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Issue
Korean Chemical Engineering Research,
Vol.42, No.4, 439-446, 2004
Co-60 감마선 조사에 의한 30% TBP-0.5% TOA/n-dodecane-HNO3계의 방사분해에 따른 Tc, Np 및 U의 추출 거동
The Extraction Behaviors of Tc, Np and U with Radiolysis of 30% TBP-0.5% TOA/n-dodecane-HNO3 System by Irradiation of Co-60 γ-ray
이일희, 김광욱, 양한범, 김원호, 유재형
본 연구는 Co-60 감마선 조사에 의한 30% TBP-0.5% TOA/n-dodecane-HNO3(Np의 산화제 포함)계의 방사분해에 따른 Tc, Np, U의 공추출 및 이의 선택적 역추출 거동을 규명하였다. 공추출의 경우 1 × 107 rad 이하에서는 Tc및 U의 추출이 추출제(TBP, TOA)와 질산의 방사분해에 따른 농도 변화가 작고, 분해생성물의 양 또한 미미하여 방사선 흡수선량에 따른 영향이 거의 없었다. 그러나 1 × 108 rad에서는 Tc의 경우 추출제의 방사분해에 따른 추출능의 감소와 질산의 방사분해에 따른 산 농도 감소에 의한 추출능의 증가가 서로 상쇄되어 추출률이 소폭 증가하고 있으나, U는 TBP의 분해생성물인 DBP의 영향으로 크게 증가하고 있다. 한편 Np은 산화제의 영향을 받아 K2Cr2O7의 경우에는 1 × 107 rad에서부터 질산의 방사분해에 의해 생성되는 HNO2등에 의해 K2Cr2O7가 산화제로서의 기능을 상실하여 추출률이 급격히 감소한다. 반면에 NH4VO3의 경우는 1 × 108 rad 까지도 Np의 산화제로서의 본래 기능을 유지하고 있으며, 추출률은 U의 경우와 같이 DBP의 영향으로 급격히 증가하고 있다. 그리고 Tc, Np및 U는 우선 강질산(초기 질산농도 7 M)으로 Tc을 역추출한 다음, acetohydroxamic acid(0.2 M)로 Np를 환원 역추출하고, 마지막으로 Na2CO3(0.2 M)로 U을 역추출하면 방사선 흡수선량 분위기하에서도 효과적으로 이들을 순차 분리할 수 있다.
In this study, the behaviors of co-extraction and selective stripping of Tc, Np and U with radiolysis of 30 vol.% tributyl phosphate(TBP)-0.5% trioctyl amine(TOA)/n-dodecane-HNO3 system (containing the oxidant of Np) were investigated. Radiolysis was carried out by an irradiation of Co-60 γ-ray. Effect of radiation absorbed dose on the extraction yield of Tc and U was negligible less than 1×107 rad, because degradation of extractant (TBP, TOA) and nitric acid were very small during the radiolysis. At 1×108 rad, however, extraction yield of Tc was slightly increased due to the set off an increase of extraction yield of Tc with decrease of nitric acid concentration by radiolysis of nitric acid against a decrease of extractability on Tc by radiolysis of extractant, and extraction yield of U was rapidly increased owing to DBP, which was one of the degradation products formed from radiolysis of TBP. On the other hand, extraction yield of Np(+6) oxidized by K2Cr2O7 was rapidly decreased, because K2Cr2O7 lost its own the function as a Np oxidant by HNO2 formed from radiolysis of nitric acid in above 1×107 rad. Extraction yield of Np(+6) oxidized by NH4VO3 was rapidly increased owing to DBP like U, because NH4VO3 filled the role of oxidant of Np up to 1×108 rad. Under the conditions with radiation absorbed dose, Tc, Np and U could be selectively separated by the subsequent stripping steps, which were composed of the Tc stripping with 7 M HNO3, the reduction stripping of Np(+6) with 0.2 M acetohydroxamic acid, and the U stripping with 0.2 M Na2CO3.
Keywords: Tc; Np; U; Radiolysis; Irradiation; Radiation Absorbed Dose; TBP; TOA
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