Exploring the improvement of HTGR economics with heat storage for variable electricity output at base-load operations

Abstract

Nuclear power plants operate most efficiently at a constant power output. This creates problems for nuclear power plants operating in electricity markets with large amounts of non-dispatchable energy generation, where the price of electricity can reach zero as a result of supply overload. Nuclear reactors must sell electricity for extremely low prices or complicate operation by adjusting the output of the reactor core. Heat storage can serve as a solution to this problem by enabling nuclear power plants to store the thermal output of a reactor and convert it to electricity at more profitable times. This study considers multiple design options for a sensible heat storage system with the intent of limiting capital investments required to construct the heat storage system. A novel design based on existing heat recuperator is proposed. This design is integrated into the primary loop of an HTGR reactor to minimize the use of inefficient heat exchangers. The proposed system is connected to the reactor outlet and inlet and operates a separate turbine loop once charged. The heat storage media is chosen to be ceramic brick made of alumina or magnesia, though cast iron and graphite are also considered as candidates. The system is housed in a prestressed concrete pressure vessel with an approximate volume of 25000 - 27000m3. A detailed cost analysis must be performed on this system, or any variation, in order to assess the viability of the design in a market setting. By providing a framework for gigawatt-hour scale thermal storage in nuclear reactors, this thesis aims to prompt a greater design focus on coupling heat storage capacity to nuclear power plants.