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Diglycolamide / Hydrolysis / Radiolysis / Sensitization effect / n-dodecane / Nitric acidSummary. Hydrolytic and radiolytic stabilities of a promising extractant, N,N,N ,N -tetraoctyl-3-oxapentane-1,5-diamide (TODGA), for actinides in high-level radioactive liquid waste from nuclear fuel reprocessing were investigated in air at room temperature. Hydrolysis by nitric acid was not observed, whereas radiolysis by gamma irradiation was notably observed. The radiolysis study showed that an amide-bond, an ether-bond, and a bond adjacent to the ether-bond tended to be broken by gamma irradiation, and dioctylamine and various N,N-dioctylmonoamides were identified as the main degradation products by GC/MS and NMR analyses. The G-value for degradation of neat TODGA was 8.5 ± 0.9, which value was higher than those for N,N -dioctyl-N,N -dimethyl-2-(3 -oxapentadecyl)-propane-1,3-diamide and N,N-dioctylhexanamide. It was obvious that n-dodecane, which was used for a diluent, had a sensitization effect on the radiolysis of these amidic extractants. In a TODGA-n-dodecane-HNO 3 system, the coexisting nitric acid showed an insignificant effect on the radiolysis of TODGA.

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By using an extractant, N,N,N ,, extraction and separation of Sr(II) from Am(III) were investigated for the partitioning of high level liquid waste (HLLW). Both metal ions, accompanied with the counter anion, NO 3 − , and HNO 3 without dissociation, were extracted by TODGA. We used two distinct methods for the separation of Am(III) and Sr(II). A mixture of TODGA and monoamide reduced the distribution ratio D of Sr(II) compared to that without monoamide, whereas D(Am) was still high value under the identical condition. After extraction of Am(III) by TODGA and monoamide, Sr(II) remaining in HLLW can be extracted by using enough concentration of TODGA at the next step. In the other method, Sr(II) was coextracted with Am(III) by TODGA. It was observed that D(Sr) decreased with an increase of HNO 3 from 3 M to 6 M HNO 3 at the same TODGA concentration, while D(Am) increased until 6 M HNO 3 . By using 6 M HNO 3 , Am(III) and Sr(II) were separated after coextraction.