Zircaloy-clad elements of bulk B4C and B4C-Sic were irradiated in pressurized hot water loops and in the Materials Testing Reactor (MTR) process water to development as high as 97 percent burnup of the Boron-10 atoms present. The B4C showed a linear volume swelling rate of approximately 0.15 percentΔv per 1020 depletions/cc up to about 90×1020 depletions/cc after which a more rapid swelling occurred as a result of B4C cracking. Elements containing B4C-Sic showed greater thickness changes as a result of occurs during irradiation of the bulk B4C and B4C-Sic poison cores, resulting in disintegration of these poison cores when exposed to the water environment in-pile.nB4C plate-type poison elements show greater thickness increases than would be expected from poison core volume swelling because of the formation of poison core-cladding gaps in the elements. The element swelling was extremely sensitive to fabrication variables.nHelium gas released from B4C during irradiation was slight and not related to gas diffusion. Lattice parameter values obtained on irradiated natural B4C indicated that the ao direction of the hexagonal B4C remained essentially constant while the co direction decreased with increasing Boron-10 depletion. Evidence of plasticity of B4C in-pile was noted.nThe irradiation behavior of the ceramic materials studied in this investigation and the wrought alloy of B-10 austenitic stainless steel poisons are compared.
展开▼
