1、An American National StandardPublished by the American Nuclear Society 555 N. Kensington AveLa Grange Park, IL 60526ANSI/ANS-8.27-2015Burnup Credit for LWR FuelANSI/ANS-8.27-2015ANSI/ANS-8.27-2015 American National Standard Burnup Credit for LWR Fuel Secretariat American Nuclear Society Prepared by
2、the American Nuclear Society Standards Committee Working Group ANS-8.27 Published by the American Nuclear Society 555 North Kensington Avenue La Grange Park, Illinois 60526 USA Approved November 10, 2015 by the American National Standards Institute, Inc. American National Standard ANSI/ANS-8.27-2015
3、 Inquiry Requests Inquiry Format The American Nuclear Society (ANS) Standards Committee will provide responses to inquiries about requirements, recommendations, and/or permissive statements (i.e., “shall,” “should,” and “may,” respectively) in American National Standards that are developed and appro
4、ved by ANS. Responses to inquiries will be provided according to the Policy Manual for the ANS Standards Committee. Nonrelevant inquiries or those concerning unrelated subjects will be returned with appropriate explanation. ANS does not develop case interpretations of requirements in a standard that
5、 are applicable to a specific design, operation, facility, or other unique situation only and therefore is not intended for generic application. Responses to inquiries on standards are published in ANSs magazine, Nuclear News, and are available publicly on the ANS Web site or by contacting the ANS S
6、cientific Publications and Standards Department. Inquiry requests shall include the following: (1) the name, company name if applicable, mailing address, and telephone number of the inquirer; (2) reference to the applicable standard edition, section, paragraph, figure, and/or table; (3) the purpose(
7、s) of the inquiry; (4) the inquiry stated in a clear, concise manner; (5) a proposed reply, if the inquirer is in a position to offer one. Inquiries should be addressed to American Nuclear Society ATTN: Scientific Publications and Standards Department 555 N. Kensington Avenue La Grange Park, IL 6052
8、6 or standardsans.org American National Standard ANSI/ANS-8.27-2015 American National Standard ANSI/ANS-8.27-2015 i Foreword (This foreword is not a part of American National Standard “Burnup Credit for LWR Fuel,” ANSI/ANS-8.27-2015.) Burnup credit is a term commonly used to account for an overall n
9、egative reactivity effect resulting from irradiation. In order to apply burnup credit, there needs to be both supporting analyses and implementation steps (such as procedures, burnup assignments, and verification techniques). Including burnup credit in the design and operation enables much improved
10、flexibility (e.g., wider range of acceptable fuel) and efficiency (e.g., higher loading capacities), as compared to spent fuel system designs based on unirradiated fuel without credit for fixed burnable absorbers. These advantages have encouraged burnup credit to be applied in the nuclear criticalit
11、y safety evaluation of storage, transportation, and disposal systems containing irradiated fuel. The scope of this standard is restricted to burnup credit for commercial light water reactor fuel applications. Burnup credit requires evaluation of the effect of irradiation on the fuel composition, whi
12、ch increases the computation complexity. However, the negative reactivity determined through burnup credit may be used to reduce the overall complexity of maintaining criticality safety. Several American National Standards Institute/American Nuclear Society (ANSI/ANS) standards provide guidance that
13、 is relevant to burnup credit. This standard supplements the guidance given in those standards and provides requirements and recommendations for handling the unique issues associated with the implementation of burnup credit. The 2015 revision to this standard was limited to two clarifications in the
14、 text of the standard. First, it clarified the combined validation approach given in Sec. 5.2 by adding a second paragraph which introduces a new term, kd, which is an allowance for the bias and uncertainty in bias of the change in k with irradiation. Second, the 2015 revision makes it clear that th
15、e burnup uncertainty can be statistically combined with other uncertainties. In addition to these clarifications, an appendix on boiling water reactor pool burnup credit was added. This standard might reference documents and other standards that have been superseded or withdrawn at the time the stan
16、dard is applied. A statement has been included in the reference section that provides guidance on the use of references. Working Group ANS-8.27 of ANS Subcommittee 8, Fissionable Materials Outside Reactors, drafted this standard. The following members participated in the preparation: D. B. Lancaster
17、 (Chair), NuclearC C. T. Rombough (Secretary), CTR Technical Services, Inc. S. Anton, Holtec International S. P. Baker, TransWare Enterprises, Inc. A. Barto, U.S. Nuclear Regulatory Commission K. L. Bennett, GE Hitachi Nuclear Energy M. C. Brady Raap, Pacific Northwest National Laboratory J. P. Cole
18、tta, Duke Energy J. C. Hannah, Global Nuclear Fuel E. Knuckles, Individual Z. Martin, Tennessee Valley Authority J. R. Massari, Constellation Energy American National Standard ANSI/ANS-8.27-2015 ii D. Mennerdahl, IndividualSweden W. A. Metwally, University of SharjahUnited Arab Emirates D. Mueller,
19、Oak Ridge National Laboratory P. Narayanan, TransNuclear, Inc. C. V. Parks, Oak Ridge National Laboratory H. Pfeifer, Nuclear Analysis Company International M. Rahimi, U.S. Nuclear Regulatory Commission D. A. Thomas, AREVA Inc. K. Wood, U.S. Nuclear Regulatory Commission A. Zimmer, General Atomics J
20、. F. Zino, GE Nuclear Energy The following is a list of people who supported the working group but were not able to actively participate throughout the entire process: A. Attard, R. Beall, J. Boshoven, D. Cacciapouti, K. Cummings, M. DeHart, M. DeVoe, J. Dunlap, D. Galvin, J. Gulliford, R. Hall, L.
21、Hassler, R. Hommerson, D. Hutson, R. Jones, J. Kessler, L. Kopp, V. Kucukboyaci, R. Kunita, A. Machiels, L. Markova, W. Marshall, M. Mason, R. McKnight, V. Mills, S. Mitake, G. OConnor, P. ODonnell, H. Toffer, S. Turner, J. Wagner, G. Walden, C. Walker, A. H. Wells, B. Wilson, C. Withee This standar
22、d was prepared under the guidance of ANS Subcommittee 8, which had the following membership at the time of its approval: L. E. Paulson (Chair), GE Hitachi Nuclear Energy M. Crouse (Secretary), Link Solutions, Inc. J. S. Baker, Savannah River Nuclear Solutions E. Elliott, Los Alamos National Laborato
23、ry D. Erickson, Savannah River Nuclear Solutions A. S. Garcia, U.S. Department of Energy B. O. Kidd, Babcock the word “should” is used to denote a recommendation; and the word “may” is used to denote permission, neither a requirement nor a recommendation. 3.2 Limitations The definitions given below
24、are of a restricted nature for the purpose of this standard. Other specialized terms are defined in Glossary of Terms in Nuclear Science and Technology 5 and Glossary of Nuclear Criticality Terms 6. 3.3 Glossary of terms burnable absorber: A burnable absorber is a material added to the fuel assembly
25、 to control reactivity via neutron absorption, mainly near the beginning of the fuel life. As irradiation progresses, the burnable absorber is converted to a less absorbing material. If the burnable absorber is physically part of the fuel assembly (nonremovable), it is said to be “fixed.” Otherwise,
26、 it is said to be “removable.” Integral fuel burnable absorbers are part of the fuel inside the cladding and are a form of fixed burnable absorber. Reference to burnable absorbers in this standard unless otherwise noted is meant to address only the fixed type. burnable absorber credit: Burnable abso
27、rber credit is the accounting for an overall reduction in reactivity associated with the presence of fixed burnable absorbers. Since the irradiation of fuel with burnable absorbers could result in increased reactivity early in its life, taking credit for burnable absorbers in irradiated fuel require
28、s depletion analysis. “Gadolinium credit” is an example of burnable absorber credit. burnup: Burnup is the amount of energy released from a region of a fuel assembly per initial mass of actinides (e.g., uranium and plutonium) in that region. The region could be a complete fuel assembly or some part
29、of the assembly. The specifications of the appropriate regions are normally clearly defined for each application to avoid ambiguity, e.g., assembly-averaged burnup, node-averaged burnup, or rod-averaged burnup. Examples of units for a uranium-based fuel with this region-specific burnup are megawatt-
30、days per tonne of initial uranium and gigawatt-days per tonne of initial uranium. Since burnup is normalized to a mass, it is also known as specific burnup. burnup credit: Burnup credit is the accounting for an overall reduction in reactivity associated with the irradiation of fuel in a reactor and
31、with cooling time. Burnup credit is a criticality safety control that includes both analysis and implementation. cooling time: The time following fuel irradiation during which radioactive decay results in changes in fuel composition. depletion analysis: Analysis of the change of the concentration of
32、 one or more specified nuclides in a material or one of its constituents. American National Standard ANSI/ANS-8.27-2015 3 irradiation: The exposure to ionizing radiation within the reactor. Irradiation refers to the exposure of the fuel (including burnable absorbers) to neutrons, and the subsequent
33、results of fission and transmutation within the fuel. 4 Criteria to establish subcriticality The calculated multiplication factor kpplus allowances for biases and uncertainties shall be equal to or less than an established, allowable neutron multiplication factor; i.e., ,p p i bc c x mkkkkkkkk+ + +
34、(1) where: kpis the calculated multiplication factor of the model for the system being evaluated. The kpshall include a bias correction if there is a negative bias due to modeling issues not addressed in the other terms; kpis an allowance for statistical or convergence uncertainties, or both, in the
35、 determination of kp, material and fabrication tolerances, uncertainties due to geometric or material representation limitations of the models used in the determination of kp; kiis an allowance for the bias and uncertainty in kpdue to depletion uncertainty in the calculated nuclide compositions. kim
36、ay be zero if the nuclide compositions are determined in a manner that assures a bounding neutron multiplication factor kp. See Sec. 5 for more information; kb is an allowance for uncertainty in kpdue to uncertainty in the assigned burnup value. kbmay be zero if it is accounted for by a reduction in
37、 the assigned burnup value as described in Sec. 7.2. Also, kbmay be zero in burnable absorber credit when the maximum multiplication factor during irradiation is used in the criticality safety evaluation. kcis the multiplication factor that results from the calculation of the benchmark criticality e
38、xperiments using a particular calculation method and nuclear cross-section data. The criticality experiments used as benchmarks in determining kcshould have physical compositions, configurations, and nuclear characteristics similar to those of the system being evaluated. If the system being evaluate
39、d has parameter(s) beyond the area of applicability established by the benchmark criticality experiments (i.e., the benchmark applicability), then the benchmark applicability may be extended by using trends in the calculated values of kcwith the parameter(s). For large extensions, the use of trends
40、should be supplemented by use of other calculation methods. The term kcaccounts for the bias relative to the benchmark criticality experiments (the bias equals kc 1).3)See ANSI/ANS-8.24-2007 (R2012) 3 for further requirements and recommendations on the benchmark applicability and extension 3) When t
41、he benchmark keffvalue does not equal 1.0, then a normalized calculation keffvalue should be used to establish trends and extensions to the benchmark applicability. American National Standard ANSI/ANS-8.27-2015 4 beyond the benchmark applicability. Also, see Sec. 5 for more information on the relati
42、onship between kcand kx; kcis an allowance for uncertainty in kcthat includes statistical or convergence uncertainties, or both, in the computation of kc, uncertainties in the benchmark criticality experiments, uncertainties due to extrapolation of kcoutside the range of experimental data (e.g., lab
43、oratory benchmark criticality experiments with well-characterized irradiated fuel could be limited), uncertainties due to geometric or material representation limitations of the models used in the determination of kc; kx is a potential supplement to kcand/or kcthat may be included to provide an allo
44、wance for the bias and uncertainty from nuclide cross-section data that might not be adequately accounted for in the benchmark criticality experiments used for kc. The value of kx shall be established using experimental data (e.g., individual isotope worth experiments). The term may be included part
45、ially or completely in kcand/or kcbut is included here to assure recognition of and to account for potential sources of additional bias and uncertainty; kmis a margin for unknown uncertainties and deemed to be adequate to ensure subcriticality of the physical system being modeled. ANSI/ANS-8.24-2007
46、 (R2012) 3 defines the right side of Eq. (1) as the upper subcritical limit. The terms in Eq. (1) contain allowances for biases and uncertainties. The statistical uncertainties (but not the biases) covered within each term (and sometimes in different terms) in Eq. (1) may be combined statistically w
47、ith appropriate justification and consideration of correlations. ANSI/NCSL Z540-2-1997 (R2012), “U.S. Guide to the Expression of Uncertainty in Measurement” 7, provides recommendations for treating some types of uncertainties. The kmterm is not a statistical uncertainty and thus shall not be involve
48、d in a statistical combination of uncertainties. In one method of validation, kiand kxare inseparable and are determined together. (See Sec. 5.2.) 5 Validation for burnup credit The methods of analysis used to determine the nuclide composition and the neutron multiplication factors shall be validate
49、d consistent with the requirements of this section. The validation of the burnup credit methodology may be accomplished by validation of each analysis component (i.e., analysis to determine the nuclide composition and analysis to determine the neutron multiplication factor) or by a combined validation approach where the bias and uncertainty terms from the individual analysis components are not determined individually. The extent to which an analysis relies on validation of the components separately or in combinati
