Technical considerations in repowering a nuclear plant for fossil fueled operation

Repowering involves replacement of the reactor by a fossil fuel source of steam. This source can be a conventional fossil fueled boiler or the heat recovery steam generator (HRSG) on a gas turbine exhaust. The existing steam turbine plant is used to the extent possible. Alternative fuels for repowering a nuclear plant are coal, natural gas and oil. In today`s world oil is not usually an alternative. Selection of coal or natural gas is largely a matter of availability of the fuel near the location of the plant. Both the fossil boiler and the HRSG produce steam at higher pressures and temperatures than the throttle conditions for a saturated steam nuclear turbine. It is necessary to match the steam conditions from the new source to the existing turbine as closely as possible. Technical approaches to achieve a match range from using a topping turbine at the front end of the cycle to attemperation of the throttle steam with feedwater. The electrical output from the repowered plant is usually greater than that of the original nuclear fueled design. This requires consideration of the ability to use the excess electricity. Interfacing of the new facility with the existing turbine plant requires consideration of facility layout and design. Site factors must also be considered, especially for a coal fired boiler, since rail and coal handling facilities must be added to a site for which these were not considered. Additional site factors that require consideration are ash handling and disposal.