Dry storage cask materials must withstand severe temperature conditions coming from conservative ambient assumptions and from envelope values of residual heat from spent fuels. TN International (TNI) research and development has consequently developed and characterized neutron-shielding materials that show high shielding capabilities and correspond to the needs of a range of temperatures. Aging tests of specimens have been performed accordingly.

This paper shows the results of aging tests on shielding material Vyal-B, a material patented by TNI.

TNI Vyal-B shielding material is composed of a thermoset resin matrix (vinylester resin in solution of styrene) and two mineral fillers (alumina hydrate and zinc borate). The cross-linking of the polymer leads to a rigid three-dimensional lattice, solid and resistant to transport conditions, especially the temperatures.

TNI Vyal-B's shielding ability for neutron radiation is related to the atomic density of hydrogen and boron. Atomic densities can be calculated from the chemical composition and bulk density of samples, and these two parameters are checked initially just after manufacturing.

Assessment of the long-term behavior of TNI Vyal-B shielding material has been carried out through exposition tests of samples at different temperatures (150°C to 170°C). The test results give the variations of chemical composition and density. After the aging tests, the new chemical compositions are taken into account in the shielding analysis of the package. Considering a degradation mechanism following Arrhenius behavior, a maximal temperature of long-term use, for example, for interim storage, was confirmed equal to 160°C.