FY18Q3 Quarterly Report: Radiation Enhanced Diffusion of Ag, Ag-Pd, Eu, and Sr in Neutron Irradiated PyC/SiC Diffusion Couples

Preparation of Diffusion Couples for Irradiation and High Temperature Testing of Representative TRISO PyC/SiC

“…This report is a summary of the diffusion couple development process. In depth description of the process summarized here has been captured in a series of quarterly reports which serve to document the development process [28,[30][31][32][33].…”

“…An in depth description of the seal-coating development can be found in the prior reports by Gerczak et al [28,[30][31][32][33]. The seal coating deposition varied from standard SiC deposition.…”

“…The FB-CVD reactor has demonstrated the ability to produce SiC below 900 ºC using a methylsilane (MS) as a precursor gas [41]. A series of depositions were pursued to develop the capability to deposit SiC at low temperatures and the subsequent stability of the MS-derived SiC [28,32]. Deposition was observed at above 700 ºC.…”

“…Post deposition heating tests show improved thermal stability of the SiC layer with elevated deposition temperature with neither layer showing complete stability above 1000 ºC. An inverse correlation with dose retention and deposition temperature was also observed with the lower temperature depositions retaining more of the initial implantation dose [28,32]. Due to the limited robustness of the MS derived SiC at high temperatures and inverse relationship of dose retention with deposition temperature a multistep seal-coating process was developed.…”

“…The first two depositions were MS-derived SiC at 700 ºC and 900 ºC, these layers provided initial barriers to loss of the implantation dose. A final MTS-derived SiC layer deposited at 1425 ºC provided high temperature stability during irradiation testing and thermal exposures [28]. The deposition conditions for the multi-step process is shown in Table 4.…”