UC Irvine

The response to high linear energy transfer (LET) radiation of a variety of aqueous systems such as biological systems and the Fricke dosimeter has frequently been studied in the literature. Linear energy transfer is a unique property of radiation which describes the special distribution with which energy from radiation is deposited and concentrated as it travels through matter and can have implications on degradation within the matter itself. The four types of ionizing radiation alpha, beta, gamma, and neutrons have different LET, classified from low for gamma and beta, to high for alpha. All types of ionizing radiation are encountered in used nuclear fuel. This radiation induces damage to solvent extraction processes designed to recycle used nuclear fuel which results in impaired selectivity and reduced process efficiencies. While the effects of low LET radiation on organic solutions have been widely studied, the effects of high LET radiation have not due to difficulties in studying this type of radiation such as short radiation path lengths on the order of 50 μm. This study investigates the effects of high LET radiation deposited in situ from fission products lithium and helium emitted in the ¹⁰B(n,α)⁷Li reaction. The reaction, studied previously in aqueous systems, is applied here to organic solvents containing ligands used in solvent extraction. Ligands studied were TBP, CMPO, and TODGA utilized in the PUREX and TRUEX processes. Results demonstrate that high LET radiation has the tendency to reduce degradation to the parent compound due to reactive products being consumed within the radiation track, while encouraging secondary degradation products to occur within the radiation track. Products of these secondary degradation reactions may be more detrimental to the solvent extraction process than primary degradation products and are therefore important to understand and monitor. Results also demonstrate the utility of using the ¹⁰B(n,α)⁷Li reaction to study the effects of high LET radiation on organic solutions encountered in used nuclear fuel recycling processes. Understanding the effects of both high and low LET radiation on solvent extraction processes will facilitate early screening of novel ligand susceptibility to radiation induced degradation while also providing a more comprehensive picture of degradation encountered during radiolysis.