Repository excavation

The M effects of repository excavation and swelling of back filling material proved to be small. Our results focus on TM effects at 100 years of repository heating in the lower formation, as described in section 3.6. The changes in fracture transmissivity as a function of radial distance from the repository centre, r, are shown in Figure 4. 

After a pubhc review by an Environmental Assessment Panel, the Panel acknowledged that from a technical perspective, the safety of the Canadian concept for nuclear fuel waste disposal was, on balance, adequately demonstrated. However, the Panel recommended that broad public support be demonstrated before proceeding to repository site selection. Work continues at the URL, and the intent of this work is to increase confidence in proposed methodologies for designing repository excavations and engineered barrier systems. 

Horizontal location and depdi Depth of repository Excavating (soft)... 

The near field of the repository includes the engineered barrier system (EBS, i.e., canister and buffer) and the waste form. Also included in the near field is the interface between the buffer and the host rock, denoted as excavation disturbed zone (EDZ). In terms of waste/water interactions, the geochemical evolution of the near field is essential as it controls the composition of the fluids that will eventually contact the waste. 

The conceptual design of the repository (Figure 2) consists of a series of parallel tunnels, where the wastes would be emplaced in boreholes excavated in the floors of the gallery. The centreline distance between adjacent tunnels is 10 m and the centreline distance between adjacent inground boreholes for the wastes is 4.44 m. The depth of each borehole is 4.13 m and the diameter is 2.22 m. The overpack for vitrified wastes would be emplaced into the borehole, and a bentonite buffer material would be compacted around the overpack. The tunnels would also be backfilled with a mixture of gravel and clay. 

Boundary conditions are as follows Temperature and hydraulic head are fixed on the top and the bottom boundary and no flow boundaries for water and heat are specified on the other boundaries. And slide boundaries are given to all the boundaries. These boundary conditions satisfy the situation that disposal pits are arrayed at regular intervals. Initial state is assumed the time that the repository is closed as initial conditions, hydraulic head in rock mass is 500 m without the effect of excavation, water content of the buffer is 14 %, water content of the backfill is 23% and temperature is 30 °C in all the domain. Heat flux from the waste canister is given as Figure 3. The points A to C in Figure 2 are the monitoring points for temperature and saturation degree. A is close to the waste canister, B is located at the center of the buffer and C is located at the rock close to the buffer. 

In Sweden, a repository design of KBS-3 system has been develop (SKB, 1999). The KBS-3 is a multibarrier system to isolate the spent nuclear fuel. The spent nuclear fuel is placed in corrosion-resistant 5-m long copper canisters. Each of the canisters is surrounded by an engineered barrier system (EBS) of bentonite clay in separate deposition holes excavated along tunnels in... 

Backblom, G., Martin, C.D. 1999 Recent experiments in hard rocks to study the excavation response Implications for the performance of a nuclear waste geological repository. Tunnelling and underground space technology 14 377-394. 

Excavation-vitrification Long-lived radionuclides Appropriate repository... 

Central section In the central section of the underground repository, the borehole sensors are distributed at three excavation levels and installed in 3 to 20 m deep boreholes. The average depth of the monitored volume is 400 m. Mining in these areas continued until the 1960s, but most of the rooms in the rock salt were mined more than 70 years ago. 

Underground excavation of fhe WIPP repository in the Salado formation salt beds began in the early 1980s. During siting and initial excavation activities, four shafts were drilled as discussed below. 

The excavated repository including the waste package, backfills or sealing materials, and those parts of the host rock whose characteristics have been or could be altered by the repository or its content. 

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