Due to increasing gap between energy demand and supply, India is planning to build significant number of nuclear reactors which will produce significant amount of High-level radioactive waste. It can generate considerable amounts of heat as a side effect of radioactive decay of nuclear wastes which will be disposed around 400 m–1000m below ground inside the underground nuclear repository. The rock chosen is granite and barrier near the canister is proposed to be clay. In this paper, thermo hydro mechanical (THM) analysis has been done to study the effect of heat on deformations, stresses and pore pressure variation in granite and clay barrier. For this purpose, finite difference method has been used. It has been found that both temperature and stresses at any point in the rock mass is below the design criteria which are 100?C for temperature.

1 Introduction

Nuclear energy has been a source of unlimited cheap power and is based on non-renewable energy sources. Nuclear power produces high level and low level radioactive wastes with long half life time periods. The major problem is due to the generation of long lived high level nuclear wastes (HLW) and it's safe disposal. Although the level of radioactivity of these wastes decay over time, it remains dangerously high that it must be isolated from the outer biosphere, until it has decayed to levels that pose less risk.

It is necessary to study the several processes at excavation stage in an underground repository laboratory (URL) and supplemented by surface based and traditional laboratory tests. A typical cross section of one such disposal tunnel with a disposal pit is shown in Fig. 1.

2 Regional Geology and Structure

Site near Bhima basin is found to be suitable for URL site (Fig. 2). Bhima basin is the smallest and youngest amongst the Proterozoic basins of Peninsular India. The basin receives it name after "Bhima River" a major tributary to the river Krishna. The Basin is exposed between lat. 16°:20'00"N–17°:35'00"N: long. 76°:15'00"E–77°:44'00"_E on the north western fringe of eastern of Dharwar Craton. The basin has a reverse sigmoidal array of outcrops between Tandur in the northeast and Muddebihal in the Southwest, for over a stretch of 160 km with a maximum width of 40 km across Sedam. The exposed area of the basin is about 5200 sq. km. Northern and northwestern extensions are concealed under Deccan traps.

The structure comprises of a major thrust plane striking NE-SW with granitic rocks riding over limestone.

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