Comparison between Different Power Sources for Emergency Power Supply at Nuclear Power Plants

Currently the Swedish nuclear power plants are using diesel generator sets and to some extent gas turbines as their emergency AC power sources and batteries as their emergency DC power sources. In the laws governing Swedish nuclear activity, no specific power sources are prescribed. On the other hand, diversification of safety functions should be considered, as well as simplicity and reliability in the safety systems. So far the choices of emergency power sources have been similar between different power plants, and therefore this project investigated a number of alternative power sources and if they are suitable for use as emergency power on nuclear power plants. The goals of the project were to: - Define the parameters that are essential for rending a power source suitable for use at a nuclear power plant. - Present the characteristics of a number of power sources regarding the defined parameters. - Compile the suitability of the different power sources. - Make implementation suggestions for the less conventional of the investigated power sources. (unconventional in the investigated application) 10 different power sources in total have been investigated and to various degrees deemed suitable Out of the 10 power sources, diesel generators, batteries and to some extent gas turbines are seen as conventional technology at the nuclear power plants. In relation to them the other power sources have been assessed regarding diversification gains, foremost with regards to external events. The power sources with the largest diversification gains are: Internal steam turbine, Hydro power, Thermoelectric generators. The work should first and foremost put focus on the fact that under the right circumstances there are power sources that can complement conventional power sources and yield substantial diversification gains. This paper is a shortened version of the report 'Comparison between different power sources for emergency power supply at nuclear power plants'. The report is financed by Elforsk - Swedish Electrical Utilities' R and D Company. The background of the report is that the Fukushima accident showed how redundant but not diversified power sources can be destroyed by external events. This might lead to increased focus on diversification, from the industry and/or the regulating authorities. A number of essential parameters for a power source to work as emergency power supply at a nuclear power plant have been identified; ten different power sources have then been evaluated with respect to these parameters. The report is supposed to work as a knowledge base and decision support when new nuclear power plants or reinvestments in old ones are considered. The studied power sources are: Diesel generators, Gas turbines, Internal steam turbines, Externals steam turbines, Hydro power plant, Batteries, Fuel cells, Stirling engines, Thermoelectric elements, Flywheels. The power sources are evaluated for five different applications, each application with its own acceptance criteria for each of the essential parameters. The five applications are: Onsite emergency AC source, Onsite emergency DC source, Alternate AC source, small, Alternate AC source, large, Alternate AC source, mobile. Mainly Swedish preconditions are considered in the report, but most of the results are applicable in any other country. (author)