Study On The Absorption And Thermal Risk Of Nitrogen Dioxide By Phosphate Esters In Spent Fuel Reprocessing

A large amount of nitrogen oxides,mainly NO and NO₂,will be generated in the process of spent fuel reprocessing.However,previous reports on“red oil”focused on TBP-HNO₃ and TBP/diluent-HNO₃ systems,and nitrogen oxides were not taken as research objects.But in our previous experimental studies,it was found that tributyl phosphate and nitrogen dioxide can cause thermal runaway at low temperature,which is worth further study.Therefore,based on the binding ability of phosphate ester and NO₂,this paper studied the stability of the combined system and conducted thermal risk assessment.The absorption experiment of tributyl phosphate/dibutyl phosphate on nitrogen dioxide was carried out by the self-built absorption device,and the corresponding combination ratio was obtained.The combination ratio of tributyl phosphate and nitrogen dioxide was about 1:1,while the ability of dibutyl phosphate to bind nitrogen dioxide was weak,about 1:0.4,and the wavelength of the infrared characteristic peak of the P=O bond is shifted after the combination.In addition,software Gaussian and Multiwfn were used to simulate the molecular configuration before and after the binding,and relevant parameters were obtained,which proved that the binding of phosphate ester and NO₂ was not a chemical reaction;and the interaction energy of TBP and NO₂(9.51 k J·mol^-1)was slightly greater than that of HDBP and NO₂(9.06 k J·mol^-1).The influence of material ratio and target temperature on thermal stability of TBP-NO₂and HDBP-NO₂ systems was investigated by using RSC.It was found that when the temperature was 120℃,the molar ratio of TBP to NO₂ was 1:2,and the molar ratio of HDBP to NO₂ was 1:1,the system began to appear very intense exothermic phenomenon.And the higher the temperature,the greater the proportion of NO₂,the more violent the system exotherms;The orthogonal experiment showed that when TBP and HDBP co-exist in the system,temperature was still the primary factor affecting the degree of exotherm of the system,followed by the proportion of TBP and HDBP,and finally the proportion of NO₂.In addition,the addition of butanol and butyric acid can increase the heat release of the system,but the more the content,the less obvious heat release.The adiabatic accelerated calorimeter was used to study the thermal risk of TBP-NO₂system under adiabatic conditions,and the difference of HDBP and TDBP under the same conditions was compared.The results were consistent with the above conclusions,and the temperature rise/pressure rise rate increased significantly at the corresponding ratio of each system.In addition,among the derivatives of phosphate esters,butyric acid and butyl nitrite made the system more susceptible to reaction.The calculated apparent activation energy of the butyric acid system was 8.2 k J·mol^-1,the pre-referential factor was 12.4 min^-1,the The thermal risk index（TRI）value of thermal risk assessment was 3.9,the reaction hazard index（RHI）value was 8.94;the apparent activation energy of the butyl nitrite system was 9.2 k J·mol^-1,the pre-referential factor was 409.7 min^-1,the TRI value was 3.79,and the RHI value was 8.86.