核废物处置安全评价的地质类比研究

本文简要论述了利用天然地质类似物（或类比体），类比评价核废物处置系统的安全性能。地质类比研究是安全评价核废物处置系统的重要方法之一，也是地质学科的新研究领域。目前已有的地质类比研究对象主要有火山玻璃，陨石玻璃，粘土矿物，铁陨石，铜矿床，铀矿床，含含Ｔｈ和ＲＥＥ的铁矿床，天然核反应堆（一种特殊的铀矿床）和火成岩接触带等。最后对我国今后从事同类研究提出了若干建议。     

高放废物地质处置数据资源集成开发进展

数据资源是高放废物地质处置库选址、安全评价、工程建设等研发的重要基础,该领域数据具有典型的大数据特性,其开发利用是一项长期、系统的科学工程。文章对我国高放废物地质处置数据资源集成开发策略、方法和现状进行了简要介绍,阐述了高放废物地质处置研发过程中产生的各类科学数据的具体特性,提出建立我国高放废物地质处置大数据平台的规划设想,重点介绍了处置库预选区地学信息集成开发现状。     

花岗岩型地质处置库情景试构建与分析

高水平放射性废物(高放废物)地质处置库关闭后长期演变情景的构建和定量分析是安全评价的关键。研究以拟建于北山预选区的花岗岩型处置库为研究对象,对情景开发及其分析进行了初步探索。采用"自下而上"的情景开发方法,构建了处置库关闭后预期演变情景和3类典型的非预期演变情景,对各类情景条件下的核素释放率进行了计算和分析。结果表明,现有条件下,处置库具备较好的安全性;为提升安全评价的可靠度,需要进一步加强情景不确定性的分析。     

盐溶液法测定非饱和膨润土的水分特征曲线

对于高放废物的最终处置，深地质处置被国内外公认为最合适的方法，而膨润土也被认为是高放废物处置库缓冲回填材料的良好基质。鉴于膨润土各项性质研究的重要性。本文介绍了利用盐溶液法进行非饱和膨润土水分特征曲线的测定工作，发现盐溶液法适合测定吸力极高的非饱和土，是一种值得推广的方法。     

Estimation of loading density of underground well repositories for solid high-level radioactive wastes

The convective transfer of radionuclides by subsurface water from a geological repository of solidified high-level radioactive wastes (HLW) is considered. The repository is a cluster of wells of large diameter with HLW disposed of in the lower portions of the wells. The safe distance between wells as a function of rock properties and parameters of well loading with wastes has been estimated from mathematical modeling. A maximum permissible concentration of radionuclides in subsurface water near the ground surface above the repository is regarded as a necessary condition of safety. The estimates obtained show that well repositories allow for a higher density of solid HLW disposal than shaft storage facilities. Advantages and disadvantages of both types of storage facilities are considered in order to estimate the prospects for their use for underground disposal of solid HLW.     

高放射性核废物地质处置库场址预选和矿产资源勘查的关系

据1999—2007年资料的不完全统计,甘肃省地勘部门在北山地区一共投入4488.2万元人民币,矿产资源潜在价值估计为13.28亿元。一旦把甘肃省北山列为高放废物处置库的预选区,则潜在的经济损失将会很大,还可能影响西北地区的土地利用程度和经济发展。核试验场有多种围岩可供处置库地质选址选择,而且远离国境线与居民区,有利于高放废物处置库的安全管理。结合中国国情,在地质和社会条件有利的核试验军事禁区开展国家高放废物处置库的预选场址工作有独特的优势。提出了尽快在中国核试验场址开展高放废物地质处置库场址预选工作的建议。     

高放废物深地质处置地下水数值模拟应用综述

开展地下水数值模拟研究是高放废物处置场地安全评价的重要组成部分,然而深地质处置介质类型的复杂性、基岩深部资料的相对匮乏性导致模拟结果存在不确定性,如何刻画深部地下水动力场并评估可能引起的风险已成为高放废物处置安全评价中重点关注的问题。在大量文献调研的基础上,综述了世界典型国家高放废物深地质处置场地的地下水数值模拟与不确定性分析应用,并归纳总结该领域研究经验,得到以下认识:（1）深地质处置场深部构造、裂隙的发育与展布决定了地下水循环条件,探究适用于基岩裂隙地区新的水文地质试验方法是提高地下水数值模型仿真性的基础;（2）不同尺度模型融合是解决深地质处置地下水模拟的有效技术方法,区域尺度多采用等效连续介质法,场地尺度使用等效连续多孔介质和离散裂隙网络耦合模型,处置库尺度使用离散裂隙网络方法,其次需重点关注未来大时间尺度下放射性核素在地质体中的迁移转化规律,模拟预测场址区域地下水环境长期循环演变对核素迁移的潜在影响;（3）考虑到不同的处置层主岩岩性以及在多介质中发生的THMC（温度场—渗流场—应力场—化学场）过程,目前国内外常用的地下水模拟软件有:Porflow、Modflow、GMS及MT3DMS等用于模拟孔隙或等效连续介质,Connectflow、Feflow及FracMan等用于模拟地下水和核素在结晶岩、花岗岩等裂隙中的迁移,TOUGH系列软件主要应用于双重介质的水流、溶质及热运移模拟;（4）指导开展有针对性的模型和参数的不确定性分析工作,减少投入工作量,提高模型精度,并可针对处置库长期演变、废物罐失效、极端降雨等多情景预测模拟,为处置库安全评价及设计提供基础数据支撑;（5）针对我国深地质处置地下水数值模拟研究现状,下一步应加强区域地质、水文地质、裂隙测量以及现场试验等相关的调查及监测工作,多介质耦合、多场耦合模拟及不确定性分析研究将会是未来的研究重点。     

高效废物处置库的混合型缓冲回填材料压缩特性研究

高放废物处置库中缓冲回填材料需要预先压缩到一定密实度,其压缩特性对处置库的安全设计、施工及运营有重要影响。目前,国内初步考虑将膨润土-砂混合物作为缓冲回填材料的首选。采用WG型单杠杆固结仪,对不同干密度、掺砂率的膨润土-砂混合物进行侧限压缩试验研究。试验结果表明：随着干密度的增大,压缩系数呈二次曲线减小;随着掺砂率的增大,压缩系数呈非线性增大。通过引入有效黏土密度和有效含水率的概念,对不同干密度、掺砂率的膨润土-砂混合物的压缩系数进行解释,并根据试验数据得到了回归的数学模型,试图为缓冲回填材料的配比优化研究提供相关依据。     

中国高放废物地质处置缓冲材料大型试验台架和热-水-力-化学耦合性能研究

缓冲材料作为高放废物深地质处置库中一道重要的人工屏障,与高放废物容器和处置库围岩直接接触,在高放废物衰变热、辐射作用和地下水等影响下产生复杂的热-水-力-化学耦合作用,为了验证缓冲材料是否能长期有效地发挥其屏障材料的作用,核工业北京地质研究院利用高庙子钠基膨润土组装并运行了模拟中国高放废物地质处置室 尺寸的大型缓冲材料膨润土试验台架（China-Mock-Up）。建立了缓冲材料试验台架的安装和试验方法,依据实测数据和理论分析,揭示了热-水-力-化学耦合作用条件下膨润土中的相对湿度是在加热器的热效应和外部供水的湿效应共同作用下发生变化的,压实膨润土中应力的变化主要是由于膨润土遇水膨胀和加热器的热效应引起的,试验验证了模拟高放废物地质处置室内加热器（废物罐）运行初期的位移过程,为缓冲材料和高放废物地质处置库的设计提供了重要的工程参数和理论依据。     

膨润土颗粒混合物的堆积性质与水-力特性研究进展

膨润土颗粒混合物是高放废物深地质处置库中的一种缓冲/回填材料,掌握其堆积性质与水-力特性是开展处置库安全性能评估的关键基础。本文全面回顾和总结了近年来国内外学者对膨润土颗粒混合物的堆积性质、持水特性、结构特征、渗透特性、胀缩特性及本构模型等方面的研究进展与取得的成果,展望了几个值得进一步研究的问题。结果表明,颗粒混合物的堆积性质与粒径级配密切相关;湿化过程中,颗粒混合物由初始松散结构逐渐转变为胶结融合结构,孔隙结构逐渐趋于均一化,并伴随着颗粒破碎和错动,进而影响其水-力特性。考虑到处置库实际运营环境的复杂性,颗粒混合物的原位填充技术以及多场(热-水-力-化)耦合条件下颗粒混合物的水-力特性是今后值得深入研究的方向。     

THM Coupled Modeling in Near Field of an Assumed HLW Deep Geological Disposal Repository

One of the most suitable ways under study for the disposal of high-level radioactive waste (HLW) is isolation in deep geological repositories. It is very important to research the thermo-hydromechanical (THM) coupled processes associated with an HLW disposal repository. Non-linear coupled equations, which are used to describe the THM coupled process and are suited to saturated-unsaturated porous media, are presented in this paper. A numerical method to solve these equations is put forward, and a finite element code is developed. This code is suited to the plane strain or axis-symmetry problem. Then this code is used to simulate the THM coupled process in the near field of an ideal disposal repository. The temperature vs. time, hydraulic head vs. time and stress vs. time results show that, in this assumed condition, the impact of temperature is very long (over 10 000 a) and the impact of the water head is short (about 90 d). Since the stress is induced by temperature and hydraulic head in this condition, the impact time of stress is the same as that of temperature. The results show that THM coupled processes are very important in the safety analysis of an HLW deep geological disposal repository.     

Principles of geomechanical safety assessment for radioactive waste disposal in salt structures

Today, a large amount of knowledge is available concerning various sites of potential high active waste (HAW) repositories in salt media. Domal Zechstein salt formations have been examined at several sites in Germany. Extensive R&D work was initiated in the former Asse Salt Mine in order to explore the suitability of salt for waste isolation by laboratory tests, theoretical studies and in-situ tests with test results forming a technological base for future repository development.

Resulting from the inhomogeneity of salt structures the demanded safety of a permanent repository for radioactive wastes can be demonstrated only by a specific site analysis in which the entire system, “the geological situation, the repository, and the form and amount of the wastes” and their interrelationships are taken into consideration.

The site analysis has three essential tasks: (1) Assessment of the thermomechanical load capacity of the host rock, so that deposition strategies can be determined for the site; (2) Determination of the safe dimensions of the mine (e.g. stability of the caverns and safety of the operations); and (3) Evaluation of the barriers and the long-term safety analysis for the authorization procedure.

The geotechnical stability analysis is a critical part of the safety assessment. Engineering–geological study of the site, laboratory and in situ-experiments, geomechanical modelling, and numerical static calculations comprise such an analysis.

Within a scenario analysis — according to the multi-barrier principle, the geological setting is checked to be able to contribute significantly to the waste isolation over long periods. The assessment of the integrity of the geological barrier can only be performed by making calculations with geomechanical and hydrogeological models. The proper idealization of the host rock in a computational model is the basis of a realistic calculation of stress distribution and excavation damage effects. The determination of water permeability along discontinuities is necessary in order to evaluate the barrier efficiency of each host rock.

In this paper some important processes for the performance assessment are described, namely creep and fracturing, permeability and infiltration, and halokinesis and subrosion.

For the future, the role and contributions of geoscientific and rock mechanics work within the safety assessment issues (e.g. geomechanical safety indicators) must be identified in greater detail, e.g. considerations of geomechanical natural analogy for calibration of constitutive laws.     

ArcGIS在北山高放废物处置库预选区地学数据管理中的应用

以甘肃北山高放废物处置预选区所积累的数据为基础,研究地学信息数据管理平台的建立,实现对各种空间数据及其他非空间数据统一管理与应用,并提出了基于ArcGIS产品的预选区数据管理与共享的解决方案。     

高放废物地质处置库预选缓冲材料压缩性能研究

缓冲材料是高放废物深地质处置多重屏障系统中非常重要的一道人工屏障，内蒙古高庙子钠基膨润土被确定为我国高放废物深地质处置缓冲材料的首选基料。通过研究该钠基膨润土（GMZ01）在不同含水量条件下的压实成型性、不同压实干密度和不同含水量压实样品的无侧限压缩性能，认为：含水量为15％的高庙子天然钠基膨润土压实成型性最好，压实干密度越大，无侧限抗压强度越大；在无侧限压缩实验时，含水量为15％的高密度压实膨润土样品比含水量为10％和20％的样品的抗压强度大，变形小。     

Subterranean microorganisms and radioactive waste disposal in Sweden

In 1987, microbiology became a part of the Swedish scientific program for the safe disposal of high level nuclear waste (HLW). The goal of the microbiology program is to understand how subterranean microorganisms will interact with the performance of a future HLW repository. The Swedish research program on subterranean microbiology has mainly been performed at two sites in granitic rock aquifers at depths ranging from 70 m down to 1240 m, the Stripa research mine in the middle of Sweden and the Äspö Hard Rock Laboratory (HRL) situated on the south eastern coast of Sweden. Some work has also been performed in cooperation with other national or international research groups in Sweden, Canada and at the natural analogue sites Oklo in Gabon and Maqarin in Jordan. The following conclusions are drawn. There is a very high probability of the existence of a deep subterranean biosphere in granitic rock. The documented presence of a deep biosphere implies that relevant microbial reactions should be included in the performance assessment for a HLW repository. A HLW repository will be situated in a subterranean biosphere that is independent of solar energy and photosynthetically produced organic carbon. The ultimate limitation for an active microbial life will be the availability of hydrogen as energy source over time, and hydrogen has indeed been found in most deep groundwaters. Sulphide producing microorganisms are active in environments typical for a Swedish HLW repository, and the potential for microbial corrosion of the copper canisters must be considered. The bentonite buffer around the copper canisters will be a hostile environment for most microbes due to the combination of radiation, heat and low water availability. Discrete microbial species can cope with each of these constraints, and it is theoretically possible that sulphide producing microbes may be active inside a buffer, although the experiments conducted thus far have shown the opposite. Microorganisms have the capability to enzymatically recombine radiolysis oxidants formed by radiation of water. It has earlier been concluded that the migration of radionuclides due to sorption on microorganisms can be neglected. The influence of microbially produced complexing agents remains to be studied at realistic conditions in deep groundwater. Microorganisms have been found in natural alkaline groundwaters, but it could not be conclusively demonstrated that they were in situ viable and growing, rather than just transported there from neutral groundwater. A possible hypothesis based on the obtained results from investigations of natural alkaline groundwaters is that fresh concrete may be a bit too extreme for active life even for the most adaptable microbe – but this remains to be demonstrated.     

Britholites as natural analogues of actinide matrices: Resistance to radiation damage

Crystallization of borosilicate glasses, used now for solidification of liquid nuclear high-level wastes (HLW), is accompanied by the formation of silicates with the apatite-type structure and high contents of actinides and REE. The stability of these silicates determines the safety of immobilization of radionuclides. As a result of radioactive decay, the crystalline phases of actinides become amorphous with time and their solubility in aqueous solutions increases. One of the ways to assess the radiation stability of compounds is the study of their natural analogues that contain radioactive elements. Minerals of the britholite group are the natural analogues of synthetic rare earth silicates and actinides with the apatite-type structure. Seven britholites of different ages and with different ThO₂ + UO₂ contents have been studied. The stages of partial damage and complete destruction of sample structures under the effect of radioactive decay were distinguished. The radiation stability of natural britholites surpasses that of their synthetic analogues. The annealing of metamict samples recovers the primary apatite-type structure without formation of any other phases. With an increase in annealing duration from 1 to 5 h, the mineral structure is recovered at a lower (by 200°C) temperature (down to 550–600°C). The temperature conditions in underground storages and the substantially longer occurrence of HLW therein will prevent crystalline matrices with the apatite-type structure from amorphization and thus ensure the retention of their stability.     

From aqueous solution to solid solutions: A process oriented review of the work performed within the FUNMIG project

The Fundamentals of Radionuclide Migration (FUNMIG) project was organised in some Research and Technological Development Components (RTDCs) integrated by a number of Work Packages (WP’s) attempting to cover the key migration processes at different scales (laboratory to repository) and in different geological media, mainly clay and granite, but also some salt rock related work was performed. The main RTDCs of interest for this review paper are numbers 1 and 2, which concerned laboratory studies of well-established and less-established migration processes. Some additional interesting outcomes arise also from RTDCs 3, 4 and 5 devoted to the upscaling and applicability of migration processes to clay, granite and salt rock environments, respectively. This review discusses the contribution of the various parts of the FUNMIG project in the process oriented context of understanding the mechanistic approximation to what can be seen as the final and thermodynamically stable stage of the long chain of processes which are covered under the general term of sorption and that culminate in the formation of solid solutions.     

高放废物深地质处置：回顾与展望

文章对我国高放废物地质处置研究的历史进行了回顾,并对未来发展进行了展望。我国的高放废物深地质处置研究开发从1985年开始,迄今为止可初步分为3个阶段：①起步和跟踪研究阶段（1985～1998）;②逐步发展阶段（1999～2005）;③政府规划指导阶段（2006至今）。20多年来,我国在国家法律法规、战略规划、选址、工程屏障、核素迁移研究等方面取得了显著进展。我国已经提出在2020年前建成地下实验室、21世纪中叶建成高放废物处置库的目标。研究开发和处置库工程建设分成3个阶段：试验室研究开发和处置库选址阶段（2006～2020）;地下现场试验阶段（2021-2040）和处置库建设阶段（2041～本世纪中叶）。经过全国筛选对比,已初步选定甘肃北山地区为重点预选区,系统的场址评价工作正在进行。已确定采用膨润土作为处置库的回填材料,并初步确定内蒙古高庙子膨润土为我国高放废物处置库的首选缓冲回填材料。工程设计、核素迁移研究和安全评价也取得了一定进展。1999年起与国际原子能机构开展了3期高放废物地质处置技术合作项目,对提高我国的技术水平起到了积极作用。20多年的研究开发工作为我国在21世纪完成高放废物地质处置任务奠定了基础。     

Consequences of the Thermal Transient on the Evolution of the Damaged Zone Around a Repository for Heat-Emitting High-Level Radioactive Waste in a Clay Formation: a Performance Assessment Perspective

A proper evaluation of the perturbations of the host rock induced by the excavation and the emplacement of exothermic wastes is essential for the assessment of the long-term safety of high-level radioactive waste disposals in clay formations. The impact of the thermal transient on the evolution of the damaged zone (DZ) has been explored in the European Commission project TIMODAZ (thermal impact on the damaged zone around a radioactive waste disposal in clay host rocks, 2006–2010). This paper integrates the scientific results of the TIMODAZ project from a performance assessment (PA) point of view, showing how these results support and justify key PA assumptions and the values of PA model parameters. This paper also contextualises the significance of the thermal impact on the DZ from a safety case perspective, highlighting how the project outcomes result into an improved understanding of the thermo–hydro–mechanical behaviour of the clay host rocks. The results obtained in the TIMODAZ project strengthen the assessment basis of the safety evaluation of the current repository designs. There was no evidence throughout the TIMODAZ experimental observations of a temperature-induced additional opening of fractures nor of a significant permeability increase of the DZ. Instead, thermally induced plasticity, swelling and creep seem to be beneficial to the sealing of fractures and to the recovery of a very low permeability in the DZ, close to that of an undisturbed clay host rock. Results from the TIMODAZ project indicate that the favourable properties of the clay host rock, which guarantee the effectiveness of the safety functions of the repository system, are expected to be maintained after the heating–cooling cycle. Hence, the basic assumptions usually made in PA calculations so far are expected to remain valid, and the performance of the system should not be affected in a negative way by the thermal evolution of the DZ around a radioactive waste repository in clay host rock.     

Isomorphism of actinides and REE in synthetic ferrite garnets

The reprocessing of spent nuclear fuel (SNF) is accompanied by the formation of liquid high-level radioactive waste (HLW). To increase the safety of handling HLW, it is proposed to extract actinide isotopes (An) and REE from them. These elements may be incorporated into crystalline matrices, e.g., based on ferrites with garnet structure, and then disposed in a geologic repository. The actinide-REE fraction is characterized by a complex composition. In addition to major components (An and REE), Al, Si, Na, and Sn occur therein in small amounts (a few wt %). Possible incorporation of the admixtures into ferrite garnets, as well as their effect on the phase composition of matrices and Th, Ce, Gd, and La contents were studied. It was shown that admixtures enter into garnet by means of isomorphic replacement. The properties of samples change only when admixtures are added in amounts exceeding their concentrations in HLW. The ability of ferrite garnets to accumulate significant amounts of An, REE, and admixture elements makes them suitable for use as matrices in immobilizing actinide-REE HLW of complex composition.