Thermo-physical behavior of borosilicate glasses in the presence of high-level radioactive liquid waste constituents

Abstract

Elemental composition of high-level radioactive liquid waste (HLW) from samples of various batches was assessed by using side-on-view inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Under robust condition (Mg ratio, 10.2 ± 0.4 at RF power 1.3 kW), t he plasma excitation temperature (Texe, 9925 ± 1950 K) was calculated using the Boltzmann plot method. Thermal behavior of major constituents (> 1 g L−1) of HLW, such as nitrates of Na+, Fe3+, Cs+, Nd3+, and UO22+ , were studied using simultaneous thermal analyzer. Subsequently, the thermal stability of five and seven components borosilicate glasses was studied in detail with the above nitrates individually added as additives. Vapor pressure of sodium metaborate (NaBO2, one of the major vapor species from the glass melt in the off-gas system during vitrification of HLW) was estimated using transpiration thermogravimetry. Based on mass loss, the equilibrium vapor pressures (2.51–26.37 Pa) over a temperature span of 1233.15–1343.15 K were estimated. The molar enthalpy of vaporization (ΔvapH°) for sodium metaborate was calculated to be 287.84 ± 0.94 kJ mol−1 using the experimental data.