Session: 02-08: Balance of Plant

Paper Number: 64632

Start Time: August 6, 2021, 03:15 PM

64632 - 100-Gigawatt-Hour Crushed-Rock Heat Storage for Variable Electricity and Heat With Base-Load Reactor Operations 

A low-carbon world needs a replacement for the combined-cycle gas turbine to provide variable heat and electricity. A 100-gigawatt hour (GWh) crushed-rock heat storage system using oil or nitrate salts is proposed to enable base-load 1000-MWe nuclear plants to provide variable electricity and heat. Such a heat storage system has the same capabilities of a large pumped-hydro facility and can provide hourly-to-weekly (weekday / weekend) heat storage. The capabilities would be similar to the Tennessee Valley Authority Hydro Pumped Storage facility with a peak output of 1.6 GW for 22 hours. Low-cost storage enables maximizing revenue from sales of electricity and heat.

 

A single insulated structure for a 100-GWh of heat storage would have a crushed rock bed 20 m by 250 m by 250 m in a fully insulated structure. The insulated roof would be supported by columns through the crushed rock. The large dimensions minimize the surface area (steel and insulation) per cubic meter of crushed rock. Crushed rock is the lowest cost heat storage material. Heat is transferred from the reactor to crushed rock by spraying on sequential sections of crushed rock (1) hot oil (LWRs) or (2) molten nitrate salt (higher-temperature reactors). The liquid flows by gravity to the drain pan at the bottom of the crushed rock and returned to the reactor to be reheated. Heat is recovered by spraying cold oil or salt on the top of the hot crushed rock with hot liquid recovered from the drain pan at the bottom going to the power cycle. The oil or nitrate salt is used for heat transfer---not heat storage. The cost of crushed rock is for heat storage is less than a tenth the cost of these fluids for heat transfer. The power block power output is sized to match electric market capacity (kW) requirements and may be several times the base-load reactor output.

 

A recent workshop (https://www.dropbox.com/s/sh0mvk69inmujsk/ANP%20189_CANES%20Report%20Nov.%202020.pdf?dl=0) organized by the author examined the system design aspects of nuclear heat-storage systems. Several advanced reactors (TerraPower, Moltex, etc.) under development propose using two tank heat storage systems with clean oil or nitrate salt stored in separate hot and cold storage tanks—the same heat storage systems used in Concentrated Solar Power systems. The capital costs of these heat storage systems exceed $20/kWh of stored heat whereas the proposed crushed rock system capital costs are $2-4/kWh. The lower cost reflects (1) using crushed rock rather than hot oil or nitrate for heat storage and (2) the lower container costs because of the much smaller surface-to-volume ratio of the large system. The crushed rock heat storage system is in the early stages of the development cycle.

Presenting Author: Charles Forsberg Massachusetts Institute of Technology

Authors:

Charles Forsberg Massachusetts Institute of Technology