US-based Holtec International has announced a combined nuclear-solar power plant design – CNSP (Combined Nuclear/Solar Plant). It combines Holtec’s SMR-300 small modular reactor (SMR) design with its HI-THERM HSP, solar thermal system as well as its Green Boiler to provide base load or on-demand power to counter the intermittency of solar plants. The Green Boiler is a three-in-one device that can store vast amounts of heat, receives high temperature heat from the solar collector, and make motive steam at the required pressure and superheat to power the turbine. Holtec President & CEO Dr Kris Singh noted: “We believe that an adroit combination of nuclear and solar embodied in the CNSP provides a compelling solution for nations seeking to move past fossil fuels.”

Holtec says the most immediate application of the CNSP technology is to facilitate the transition from “coal to clean”. Coal-fired plants typically have sufficient land area to house the CNSP, which would use the coal plant’s power block minimising the cost of transition. The steam production part of the coal plant will be decommissioned, freeing up most of the plant’s land area for the solar plant. Holtec plans to offer the CNSP technology principally in those regions of the world where solar radiation level is adequate to be harvestable.

“Our SMR-300 small modular reactor is premised on the most proven type of light water technology used in most land-based reactors and in submarines and aircraft carriers,” Holtec notes. SMR-300 has added defence-in-depth features that are gravity-actuated and “confer fail-safe emergency recovery capability to the nuclear plant qualifying it for the moniker ‘walk away safe’”.

Solar’s contribution to the CNSP will be through the HI-THERM HSP hybrid solar plant, “which is considerably more efficient than its predecessor technologies, yielding as much as 8 MWH of solar heat per acre in equatorial and subtropical locales”. The nuclear reactor’s steam supply system and heat from the solar thermal plant “are conjugated in the Green Boiler which is a multi-function device engineered to produce steam at the desired pressure and superheat to run the coal plant’s existing turbogenerator”.

At sites with no pre-existing fossil plant, the solar thermal plant can be as large as the available land area will accommodate. Holtec says experts in power plant cycle design would appreciate that the CNSP will have a much higher thermodynamic efficiency than the nuclear plant alone and would make solar power an integral part of base load supply. “The CNSP does not use any batteries, which have been the Achilles heel of the renewable energy industry. In fact, CNSP contains no fragile parts or materials that may limit its service life, which is expected to exceed 60 years.”

Image: Artist's impression of Holtec’s SMR-300 small modular nuclear plant (courtesy of Holtec)