γ-Ray radiolysis of acetohydroxamic acid in HNO₃ and its radiolytic product

γ-Ray radiolysis of acetohydroxamic acid in HNO 3 and its radiolytic product 1 corresp first-author Corresponding author. Email: jinhuawang@staff.shu.edu.cn; Corresponding author. Email: jinhuawang@staff.shu.edu.cn; jinhuawang@staff.shu.edu.cn 1 1 1 2 corresp Corresponding author. Email: wfazh@ciae.ac.cn; Corresponding author. Email: wfazh@ciae.ac.cn; wfazh@ciae.ac.cn 2 School of Environmental and Chemical Engineering, Shanghai University, 99 Shangda Road, Shanghai 200444, China School of Environmental and Chemical Engineering, Shanghai University, 99 Shangda Road, Shanghai 200444, China Radiochemistry Department, China Institute of Atomic Energy, Box 275, Beijing 102413, China Radiochemistry Department, China Institute of Atomic Energy, Box 275, Beijing 102413, China Acetohydroxamic acid (AHA) is a novel salt-free reagent used for the separation of Pu and Np from U in the advanced Purex process. This paper reports the γ-ray damage of AHA in HNO 3 and its radiolytic product. For 0.2 mol·L -1 AHA in 0.2-2.0 mol·L -1 HNO 3 irradiated at a dose of 5-25 kGy, the radiolytic rate of AHA is 6.63%-77.5%, and it increases with the HNO 3 concentration and absorbed dose. The main radiolytic gases are N 2 O and H 2 , with volume fractions of (0.500-16.2) ×10 -2 and (1.30-11.8)×10 -3 , respectively, and they increase with the absorbed dose; the H 2 volume fraction decreases with increasing HNO 3 concentration. The main liquid radiolytic products are CH 3 COOH and HNO 2, and their concentrations are (3.40-19.7) ×10 -2 and (0.200-4.80) ×10 -3 mol·L -1 , respectively, which increase with the HNO 3 concentration. Since a significant concentration of HNO 2 is present in the irradiated AHA-HNO 3 solution, a holding reductant must be used to destroy HNO 2 and stabilize Pu (III) and Np(V) when AHA is applied for the separation of Pu and Np from U. Acetohydroxamic acid γ-ray radiolysis Radiolytic product Complexant reductant Purex process Ⅰ Introduction 1 In order to realize a closed nuclear fuel cycle, the spent fuel discharged from nuclear power reactors must be reprocessed for isolating and recycling the unburned U and Pu generated. In the partition cycle of the improved Purex process used for the reprocessing of spent fuel, both Pu and Np are expected to be separated from U. On the other hand, U purification also involves the removal of Pu and Np. Two methods have been proposed for the separation of Pu and Np from U: one is the reduction of Pu(IV) and Np(VI) to Pu(III) and Np(V), which are unextractable by tri-butyl-phosphate (TBP), the other is to complex Pu(IV) and Np(IV), while U(VI) is unaffected. In the partition cycle, the concentrations of Pu and Np are relative higher, and hence, an appropriate reductant or complexant can effectively separate these nuclides from U. In the U purification cycle, however, the Pu and Np contents are very low; thus, only a complexant would be effective for the decontamination of U from Pu and Np [ 1 1 , 2 2 ]. A series of organic ligands, namely, carboxymethylamine, formic acid, acetic acid, butyric acid, pyruvic acid, glycolic acid, formohydroxamic acid, acetohydroxamic acid (AHA), and n -propionyl-hydroxamic acid were proposed and tested. The results showed that AHA is the best [ 2 2 - 6 6 2-6 ]. Many researchers studied the complexation of AHA with Pu(IV), Np(IV), and U(VI) [ 2 2 - 4 4 2-4 , 7 7 - 11 11 7-11 ] and found that the stability constants for AHA-Pu(IV) and AHA-Np(IV) are much higher than that for AHA-U(VI). Therefore, AHA can preferentially strip Pu(IV) and Np(IV) from the TBP phase into the aqueous phase, while U(VI) is unaffected. In addition, AHA can rapidly reduce Np(VI) to Np(V); U(VI) is not reduced, but Pu(IV), after initial complex formation, is slowly reduced to Pu(III) [ 3 3 , 12 12 ]. As AHA-Pu(IV), AHA-Np(IV), Np(V), and Pu(III) are unextractable by TBP, Pu and Np can be well separated from U by AHA [ 5 5 , 13 13 - 18 18 13-18 ]. AHA is composed of C, H, O, and N, and it can be completely incinerated to NO 2 and CO 2 . Since no solid waste is generated by the addition of AHA [ 16 16 ], it is expected to be useful for the reprocessing of spent fuel. However, AHA might suffer from radiation damage during its use, which would affect its efficiency, and the resulting radiolytic products may hinder effective separation. Karraker [ 19 19 ] studied the radiolysis of AHA in HNO 3 at doses up to 11 kGy, which was estimated from the spent fuel to be reprocessed, and found that radiation decomposed a minor fraction of AHA compared to the loss by hydrolysis, and that AHA radiolysis showed weak dependence on both the HNO 3 concentration and the absorbed dose. In his study, the residual AHA content was analyzed by the light absorption of an Fe (III)-AHA complex. However, he compared the effect of radiation damage on AHA based on the light absorption value of the diluted samples and not the residual concentration of AHA. As the irradiated samples were diluted 100 to 400 times, even a slight change in absorption may cause a significant difference in the AHA concentration, and the absorbance value obtained will not be representative of the AHA concentration; hence, these results are not reliable. In this study, the radiolysis of AHA is monitored based on the change in the AHA concentration, and the radiolytic product of AHA is also reported. These results are expected to serve as an important reference for the application of AHA in the reprocessing of spent fuel. Ⅱ Experiment 1 2.1 Reagent 2 AHA was supplied by Aldrich Chemical Company, and its purity was 98%. Two kinds of standard gas mixtures were supplied by Shanghai Institute of Measurement and Testing Technology: one was composed of 2.50% hydrogen, 1.00% carbon monoxide, 1.00% carbon dioxide, 0.30% methane, 0.01% ethane, 0.01% ethene, and 95.18% nitrogen; the other contained 3.00% nitrous oxide and 97.00% nitrogen. 2.2 Main equipment and accessories 2 A 3.7 × 10 15  Bq 60 Co-γ ray irradiator was supplied by Shanghai Institute of Applied Physics, Chinese Academy of Sciences. A T90 UV-VIS spectrophotometer was supplied by Beijing Purkinje General Instrument Co. Ltd. An ion chromatograph (research-style) was obtained from Switzerland Metrohm Co. Ltd. A GC900A gas chromatograph and a packed column with 5 Å molsieve (2 m × 3 mm) were supplied by Shanghai Ke Chuang Chromatograph Instruments Co. Ltd. A capillary column with aluminum oxide (50 m × 0.53 mm) was supplied by Lanzhou Institute of Chemistry and Physics, Chinese Academy of Sciences. 2.3 Sample preparation, irradiation, pretreatment, and analysis 2 0.2 mol·L -1  AHA solutions containing different concentrations of HNO 3 were prepared as follows. A certain amount of AHA was put in a beaker, which was then placed in an ice-water bath. A certain amount of 0.5 mol·L -1  HNO 3 was slowly dropped into the beaker with stirring, and then, a certain amount of slightly diluted HNO 3 was added. The solution was transferred to a 100-mL measuring flask to a constant volume. Thus, solutions in which the AHA concentration was 0.2 mol·L -1 and the HNO 3 concentration was 0.2, 0.5, 1.0, and 2.0 mol·L -1 were prepared. Four milliliters of each solution was placed in 7-mL glass vials, which were sealed with a sealing machine. The samples were irradiated by 60 Co γ-ray to 5, 10, 15, 20, and 25 kGy, and the absorbed doses were monitored by dichromate dosimeters. Control samples were used for comparison of the radiation effect on the loss of AHA by hydrolysis as well as on the amount of radiolytic product. The gases evolved from the irradiated AHA solutions were tested by gas chromatography for the analysis of H 2 , N 2 O, CH 4 , and C 2 H 6 . The irradiated AHA solutions and control samples were neutralized by KOH solution and then diluted to the suitable concentrations. Finally, these pretreated samples were tested by ultraviolet-visible spectrophotometry and ion chromatography for the analysis of AHA, HCOOH, and HNO 2 . 2.4 Analysis of AHA and its radiolytic products 2 Quantitative analysis of AHA was performed by ultraviolet-visible spectrophotometry. 2.7, 5.3, 8.0, and 10.7 m mol L -1 standard AHA solutions were prepared using high-purity water. 1.00 milliliter of each solution was placed in a 10 mL measuring flask, to which 3.00 mL FeCl 3 solution (10 wt %) and 4.00 mL CCl 3 COOH solution (2.5 wt %) were separately added. Then, water was added to constant volume, and the solutions were shaken well. The reference solution was prepared in the same manner as the standard AHA solutions but without AHA. These standard AHA solutions were tested at 502 nm by using an ultraviolet-visible spectrophotometer. The response curve for AHA was obtained from the AHA concentrations and the corresponding absorbance. The irradiated AHA solutions and control samples were neutralized by KOH solutions and diluted to suitable concentrations. These pretreated samples were tested by using the ultraviolet-visible spectrophotometer. From the response curve for AHA and the absorbance of the diluted samples, the residual AHA concentrations in the samples were calculated. H 2 , N 2 O, CH 4 , and C 2 H 6 were analyzed by gas chromatography. For H 2 analysis, a 5 Å molsieve packed column was used, and the column temperature was 80 ℃; a thermal conductivity detector (TCD) was employed, and its temperature was 110 ℃. The carrier gas was Ar, with a flow rate of 10 mL min -1 . N 2 O analysis was conducted using a packed shincarbon T column and a TCD detector. H 2 was used as the carrier gas, and its flow rate was 25 mL· min -1 . The column temperature was programmed as follows: initial temperature, 100℃; initial isothermal period, 7 min; programmed heating rate, 35 ℃·min -1 ; final temperature, 220 ℃; and final isothermal period, 1 min. The TCD temperature was 120 ℃. CH 4 and C 2 H 6 were analyzed using a PLOT Al 2 O 3 column and a flame ionization detector (FID). The carrier gas was N 2 , and its flow rate was 19 mL·min -1 . The column temperature was 40 ℃, and the FID temperature was 110 ℃. CH 3 COOH and HNO 2 were analyzed by ion chromatography with an electric conductivity detector, using a METROSEP A SUPP 5-250 column. The eluent was a solution containing 3.2 mmol·L -1 Na 2 CO 3 and 1.0 mmol·L -1 NaHCO 3 , and its flow rate was 0.7 mL·min -1 . 2.5 Formulae used in the paper 2 The hydrolysis rate of AHA is defined as follows: hydrolysis rate = (C 0 -C c )/C 0 ×100%, where C 0 is the original AHA concentration and C c is the AHA concentration in the control sample. The radiolysis rate of AHA is defined by the equation: radiolysis rate=(C c -C i )/C c ×100%, where C i is the AHA concentration in the irradiated sample. The volume fraction of the gas product is calculated as follows: if the response curve equation of a component is y = ax + b, the X axis is the injected volume of the standard gas mixture, and the Y axis is the corresponding peak area of the component. Then, the volume fraction of the component is calculated by the following formula: volume fraction= (A-b)c/ae, where A is the component peak area in the gas chromatogram of the gas sample, c is the volume fraction of the component in the standard gas mixture, and e is the injected volume of sample gas. Ⅲ Results and Discussion 1 3.1 Radiolysis of AHA in HNO 3 solution 2 As AHA can complex with Fe(III) in an acidic solution to yield a colored product, it can be analyzed by ultraviolet-visible spectrophotometry [ 15 15 ]. The response curve for AHA is y=114.38x+0.0142 (concentration range: 2.70-10.7 m·mol L -1 ), and the correlation coefficient (R 2 ) is 0.9994. The AHA concentration in control samples decreases drastically with increasing HNO 3 concentration. When the HNO 3 concentration is 0, 0.2, 0.5, 1.0, and 2.0 mol·L -1 , the hydrolysis rate of AHA is 8.20%, 23.1%, 41.2%, 66.2%, and 85.9% respectively, indicating that the rate increases with the HNO 3 concentration. This result is consistent with that reported by Taylor [ 20 20 ] and Tkac [ 10 10 ]. In an acidic solution, AHA hydrolyzes to acetic acid and hydroxylamine: <math display="block" id="M1"><mrow><mi>C</mi><msub><mi>H</mi><mn>3</mn></msub><mi>C</mi><mi>O</mi><mi>N</mi><mi>H</mi><mi>O</mi><mi>N</mi><mo>+</mo><msub><mi>H</mi><mn>2</mn></msub><mi>O</mi><mover><mo>→</mo><mrow><msup><mi>H</mi><mo>+</mo></msup></mrow></mover><mi>C</mi><msub><mi>H</mi><mn>3</mn></msub><mi>C</mi><mi>O</mi><mi>O</mi><mi>H</mi><mo>+</mo><mi>N</mi><msub><mi>H</mi><mn>2</mn></msub><mi>O</mi><mi>H</mi></mrow></math> As the time lag among sample preparation, irradiation, and neutralization is very long (about 9h), this observation cannot be used to elucidate the hydrolysis of AHA employed in the advanced Purex process. In the separation of Pu and Np from U by countercurrent liquid-liquid extraction, the residence time is about 30 min; if the separation occurs in the centrifugal contactor, the residence time is much shorter. We have studied the hydrolysis of AHA in HNO 3 at different times [ 21 21 ]. At 0.2 mol·L -1 AHA, with 0.2, 0.5, 1.0, and 2.0 mol·L -1 HNO 3 , the hydrolysis rate of AHA at 0.5h is 2.40, 5.30, 7.60, and 8.40 respectively; thus, the hydrolysis of AHA in 0.2-2.0 mol·L -1 HNO 3 would not be drastic. In addition, fast complexation of AHA with a metal leads to slower hydrolysis and stabilization of AHA in solution [ 10 10 ], so the hydrolysis of AHA will not affect its application in the separation of Pu and Np from U. Fig.1 Fig.1 illustrates the radiolysis rate of AHA as a function of dose. Fig.1 Fig.1 shows that the radiolysis rate of AHA is 6.63%-77.5 % in AHA solution irradiated to 5-25 kGy, and it increases with the dose and HNO 3 concentration. Karraker [ 19 19 ] reported that AHA radiolysis shows weak dependence on both HNO 3 concentration and absorbed dose, and this differs from our experimental results . When the dose is increased fivefold, from 5 to 25 kGy, the radiolysis rate increases 1.3-2.8 times. When the HNO 3 concentration is increased fivefold, from 0.2 to 1.0 mol·L -1 , the radiolysis rates increases 2.3-4.2 times. Thus, the effect of HNO 3 concentration on the radiolysis of AHA is stronger than that of the dose. Water radiolyzes to produce ·OH, e -1 aq ,·H, and so on: http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325917&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325916&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325917&type= ·OH may react with HNO 3 by H abstraction to form ·NO 3 [ 22 22 ]: <math display="block" id="M2"><mrow><mo>·</mo><msub><mrow><mtext>OH+HNO</mtext></mrow><mtext>3</mtext></msub><mo>→</mo><mo>·</mo><msub><mrow><mtext>NO</mtext></mrow><mtext>3</mtext></msub><msub><mrow><mtext>+H</mtext></mrow><mtext>2</mtext></msub><mtext>O</mtext></mrow></math> When using 0.2-2.0 mol·L -1 HNO 3 , most of the acid dissociates to form NO 3 - . γ-ray may react directly with HNO 3 and NO 3 - to produce ·NO 3 [ 23 23 ]: http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325920&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325919&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325920&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325923&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325922&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325923&type= ·OH and ·NO 3 are oxidative radicals, and they may react with AHA as follows [ 24 24 ]: <math display="block" id="M3"><mrow><mtext>HO</mtext><mo>⋅</mo><msub><mrow><mtext>+CH</mtext></mrow><mtext>3</mtext></msub><mtext>CONHON</mtext><mo>→</mo><msub><mrow><mtext>CH</mtext></mrow><mtext>3</mtext></msub><mtext>CONHO</mtext><mo>⋅</mo><msub><mrow><mtext>+H</mtext></mrow><mtext>2</mtext></msub><mtext>O</mtext></mrow></math> <math display="block" id="M4"><mrow><mo>⋅</mo><msub><mrow><mtext>NO</mtext></mrow><mtext>3</mtext></msub><msub><mrow><mtext>+CH</mtext></mrow><mtext>3</mtext></msub><mtext>CONHOH</mtext><mo>→</mo><msub><mrow><mtext>CH</mtext></mrow><mtext>3</mtext></msub><mtext>CONHO</mtext><mo>⋅</mo><msub><mrow><mtext>+HNO</mtext></mrow><mtext>3</mtext></msub></mrow></math> Since the concentrations of ·OH and ·NO 3 increase with dose (Eqs.2, 4-5) and the ·NO 3 concentration increases with HNO 3 concentration (Eqs.3-5), the radiolysis rate increases with both dose and HNO 3 concentration. 3.2 Radiolytic product of AHA 2 HNO 3 ionizes to produce H + , and e -1 aq can react with H + to form H: http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325927&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325926&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325927&type= H· may react with AHA to form H 2 : <math display="block" id="M5"><mrow><mtext>H</mtext><mo>⋅</mo><msub><mrow><mtext>+CH</mtext></mrow><mtext>3</mtext></msub><mtext>CONHON</mtext><mo>→</mo><msub><mrow><mtext>CH</mtext></mrow><mtext>3</mtext></msub><mtext>CONHO</mtext><mo>⋅</mo><msub><mrow><mtext>+H</mtext></mrow><mtext>2</mtext></msub></mrow></math> e aq - and ·H· may also react with NO 3 - generated from the ionization of HNO 3 , as follows [ 22 22 ]: <math display="block" id="M6"><mrow><mo>⋅</mo><msubsup><mrow><mtext>H+NO</mtext></mrow><mtext>3</mtext><mtext>-</mtext></msubsup><mo>→</mo><msubsup><mrow><mtext>HNO</mtext></mrow><mtext>3</mtext><mtext>-</mtext></msubsup><mo>→</mo><mo>⋅</mo><msub><mrow><mtext>NO</mtext></mrow><mtext>2</mtext></msub><msup><mrow><mtext>+OH</mtext></mrow><mtext>-</mtext></msup></mrow></math> <math display="block" id="M7"><mrow><msubsup><mtext>e</mtext><mrow><mtext>aq</mtext></mrow><mtext>-</mtext></msubsup><msubsup><mrow><mtext>+NO</mtext></mrow><mtext>3</mtext><mtext>-</mtext></msubsup><mo>→</mo><msubsup><mrow><mtext>NO</mtext></mrow><mtext>3</mtext><mrow><mn>2</mn><mo>−</mo></mrow></msubsup><mover><mo>→</mo><mrow><msub><mtext>H</mtext><mtext>2</mtext></msub><mtext>O</mtext></mrow></mover><mo>⋅</mo><msub><mrow><mtext>NO</mtext></mrow><mtext>2</mtext></msub><mo>+</mo><mn>2</mn><msup><mrow><mtext>OH</mtext></mrow><mtext>-</mtext></msup></mrow></math> Two ·NO 2 radicals may react with each other to form N 2 O 4 , which can react with water to produce HNO 2 : <math display="block" id="M8"><mrow><mo>⋅</mo><msub><mrow><mtext>NO</mtext></mrow><mtext>2</mtext></msub><mtext>+</mtext><mo>⋅</mo><msub><mrow><mtext>NO</mtext></mrow><mtext>2</mtext></msub><mo>→</mo><msub><mtext>N</mtext><mtext>2</mtext></msub><msub><mtext>O</mtext><mtext>4</mtext></msub><mover><mo>→</mo><mrow><msub><mtext>H</mtext><mtext>2</mtext></msub><mtext>O</mtext></mrow></mover><msub><mrow><mtext>HNO</mtext></mrow><mtext>2</mtext></msub><msub><mrow><mtext>+HNO</mtext></mrow><mtext>3</mtext></msub></mrow></math> The C-C bond in the excited AHA molecule may be broken as follows [ 25 25 ]: http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325930&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325929&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325930&type= ·CH 3 may react with AHA by H abstraction to form CH 4 , or two ·CH 3 radicals may also react with each other to produce C 2 H 6 : <math display="block" id="M9"><mrow><mo>⋅</mo><msub><mrow><mtext>CH</mtext></mrow><mtext>3</mtext></msub><msub><mrow><mtext>+CH</mtext></mrow><mtext>3</mtext></msub><mtext>CONHOH</mtext><mo>→</mo><msub><mrow><mtext>CH</mtext></mrow><mtext>4</mtext></msub><msub><mrow><mtext>+CH</mtext></mrow><mtext>3</mtext></msub><mtext>CONHO</mtext><mo>⋅</mo></mrow></math> <math display="block" id="M10"><mrow><mo>⋅</mo><msub><mrow><mtext>CH</mtext></mrow><mtext>3</mtext></msub><mtext>+</mtext><mo>⋅</mo><msub><mrow><mtext>CH</mtext></mrow><mtext>3</mtext></msub><mo>→</mo><msub><mtext>C</mtext><mtext>2</mtext></msub><msub><mtext>H</mtext><mtext>6</mtext></msub></mrow></math> Two CH 3 CONHO· radicals may react with each other to produce CH 3 CON=O [ 26 26 ]: http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325935&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325933&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325935&type= CH 3 CON=O may hydrolyze to form acetic acid and nitroxyl [ 27 27 - 28 28 27-28 ]: http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325942&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325939&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10325942&type= Two nitroxyls can react with each other to generate N 2 O: <math display="block" id="M11"><mrow><mtext>HN=O+HN=O</mtext><mo>→</mo><msub><mtext>N</mtext><mtext>2</mtext></msub><msub><mrow><mtext>O+H</mtext></mrow><mtext>2</mtext></msub><mtext>O</mtext></mrow></math> Thus, the main radiolytic product of AHA in HNO 3 may be H 2 , N 2 O, CH 4 , C 2 H 6 , CH 3 COOH, and HNO 2 . 3.2.1 H 2 generated by the radiolysis of AHA in HNO 3 3 H 2 was analyzed by gas chromatography using a packed 5 Å molsieve column and a TCD detector [ 29 29 ]. The response curve of H 2 is y=2297.8x+48.87 (volume range: 0.100-1.20 mL), and R 2 is 1.000. The volume fraction of H 2 as a function of dose is shown in Fig.2 Fig.2 . Fig.2 Fig.2 shows that the volume fraction of H 2 evolved from the AHA solutions irradiated with a dose of 5-25 kGy is (1.30-11.8) × 10 -3 . The H 2 volume fraction increases with the dose but decreases with increased HNO 3 concentration. H 2 is produced by the reaction of H· and AHA (Eq.9). H· is generated from the radiolysis of H 2 O (Eq.2), and it may also be produced by the reaction of H + and e aq - (Eq.8). As the concentrations of H· and e aq - increase with the dose, the H 2 volume fraction also increases with increasing dose. Upon the addition of HNO 3 , NO 3 - can react with ·H and e aq - (Eqs.10-11), so that the ·H concentration is reduced; hence, the volume fraction of H 2 decreases with increased HNO 3 concentration. 3.2.2 N 2 O generated from the radiolysis of AHA in HNO 3 3 We used gas chromatography with a packed shincarbon T column and a TCD detector to analyze N 2 O. The response curve of N 2 O is y=220.83x–17.67 (volume range: 0.020-3.00 mL), and R 2 is 0.9933. The volume fraction of N 2 O as a function of dose is shown in Fig.3 Fig.3 . Fig.3 Fig.3 shows that the volume fraction of N 2 O produced from AHA solutions irradiated up to a dose of 5-25 kGy is (3.29 -16.2) × 10 -2 . The N 2 O volume fraction increases with the dose and with the HNO 3 concentration when the acid concentration is ≤ 0.5 mol·L -1 . The dependence of the N 2 O volume fraction on the HNO 3 concentration is not obvious when the acid concentration is higher than 0.5 mol·L -1 . ·OH, ·NO 3 , ·H, and ·CH 3 react with AHA to form CH 3 CONHO· (Eqs. 6-7, 9, 14), and two CH 3 CONHO· radicals react to produce CH 3 CON=O (Eq.16). After hydrolysis, the HNO produced generates N 2 O (Eqs.17-18). Since the concentrations of ·OH, ·NO 3 , ·H, and ·CH 3 increase with the dose (Eqs.2-5, 13), the volume fraction of N 2 O also increases with the dose. On the other hand, the higher the HNO 3 concentration, the higher is the concentration of ·NO 3 , CH 3 CONHO·, CH 3 CON=O, and HNO (Eqs.3-5, 7, 16-17). N 2 O is produced by the reaction between two moieties of HNO (Eq.18), and thus, the volume fraction of N 2 O increases with HNO 3 concentration. However, as discussed above, the radiolysis rate of AHA increases with HNO 3 concentration, and the reduction of AHA concentration causes a decrease in the N 2 O content (Eqs. 7, 16-17). At higher HNO 3 concentration, The increase in N 2 O content resulting from the increased HNO 3 concentration is balanced by the decrease in N 2 O content due to the reduced AHA concentration; consequently, the volume fraction of N 2 O changes very slightly at high HNO 3 concentrations. 3.3.3 CH 4 and C 2 H 6 generated from radiolysis of AHA in HNO 3 3 CH 4 and C 2 H 6 were analyzed by gas chromatography with a PLOT Al 2 O 3 column and a FID detector [ 21 21 ]. The response curves of CH 4 and C 2 H 6 are y=242.7x+193.8 and y=25.56x-171.3, respectively. The volume range is 2.0 to 200.0 μL, and the corresponding R 2 values are 0.9998 and 0.9956. The volume fractions of CH 4 and C 2 H 6 evolved from AHA solutions irradiated up to 5-25 kGy are (1.90-47.4) × 10 -5 and (0.200-1.00) × 10 -5 , respectively; the volume fraction of CH 4 is much higher than that of C 2 H 6 . CH 4 is produced by the reaction of ·CH 3 and AHA (Eq.14), while C 2 H 6 is generated by the reaction of two ·CH 3 radicals (Eq.15). As the concentration of AHA exceeds that of ·CH 3 , the volume fraction of CH 4 is much higher than that of C 2 H 6 . Fig.4 Fig.4 shows that the volume fraction of CH 4 increases with the dose and with the HNO3 concentration at HNO3≤1.0 mol·L-1. When the HNO3 concentration increases from 1.0 to 2.0 mol·L -1 , there is no obvious change in the CH 4 volume fraction. CH 4 is generated by the reaction of ·CH3 and AHA (Eq.14). The ·CH3 concentration increases with the dose, so the volume fraction of CH 4 also increases with the dose. ·CH3 may react with HNO 3 as below: <math display="block" id="M12"><mrow><mo>⋅</mo><msub><mrow><mtext>CH</mtext></mrow><mtext>3</mtext></msub><msub><mrow><mtext>+HNO</mtext></mrow><mtext>3</mtext></msub><mo>→</mo><msub><mrow><mtext>CH</mtext></mrow><mtext>4</mtext></msub><mtext>+</mtext><mo>⋅</mo><msub><mrow><mtext>NO</mtext></mrow><mtext>3</mtext></msub></mrow></math> Thus, the volume fraction of CH 4 increases with the HNO 3 concentration. However, the radiolysis rate of AHA also increases with the HNO 3 concentration, as shown above, and the reduction of AHA concentration leads to a decrease in the CH 4 content (Eq.14). At higher HNO 3 concentration, the reduction in CH 4 content caused by the decrease of AHA concentration is balanced by the increase in CH 4 content resulting from the increase of HNO 3 concentration; hence, the volume fraction of CH 4 changes slightly at high HNO 3 concentrations. The volume fractions of N 2 O, H 2 , CH 4 , and C 2 H 6 have the following relationship: N 2 O ≈ 10 H 2   . ≈ 150 CH 4  ≈ 7500 C 2 H 6 . 3.3.4 CH 3 COOHand HNO 2 generated by radiolysis of AHA in HNO 3 3 Under alkaline conditions, CH 3 COOH and HNO 2 can be converted into CH 3 COO - and NO 2 - , which can be analyzed by ion chromatography. The response curves of CH 3 COOH and HNO 2 are y=872.97x and y=3766.1x, respectively. The concentration range for CH 3 COOH is 0.169-1.70 m·mol L -1 , and that for HNO 2 is 0.0217-0.435 m·mol L -1 . The R 2 values for the response curves of CH 3 COOH and HNO 2 are 0.9998 and 0.9984, respectively. Fig.5 Fig.5 shows that the CH 3 COOH concentration is (4.64-19.7) × 10 -2  mol·L -1 in AHA solutions irradiated up to 5-25 kGy. The CH 3 COOH concentration increases markedly with HNO 3 concentration and slightly with the dose. ·OH, ·NO 3 , ·H, and ·CH 3 react with AHA to form CH 3 CONHO· (Eqs.6-7, 9, 14); these radicals react with each other to produce CH 3 CON=O (Eq.16), which in turn hydrolyzes to produce CH 3 COOH (Eq.17). Since the concentration of ·OH, ·NO 3 , ·H, and ·CH 3 increases with the dose (Eqs.2-5, 13), the CH 3 COOH concentration also increases with the dose. When the HNO 3 concentration is high, the concentration of ·NO 3 , CH 3 CONHO·, and CH 3 CON=O (Eqs.3-5, 7, 16) also increases, as does the concentration of CH 3 COOH (Eq. 17). For this reason, the CH 3 COOH concentration increases with HNO 3 concentration. Fig.6 Fig.6 shows that the HNO 2 concentration is (0.321-4.80) × 10 -3  mol·L -1 in AHA solutions irradiated at a dose of 5-25 kGy; the concentration of HNO 2 increases with increasing concentration of HNO 3 . When the HNO 3 concentration is ≤1.0 mol·L -1 , the dependence of the HNO 2 concentration on the dose is not obvious. At a HNO 3 concentration of 2.0 mol·L -1 , the HNO 2 concentration increases with the dose at lower dose levels, reaching the maximum value at 15 kGy, and then decreases with a further increase in the dose but changes only slightly beyond 20 kGy. Some papers [ 27 27 , 29 29 , 30 30 ] reported that AHA can react with HNO 2 and can scavenge HNO 2 and stabilize Pu(III) and Np(V); thus an additional holding reductant is unnecessary[ 17 17 ]. The above mentioned results show that a significant concentration of HNO 2 exists in the irradiated AHA-HNO 3 solution; this means that AHA cannot effectively destroy HNO 2 , so a holding reductant should be used when AHA is applied for the separation of Pu and Np from U. Ⅳ Conclusion 1 AHA is a potential complexant and reductant used in the separation of Pu and Np from U in the advanced Purex process for the reprocessing of spent fuel. The radiation stability of AHA in HNO 3 depends on the absorbed dose and HNO 3 concentration, but the effect of the latter is greater than that of the former. At a dose of 5-25 kGy, 0.2 mol·L -1 AHA is recommended for use in HNO 3 with concentrations lower than 0.5 mol·L -1 , where the radiolytic rate of AHA is lower than 29%. The use of AHA with 2.0 mol·L -1 HNO 3 should be avoided, as the radiolytic rate of AHA is higher than 57%. The main gaseous products are N 2 O and H 2 , and the volume fraction of N 2 O is higher than that of H 2 . 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(Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, ChineseNuclear Society and Springer Nature Singapore Pte Ltd. 2018 This is a post-peer-review, pre-copyedit version of an article published in Nuclear Science and Techniques. The final authenticated version is available online at: http://dx.doi.org/10.1007/s41365-018-0360-x http://dx.doi.org/10.1007/s41365-018-0360-x . 2018 Nuclear Science and Techniques 02 29