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氧化还原电势(Eh)是影响高放废物处置库长期安全性能的重要参数之一。然而,直接测定地下水的Eh值面临较多不确定性因素。北山花岗岩中存在一定量的含铁矿物,由此可能控制地下水中铁的含量。本工作基于北山三号井400m深处的地下水,水中铁质量浓度为0.033mg/L及钻孔岩芯中Fe~(2+)/Fe_(tot)的比值为96.86%条件下,提出了一个推测北山地下水氧化还原电势的可能方法,计算得到北山三号井地下水的Eh=83.2mV。该值与利用针铁矿的沉淀饱和指数估算得到的101.8 mV相接近,但需进一步开展现场的Eh测量工作来验证及比对。依据此Eh,利用PHREEQC程序及OECD/NEA发布的最新热力学数据,并加入MUO_2(CO_3)_3~(2-)和M_2UO_2(CO_3)_3~0(M=Ca、Mg、Sr)的稳定常数,计算了可变价核素U、~(99)Tc、~(79)Se和Np在北山地下水中的形态分布和溶解度。结果表明,U和Tc的溶解度相对较高(约10~(-5)~10~(-4) mol/L),Se的溶解度相对较低(约10~(-8) mol/L),Np的溶解度则极低(约10~(-18) mol/L);此外,溶解态的U、Tc和Se主要以阴离子形式存在,具有较强的迁移性。另一方面,北山花岗岩富含二价铁离子,因此需进一步开展其对可变价核素还原沉淀作用的实验研究,以综合评价处置场的安全性能。
The redox potential (Eh) is one of the important parameters that affect the long-term safety performance of HLW repositories. However, there are a lot of uncertainties in the direct determination of Eh of groundwater. There is a certain amount of iron-bearing minerals in Beishan granite, which may control the iron content in groundwater. Based on the groundwater depth of 400m deep in Beishan No.3 well, the mass concentration of iron in water is 0.033mg / L and the ratio of Fe ~ (2 +) / Fe tot in core is 96.86% The possible method of inferring the redox potential of Beishan groundwater was calculated and Eh = 83.2mV of Beishan No.3 well groundwater was calculated. This value is close to 101.8 mV estimated using the sedimentation saturation index of goethite, but further field Eh measurements are needed to validate and compare it. According to this Eh, the stability constants of MUO_2 (CO_3) _3 ~ (2-) and M_2UO_2 (CO_3) _3 ~ 0 (M = Ca, Mg, Sr) were obtained by using the latest thermodynamic data released by PHREEQC program and OECD / NEA. The morphological distribution and solubility of variable valent nuclides U, ~ (99) Tc, ~ (79) Se and Np in Beishan groundwater were calculated. The results showed that the solubility of U and Tc was relatively high (about 10 -5 to 10 -4 mol / L), and the solubility of Se was relatively low (about 10 -8 mol / L) The solubility of Np is very low (about 10 ~ (-18) mol / L). In addition, dissolved U, Tc and Se are mainly in the form of anions with strong mobility. On the other hand, Beishan granite is rich in ferrous ions, therefore, it is necessary to further carry out its experimental study on the reduction and precipitation of variable-valent nuclides to comprehensively evaluate the safety performance of disposal sites.