Pu在处置库地下水中的种态模拟及影响特征

SPECIATION SIMULATION AND INFLUENCE OF PLUTONIUM IN GROUNDWATER OF DISPOSAL REPOSITORY

采用PHREEQC对Pu在西南某低放废物处置库、甘肃北山高放处置库五一检测井和三号井地下水中的种态及影响进行对比分析,并探讨了pH、pE和离子浓度对Pu在地下水溶液中的影响分布。结果表明:Pu在地下水中主要以Ⅳ价的Pu(OH)_4和Pu(OH)_3^+为主,其次有少量Ⅴ价的PuO_2^+存在。pE和pH对Pu在地下水中的种态存在影响较大,强酸环境中溶液主要以Pu(Ⅲ)存在,中性及碱性环境中,溶液主要以Pu(Ⅳ)存在。离子浓度对Pu在地下水中的种态有一定影响,主要原因是CO_3^(2-)和SO_4^(2-)易与Pu结合形成新的络合物。因此,放射性废物处置库选址与安全评价工作等需要充分考虑周边地下水溶液的离子浓度、pH和pE等影响因素。

Via PHREEQC,contrastive studies on effects and valences of Pu are investigated in the groundwater samples from three sites： A low radioactive waste disposal repository in the southwestern part of China,two drill wells in the highly radioactive waste disposal repository in north of Gansu. And the effect of pH,pE and ions＇ concentration on the distribution form of Pu in groundwater is discussed in this paper. The experimental results demonstrate that Plutonium（ VI） is mainly taken up by Pu（ OH）4 and Pu（ OH）3^＋ and a few Pu（ V） is in a form of PuO2^＋ in groundwater; pE and pH in groundwater dramatically decide valence state of Pu in solutions,Pu（ Ⅲ） mainly in an acid environment and Pu（ Ⅳ） in the neutral and alkaline environment. The concentrations of ions（ dominated by CO3^2-and SO4^2-） determine the chemical genres of Pu due to the susceptibility to form new coordination complex compounds with Pu combined with CO3^2-,SO4^2-. Thus pH,pE and concentrations of different ions in groundwater of surrounding environment should be addressed in a comprehensive perspective for sites choice of radioactive waste disposal repositories and corresponding safety assessments.