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Hydrogen Production and Uses
(Updated September 2020)

Hydrogen directly from nuclear heat
Several direct thermochemical processes are being developed for producing hydrogen from water. For economic production, high temperatures are required to ensure rapid throughput and high conversion efficiencies. They essentially do not use electricity.
In each of the leading thermochemical processes the high-temperature (800-1000°C), low-pressure endothermic (heat absorbing) decomposition of sulfuric acid produces oxygen and sulfur dioxide:
2H2SO4 ? 2H2O + 2SO2 + O2
There are then several possibilities. In the iodine-sulfur (IS) process invented by General Atomics in the 1970s, iodine combines with the SO2 and water to produce hydrogen iodide. This is the Bunsen reaction and is exothermic, occurring at low temperature (120°C):
I2 + SO2 + 2H2O ? 2HI + H2SO4
The HI then dissasociates to hydrogen and iodine at about 350-450°C, endothermically:
2HI ? H2 + I2
This can deliver hydrogen at high pressure.
Combining all this, the net reaction is then:
2H2O ? 2H2 + O2
All the reagents other than water are recycled, there are no effluents, hence it may be called the sulfur-iodine cycle, with zero-carbon hydrogen and oxygen byproducts.
In February 2010 the Japan Atomic Energy Agency (JAEA) set up the HTGR Hydrogen and Heat Application Research Centre at Oarai to progress operational technology for an IS plant to make hydrogen thermochemically. It has demonstrated laboratory-scale and bench-scale hydrogen production with the IS process, up to 30 litres/h. In parallel with JAEA’s HTTR developments a pilot plant test project producing hydrogen at 30 m3/h from helium heated with 400 kW tested the engineering feasibility of the IS process. An IS plant producing 1000 m3/h (90 kg/h, 2t/day) of hydrogen was to be linked to the HTTR to confirm the performance of an integrated production system, envisaged for the 2020s. In 2014 hydrogen production at up to 20 L/h was demonstrated. In January 2019 it used the HTTR to produce hydrogen using the iodine-sulfur process over 150 hours of continuous operation. JAEA aims to produce hydrogen at less than $3/kg by about 2030 with very high temperature reactors.
The US Nuclear Energy Research Initiative (NERI) launched in 1999 was refocused in 2004 to include the Nuclear Hydrogen Initiative (NHI), allied to the Next Generation Nuclear Plant (NGNP) programme established in 2005. NGNP envisaged construction and operation of a prototype high-temperature gas-cooled reactor (HTR) and associated electricity or hydrogen production facilities by 2021, but funding was cut back under the Obama administration and prelicensing activities were suspended in 2013.
Under an International NERI agreement, Sandia National Laboratories in the USA and the French CEA with General Atomics in the USA were also developing the IS process with a view to using high-temperature reactors for it. They had built and operated a laboratory-scale loop for thermochemical water-splitting.
South Korea has also demonstrated thermochemical water-splitting at laboratory scale, supported by General Atomics. In December 2008, the ROK Atomic Energy Commission officially approved nuclear hydrogen development as a national programme, with the development of key and basic technologies through 2017 and the goal of demonstrating nuclear hydrogen production using the S-I process and a very high-temperature reactor (VHTR) by 2026.
The economics of hydrogen production depend on the efficiency of the method used. The IS cycle coupled to a modular high temperature reactor is expected to produce hydrogen at about $2.00/kg. The oxygen byproduct also has value. General Atomics earlier projected $1.53/kg based on a 2400 MWt HTR operating at 850°C with 42% overall efficiency, and $1.42/kg at 950°C and 52% efficiency (both 10.5% discount rate). Such a plant could produce 800 tonnes of hydrogen per day.
For thermochemical processes an overall efficiency of greater than 50% is projected.
https://www.world-nuclear.org/information-library/energy-and-the-environment/hydrogen-production-and-uses.aspx
https://www.iaea.org/topics/non-electric-applications/nuclear-hydrogen-production
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