Under the agreement between the Federal Government of the Federal Republic of Germany and the utility companies of June 2000 and the subsequent amendments to the Atomic Energy Act in April 2002, so-called on-site (decentralised) interim storage facilities were built at nuclear power plant sites between 2004 and 2007.

Decentralised interim storage facilities are those in which burned-out fuel elements are kept under controlled conditions at nuclear power plant sites for relatively long periods before being moved to final storage.

Interim storage facilities can be divided into two basic types:

— WTI design

Lightweight double-bay hall structures, walls approx. 70 cm thick, roof slabs approx. 55 cm thick, double-bay buildings consisting of two halls separated by a partition wall.

This model is based on the interim storage facilities at Gorleben, Ahaus and Lubmin/- Greifswald (northern interim storage facility).

Integrated operating areas with two cranes, stored in double rows (Figures 4.8 and 4.9)

— STEAG design

Solid single-aisle hall design with walls approx. 1.20 m thick, roof slabs approx. 1.30 m thick with separate operating building, one crane, compact storage (Figures 4.10 and 4.11).

The STEAG design was developed in view of using more cost-effective containment models in the future.

In accordance with the multiple barrier principle in nuclear technology the strength­ened building structure and future containment generation are designed to serve as additional barriers.

Both models share the same basic features: single-storey reinforced concrete halls with wall and roof slab openings for natural cooling. Inside the halls, a partition wall separates the reception/trans-shipment area from the storage area. Both storage designs have 1401 crane systems; the WTI halls need two of these because of their two-bay structure. For the building design of interim storage facilities see Section 4.3.2.3.

Once taken into store, the containers, which essentially contain irradiated fuel rods, can be described approximately as follows: height 6.50 m, diameter 2.80m and a dead weight of 1251. The container walls in the cylindrical and floor areas are approx. 420 mm thick.

The containers are sealed tightly using a cover system, using mainly CASTOR V/19 (Castor: cask of storage and transport of radioactive material) containers to date. These containers can hold up to 19 fuel elements (Figure 4.12).

The top of the container body is stepped to take the cover. At the head and foot of the container body are two overlapping carrying frames to which the storage hall crane lifting gear can be attached.

Containers are transported by rail or road exclusively and delivered to the interim store. Storage containers are transported horizontally to be stored in the interim store.

To unload containers, the storage hall crane attaches to them via the carrying frames provided, and the transporter vehicle takes them. Containers are then driven to their preset storage positions, set down upright and connected to a container monitoring system.