Expected near-field thermal environments in a sequentially loaded spent-fuel or high-level waste repository in salt

ABSTRACTRedox conditions were assessed for a spent fuel and high-level waste (SF/HLW) and an intermediate-level waste (ILW) repository. For both cases our analysis indicates permanently reducing conditions after a relatively short oxic period. The canister-bentonite near field in the HLW case displays a high redox buffering capacity because of expected high activity of dissolved and surface-bound Fe(II). This is contrary to the cementitious near field in the ILW case where concentrations of dissolved reduced species are low and redox reactions occur primarily via solid phase transformation processes.For the bentonite-canister near field, redox potentials of about -100 to -300 mV (SHE) are estimated, which is supported by recent kinetic data on U, Tc and Se interaction with reduced iron systems. For the cementitious near field, redox potentials of about -200 to -800 mV are estimated, which reflects the large uncertainties related to this alkaline environment.

Download Full-text

Criticality in a Repository for Spent Fuel: Lessons From Oklo

MRS Proceedings ◽

10.1557/proc-506-781 ◽

1997 ◽

Vol 506 ◽

Cited By ~ 1

Author(s):

V. M. Oversby

Keyword(s):

Nuclear Reactor ◽

Critical Mass ◽

Granitic Rocks ◽

High Level Waste ◽

Fissile Material ◽

Spent Fuel ◽

Nuclear Reactor Fuel ◽

Sequence Of Events ◽

Waste Repository ◽

High Level

ABSTRACTThe conditions that are needed to achieve criticality in a high level waste repository for spent nuclear reactor fuel are reviewed. The effect of initial enrichment of the fuel, burnup, and of mixed oxide fuels on the conditions for criticality are discussed. The situations that produced criticality at Oklo, Gabon, 2000 million years ago are summarized. A model based on the Oklo conditions is presented for estimating the amount of fissile material that must be assembled to create a critical mass in typical granitic rocks. Mechanisms for movement of uranium and plutonium to achieve a critical configuration are discussed and compared to the conditions that are likely to occur in a repository in granite. The sequences of events needed to produce a critical assemblage are shown to be in conflict with the conditions expected in the repository and, in some cases, to require internally inconsistent assumptions to produce the postulated sequence of events. No credible scenario for achieving criticality in a high level waste repository has been found.

Download Full-text

Packaging of High Burnup UO2 and MOX Spent Fuel Considering Temperature Restrictions in the Near Field of a Repository

MRS Proceedings ◽

10.1557/proc-506-927 ◽

1997 ◽

Vol 506 ◽

Author(s):

D.F. McGinnes ◽

J. W. Schneider

Keyword(s):

Near Field ◽

Management Program ◽

High Level Waste ◽

Heat Output ◽

Spent Fuel ◽

Ambient Temperatures ◽

Heat Loading ◽

High Burnup ◽

Maximum Temperatures ◽

High Level

ABSTRACTThe direct disposal of spent fuel is one of the options considered in the Swiss high level waste management program. One of the important questions, within this program, is the heat generation from high-burnup UO2and MOX spent fuels. Depending on the repository boundary conditions (e.g. ambient temperatures at depth, thermal properties of the host rock etc.), on the maximum temperatures allowed in the near field and on the heat output of the fuel, it may not always be possible to completely fill the conceptual waste canister. The aim of this paper is to address the potential loading of spent fuel into canisters for different possible repository heat loading restrictions

Download Full-text

Integrated Model of Korean Spent Fuel and High Level Waste Disposal Options

ASME 2009 12th International Conference on Environmental Remediation and Radioactive Waste Management, Volume 1 ◽

10.1115/icem2009-16091 ◽

2009 ◽

Author(s):

Yongsoo Hwang ◽

Ian Miller

Keyword(s):

Nuclear Fuel ◽

Spent Nuclear Fuel ◽

Fuel Cycle ◽

Near Field ◽

Integrated Model ◽

High Level Waste ◽

Spent Fuel ◽

Parameter Uncertainties ◽

Design Concepts ◽

High Level

This paper describes an integrated model developed by the Korean Atomic Energy Research Institute (KAERI) to simulate options for disposal of spent nuclear fuel (SNF) and reprocessing products in South Korea. A companion paper (Hwang and Miller, 2009) describes a systems-level model of Korean options for spent nuclear fuel (SNF) management in the 21’st century. The model addresses alternative design concepts for disposal of SNF of different types (CANDU, PWR), high level waste, and fission products arising from a variety of alternative fuel cycle back ends. It uses the GoldSim software to simulate the engineered system, near-field and far-field geosphere, and biosphere, resulting in long-term dose predictions for a variety of receptor groups. The model’s results allow direct comparison of alternative repository design concepts, and identification of key parameter uncertainties and contributors to receptor doses.

Download Full-text

Modelling sorption data for the actinides Am(III), Np(V) and Pa(V) on montmorillonite

Radiochimica Acta ◽

10.1524/ract.2006.94.9-11.619 ◽

2006 ◽

Vol 94 (9-11) ◽

Cited By ~ 34

Author(s):

Michael H. Bradbury ◽

B. Baeyens

Keyword(s):

Near Field ◽

High Level Waste ◽

Spent Fuel ◽

Data Set ◽

Sorption Data ◽

Deep Geological Disposal ◽

Retention Characteristics ◽

High Level ◽

Trace Concentrations ◽

First Time

The retention characteristics of the bentonite near-field engineered barrier proposed in most of the concepts for the deep geological disposal of high-level waste and spent fuel are an important component in repository performance assessment studies. Montmorillonite generally constitutes 65 to 90 wt.% of the bentonite. Sorption edge measurements have been performed at trace concentrations for the actinides Am(III), Np(V) and Pa(V) on purified and conditioned SWy-1 montmorillonite under anoxic, carbonate free conditions. To the best of the author´s knowledge, this is the first time a sorption data set has been measured for

Download Full-text

The IAEA Coordinated Research Programme on the Performance of High-Level Waste Forms and Packages Under Repository Conditions

MRS Proceedings ◽

10.1557/proc-294-719 ◽

1992 ◽

Vol 294 ◽

Author(s):

Vladimir S. Tsyplenkov

Keyword(s):

Near Field ◽

Research Programme ◽

High Level Waste ◽

Future Research ◽

Spent Fuel ◽

Waste Forms ◽

Safety Assessments ◽

High Level ◽

Coordination Meeting

ABSTRACTThe IAEA initiated, in 1991, a Coordinated Research Programme (CRP), with the aim of promoting the exchange of information on the results obtained by different countries in the performance of high-level waste forms and waste packages under conditions relevant to final repository. These studies are being undertaken to obtain reliable data as input to safety assessments and environmental impact analyses, for final disposal purposes. The CRP includes studies on waste forms that are presently of interest worldwide: borosilicate glass, Synroc and spent fuel.Ten laboratories leading in investigation of high-level waste form performance have already joined the programme. The results of their studies and plans for future research were presented at the first Research Coordination Meeting, held in Karlsruhe, Germany, in November 1991. The technical contributions concentrated on effecting an understanding of dissolution mechanisms of waste forms under simulated repository conditions. A quantitative interpretation of the chemical processes in the near field is considered a prerequisite for long-term predictions and for the formulation of a "source term" for performance assessment studies.

Download Full-text

Thermal Conductivity of Korean Compacted Bentonite Buffer Materials for a Nuclear Waste Repository

Energies ◽

10.3390/en11092269 ◽

2018 ◽

Vol 11 (9) ◽

pp. 2269 ◽

Cited By ~ 11

Author(s):

Seok Yoon ◽

WanHyoung Cho ◽

Changsoo Lee ◽

Geon-Young Kim

Keyword(s):

Thermal Conductivity ◽

Near Field ◽

High Level Waste ◽

Nuclear Waste Repository ◽

Spent Fuel ◽

Decay Heat ◽

Bentonite Buffer ◽

Buffer Material ◽

Overall Evaluation ◽

High Level

Engineered barrier system (EBS) has been proposed for the disposal of high-level waste (HLW). An EBS is composed of a disposal canister with spent fuel, a buffer material, backfill material, and a near field rock mass. The buffer material is especially essential to guarantee the safe disposal of HLW, and plays the very important role of protecting the waste and canister against any external mechanical impact. The buffer material should also possess high thermal conductivity, to release as much decay heat as possible from the spent fuel. Its thermal conductivity is a crucial property since it determines the temperature retained from the decay heat of the spent fuel. Many studies have investigated the thermal conductivity of bentonite buffer materials and many types of soils. However, there has been little research or overall evaluation of the thermal conductivity of Korean Ca-type bentonite buffer materials. This paper investigated and analyzed the thermal conductivity of Korean Ca-type bentonite buffer materials produced in Gyeongju, and compared the results with various characteristics of Na-type bentonites, such as MX80 and Kunigel. Additionally, this paper suggests various predictive models to predict the thermal conductivity of Korean bentonite buffer materials considering various influential independent variables, and compared these with results for MX80 and Kunigel.

Download Full-text

Evaluation of temperature-induced effects on safety-relevant properties of clay host rocks with regard to HLW/SF disposal

Mineralogical Magazine ◽

10.1180/minmag.2015.079.6.14 ◽

2015 ◽

Vol 79 (6) ◽

pp. 1389-1395 ◽

Cited By ~ 3

Author(s):

M. Jobmann ◽

A. Meleshyn

Keyword(s):

Current Knowledge ◽

Near Field ◽

High Level Waste ◽

Major Influence ◽

Thermal Impact ◽

Spent Fuel ◽

Thermally Induced ◽

Improved Performance ◽

High Level ◽

Host Rocks

AbstractDBE TECHNOLOGY, BGR and GRS are developing a methodology to demonstrate the safety of a repository for high-level waste and spent fuel (HLW/SF) in clays according to the requirements of the German regulating body. In particular, these requirements prescribe that the barrier effect of host rocks must not be compromised by a thermal impact resulting from HLW/SF emplacement. To substantiate and quantify this requirement, we carried out a literature survey of research on thermally-induced changes on clay properties. Effects thus compiled can be divided into thermo-hydro-mechanical and chemical-biological-mineralogical effects and were analysed with regard to their relevance to the integrity of clay host rocks. This analysis identified one effect of major influence within each group: thermal expansion and compaction as well as results of microbial activities. Importantly, it further revealed that a moderate temperature increase above 100°C cannot be expected to compromise the integrity of the geological barrier according to the current knowledge state. Evidence is presented in this paper that temperature increases up to 150°C can actually contribute to an improved performance of a radioactive waste repository by increasing the consolidation of the clay and sterilizing the repository's near-field to depress the deteriorative microbial effects. A quantitative temperature criterion for thermal impact of HLW/SF on clay host rocks is accordingly proposed.

Download Full-text