NANOHMICS INC — Department of Energy SBIR Phase I: 20

Description

Plasma fusion promises safer, lower cost, power generation with no carbon emissions. Of concern in all plasma fusion systems is the ability of reduced activation ferritic martensitic (RAFM) structural materials to not only withstand operating conditions but to limit the amount of tritium permeation. Tritium retention/transmission not only creates a safety hazard but also increases operational costs of the reactor. Statement of how this problem or situation is being addressed Incorporating a thin hydrogen isotope permeation barrier within RAFM structures provides an optimal solution for limiting tritium permeation. Specifically the barrier is shielded from the worst of the environment and experiences limited erosion allowing it to maintain a high permeation reduction factor (PRF) over the life of the structure. In a recent effort we constructed and tested a W plate with a thin sputtered SiC diffusion layer topped with a sputtered W layer. Tests demonstrated the SiC barrier provided an excellent permeation barrier to Hydrogen isotopes. Further the close match in thermal expansion coefficients between SiC and W allowed multiple thermal cycles to be performed with no delamination. A similar structure involving RAFM and sputtered SiC would provide the same benefits. The mismatch in thermal conductivities may be mitigated by a thermal buffer layer, a gradient composite from RAFM to pure SiC or tungsten. Phase I/II effort In the proposed Phase I, samples consisting of a RAFM base, thermal buffer layer, sputtered SiC permeation barrier and tungsten topcoat will be constructed and specific tests will be performed to provide metrics for optimization of the construction. These test will include multiple (100’s) of thermal cycles, thermal conductivity measurements of the SiC layer and the ability of the stack to withstand the irradiation environment and maintain an adequate PRF. Further a fully dense tungsten topcoat for protecting SiC permeation barrier layer must be constructed that will survive an operating fusion environment. In Phase II optimizing the deposition parameters will be continued and a means to commercially manufacture large numbers of RAFM components will be developed. Commercial Applications and Other Benefits: The reliable manufacture of RAFM structural components with low tritium permeation is a critical challenge to the development of successful fusion power facilities. Materials R&D will play a major role in the successful deployment of fusion technology for the benefit of the public energy needs. Key Words: RAFM steels, hydrogen permeation barrier, tritium