Dry vault for spent fuel depository. Basic outsets, operating results and safety of the ''CASCAD'' plant

Reprocessing and recycling of fissile materials is the preferred approach to spent fuel management in France. However, a number of spent fuel elements from prototype and experimental nuclear reactors cannot be reprocessed in the existing industrial facilities, either because such facilities are booked to full capacity, or due to technical factors such as non standard nature of fuel or limited series of fuel. The CEA therefore built a facility in which spent fuel can be stored for a few decades (50 years), until favourable conditions prevail for its disposal. The main features of this project consist in a dry depositary, which presents a low cost of working, against a wet one which is more expensive due to the circulation and the continuous controls of the water. Therefore, this is a fair solution because the experimental fuels will present a rather low residual heat power after decay in the nuclear reactor. At this stage, it becomes possible to cool the fuel elements by a fully passive air circulation. This process allows a good efficiency without mechanical equipment and works all the better as the amount of heat to exhaust is great, in the limits of the design. However, we will see that this concept may be extended to a depository of standard spent fuel elements. This facility, known as ''CASCAD'' (shortening for CASemate (=vault) CADarache) started up in 1990, and received its first canister of fuel on May 29th 1990. This paper reviews the basic design data of the facility, outlines the main techniques used for its construction, draws the safety concepts and presents the first results determined by a looking-back over 4 years of working. (author)