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 to maximize plant revenue. Such a heat storage system has the same capabilities as a large pumped-hydro facility and can provide hourly-to-weekly heat storage. The capital cost goal is $2–4/kWh of heat — more than an order of magnitude below electricity storage technologies (batteries, pumped storage, etc.). Oil (LWR) or nitrate salts (higher-temperature reactors) transfer heat from the reactor to storage and from storage to the non-nuclear power block. The non-nuclear power block output is several times base-load nuclear capacity.
The insulated heat storage structure would have a crushed rock bed 20 m by 250 m by 250 m. The large dimensions minimize the surface area (steel and insulation) and cost per cubic meter of crushed-rock storage. 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 or (2) molten nitrate salt. The liquid flows by gravity to the drain pan at the bottom of the crushed rock and is returned to the reactor to be reheated. Heat is recovered by spraying cold fluid 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 for heat storage, thus, minimize the quantity and cost of the heat transfer fluid.