ANSI/ANS-8.21-2023, Use of Fixed Neutron Absorbers in Nuclear Facilities Outside Reactors, has just been issued by the American Nuclear Society Standards Committee. The standard was approved by the American National Standards Institute (ANSI) on June 20, 2023, as a revision and consolidation of ANS-8.21-1995 (R2019) (withdrawn) (same title) and ANS-8.5-1996 (R2022) (withdrawn), Use of Borosilicate-Glass Raschig Rings as a Neutron Absorber in Solutions of Fissile Material. ANSI/ANS-8.21-2023 provides guidance for the use of neutron absorbers, including Raschig rings, as an integral part of nuclear facilities equipment, fissile material, or fuel components outside reactors, where such absorbers are credited to provide criticality safety control.
Neutron absorbers (poisons) are frequently used as part of the overall nuclear criticality safety control measures. ANSI/ANS-8.1-2014 (R2023), Nuclear Criticality Safety in Operations with Fissionable Materials Outside Reactors, covers general considerations of neutron absorbers for criticality accident prevention. ANSI/ANS-8.21-2023 supplements guidance provided in ANSI/ANS-8.1-2014 (R2023) and in ANSI/ANS-8.17-2004 (R2019), Criticality Safety Criteria for the Handling, Storage, and Transportation of LWR Fuel Outside Reactors. For soluble neutron absorbers, see ANSI/ANS-8.14-2004 (R2021), Use of Soluble Neutron Absorbers in Nuclear Facilities Outside Reactors.
ANSI/ANS-8.21-2023 provides additional, detailed guidance on the use of fixed neutron absorbers, including Raschig rings, referred to as neutron absorbers, in the design, construction, and operation of nonreactor nuclear facilities. For the purpose of this standard, neutron absorbers involve materials with neutron absorption properties that are an integral part of a facility, equipment, or fuel components and are credited to provide criticality safety margins under normal and credible abnormal conditions. The guidance applies to the design, construction, and operation of facilities used for handling, processing, and storing of fissile materials. This guidance also applies to equipment associated with the transportation of fissile material. This standard requires consideration of depletion, or potential depletion, of neutron absorbers due to irradiation. Analysis of depletion of neutron absorbers in operating nuclear reactors, when the depletion effects are subsequently credited in criticality safety, is not covered by this standard. ANSI/ANS-8.27-2015 (R2020) provides guidance for analysis of such depletion.
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