Hydrology, repository

Fig. 3. Schematic illustration of the interface of the nuclear fuel cycle with geochemical/hydrological cycles. The geological repository is the interface for these two cycles. The principal sources of radioactivity (over the long term) are indicated by the radionuclides listed at the centre of each cycle. Total background exposures to radiation are less than 300 mrem/y. The total radiation exposure that can be attributed to the nuclear fuel cycle is less than 3 mrem/y.

Missana, T., Alonso, U. Turrero, M. J. 2002. Generation and stability of bentonite colloids at the bentonite/granite interface of a deep geological radioactive waste repository. Journal of Contaminant Hydrology, 61, 17-31. 

Future penetration of the repository by man is one of the several potential failure scenarios which has been calculated. One particular scenario which will be described assumes an open, unplugged borehole penetrates through the repository and connects aquifers above and below the salt. This case is of much greater concern than for a hole which terminates within the salt. In this latter instance, there is no mechanism to continue dissolutioning of salt and the hole will gradually be squeezed closed. Using the hydrologic parameters... 

Consider now the effects of the waste and emplacement of the waste on the hydrology of the system. Present thinking suggests that a mined underground cavity in bedded salt will be the first choice for a repository for high-level waste. The rationale for... 

Caves act as repositories for secondary deposits of many kinds, some locally derived such as breakdown from collapse of cavern roofs, some transported such as sand and silt carried by underground streams, and some the result of chemical deposition in the cavern void space such as calcite and gypsum speleothems. Textbooks on karst hydrology commonly provide descriptions and overall classifications of cave sediments (e.g. Bogli,... 

Rutqvist, J M. Chijimatsu, L. Jing, A. Millard. T.S. Nguyen, A. Rejeb, Y.Sugita and C.F. Tsang, Evaluation of the impact of thermal-hydrological-mechanical couplings in bentonite and near-field rock barriers of a nuclear waste repository in sparsely fractured hard rock, this volume, 2004. 

Abstract Results from the four-year long heating phase of the Drift-Scale Heater Test at the Exploratory Studies Facility at Yucca Mountain, Nevada, provide a basis to evaluate conceptual and numerical models used to simulate thermal-hydrological coupled processes expected to occur at the proposed repository. A three-dimensional numerical model was built to perform the analyses. All model simulations were predicated on a dual (fracture and matrix) continuum conceptualization. A 20-percent reduction in the canister heat load to account for conduction and radiation heat loss through the bulkhead, a constant pressure boundary condition at the drift wall, and inclusion of the active fracture model to account for a reduction in the number of fractures that were hydraulically active provided the best agreement between model results and observed temperatures. The views expressed herein are preliminary and do not constitute a final judgment of the matter addressed or of the acceptability of its use in a license application... 

Abstract Geological disposal of nuclear fuel wastes relies on the concept of multiple barrier systems. In order to predict the performance of these barriers, mathematical models have been developed, verified and validated against analytical solutions, laboratory tests and field experiments within the international DECOVALEX project. These models in general consider the full coupling of thermal (T), hydrological (H) and mechanical (M) processes that would prevail in the geological media around the repository. This paper shows the process of building confidence in the mathematical models by calibration with a reference T-H-M experiment with realistic rock mass conditions and bentonite properties and measured outputs of thermal, hydraulic and mechanical variables. 

EVALUATION OF THE IMPACT OF THERMAL-HYDROLOGICAL-MECHANICAL COUPLINGS IN BENTONITE AND NEAR-FIELD ROCK BARRIERS OF A NUCLEAR WASTE REPOSITORY IN SPARSELY FRACTURED HARD ROCK... 

The long-term performance of the repository at Yucca Mountain will be affected by the coupling of thermal, hydrological and chemical (THC) processes in the rock around the emplacement drifts. The transport of heat, fluid, and vapor will result in changes in water and gas chemistry, as well as mineral dissolution and precipitation which may lead to permanent changes in porosity, permeability and unsaturated hydrological properties. The purpose of this contribution is to describe the approach used to model reaction-transport processes in the Drift Scale Test (DST) with comparisons of simulation results to measured geochemical data on water, gas, and minerals. 

In a HLW repository, the coupled thermo -hydro -mechanical and chemical (T-H-M-C) processes will occur, involving the interactive processes among radioactive decay heat of the vitrified waste (thermal processes), infiltration of groundwater (hydrological processes), swelling pressure of buffer material due to saturation (mechanical processes) and chemical evolution of buffer material and porewater (chemical processes). 

The main objection against nuclear power is the risk of spread of "radioactivity" (radioactive elements) to the environment where it may cause health effects in humans. We have already discussed such effects (Ch. 18). Here, we are concerned with the chemical aspects of the sources of releases and of the migration of the radionuclides in the environment. Their chemical properties, together with hydrology, determine how fast they will move from their point of entry into the groundwater to water resources used by man this is schematically illustrated in Figure 22.1. In particular we discuss actinide behavior as these elements have the most hazardous radionuclides which may be released in the different steps of the nuclear fuel cycle, and, especially, from nuclear waste repositories. 

Braney, M. C., Haworth, A., Jefferies, N. L. Smith, A. C. 1993. A study of the effects of an alkaline plume from a cementitious repository on geological materials. Journal of Contaminant Hydrology, 13, 379-402. 

---