Performance Assessment Of Geological Disposal Research Articles

Modelling of failure and fracture development of the Callovo-Oxfordian claystone during an in-situ heating experiment associated with geological disposal of high-level radioactive waste

To ensure the safety of geological disposal of high-level radioactive waste, in-situ experiments have been carried out to examine the behavior of rocks in underground research laboratories (URLs). At the Meuse/Haute-Marne URL in France, the French National Radioactive Waste Management Agency (Andra) has been assessing the Callovo-Oxfordian claystone (COx) as potential host rock of geological disposal by subjecting the COx to in-situ heating mimicking exothermic radioactive waste. Results of the in-situ experiments are used to validate and bolster the numerical simulators for predicting the thermo-hydromechanically (THM) coupled behavior of the COx. The numerical simulators are, however, yet to be tested for predicting the failure and fracture development of the COx during heating, which is of paramount importance to the safety of the geological disposal. In this research, we modelled a recently carried out in-situ experiment at the Meuse/Haute-Marne URL using the TOUGH-FLAC simulator to predict the failure and fracture development of the COx during heating. The objectives are to examine the effects of (i) the weak bedding planes, (ii) the softening rate of matrix/weak plane strengths, and (iii) the stiffness anisotropy of the COx on the development of shear and tensile fractures during heating. Results show that considering failure along the weak planes enabled accurate predictions of fracture development. Also, fracture development intensified at a softening rate beyond a threshold level and the geometry of fractures was significantly affected by the stiffness anisotropy. These results will help boost the reliability of the safety and performance assessment of geological disposal in claystone.

Methodology Development and Determination of Solubility-limiting Solid Phases for a Performance Assessment of Geological Disposal of High-level Radioactive and TRU Wastes

Methodology Development and Determination of Solubility-limiting Solid Phases for a Performance Assessment of Geological Disposal of High-level Radioactive and TRU Wastes

Development of Thermodynamic Database for Performance Assessment of Geological Disposal of High-level Radioactive Waste and TRU Waste

高レベル放射性廃棄物や地層処分相当TRU廃棄物などの地層処分システムの性能を評価することを目的として，廃棄体が地下水に接触したあとの放射性核種の溶解および錯生成挙動を評価するために使用する熱力学データベース(TDB)が国内外で整備されている。本報告では，経済協力開発機構原子力機関(OECD/NEA)が実施している国際プロジェクトを中心に，わが国および欧米各国で整備されているTDBを概説する。

地層処分性能評価のための岩石に対する収着分配係数の設定手法の構築：花崗岩を対象とした適用性評価

地層処分性能評価のための岩石に対する収着分配係数の設定手法の構築：花崗岩を対象とした適用性評価

放射性廃棄物の地層処分における国内の地下水コロイド研究の現状と今後の展開

本総説は，放射性廃棄物の地層処分における地下水に存在するコロイド（地下水コロイド）の影響に関連した国内の研究を紹介し，それらの実質的なネットワーク化と処分システムの性能評価におけるコロイド影響の取り扱い方等について，今後の研究の方向性に関する提案を取りまとめた．

Mine-by Experiment in a deep shaft in Neogene sedimentary rocks at Horonobe, Japan

The Japan Atomic Energy Agency (JAEA) has been implementing several research studies at the Horonobe Underground Research Laboratory (URL) in support of the Japanese R&D program for the geological disposal of High-Level Radioactive Waste (HLW). Understanding the development and properties of an EDZ (excavation disturbed or damaged zone), including the rock mechanical, hydrogeological and geochemical responses around excavated openings, is important to the design of plugs and sealing material and for performance assessment of geological disposal. The Mine-by Experiment described in this paper was carried out to investigate the development of an EDZ in one of the deep vertical shafts excavated in Neogene sedimentary rocks at the Horonobe URL site. The objective of this study is to obtain fundamental parameters of an EDZ in Neogene sedimentary rock, where case studies are few, in support of the geological disposal studies in Japan. Before and after shaft sinking, BTV (borehole television), borehole expansion tests, permeability tests and seismic velocity logging were carried out to determine initial conditions and changes in the mechanical and hydraulic properties. During shaft sinking, extensometers were installed in the rock mass to determine rock mass response to excavation. The variation of hydraulic properties was largest within one meter of the shaft wall and the variation in hydraulic conductivity was in the range of one order of magnitude.

Solubility Measurement of Iron-Selenium Compounds under Reducing Conditions

ABSTRACTChemical behavior of selenium (Se), which was one of the important elements for performance assessment of geological disposal of high-level radioactive waste, was investigated under reducing and iron-containing conditions. A washing method for an iron diselenide (FeSe2(cr)) reagent with acidic and basic solutions was carried out for the purification of FeSe2(cr) reagent, which was considered to be a solubility limiting solid for Se under the geological disposal conditions. Furthermore, solubility of FeSe2(cr) was measured in alkaline solutions under reducing conditions, and thermodynamic data on equilibrium reactions between Se in solution and Se precipitate were obtained. It was found that the dependencies of solubility values on pH and redox potential (Eh: vs. standard hydrogen electrode) were best interpreted assuming that the solubility limiting solid was not FeSe2(cr) but Se(cr) and the aqueous species was SeO32- in the present experimental conditions. The equilibrium constant between Se(cr) and SeO32- at zero ionic strength was determined and compared with literature values. The chemical behavior of Se under geological disposal conditions was discussed.

Performance Assessment of Geological Disposal of High-level Radioactive Waste in a Plastic Clay formation

ABSTRACTIn Belgium the possibilities to dispose of high-level waste in the plastic Boom Clay formation has been studied since 1975. Consequently many results of the site characterisation programme are already available. Various performance assessments have been carried out dealing with the disposal of high-level waste arising from reprocessing and with direct disposal of spent fuel. The performance assessment consists of two main steps: scenario development and consequence analyses. The scenario analysis is based on a catalogue of features, events and processes (FEPs) having the potential to influence the behaviour of the repository system. Two main groups of scenarios are distinguished. The normal evolution scenario, including a number of variants, treats the FEPs that are fairly sure to take place. Altered evolution scenarios focus on FEPs having a probability of occurrence lower than one but that might influence the performance of the repository system. For the impact analyses, a robust concept approach was introduced, which focused the analyses on a limited number of well-characterised barriers and processes. The impact analyses are complemented with sensitivity and uncertainty analyses based on deterministic and probabilistic approaches.

Diffusion of Ni in Compacted Sodium Bentonite

Diffusion coefficients of key nuclides in bentonite are one of the important parameters required for performance assessment of geological disposal of high-level radioactive waste (HLW). Diffusion is generally classified into two states: non-steady state and steady state. Nonsteady state diffusion represents the diffusion coefficient in a transient state, which is called apparent diffusion coefficient (Da). In performance assessment, Da is accounted as an important parameter for evaluating nuclide retardation in bentonite. Nickel-59 is produced by activation of the corrosion products in a power reactor and is one of the important radionuclides for performance assessment because of its long half-life of 7.5×104 yr. Christiansen and Torstenfelt have reported Da of Ni in bentonitew(1). However, Da for Ni in Kunigel V1R bentonite (Kunimine Industries Co., Ltd.), which is produced in Japan, has not been measured yet. In underground, such 1, 000m deep, bentonite temperature is higher than that of ground surface because of temperature gradient(2). This temperature increase may affect diffusion behaviors of nuclides in bentonite. For example, it has been reported that the apparent diffusion coefficients for Cs, Na, HTO and Sr in bentonite become larger with increasing temperature(3)-(7). However, studies for temperature dependence on diffusion of nuclides in compacted bentonite are quite limited. In this study, the apparent diffusion coefficients for Ni in Kunigel V1 were measured as functions of density of the bentonite and temperature, then the activation energy for diffusion was calculated from the temperature dependence of the Da.