing hypothesis in the models).4 ISO 2013 All rights reserved ISO 16117:2013(E) Annex A (informative) Flow diagram of a criticality accident analysis(from ISO 27467:2009) ISO 2013 All rights reserved 5 ISO 16117:2013(E) ? m T mb 1 P b g: mp g xp m L L mA h Ph pw mp b gA DTY D m h v m h h g g m m m w w ? xp m - mp g Dm ADTGYPLAGADP ADLGALQ ADATADTAATK PHY / DTT A D A
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