Comparative tests of chemical absorbents for neutralization of fluoride gases under low pressure conditions

Background: Increasing the service life of pumping collector equipment at uranium isotope separation plants and the degree of exhaust gas neutralization, as well as reducing the mass of radioactive waste represent urgent tasks for the isotopes separation industry.

Aim: To perform a comparative study on the efficiency of neutralizing gaseous fluoride ion under low pressure conditions for a number of chemical absorbents used in pumping collectors of uranium isotope separation plants.

Materials and methods: The studied sources of gaseous F‑ion include HF and UF₆ as the main and impurity one (< 0.3 vol.%), respectively. The tested chemical absorbents of the K‑09-01 pump collector are Ca(OH)₂, Ca₂(OH)₂CO₃, CaCO₃, Al₂O₃, Na₂CO₃, Mg(HCO₃)₂, as well as vinylpyridine cationite, mercerized wood with NaOH, and modified mercerized wood admixed with Na₂SO₃.

Results: Under pumping collector conditions of t = 25 ± 3 °C and 0.4 < P < 1.3 kPa, the degree of absorption for F‑ and U‑containing gas components by lime and mercerized wood absorbents has reached 99.7 and almost 100%, respectively; other absorbents have proved themselves ineffective. Acting as a neutron moderator due to carbon, spent mercerized wood absorbents have been established to contain a small amount of uranium.

Conclusion: Mercerized wood and lime chemical absorbents demonstrate the highest absorption efficiency for UF₆ and HF fluorine-containing gaseous compounds. Thus, they can be used in pumping collectors of uranium isotope separation plants. Spent mercerized wood absorbents cannot be attributed to nuclear hazardous objects and should be classified as radioactive waste.