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γ Radiation Stability and Radiolysis Products of Acetohydroxamic Acid and Dihydroxyurea

Author: LiZuo
Tutor: WangJinHua
School: Shanghai University
Course: Applied Chemistry
Keywords: Acetohydroxamic acid (AHA) Dihydroxyurea (DHU) γ radiolysis stability nitric acid
CLC: TL241.14
Type: Master's thesis
Year: 2013
Downloads: 2
Quote: 0
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Abstract

Among solar energy, hydropower, wind power, biomass energy and nuclearpower these five kinds of cleaner energy, nuclear power is the only one that has abilityto replace fossil fuels in large-scale. In china，the vigorous development of nuclearpower will definitely produce large amounts of spent nuclear fuel. Purex （plutonium–uranium reduction extraction） process is the only process of spent fuel reprocessingthat has been used in industry. It using tributyl phosphate （TBP） as extractant,separated and purified U from Pu by taking advantage of differences of uranium （U）,plutonium （Pu） and the fission products in the behavior of being extracted. Reductivestripping agent selection is a major point of Purex process. Recently, the research ofreductive stripping agent is primarily focusing on newly salt-free organic reagents.Acetohydroxamic acid （AHA） can form a stable hydrophilic complexes with Pu（Ⅳ）and Np（Ⅳ） under the conditions of U（Ⅵ） existence. Therefore U can be separatedfrom Pu and Np. Dihydroxyurea （DHU） can rapidly reduce Pu（Ⅳ） and Np（Ⅵ） toPu（Ⅲ） and Np（Ⅴ）. Therefore U can be separated from Pu and Np. It can also reactfast with nitrous acid and no support reductant is needed when DHU is used in thereprocessing of the spent fuel. The main decomposition products of DHU are gases.Therefore, AHA and DHU are both newly salt-free reagents with applicationprospects.In this thesis, we studied stability and hydrolysis products, γ radiation stabilityand radiolysis products of AHA in nitric acid solution. We also studied optimization ofDHU synthesis process and γ radiation stability, radiolysis products of DHU in bothaqueous solution and nitric acid solution. The results of this study will providereferences for application of AHA and DHU in Purex process. The main results are:1) The analysis of AHA and DHU were performed by Ultraviolet-visibleSpectrophotometer. Hydrogen, methane, ethane, ethylene, carbon dioxide andnitrous oxide were performed by Gas Chromatography. Acetic acid, nitrous acidand ammonium ion were analyzed by Ion Chromatography. Nitrous acid was alsoanalyzed by Ultraviolet-visible Spectrophotometer. 2)In HNO₃-0.2mol/L AHA solution, stability of AHA decreases as storage time orconcentration of HNO₃increases. The main hydrolysis product of AHA is aceticacid, and its concentration increases with increasing storage time or concentrationof HNO₃. In0.2mol/L AHA-1.0mol/L HNO₃solution, stability of AHA decreasesas temperature rises or storage time increases, and effect of temperature is moreobvious; concentration of acetic acid increases obviously as temperature rises. Inmethyl hydrazine-0.2mol/L AHA-1.0mol/L HNO₃solution, stability of AHAincreases obviously as methyl hydrazine added into solution, and AHA is morestable as concentration of methyl hydrazine is higher. Concentration of acetic aciddecreases obviously as methyl hydrazine added in; the more methyl hydrazine isadded to solution, the lower concentration of acetic acid is. It means that, stabilityof AHA is better with existence of methyl hydrazine.3)In HNO₃-0.2mol/L AHA solution, the γ radiation stability of AHA decreases withincreasing dose or concentration of nitric acid. The main radiolysis products arehydrogen, methane, nitrous oxide, acetic acid and nitrous acid. The volumefractions of methane increase as dose increases; as concentration of nitric acid isless than or equal to1.0mol/L, the volume fraction of methane increases withincreasing concentration of nitric acid but has no obvious relationship with it asconcentration of nitric acid is between1.0and2.0mol/L. The volume fraction ofhydrogen increases with increasing dose but decreases with increasingconcentration of nitric acid. The volume fraction of nitrous oxide and theconcentration of acetic acid increase as dose increases or concentration of nitricacid increases. The concentration of nitrous acid increases with increasingconcentration of nitric acid; as concentration of nitric acid is less than or equal to1.0mol/L, the concentration of nitrous acid has no obvious relationship with dose;however, it increases with the increasing dose before the max, but decreases withincreasing dose after the max as concentration of nitric acid is between1.0and2.0mol/L.4)In synthesis process of DHU, productive rate and purity quotient of DHU can beincreased by improved synthesis and recrystallization methods. 5)In DHU aqueous solution, the γ radiation stability of DHU decreases withincreasing dose but increases with increasing initial concentration of DHU. Themain radiolysis products of are hydrogen, carbon dioxide, ammonium ion andnitrous acid. The volume fraction of hydrogen increases as the initial concentrationof DHU increases; and it increases with the increasing dose as the initialconcentration of DHU is0.5mol/L, however, as the initial concentration of DHU isless than or equal to0.2mol/L, it increases with the increasing dose before the max,but decreases with increasing dose after the max. The volume fraction of carbondioxide and the concentration of ammonium ion increase with increasing dose orinitial concentration of DHU. The concentration of nitrous acid decreases as initialconcentration of DHU increases; it increases with the increasing dose before themax, but decreases with increasing dose after the max.6)In HNO₃-0.2mol/L DHU solution, the γ radiation stability of DHU decreases asdose or concentration of nitric acid increases. The main radiolysis products arehydrogen, carbon dioxide, nitrous oxide, ammonium ion and nitrous acid. Thevolume fraction of hydrogen increases with increasing dose but decreases withincreasing concentration of nitric acid. The volume fractions of carbon dioxide andnitrous oxide and the concentration of ammonium ion increase as dose orconcentration of nitric acid increases. The concentration of nitrous acid increases asconcentration of nitric acid increases; it increases with the increasing dose beforethe max, but decreases with increasing dose after the max.

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