Designed, constructed and commissioned by INVAP at Embalse Nuclear Power Plant - Candu type 600 MW Argentina, in 1993.

The ASECQ is a system devised and built by INVAP for the storage of spent fuel from nuclear power plants. ASECQ stands for Almacenamiento en Seco de Elementos Combustibles Quemados which is Spanish for Dry Storage of Spent Fuel Elements. For purposes of clarity the system will herein be referred to as the ASECQ.

As a rule, spent fuel elements in nuclear reactors are removed from the core and stored underwater in special pools. The water serves as the necessary radiation shielding and coolant for the fuel elements as they decay. The air in the room of the pools, as well as the water in the pools must permanently be monitored and treated.

The ASECQ is an alternative to this storage system. It offers a cheaper and safer way to store spent fuel which has been subject to prior decay in a pool. The ASECQ uses above-ground reinforced concrete silos.

The spent fuel elements are put into steel canisters before being lifted out of the water of the storage pool at the power plant. Each canister holds several spent elements.

The canister is removed from the pool and submitted to a drying process inside a shielded transference cell. Next, a lid is welded on so now the canister is hermetically sealed.

Following this, the sealed canisters are transported in a shielded container to their lodging in concrete silos.

Each silo consists of a steel cylinder sheathed in reinforced concrete shielding. The canisters are stacked inside the steel cylinder to its full capacity. Several canisters fit in each silo. When the silo is full, it is fitted with a steel and reinforced concrete lid that is welded on, hermetically sealing the cylinder.

The concept of ASECQ addresses the issue of what to do with spent fuel elements from power plants by offering dry storage that is simple and safe. The ASECQ system of dry storage for spent fuel features the following advantages.

• The fuel elements are not subject to corrosion as they are in water.
• The construction of the facility is modular i.e. the silos can be planned and built to meet arising requirement.
• The entire facility is cheaper to run: storage, guarding, supervision, inspection and radiation monitoring are more expensive to carry out at a pool.
• The silo concept features facilities which permit regular inspections to monitor the integrity of the primary containment barrier as well as inspections on the part of the IAEA (International Atomic Energy Agency) for the safeguarding of spent fuel elements.
• In the future, the spent fuel elements could readily be retrieved from the silos.
• The ASECQ ensures simple and easy storage for spent fuel from nuclear power plants.

Both personnel operating the storage facility, and the environment are guaranteed maximum safety and radiation protection by the barrier system it features.

The barrier system can be classified as physical and radiation barriers. In both cases, their design criteria are based on duplication and redundancy thus bestowing the system with maximum reliability.

Physical barriers

The physical barriers prevent any contact of the spent fuel elements with the environment. Though the metal cladding containing the uranium pellets of the fuel element itself is in fact a physical containment, we do not count it here as such because it is an integral part of the spent fuel element that is the object of the storage system.

In the ASECQ scenario, the steel canister is the primary barrier - hermetically sealed, it constitutes the physical confinement of solid and gaseous products.

The second physical barrier is the inner steel cylinder of the silo. The cylinder is hermetically sealed and constitutes the physical confinement of the primary barrier, i.e. the canisters. The second barrier is reinforced by the concrete encasing which is responsible for the proper resistance to seismic activity.

Radiation barriers

The radiation barriers are responsible of attenuating the radiation emitted by the spent fuel elements so operators are sure to receive doses far under the level fixed by international norms. The design criterion adopted is ALARA (As Low As Reasonably Achievable).

The primary barrier is the reinforced concrete of the silo that constitutes appropriate radiation shielding. This barrier is designed in such a way that it permits the dissipation of the heat resulting from the decay of the stored spent fuel.

The fence around the facility constitutes the secondary barrier. Only personnel with proper authorization can gain access to the area.