Accumulation and yield of helium and tritium in boron carbide irradiated in the BN-600 reactor

The experimental results of the study of boron carbide samples irradiated in the BN-600 reactor to determine the accumulation and release of gaseous products of nuclear fission depending on burnout, temperature and atmospheric composition above the samples are presented. When irradiated, boron carbide, in addition to helium, accumulates a gaseous product of nuclear reactions - the radioactive isotope of hydrogen - tritium. Its accumulation occurs by reactions: ¹⁰B(n, α)⁷Li(n, nα)T; ¹⁰B(n, α)⁷Li(n, 2n)⁶Li(n, α)T; ¹⁰B(n, 2α)T; ¹¹B(n,T)⁹Be. The issues of assessing the accumulation and release of radioactive tritium in boron-containing regulatory authorities are of great importance for ensuring environmental safety when developing a technology for their disposal or recycling. For the study, hot-pressed boron carbide tablets were used, which were spent in the BN-600 reactor for 502 effective days, with boron burnout (1,8; 5,1; 6,2; 7,2; 8,4)×10²¹ capt/cm³. The accumulation of helium and tritium in irradiated boron carbide was determined by burning prepared samples with subsequent analysis of the obtained products on an omegatron mass spectrometer. The content of helium and tritium in the samples of the vapor-gas medium was measured using a radiochromatograph. The values of the accumulation of helium and tritium in boron carbide irradiated in the BN-600 reactor, depending on the burnout of boron, can be estimated by dependencies (B - boron burnout, 10²¹ capt/cm³): - accumulation of ³T with an error of 8 %: V_T = (-0.0062 + 0.0078B/10²¹) ncm³/g B₄C; - accumulation of ⁴He with an error of 3 %: V_He = (-7.03 + 16.03B/10²¹) ncm³/g B₄C. The values of the helium yield from boron carbide in the argon stream and water vapor + argon at a temperature of 1200 °C, depending on the burnout of boron with an error of 3 %, can be estimated by the dependencies: - in the argon stream: V_outletHe = (-0.073 + 0.059B/10²¹) ncm³/g B₄C; - in the flow of argon + water vapor: V_outletHe = (0.57 + 0.083B/10²¹) ncm³/g B₄C. The values of the tritium yield from boron carbide in the argon stream and argon + water vapor at a temperature of 1200 °C, depending on the burnout of boron with an error of 8 %, can be estimated by the dependencies: - in the argon stream: A_outletT = (-11.42 + 9.01B/10²¹)×10⁷ Bg/g B₄C; - in the flow of argon + water vapor: A_outletT = (73.42 + 14.13B/10²¹)×10⁷ Bg/g B₄C.