Hydrogen energy is a clean secondary energy, which has broad application prospects in clean combustion and hydrogen fuel cells.  More importantly, hydrogen can decouple the production and consumption of electricity and, as a carrier of clean energy, can be stored and transported in various forms, such as gas, liquid and solid oxide, with high energy density and long storage time. Therefore, it is a means of large-scale and long-cycle energy storage.  

To realize the wide application of hydrogen, it is necessary to develop clean, efficient and large-scale hydrogen production technology.  Currently, the world consumes about 50 million tons of hydrogen each year, of which more than 95 percent comes from gray hydrogen from fossil fuels.  China is the world's largest hydrogen producer, with a hydrogen production capacity of about 40 million tons/year and an output of about 33 million tons/year, mainly composed of hydrogen production from fossil fuels and industrial by-production.  According to the White Paper on China's Hydrogen Energy and Fuel Cell Industry released by China Hydrogen Energy Alliance in 2021, hydrogen energy will account for about 10% of China's energy supply by 2050, with hydrogen demand approaching 60 million tons and annual economic output exceeding 10 trillion yuan.  

After more than half a century of development, nuclear energy has become an important component of global clean energy.  Hydrogen production from nuclear energy is coupled with nuclear reactor and hydrogen production process, which not only realizes no carbon emission in hydrogen production process, but also effectively expands the utilization of nuclear energy and improves the economic competitiveness of nuclear power plants.  

In the global process of promoting "carbon neutrality", the United States, the European Union, the United Kingdom and Japan are actively promoting the relevant research on nuclear hydrogen production. However, the ideal nuclear hydrogen production scheme must rely on high-temperature/ultra-high-temperature reactors, which are not mature and large-scale applied at present, and the electrolysis hydrogen production cost is relatively high in the absolute mainstream current water-cooled reactor nuclear power units.  Without competitive advantages, it is difficult to scale promotion.  The author believes that the application prospect of hydrogen production from nuclear energy depends on the mass construction of high-temperature/ultra-high-temperature reactors. At present, the economic problem of high-temperature reactors is the biggest obstacle.  

There are two technical paths  

The technical route of nuclear hydrogen production can be divided into three types: nuclear hydrogen production (unit provides electric energy for hydrogen production), nuclear hydrogen production (unit provides thermal energy for hydrogen production) and electric hybrid hydrogen production (unit provides thermal energy and electric energy for hydrogen production).  There are many options for reactors that can be coupled to the hydrogen production process, but from the point of view of hydrogen production, hydrogen production efficiency is closely related to the operating temperature, with high temperature (outlet temperature 700-950℃) and ultra-high temperature reactors (outlet temperature above 950℃) being the optimal choices.  

Hydrogen production from nuclear power is the general hydrogen production from water electrolysis. The hydrogen production efficiency (55%-60%) of this process is low. SPE advanced water electrolysis technology developed in the United States can improve the electrolysis efficiency to 90%.  In the current mature hydrogen production process, the cost of hydrogen production by electrolysis of water is the highest, so nuclear hydrogen production is basically not competitive advantage at present, it is difficult to scale promotion and application.  

Nuclear hydrogen production, also known as thermo chemical hydrogen production, is the coupling of a nuclear reactor and a thermochemical circulating hydrogen production device to catalyze the thermal decomposition of water at 800℃ to 1000℃, so as to produce hydrogen and oxygen. The conversion rate from heat to hydrogen energy can reach 60% or even higher. At present, the best solution is the iodine-sulfur cycle developed by General Atomic Energy Corporation of the United States.  

Electrothermal hybrid hydrogen production uses process heat (about 30%) and electric energy (about 70%) provided by advanced nuclear reactors to electrolysis water vapor into hydrogen and oxygen at a high temperature of 750℃ to 950℃, and its hydrogen production efficiency is close to 60%.  

At present, the technology maturity of nuclear hydrogen production and electrothermal hybrid hydrogen production is still low, and the main challenge is the research and development of high temperature resistant materials.  All hydrogen production processes require nuclear reactors to provide high temperature process heat, but all these reactors belong to the fourth generation reactors. At present, except for the demonstration project of high temperature gas-cooled reactors, other reactors are all in the research and design stage, and have not yet been verified by engineering. There is still a long time to go before commercial promotion, and they face great uncertainties.  Therefore, the United States, Britain, Japan, China and other major nuclear powers currently regard high-temperature gas-cooled reactor as the first choice for hydrogen production.