Cleaning and decontamination of cooling fins on spent fuel transport casks.

In 1985, regular transports of spent fuel from the twelve Swedish nuclear power stations to CLAB, the central interim storage for spent nuclear fuel, started. Until now, Aug 2001, around 3 600 tonnes of spent fuel, corresponding to 1200 casks have been transported to CLAB. The transports have been performed using a purpose built sea transport system where the ship M/S Sigyn is an important and the most well known part. Yearly, about 200 tonnes of spent fuel are transported to CLAB corresponding to around 15 sea voyages with the ship. The CLAB facility is owned by SKB but operated by staff from the OKG AB, which owns and operates the three nuclear power plants at site. OKG AB is also one of the owners of SKB. SKB operates 10 transport casks for spent fuel of the French design TN 17/2. This cask is made of forged steel and has a length of about 6 meters and a diameter of about 2 meters. Its weight is 80 tonnes and the loading capacity is about 3 tonnes of spent fuel. The transports are performed under dry conditions and the cask is cooled by natural air circulation around the 40 000 cooling fins. The fin area is roughly 4 meters long with a diameter of about 2 meters. During loading and unloading operations at the power plants and CLAB a metallic skirt protects the fin area by circulation of clean water which also cools down the cask. Under normal road transports the cask is covered by a canapé preventing the fins from dirt and dust. Despite these protection measurements it is almost impossible to keep the cask and the fins completely clean during all transport and loading operations.