Committee C26 on Nuclear Fuel Cycle
New Practice to Guide Designers of Neutron Absorbers
Neutron absorbers have been used for criticality control in spent nuclear fuel pools and in spent fuel transportation casks for decades. ASTM International standards such as C 992, Specification for Boron-Based Neutron Absorbing Material Systems for Use in Spent Fuel Storage Racks, and C 1187, Guide for Establishing Surveillance Test Program for Born-Based Neutron Absorbing Material Systems for Use in Nuclear Spent Fuel Storage Racks, cover neutron absorbers used in spent nuclear fuel pools.
However, since the late 1980s, as spent fuel storage pools have been filled, utilities have transferred spent fuel into dry dual-purpose (storage/transportation) canisters. The neutron absorbers used in dual-purpose canisters are subjected to different operating conditions than materials used in spent fuel pools. Because of these differences, ASTM International Committee C26 on Nuclear Fuel Cycle has developed a new standard, C 1671, Practice for Qualification and Acceptance of Boron Based Metallic Neutron Absorbers for Nuclear Criticality Control for Dry Cask Storage Systems and Transportation Packaging. C 1671 is under the jurisdiction of Subcommittee C26.03 on Neutron Absorber Materials Specifications.
James Hobbs, Nuclear Fuel Services and C26 member, says that the new standard was developed because there were several existing material suppliers, new suppliers in the process of qualifying new products, canister designers/suppliers and testing organizations, each using one or more of the several approved but different approaches to qualification and acceptance testing. “The NRC [U.S. Nuclear Regulatory Commission] wanted to codify industry practices and develop a consensus industry standard to guide canister designers, neutron absorber manufacturers and the end users toward a consistent approach for qualification and acceptance testing, as well as to provide the NRC with a consistent basis for evaluating new materials for regulatory approval,” says Hobbs.
“Unlike neutron absorbers used in spent fuel pool racks, it is not practical to inspect or conduct surveillance on the neutron absorbers material used in dual-purpose canisters during their operating lifetime because redundant closure lids are welded to the canister,” Hobbs says. Because of this, it is important to conduct a comprehensive test program on the neutron absorber material prior to the material going into service. NRC regulations require two sets of tests — qualification tests and acceptance tests. Qualification tests are a one-time set of tests that establish the mechanical properties, material durability and the effectiveness of the material, while acceptance tests confirm that the as-manufactured products meet the customer specifications and the same level of quality as the material that was qualified.
“The standard provides a consistent basis for qualification and acceptance for a variety of different material and different canister designs,” says Hobbs. Canister designers, manufacturers of neutron absorber materials, testing organizations, regulators and utility end-users will all find the standard useful, according to Hobbs.
Subcommittee C26.03 welcomes participation in its standards developing activities. The task group responsible for C 1671 will soon be working on a proposed new standard for neutron absorber material to be used by the U.S. Department of Energy repository package, the transportation, aging and disposal, or TAD, canisters. The Department of Energy has qualified one material, grade A borated stainless steel (covered by A 887, Specification for Borated Stainless Steel Plate, Sheet and Strip for Nuclear Application) for use in TAD canisters. “As with the dual purpose canisters, material suppliers will try to develop competitive neutron absorber products for the TAD canisters,” says Hobbs. “Industry and the NRC would like to have a standard specifically for the TAD neutron absorber material.”
Technical Information: James Hobbs, Nuclear Fuel Services, Erwin, Tenn.
ASTM Staff: Joe Koury