T. Takahashi et al., CHANGES IN THE MICROSTRUCTURE AND DENSITY OF LI2O DURING IRRADIATION IN BEATRIX-II, PHASE-I, Fusion engineering and design, 28, 1995, pp. 271-277
BEATRIX-II, phase I was an in situ tritium recovery experiment carried
out on Li2O to lithium burnups in excess of 4%. Solid Li2O specimens
were irradiated under a temperature gradient in the range from 700 K a
t the outer diameter to 1270 K at the center. A ring specimen of Li2O
operated at a nearly uniform temperature with the capability of changi
ng the temperature in the range 780-920 K. Li2O single crystals with t
wo different Li-6 enrichments (0.07 and 1.8 at.%) were irradiated at 6
50 K in non-vented canisters. The microstructures of these specimens b
efore and after irradiation were investigated using optical and scanni
ng electron microscopy. Substantial microstructural change was found t
o have occurred in the solid specimen during irradiation and this chan
ge was characterized by the development of large columnar grains, lent
icular pores and a center void. The development of columnar grains and
the formation of the center void was attributed to the migration of l
enticular pores up the thermal gradient by an evaporation-condensation
process. Morphological changes on fracture surfaces were observed for
both polycrystalline (solid and ring) specimens and single-crystal sp
ecimens. Measurements of density were used to characterize further the
effects of irradiation on the open and closed porosity distributions
in all the specimens. Although extensive microstructural and density c
hanges occurred during irradiation, these changes had no significant i
mpact on the integrity of Li2O during irradiation, and therefore these
results support the use of Li2O as a fusion solid breeder.