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A revolutionary reactor concept

ORNL proposes a brand new nuclear reactor concept for economically producing hydrogen.



Primary heat exchanger loop for the Advanced High-Temperature Reactor, conceived by an ORNL researcher and two other collaborators.

A revolutionary nuclear reactor concept, based partly on ORNL's past coolant and fuel research, could be an economical source of hydrogen. Called the Advanced High-Temperature Reactor(AHTR), it would cost only half as much as current gas-cooled reactor concepts.

In January 2003, Charles Forsberg of ORNL's Nuclear Science and Technology Division explained the AHTR to the National Academy of Sciences. The Academy is interested in determining the most economical ways to produce hydrogen.

"More than 30 years have passed since a brand new nuclear reactor concept has been proposed," Forsberg says. "The Academy is very interested in our concept for making larger quantities of hydrogen more cheaply."

The AHTR, which could also be used to produce electricity, was conceived in 2001 by Forsberg, Paul S. Pickard of DOE's Sandia National Laboratories, and Per Peterson of the University of California at Berkeley. The AHTR is basedon three technological feats: a molten-salt coolant developed at ORNL for the nuclear aircraft propulsion program of the 1950s and the molten salt breeder reactor program of the 1960s; fuel elements made of coated nuclear fuel particles embedded in a graphite matrix, developed in the 1970s at ORNL for the gas-cooled reactor program; and passive safety systems devised by industry for gas-cooled and liquid-metal reactors.

In the AHTR concept, the primary molten-fluoride salt coolant flows through the reactor core, dumps the heat it picks up on an external heat exchanger, and returns to the core. The "dumped" heat is carried by molten salt through a long pipe to a thermochemical plant, where hydrogen is produced from water using chemical reagents such as hydrogen iodide and sulfuric acid.

The AHTR's fuel and coolant allow the reactor to be operated at 750oC, producing 2400 megawatts of thermal energy (MWt) in a vessel the same size as that of a 600-MWt gas-cooled reactor. Its molten-salt coolant enables reactor operation at atmospheric pressure, avoiding the need for an expensive high-pressure reactor vessel, albeit with increased corrosion concerns. The liquid coolant transfers heat more efficiently than high-pressure gas. The combination allows the use of passive safety systems in a large reactor, lowering the AHTR's costs per unit output to 60% of gas reactor costs.

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