M n+1 AX n (MAX) phase Ti 3 SiC 2 materials were neutron irradiated at ~400, ~630, and 700°C to a fluence of ~2 x 10 25 nm-2 (E > 0.1 MeV). After irradiation at ~400°C, anisotropic c-axis dilation of ~1.5% was observed. Room temperature strength was reduced from 445±29 MPa to 315±33 MPa and the fracture surfaces showed flat facets and transgranular cracks instead of typical kink-band deformation and bridging ligaments. XRD phase analysis indicated an increase of 10-15 wt% TiC. After irradiation at ~700°C there were no lattice parameter changes, ~5 wt% decomposition to TiC occurred, and strength was 391±71 MPa and 378±31 MPa. The fracture surfaces indicated some kink-band based deformation but with lesser extent of delamination than as-received samples. Ti 3 SiC 2 appears to be radiation tolerant at ~400°C, and progressively radiation resistant at ~630-700°C, but a higher temperature may be necessary for full recovery. Recent ion irradiations of both Ti 3 SiC 2 and Ti 3 AlC 2 have been accompanied by transmission electron microscopy (TEM), and acquisition of crystallographic data by Low or Grazing Incidence X-ray Diffraction (XRD). 6-9 The intact lamellae after irradiation represent undisturbed "A-layers" and MX layers; this proposes confinement defect growth, satisfying a criteria of irradiation performance. 9-12 However, Ti 3 SiC 2

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There is significant current interest in the commercial power industry in developing nuclear reactor concepts using molten salt as a coolant or as a fuel-bearing medium and coolant. The Molten Salt Reactor Experiment (MSRE), which was performed at Oak Ridge National Laboratory from 1964-1969, established the feasibility of this reactor design and performed some of the early work in qualifying appropriate structural materials and coolant salts. However, modern versions of this design often incorporate aspects that are beyond the design basis of the MSRE. For example, some designs intend to operate at a higher temperature, use a different structural material, or a different salt altogether. These new designs will eventually require irradiation testing in a variety of reactors and conditions. This document specifically evaluates the possibilities and requirements associated with the most difficult of these conditions: a flowing salt irradiation under high neutron flux.

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This report discusses the initial progress made at the Oak Ridge National Laboratory to support direct disposal of dual-purpose canisters (DPCs) using filler materials to demonstrate that the probability of criticality in DPCs during disposal to be below the probability for inclusion in a repository performance assessment. In the initial phase of a multi-phase effort that will result in a full-scale demonstration, a computational fluid dynamics (CFD) model was developed to gauge the filling process and to uncover any unforeseen issues. The initial filling simulations of the lower region (mouse holes) of a prototypic DPC show successful removal of the inner space voids and smooth, even progression of the liquid level. In the initial phase, flow through a pipe that is similar to the drain pipe in a DPC will be investigated separately to gain valuable insight of flow regime inside a pipe. The initial experimental setups for validating the computational filling model have been designed, and the various assembly parts are being procured. The experience gained from the initial experiments will be applied to the next steps toward a full-scale demonstration and to the validation of multiphysics filling simulation models.