1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 11311:2011Nuclear criticality safety Critical values forhomogeneous plutonium-uranium oxide fuel mixturesoutside of reactorsBS ISO 11311:2011 BRITISH STANDARDNational fore
2、wordThis British Standard is the UK implementation of ISO 11311:2011.The UK participation in its preparation was entrusted to TechnicalCommittee NCE/9, Nuclear fuel cycle technology.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does
3、 not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. BSI 2011ISBN 978 0 580 62437 7ICS 27.120.30Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of t
4、heStandards Policy and Strategy Committee on 31 July 2011.Amendments issued since publicationDate Text affectedBS ISO 11311:2011Reference numberISO 11311:2011(E)ISO 2011INTERNATIONAL STANDARD ISO11311First edition2011-07-01Nuclear criticality safety Critical values for homogeneous plutonium-uranium
5、oxide fuel mixtures outside of reactors Sret-criticit Valeurs critiques pour oxydes mixtes homognes de plutonium et duranium hors racteurs BS ISO 11311:2011ISO 11311:2011(E) COPYRIGHT PROTECTED DOCUMENT ISO 2011 All rights reserved. Unless otherwise specified, no part of this publication may be repr
6、oduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22
7、749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2011 All rights reservedBS ISO 11311:2011ISO 11311:2011(E) ISO 2011 All rights reserved iiiContents Page Foreword iv Introduction.v 1 Scope1 2 Normative references1 3 Terms and definitions .1 4 Re
8、ference systems concerned by this International Standard 1 4.1 Reference fissile media.1 4.2 Moderation conditions3 4.3 Geometrical models 4 4.4 Reflecting conditions4 5 Critical values 4 5.1 Presentation of the results .4 5.2 Requirements.4 6 Subcritical limits and margin of safety .5 Annex A (info
9、rmative) Reference fissile media6 Annex B (informative) Criticality schemes used for the calculations .7 Annex C (normative) Critical dimensions for a water reflection of 30 cm 9 Annex D (normative) Critical dimensions for a water reflection of 2,5 cm .10 Annex E (normative) Critical parameters for
10、a water reflection of 30 cm.11 Annex F (normative) Critical parameters for a water reflection of 2,5 cm 12 Bibliography13 BS ISO 11311:2011ISO 11311:2011(E) iv ISO 2011 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standard
11、s bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. 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 organiz
12、ations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in
13、the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % o
14、f the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 11311 was prepared by Technical Committee ISO/TC 85, Nuclear
15、energy, nuclear technologies, and radiological protection, Subcommittee SC 5, Nuclear fuel cycle. BS ISO 11311:2011ISO 11311:2011(E) ISO 2011 All rights reserved vIntroduction This International Standard provides specifications to establish process and equipment limits for controlling the nuclear cr
16、iticality hazard (e.g. choice of process monitoring modes, choice of equipment geometry) in facilities (outside of nuclear reactors) involving mixed uranium-plutonium oxide (MOX) fuel. The criticality risk for this type of fuel results from the presence of the fissile nuclides 239Pu, 241Pu and 235U,
17、 and from other fissionable nuclides, such as 242Pu, 240Pu and 238U, more or less neutron absorbing. The systems considered are uniform and homogeneous mixtures, moderated and reflected by water. The geometries concerned are single units of spheres, cylinders and slabs. A limited number of important
18、 safety parameter values are then selected. Actually, regarding the field of MOX fuel, there are insufficient directly representative experiments of damp powders for establishing the bias between calculations and measurements. Therefore, an inter-code comparison is done to conservatively estimate cr
19、itical values for different fissile material specifications. Because the use of calculation codes can be associated with different nuclear libraries, the preceding comparison is extended to the results obtained with the most common nuclear data libraries. Consequently, this International Standard pr
20、ovides reference critical values for the safety parameters selected. These values are determined by inter-code comparisons with an acceptable accuracy and are defined as the lowest calculated critical values of the selected safety parameters. These values will help nuclear criticality safety assesso
21、rs during their analysis to make technical prescriptions for criticality risk prevention and for production purposes. BS ISO 11311:2011BS ISO 11311:2011INTERNATIONAL STANDARD ISO 11311:2011(E) ISO 2011 All rights reserved 1Nuclear criticality safety Critical values for homogeneous plutonium-uranium
22、oxide fuel mixtures outside of reactors 1 Scope This International Standard specifies common reference critical values (of which the effective neutron multiplication factor, keffis equal to 1) for homogeneous water-moderated plutonium-uranium oxide mixtures based on an inter-code comparison of calcu
23、lated critical values. It is applicable to operations with unirradiated mixed uranium-plutonium oxide (MOX) outside nuclear reactors. A classical validation approach for these systems is difficult because of the paucity of critical experiments for MOX fuel. Various reference systems, in terms of iso
24、topic compositions, thicknesses of water reflection, and densities of oxide are evaluated by different combinations of calculation codes and nuclear data libraries (i.e. different calculation schemes, see Annex B). The critical values defined in this International Standard are the lowest of those ca
25、lculated by each of these calculation schemes and accepted as credible. The values in this International Standard are reference values and not absolute critical values. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated referen
26、ces, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 921, Nuclear energy Vocabulary ISO 1709, Nuclear energy Fissile materials Principles of criticality safety in storing, handling and processing 3 Terms an
27、d definitions For the purposes of this document, the terms and definitions given in ISO 921 apply. 4 Reference systems concerned by this International Standard 4.1 Reference fissile media 4.1.1 Description The reference fissile media are homogeneous and uniform mixtures of uranium and plutonium diox
28、ides in water. BS ISO 11311:2011ISO 11311:2011(E) 2 ISO 2011 All rights reserved4.1.2 Plutonium content The plutonium content in the mixture, wPu, expressed as a percentage mass fraction, is defined by Equation (1): PuPuUPumwmm=+(1) where mPuis the mass, in grams, of plutonium in the mixture; mUis t
29、he mass, in grams, of uranium in the mixture. Plutonium contents used in the reference fissile media are: a) wPu= 35,0 %; b) wPu= 12,5 %. 4.1.3 Oxide density ranges Two ranges of oxide (UO2+ PuO2) density, expressed in grams per cubic centimetre, are considered: up to 3,50 g/cm3, if the plutonium co
30、ntent is 35,0 % mass fraction; up to 11,03 g/cm3, if the plutonium content is 12,5 % mass fraction. NOTE The latter density is the theoretical dry density for this specific isotopic MOX composition. 4.1.4 Isotopic composition 4.1.4.1 Notation In this subclause, the following notation is used: Uim is
31、 the mass, in grams, of isotope i of uranium; mU,totalis the mass, in grams, of uranium; Puim is the mass, in grams, of isotope i of plutonium; mPu,totalis the mass, in grams, of plutonium. 4.1.4.2 Uranium The uranium composition considered corresponds to natural uranium: 235 U,totalU/ 0,718 %mm= 23
32、8 U,totalU/ 99,282 %mm= NOTE The fissile systems with depleted uranium are bounded by the natural uranium systems considered in this International Standard. BS ISO 11311:2011ISO 11311:2011(E) ISO 2011 All rights reserved 34.1.4.3 Plutonium Three plutonium compositions, P0, P5 and P20, are considered
33、: c) composition P0 is defined by: 239 Pu,totalPu/ 100,000 %mm= d) composition P5 is defined by: 239 Pu,totalPu/ 95,000 %mm= 240 Pu,totalPu/ 5,000 %mm= e) composition P20 is defined by: 240 Pu,totalPu/ 20,000 %mm= 241 240 1Pu Pu/ R 11/17mm= 242 241 2Pu Pu/ R 1/11mm= 239 240 241 240 242 241240 240 24
34、0Pu,total Pu,totalPu Pu Pu Pu Pu PuPu,total Pu,total 1 Pu,total 1 2Pu Pu Pu/1/ / /1/ (/ R)(/ RR)mm mm mm mmmm mm mm= = 4.1.5 Resulting fissile media The six reference fissile media resulting from these physical and chemical forms and from these isotopic compositions are presented in Annex A. 4.2 Mod
35、eration conditions Two water moderation degrees are considered: a) a limited moderation corresponding to a water mass fraction less than or equal to 3,0 %, according to Equation (2): 22222HOHOHO PuO UO3%mwmm m=+(2) where 2HOm is the mass, in grams, of water in the mixture; 2PuOm is the mass, in gram
36、s, of plutonium dioxide in the mixture; 2UOm is the mass, in grams, of uranium dioxide in the mixture. NOTE This degree of moderation is selected because MOX fuel is usually fabricated from mixtures of nearly dry powder and hydrogenated additives. b) optimum moderation (minimal critical values obtai
37、ned whatever the moderator-to-fuel ratio is). BS ISO 11311:2011ISO 11311:2011(E) 4 ISO 2011 All rights reservedThese moderations are considered homogeneous in the fissile medium. The mixture of MOX and water leads to a decrease in the MOX density from the theoretical density (full crystal dry densit
38、y) as the water content increases in the mixture. For each mixture of MOX and water, the sum of their volume fractions (actual density divided by theoretical density) is unity. In the case of a MOX density up to 3,50 g/cm3, an initial void fraction is defined by this maximal density divided by the t
39、heoretical MOX density. The initial void fraction then allows a certain water content in the mixture with a constant MOX density. A further increase in the water content leads to a decrease in the MOX density. For each mixture of MOX and water, the sum of their volume fractions and the void fraction
40、 is unity. 4.3 Geometrical models Critical values are given for the three following simple geometries of the fissile material: sphere; infinite length cylinder; infinite section slab. 4.4 Reflecting conditions The critical values are given for a 2,5 cm and a 30,0 cm water reflector. The water reflec
41、tor is close-fitting around the fissile material, with a free boundary beyond the reflector. 5 Critical values 5.1 Presentation of the results Annex C (for a 30 cm water reflection) and Annex D (for a 2,5 cm water reflection) specify the lowest values of critical dimensions for a sphere, an infinite
42、 length cylinder, and an infinite section slab. These critical dimensions are the radius, in centimetres, and the volume, in litres, of the sphere, the diameter, in centimetres, of the infinite cylinder, and the thickness, in centimetres, of the infinite slab geometry. The critical volume of a spher
43、e is the minimal critical volume whatever the credible fissile material geometry is. Annex E (for a 30 cm water reflection) and Annex F (for a 2,5 cm water reflection) specify the lowest values of the critical parameters for the three reference geometries, in terms of mass, in kilograms, of actinide
44、 (U and Pu) for a sphere, linear density, in grams per centimetre, of actinide for a cylinder, and surface density, in grams per centimetre squared, of actinide for a slab geometry. Each of these results is the lowest value resulting from the comparison of 12 to 17 values calculated with different c
45、alculation routes among those given in Annex B. For each value, at least four different computer codes and four different data libraries were used. NOTE 1 All the computational results are extracted from References 1 to 7. These calculations were performed with a temperature of 293 K. NOTE 2 The res
46、ults from References 1 to 7 show that the critical values for MOX with depleted uranium are not notably lower than the critical values in Annexes C to F for MOX with natural uranium. 5.2 Requirements 5.2.1 Nuclear criticality safety assessors preparing specifications relative to fissile systems desc
47、ribed in Clause 4 shall compare their own critical values with the critical values presented in Annexes C to F. BS ISO 11311:2011ISO 11311:2011(E) ISO 2011 All rights reserved 55.2.2 In the absence of technical arguments, the nuclear criticality safety assessors shall use the lowest values between t
48、heir own critical values and the critical values presented in Annexes C to F. Otherwise, they shall justify the use of higher values by safety margin considerations. 5.2.3 The nuclear criticality safety assessors shall interpret any discrepancy observed between the results of their own calculation c
49、ode and the results of this International Standard. 6 Subcritical limits and margin of safety Subcritical limits and a margin of safety shall be determined in accordance with ISO 1709. The margin of safety shall take into account the lack of applicable experiments and the interpretation required in 5.2.3. BS ISO 11311:2011ISO 11311:2011(E) 6 ISO 2011 All rights reservedAnnex A (informative) Reference fissile media Mass fraction of plutoniumawPuMOX density Isotopic composition of uraniumb%
