Irradiation Stability Of The TBP Solvent Extraction System

In the Purex spent fuel reprocessing process, tributyl phosphate （TBP） solventextraction system becomes degraded due to radiolytic and chemical attacks, resulting ina series of temporary degradation products and permanent degradation products.Through alkali washing, the former can be removed but the latter are difficult to beremoved from the solvent. These degradation products can cause various physical andchemical damage, and the extraction characteristics of the solvent become deteriorated,leading to impairment of the phase separation, decrease of the mass transfer coefficientof uranium and plutonium, and retention of the fission products in the uranium andplutonium streams.In order to control and optimize the technological conditions of reprocessingprocess and reduce the irradiation damage of the solvent system, the gamma and alphairradiation stabilities of TBP/n-dodecane system have been studied in this thesis, inwhich60Co and238Pu are adopted as gamma and alpha irradiation sources respectively.The main degradation products dibutyl phosphate （DBP） and monobutyl phosphate（MBP） have been detected by the gas chromatography-mass spectrometry （GC-MS）, andthe radiation degradation degree of the solvent extraction system has been measured bythe test of Pu retention. The effects of the irradiation dose, the concentration ofpre-equilibrium nitric acid, the accumulative irradiation dose, and the metal ions on theextraction behaviors of the system have been systematically investigated.The experiment results indicate that:（1） In the range of the absorbed dose studied, the yields of DBP, MBP and the Puretention of the system all increase with the increase of the absorbed dose after gammairradiation; the pre-equilibration nitric acid concentration has a significant effect on theyield of DBP and the Pu retention, but has little impact on the output of MBP; the morethe number of irradiation, the larger the Pu retention value. Moreover, the Pu retention ofthe system by accumulated radiation is greater than that by a single radiation under thesimilar absorbed dose.（2） In the range of the absorbed dose studied, the Pu retention of the system increased with the increase of the absorbed dose after alpha irradiation. When theabsorbed dose is1×10⁶Gy, the Pu retention approaches40%; the effect of thepre-equilibration nitric acid concentration on the Pu retention is not obvious; theexistence of Zr⁴⁺ions in the solvent system inhibits irradiation damage of the system,and the Pu retention reduces monotonically with the increase of the concentration ofeither of the two metal ions.（3） At the similar absorbed dose, the Pu retention of the system by alpha irradiationis slightly larger than that by gamma irradiation.