Concrete canister

AECL began to study dry storage for spent nuclear fuel in the early 1970s. Silo-like structures called concrete canisters were first developed for the storage of research reactor enriched uranium fuel and then perfected for spent CANDU NUE fuel. By 1987, concrete canisters were being used for the safe and economical storage of all spent fuel accumulated during the operation of AECL s decommissioned prototype reactors. Each canister contains a stack of spent fuel baskets. 

The same basic technology was then applied to on-site dry storage of spent fuel generated by operating CANDU power generating plants. The spent fuel baskets have air as the fuel cover gas. The basket is dried and welded in a shielded work station and transferred by a shielded transfer flask into the dry storage canister. The concrete canisters typically hold 9 baskets of 60 bundles with four or five canisters containing one year s worth of spent fuel. 

In 1989, AECL began development (in cooperation with Transnuclear, Incorporated) of a monolithic, air-cooled, concrete structure for dry storage called MACSTOR (Figure 15.8). MACSTOR modules require less land area than concrete canisters for the same amount of spent fuel and are also suitable for storage of spent fuel assemblies from other reactor types (PWR, BWR, VVER) as well as CANDU. The MACSTOR modules store 12,000 bundles in 20 storage cylinders, each holding 10 baskets of 60 bundles (Figure 15.9). 

Concrete canister (or Silo). A massive container comprising one or more individual storage cavities. It is usually circular in cross-section, with its long axis vertical. An inner sealed liner and the massive concrete of the canister body provide the necessary containment and shielding of the radioactive material inside the container. Heat removal is accomplished by radiant emission, conduction and convection within the body of the canister, and by natural convection on its exterior surface. Canisters may be located in enclosed or non-enclosed areas. 

Argentina concrete canisters Dry storage containers in operation at Embalse, planned for Atucha... 

Canada concrete canisters. Concrete canisters used at 5 sites. 

There were studied two types of SNF canisters storage in steel tubes, placed in the air medium ( CASCADE type) and in steel tubes, placed in a concrete body inside a built-in structure. The modeling of radioactive decay heat removal was implemented based on the initial integral value of RHR of NP SNF by 2010. 

As a result of the calculations, it was foimd that when tubes are placed in a concrete body with 50 cm spacings the maximum predictable temperature in the storage (inside canisters and the adjoining concrete body layers) may reach 200 °C. Fig. 4 and 5 show the results of calculations for the variant with 72 cm spacings. In those calculations the... 

Figure 6. Characteristics of nuclear safety, when storing SF canisters in steel tubes, placed in the module of underground storage 1 - inside a concrete body 2 - in the air...

The preliminary technical-and-economic assessment has been performed for the two variants of the near surface SNF storage facility configuration variant 1 - SNF is placed into canisters within a built-in reinforced concrete structure variant 2 - SNF is placed in metal concrete containers. The variants suggested are characterized by the following values ... 

Following that, we developed another alternative conceptual design for a modular, natural circulation, air-cooled vault concept in which overpacked canisters would be stored in steel-lined, concrete vaults through which air is convectively circulated. Figure 2 shows this approach. 

What can be done after that point to isolate the radioisotopes with long half-lives The plan that currently holds the most promise is to incorporate the unstable nuclei into stable material such as glass, which is then surrounded by canisters made of layers of steel and concrete. The canisters can then be buried deep undergroimd in stable rock formations, as shown in Figure 21.22. The storage sites would be located in a dry, remote area. 

The in situ test consists of a near to full-scale simulation of a HLW disposal facility, following the scheme shown in Figure 3. Two electrical heaters, of dimensions and weight equivalent to those of the nuclear canister were placed in the drift just described, the entire space surrounding the heaters being filled with blocks of compacted bentonite to complete the 17.4 m of barrier for the test section. This test zone was closed with a concrete plug. 

Thermal sources for the heated drift consisted of 9 canister heaters, placed end to end on the concrete inverts of the heated drift, and 50 wing heaters (25 on either side) placed in horizontal boreholes drilled into the sidewalls of the heated drift approximately 0.25 m below the springline. The wing heaters were spaced 1.83 m apart and separated from the heater drift by 1.5 m. 

Figure I. Partial view of 2-D numerical mesh for the DST (adapted from Birkholzer and Tsang, 1998). Symbols represent the central canister heater (red circle), wing heater locations (purple diamonds and red squares), concrete invert (green squares), arui drift wall and invert top blocks (small red squares).

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