Neutron Absorbers: Qualification and Acceptance Tests

Materials containing the element boron, as well as other materials with a high cross-section for absorbing thermal neutrons, are used widely in the nuclear industry. These materials are most commonly produced in the shapes of plates and rods. One common use of these absorber materials is to ensure subcriticality during normal and off-normal/accident service conditions inside storage casks and transportation packages of spent nuclear fuel. Frequently, little or no structural credit is given to these materials. The boron isotope, 10B, with its high cross section for thermal neutrons, is one component that can be used to prevents criticality. Commercial products are tailored to meet a particular material specification of minimum areal density of the 10B isotope. When an absorber material is introduced into the marketplace, acceptance tests and qualification tests must be performed to ensure compliance with regulatory requirements. The materials must be demonstrated to contain prescribed levels of the 10B isotope, that are homogeneously distributed throughout the product. In addition, the products must be sufficiently durable to withstand the conditions of service. For each product and manufacturing process, qualification tests are conducted at least once. These tests are used to demonstrate that the material will be of adequate quality and durability for the intended service. In addition to qualification tests, acceptance tests are used to ensure that material properties for plates and other shapes are in compliance with the licensing requirements of the application. Usually this is a demonstration for a production run that the distribution and level of 10B is adequate for all plates that will be used in service. Statistical information on selected parameters can be used to ensure that the product will meet the service requirements.