北山地下水中可变价核素的溶解度和种态分布研究

辐射防护 ›› 2020, Vol. 40 ›› Issue (4): 316-324.

北山地下水中可变价核素的溶解度和种态分布研究

程曦¹, 康明亮¹, 杨广泽², 马悦¹, 王驹³

1.中山大学中法核工程与技术学院,广东珠海 519082;
2.国核电力规划设计研究院,北京 100095;
3.核工业北京地质研究院,北京 100029

收稿日期:2019-12-27 出版日期:2020-07-20 发布日期:2020-09-21
通讯作者: 康明亮。E-mail: kangml3@mail.sysu.edu.cn
作者简介:程曦（1994—），女，2017年本科毕业于华南理工大学核工程与核技术专业，现为中山大学中法核工程与技术学院核技术及应用专业2017级在读硕士研究生。E-mail:chengx56@mail2.sysu.edu.cn
基金资助:
国家自然科学基金(No. 41773095)及中山大学科研培育专项项目(No.45000-18833403)。

Investigation on solubility and speciation of valence-variable radionuclides in Beishan underground water

CHENG Xi¹, KANG Mingliang¹, YANG Guangze², MA Yue¹, WANG Ju³

1.Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-sen University, Guangdong Zhuhai 519082;
2.State Nuclear Electric Power Planning Design & Research Institute Co. LTD., Beijing 100095;
3.Beijing Research Institute of Uranium Geology, Beijing 100029

Received:2019-12-27 Online:2020-07-20 Published:2020-09-21

摘要/Abstract

摘要： 北山28号钻孔(BS28)毗邻我国拟建高放废物处置库首座地下实验室场址。近期,基于现场动态连续测量,并结合地下水中溶解铁含量及围岩中Fe^2＋/Fe^3＋的比例推算,获得该钻孔365～690 m深处地下水在温度为18.4 ℃和pH值为(8.1±0.2)条件下,Eh值范围为-56至98 mV。基于此,本文利用PHREEQC程序及碳酸铀酰与Mg、Ca和Sr的三元配合物的热力学数据,计算了U、⁹⁹Tc、⁷⁹Se和Np在该地下水中的溶解度及种态分布情况。结果表明,地下水的pH值为8.1,Eh值在-56 mV到98 mV之间时,U、Tc和Se的溶解度范围分别为10^-9～10^-6 mol/L、10^-14～10^-4 mol/L和10^-14～10^-7 mol/L,而Np的溶解度始终低于10^-15 mol/L。在上述条件下,溶解态U、Se与Tc主要以Ca₂UO₂(CO₃)₃、CaUO₂(CO₃)₃^2-、HSeO₃^-、SeO₃^2-、TcO₄^-等中性分子或阴离子形式存在。在假定地下水氧气分压不变的情况下,在pH值为8.1时Eh值分别取-56 mV(最小值)、21 mV(中间值)和98 mV(最大值),本文也研究了pH 值在5～11范围内变化的影响。本工作仅针对均相溶液体系进行模拟,由于北山花岗岩围岩中富含二价铁,针对地下水-岩体系的实际情况,仍需进一步开展相关核素的还原固定实验研究。

关键词: 北山, 可变价核素, 溶解度, 种态分布

Abstract: The borehole 28 (BS28) at Beishan is adjacent to the site of the proposed first underground laboratory of high-level radioactive waste repository in China. By combination of on-site continuous measurements and examination of the dissolved iron content in the groundwater and the Fe^2＋/Fe^3＋ ratios in the surrounding rock, we proposed recently a redox potential (Eh) range of -56 to 98 mV with a temperature of 18.4 ℃ and pH of 8.1±0.2 for BS28 groundwater at 365-690 m depth. Based on the above conditions, the speciation and solubility of U, ⁹⁹Tc, ⁷⁹Se and Np are calculated by PHREEQC using thermodynamic data containing ternary complexes of uranyl and carbonate with Mg, Ca and Sr. When the pH of groundwater is 8.1, and Eh is between -56 mV and 98 mV, the solubility of U, Tc and Se range from 10^-9 to 10^-6 mol/L, 10^-14 to 10^-4 mol/L and 10^-14 to 10^-7 mol/L, respectively, while the solubility of Np remains below 10^-15 mol/L. In the above conditions, dissolved U, Se and Tc mainly exist in the forms of Ca₂UO₂(CO₃)₃, CaUO₂(CO₃)₃^2-, HSeO₃^-, SeO₃^2- and TcO^4-. On the condition of an invariable partial pressure of oxygen, we also investigated the influence of pH in the range of 5-11 assuming an Eh of -56 mV (minimum value), 21 mV (middle value) and 98 mV (maximum value) at pH 8.1. It is worth emphasizing that this work only simulates the homogeneous solution system, further studies on reductive immobilization of radionuclides are necessary in representative underground water-rock system, as the surrounding rock of Beishan granite is rich in ferrous iron.

Key words: Beishan site, valence-variable radionuclides, solubility, speciation

中图分类号:

TL942+.1

程曦, 康明亮, 杨广泽, 马悦, 王驹. 北山地下水中可变价核素的溶解度和种态分布研究[J]. 辐射防护, 2020, 40(4): 316-324.

CHENG Xi, KANG Mingliang, YANG Guangze, MA Yue, WANG Ju. Investigation on solubility and speciation of valence-variable radionuclides in Beishan underground water[J]. RADIATION PROTECTION, 2020, 40(4): 316-324.

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