Turning the heat on water

Hydrogen to fuel cars, industry and homes could be produced cleanly
and, crucially, economically using the heat generated by nuclear power
stations, US researchers claim.

Hydrogen to fuel cars, industry and homes could be produced cleanly and, crucially, economically using the heat generated by nuclear power stations, US researchers claim. A study by the US Savannah River National Laboratory, South Carolina has shown that reactor heat can be used to help crack water into hydrogen and oxygen.

The method is much cleaner than using steam to break down natural gas, the most efficient way of producing hydrogen. It does not produce carbon dioxide which then needs to be captured and disposed of to prevent it entering the atmosphere and contributing to global warming. The cost of carbon dioxide capture and storage is a major concern in the move towards a hydrogen economy.

But the Savannah River team says high-temperature helium gas- cooled reactors, currently being designed for next-generation power stations, could provide heat at around 800°C. This is the level required to fuel the chemical reaction to split water.

This is the most developed of the possible next generation of nuclear reactors, known as Gen IV. The design used by the Savannah River team was based on the modular helium reactor currently under development by General Atomics. This employs a graphite moderator and coated particle (TRISO) fuel.

A typical nuclear plant would use four reactors, operating with an outlet helium temperature of up to 1,000°C. A second helium cooling loop would be heated to 925-975°C in an intermediate heat exchanger. The secondary helium would deliver heat to the thermochemical process for the production of hydrogen.

The thermochemical process, known as the sulphur-iodide cycle, consists of three linked chemical reactions involving the thermal decomposition of sulphuric acid and hydrogen iodide. Heat and water are the only system inputs as the chemical reagents are recycled. Oxygen is created as a by-product and can be sold on to industry.

By modelling the process the researchers estimate that, despite the infrastructure costs of nuclear power, the plant should be able to produce hydrogen at a price that can compete with hydrogen produced from natural gas, particularly when rising gas prices and the future imposition of carbon taxes are taken into account.

The cost of hydrogen production would be $1.65 (92p) per kilogramme without oxygen being sold as a by-product, and $1.36 (76p) a kilo with the oxygen credit.

The study is part of a three-year project supported by the US Department of Energy’s Nuclear Energy Research Initiative (NERI). It aims to examine the technical and economic issues connected with using nuclear power to make hydrogen.

The project’s goal is to develop commercial-scale production of hydrogen using nuclear power. This could lead to large-scale emissions-free domestic hydrogen production capable of removing the need for the US to rely on imports of natural gas as a fuel.

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