Effect of Fast Neutron Irradiation on the Properties of Boron Carbide Pellet

Abstract

Boron carbide pellets were irradiated in the experimental fast reactor "JOYO" to log burnup of up to 1 7 0~1 0~~ cap/m3, fluences of 2x102'/m2 (E>0.1 MeV), and maximum temperatures of about 1,200"C. Post irradiation examinations were made of microstructural changes, helium release, swelling, and thermal conductivity.Boron carbide pellets irradiated to high burnups developed extensive cracking. Helium release from the pellets was initially low, but enhanced helium release was observed at high burnups and high temperatures. The swelling linearly increased with burnup, and when boron carbide was irradiated at high temperatures, the swelling rate began to decrease corresponding to the beginning of enhanced helium release. The correlation between swelling and the helium release was studied and the swelling was interpreted in terms of accumulation of helium in the boron carbide pellet. The thermal conductivity of the boron carbide pellets decreased rapidly by neutron irradiation accompanied with loss of temperature dependence.

The influence of irradiation induced vacancies on the mobility of helium in boron carbide

“…The goal was, however, mainly phase stability and not the properties of isolated defects, nor their role in mass transport kinetics. In spite of a number of experimental works devoted to helium bubbles [11,12,13,14,15,16,17,18,19,20,21] and the related question of helium kinetics [20,22,23,24], not much is known on self-diffusion.…”

Evolution of thermo-physical properties and annealing of fast neutron irradiated boron carbide

“…The similar distribution of the swelling confirms a quasi-linear variation as a function of burnup at least up to 10 22 /cm 3 , about 0.15 vol. % per 10 20 capt./cm 3 [2,4,12].…”

“…It is then of primary importance to have a good knowledge of the thermal conductivity of the material and its evolution during irradiation. It is now well known that the thermal conductivity degrades under neutron irradiation [1,2,3,4,5]. We present here results we have obtained from materials irradiated in the French LMFBR Phenix reactor.…”

First-principles study on the helium migration energies in B12X2(X=O, Si, P, As) crystals for neutron absorber use

“…Boron carbide (B 4 C) is the leading candidate for a neutron absorber for next-generation fast reactors, which are entrusted with the important task of providing sustainable nuclear energy [1,2]. However, due to the helium gas produced from the 10 B[n, α] 7 Li reaction, the volume swelling of the B 4 C pellets during use has been a critical safety issue for the longterm use of the control rods [3][4][5]. Moreover, the brittleness of B 4 C makes the pellets very easy to break into small fragments under the internal stress induced by the heat gradient and helium gas production.…”