Heat Storage Coupled to Generation IV Reactors for Variable Electricity from Base-load Reactors

Report Date: September 2019
Appendices: No

Abstract

Electricity markets are changing because of (1) the addition of wind and solar that creates volatile electricity prices including times of zero-priced electricity and (2) the goal of a low-carbon world that requires replacing fossil fuels that provide (a) energy, (b) stored energy and (c) dispatchable energy. Wind and solar provide energy but not the other two other energy functions that are provided fossil fuels. Nuclear energy with heat storage can provide all three functions and thus replace fossil fuels.

To address the challenges and opportunities for nuclear energy in this changing market the Massachusetts Institute of Technology (MIT), Idaho National Laboratory (INL) and Exelon conducted a workshop on July 23-24, 2019 in Idaho Falls on Heat Storage Coupled to Generation IV Reactors for Variable Electricity from Base-load Reactors: Changing Markets, Technology, Nuclear-Renewables Integration and Synergisms with Solar Thermal Power Systems. The results from this workshop are described herein. The workshop included participation of the concentrated solar power (CSP) community because nuclear energy and CSP produce heat and thus face many of the same technological and institutional challenges. Some CSP plants today have several gigawatt-hours of heat storage to better match market needs.

The changing market requires a different nuclear plant design that incorporates heat storage. The base-load reactor sends variable heat to (1) the turbines to provide variable electricity to the grid and (2) storage. At times of high electricity prices, all the heat from the reactor and heat from storage is used to produce peak electricity output significantly greater than the base-load capacity of the reactor. At times of low or negative electricity prices, (1) minimum steam is sent to the turbine and (2) there is the option that electricity from the turbine operating at minimum output and electricity from the grid is converted into heat that is sent to storage. The nuclear plant has the capability to buy and sell electricity to increase revenue in these markets relative to a base-load nuclear power plant. Heat storage (salt, rock, concrete, etc.) is much less expensive than electricity storage (batteries, etc.) because of the low cost of the materials used in heat storage systems relative to materials used in electricity storage systems.

Generation IV reactors deliver heat at higher temperatures to the power cycles compared to water-cooled reactors. This lowers the cost of heat storage by two mechanisms. First, if the hot-to-cold temperature swing in a sensible heat storage system is doubled, the cost of heat storage is reduced by a factor of two assuming all other factors are equal. Second, the higher heat-to-electricity efficiency reduces the storage requirements per unit of electricity storage. This may become the primary economic incentive to develop Generation IV reactor technology Twelve heat storage technologies applicable at the gigawatt-hour storage scale were discussed that can be deployed between the reactor and the power cycle. Several of these technologies are deployed at CSP facilities. Nitrate salt heat storage is used at the gigawatt-hour scale in CSP systems and is proposed for salt and sodium-cooled nuclear plants.

Two storage technologies were examined that are incorporated into advanced Brayton power cycles. One proposes to use cold water to boost power when needed. The other uses a thermodynamic peaking cycle with incremental heat-to-electricity efficiencies of 70 to 75% when coupled to high-temperature reactors providing heat to the lower-temperature bottoming cycle. The heat for the topping cycle can be provided by natural gas, hydrogen or stored heat produced by converting low-price electricity into high-temperature stored heat. A nuclear plant capable of producing, selling and buying electricity is different than any existing plant. There are large incentives to demonstrate heat storage in existing LWRs to improve LWR economics and address many of the operational, grid, and regulatory challenges that are common to all heat storage systems coupled to nuclear plants. There are large incentives for joint nuclear/CSP heat storage development and demonstration programs because the same technologies are being used.

Program:     ANP : Advanced Nuclear Power Program

Type:     TR 

RPT. No.: 185