GB 15146.8-1994 Nuclear criticality safety of fissile materials outside the reactor Nuclear criticality safety criteria for the operation, storage and transportation of light water reactor fuel units outside the reactor
Some standard content:
National Standard of the People's Republic of China
Nuclear criticality safety for fissile materials outside reactors-Criticality safety criteria for the handling, storage and transportation of LWR fuel unit outside reactors1 Subject content and scope of application
GB 15146.8—94
This standard specifies the basic requirements and criteria for nuclear criticality safety for the handling, storage and transportation of LWR fuel unit outside reactors. This standard applies to the handling, storage and transportation of LWR fuel unit outside reactors. 2 Referenced standards
GB11806 Regulations on the safe transportation of radioactive materialsEJ279 Performance requirements and inspection regulations for supercritical accident alarm systems3 Terminology
3.1 Controlled parameters
A certain parameter that needs to be limited within a specified range and can affect subcriticality. 3.2 Fuel element
The smallest structurally independent component used in light water reactors with nuclear fuel as the main component. Its shape can be rod, plate or sphere. 3.3 Fuel unit
An object treated as a single object during operation, storage or transportation. It can be a single fuel element, a fuel assembly, spent fuel packed together or a group of fuel elements densely packed together. 3.4 Array
Any fixed arrangement of fuel units maintained by appropriate means. 4 General safety criteria
4.1 Nuclear criticality safety design and evaluation analysis must be carried out for the operation, storage and transportation of nuclear fuel units in accordance with relevant management regulations to ensure the nuclear criticality safety of the operation, storage or transportation of fuel units under normal conditions and credible abnormal conditions. Note: Examples of normal conditions and credible abnormal conditions are shown in Appendix A. 4.2 Nuclear criticality safety analysis must be carried out according to credible fuel design parameters, array dimensions, fuel unit operation procedures, moderation conditions and reflection conditions that will make the reactivity reach a maximum. 4.3 For fuel units with known irradiation history and irradiation conditions, the fuel burnup can be considered based on the actual irradiation history and irradiation conditions, but a certain margin must be left.
Approved by the State Administration of Technical Supervision on July 7, 1994 186
Implementation on January 1, 1995
GB15146.8-94
For fuel units with unknown irradiation history and irradiation conditions, if the reactivity of the fuel unit decreases with irradiation, it must be considered as an unirradiated fuel unit; if the reactivity of the fuel unit increases with irradiation, it must be considered as the maximum reactivity that the fuel unit may reach. 4.4 The corresponding nuclear criticality safety analysis and nuclear criticality safety design must be written into written documents in accordance with relevant regulations. Such documents must be complete and well-organized, sufficient for the reviewer to make an independent judgment. 4.5 The nuclear criticality safety analysis documents and nuclear criticality safety design documents must clearly specify the controlled parameters and their design limits and operating limits on which nuclear criticality safety depends.
4.6 For new projects that operate, store or transport fuel units, their nuclear criticality safety analysis documents and nuclear criticality safety design documents must be independently reviewed.
4.7 Before carrying out specific operations of operation, storage and transportation, the operating unit must verify that the existing conditions are consistent with the conditions and limits described or specified in Articles 4.4 and 4.5.
4.8 If necessary, the subcriticality of the array that occurs during operation, storage and transportation can be confirmed by the method of in-situ measurement of neutron multiplication. 4.9 The double accident principle should be implemented when operating, storing and transporting fuel units, that is, a criticality accident can only occur when at least two unlikely to change, independent operating, storage or transportation conditions change simultaneously or successively. 4.10 Nuclear criticality safety can be ensured by adding neutron absorbers to fuel units, components and equipment, but control measures must be taken to keep the poison in a predetermined distribution and concentration. When using liquid absorbers, it is difficult to implement such control, so special care must be taken when using them. For fuel units containing combustible poisons, special care must be taken when determining the conditions of maximum reactivity that need to be considered. 4.11 Whether a criticality alarm device needs to be installed should be determined based on actual conditions. If it is necessary to install it, the device should be selected and arranged in accordance with the requirements of EJ279.
4.12 Fuel units operated, temporarily stored, and transported outside the plant must also comply with the requirements of GB11806. 5 Nuclear Criticality Safety Measures
5.1 Administrative Measures
5.1.1 The relevant general administrative regulations on nuclear criticality safety must be followed during operation, storage, and transportation. 5.1.2 The operators, maintenance personnel, and management personnel must be trained and assessed to make them aware of their nuclear criticality safety responsibilities within their work scope. 5.1.3 The management department must formulate detailed operating rules for controlling nuclear criticality. 5.1.4 For regular operations, a review must be conducted at least once a year to find out whether the various procedures are followed and whether there are any changes in the operating, storage, and transportation conditions that affect nuclear criticality safety. The operation review must be conducted by nuclear criticality safety professionals who are not directly responsible for the operation in consultation with the operating personnel. 5.1.5 Emergency procedures must be developed and submitted to the management department for approval. All relevant units that need to respond to emergency events must be aware of the situations that may be encountered, and these units should participate in the development of response action procedures related to them. 5.2 Technical measures
Nuclear criticality safety can be ensured by controlling one or more factors related to the effective multiplication coefficient keft of the fissile system. When these control methods are adopted, reliable measures must be taken to ensure the implementation of such control. 6 Criteria for determining subcritical limits of controlled parameters 6.1 If experimental data are available, subcritical limits must be determined based on experimental data. When there are no directly applicable experimental values, subcritical limits can be derived by calculation, but the calculation method must be verified and proven to be effective. 6.2 When calculating the maximum permissible neutron multiplication coefficient k by analytical methods, the following inequality must be satisfied: k, ke Ak. ke- Akm
Where: k. k. The calculated value of the maximum permissible neutron multiplication coefficient of the evaluated system under all normal conditions or credible abnormal conditions or events,
GB15146.8-94
k. The average value obtained by calculating thousands of benchmark critical experiments (the benchmark critical experiments should be similar to the evaluated system in terms of physical composition, configuration, nuclear characteristics, reflector, etc.) using a specific calculation method. If the various tolerance values calculated for each critical experiment show a certain trend with a certain parameter, then the dead value must be obtained by extrapolation based on the best fit of the calculated value; △. is the margin left for the allowable deviation of. This allowable deviation is caused by the following situations: the uncertainty of the calculation method itself when calculating k., the allowable error of material composition and the allowable tolerance of machining, the uncertainty caused by the approximate treatment of materials or geometric conditions,
give. The margin left for the uncertainty of. This uncertainty is caused by the following reasons: the uncertainty of critical experiments, the calculation of Ak
The uncertainty of the calculation method itself, the uncertainty caused by extrapolation beyond the range of experimental data, the uncertainty caused by approximate treatment of geometric conditions and materials, Akm——-to ensure that k is a subcritical value and the additional margin is added. 188
GB15146.8-94
Appendix
Nuclear criticality safety factors to be considered when operating, building and transporting fuel units (reference)
When conducting nuclear criticality safety analysis for operating, storing and transporting fuel units, it is generally necessary to consider the design parameters of the fuel, the size of the storage column, the fuel operation procedures, the moderation and reflection conditions, etc., to ensure that the state of the combustion under consideration is the state with the highest credible reactivity. 4.1. The requirement is to consider normal conditions and credible abnormal conditions related to the controlled parameters and consider various uncertainties (including the allowable deviation of the design). The representative parameters and conditions are as follows:
Parameters of A1 fuel elementswwW.bzxz.Net
. Content, morphology, density, nuclear properties and distribution of fissile materials: composition, density and distribution of burnable poisons (note: the reactivity of irradiated fuel containing burnable poisons can exceed the reactivity of unirradiated fuel).
, geometric conditions of fuel elements, and materials and dimensions of cladding: bonds, other materials in fuel elements that may affect reactivity. A2 Composition of fuel units
Number of fuel elements and their positions in fuel units; dimensions of fuel units;
other materials that may be present.
A3 Array parameters
Distance between fuel units
Fixed neutron poisons between fuel units Structural materials and other materials that may be present in the array (nuclear properties, number, position and size): The impact of loading and unloading of fuel units on array parameters. A4 Moderators
Credible moderation conditions within and between fuel units, for example, the presence of plastic gaskets or other possible moderator materials (snow, staff, etc.) during dry storage Density and temperature of water when storing fuel units underwater Conditions include the conditions of voids formed by boiling.
A5 Reflectors and interaction conditions
Composition, shape and position of reflectors;
. Interaction with other fissile materials. A6 Abnormal conditions and accident conditions
Consequences caused by earthquakes, explosions, fires, flooding, etc. h. Abnormal position of fuel units;
Geometric deformation caused by accidents such as the fall of fuel or containers, or the overturning of fuel racks during transportation; Caused by loss of poison or changes in conditions such as moderation, geometry, reflection, etc. Credible accidents: Accident conditions specified in GB11806 during transport outside the plant. 189
Additional notes:
This standard was proposed by China National Nuclear Corporation. G15146.8--94
This standard was drafted by the Second Research and Design Institute of Nuclear Industry. The main drafter of this standard is Wang Weishan.
This standard refers to the American National Standard ANSI/ANS8.17-1984 "Nuclear Criticality Safety Criteria for Off-Pile Operation, Storage and Transport of Light Water Reactor Nuclear Fuel Elements"
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