TWICE AS SAFE AND TWICE AS EFFICIENT

The spent nuclear fuel in Sweden is continuously transported from the nuclear power plants to the national intermediate storage, Clab. Lack of a reliable transport system would shortly have a severe impact on the operation for all nuclear power plants since the fuel pools on the sites are quite small. The ability of transporting spent fuel is therefore essential to the operation of the nuclear power plants in Sweden. Swedish Nuclear Fuel and Waste Management Co. (SKB) own ten casks for spent nuclear fuel which has been in use since 1985. Due to the double barrier requirement against water intrusion in accident condition the casks will not be relicensed in the future. Consequently they will not be validated for the use in Sweden. To secure the need for transport of spent fuel a new fleet of transport casks that fulfil today’s requirements by authorities and international regulations has to be provided. The cask design challenge is to solve the right problem and still create reasonable flexibility for needs that may occur in the future. Typically cool down periods at the power plants for the fuel in the Swedish system is about 20 months before transport. This is a very short required cool down time for high burn-up fuel. It will be very challenging to design a high capacity cask, keeping the weight low and still fulfil requirements both regarding residual heat dissipation and radiation shielding. An early feasibility study clearly showed that new casks well designed could lead to substantial improvements of the technical performance for the transport system, beneficial for both the nuclear power plants and the intermediate storage. A safety upgrade has proven to be not only mandatory expense but an important opportunity to enhance system flexibility and to cut doses to staff.