A CONTAINER BASED ON POLYMER COMPOSITE MATERIALS FOR THE ULTIMATE DISPOSAL OF SPENT NUCLEAR FUEL AND RADIOACTIVE WASTE

This work demonstrates the feasibility of fabricating containers for the ultimate disposal of spent nuclear reactor fuel and high-level radioactive waste using polymer-based composite materials. The study has identified three engineering polymers suitable for this demanding application: polyetheretherketone (PEEK), polyetherimide (PEI), and polysulfone (PSU). PEEK and PEI are used as composite materials components, with 30% carbon and glass fiber, respectively, whereas PSU is used as a virgin (nonreinforced) material. The rationale for the choice of polymer composites comes from their superior physical, mechanical, and chemical performance, in addition to their economical advantage. In particular, they display better resistance to corrosion and to structural weakening from irradiation. Scaled-down containers were fabricated using these materials. They were subjected to a battery of tests under conditions similar to those expected for the disposal environment of actual radioactive waste-filled containers. In particular, the container models were irradiated in the pool of a SLOWPOKE-2 nuclear research reactor, accumulating doses from a mixed-radiation field that were comparable to total doses accumulated over 500 yr at a deep underground waste repository site. Mechanical compression tests mimicked the large hydrostatic pressures incurred from granite rock at depths of some 1000 m within the Canadian Shield. Several composite materials were tested, and for the three engineering materials listed above, some of the results are as follows: 1. variation in elastic modulus following a 28.9-kGy radiation dose-PEEK, -6.66% +/- 0.47%; PEI, +5.63% +/- 0.23%; PSU, +3.16% +/- 0.13% 2. compression results for the irradiated container models and load at break and strain-PEEK, 2.152 MPa and 1178 mu m m(-1); PEI, 1.236 MPa and 1171 mu m m(-1); PSU, 1.190 MPa and 2576 mu m m(-1), respectively 3. cost analysis-costs for the fabrication of the prototype containers based on PEEK, $273 610; PEI, $145 920; PSU, $257 460. The work also provided insight into potential problems in the fabrication of full-sized containers and into the best fabrication methods to adopt. The method of filament winding would be more appropriate for the PEEK- and the PEI-based composite materials, while blow forming would be the preferred method for the PSU material. In particular, this research could determine the best way to design the container lids.