The use of a nuclear power plant to produce hydrogen or for other process heat applications will present challenges to the licensing process. Potential safety and regulatory issues have been evaluated to identify possible research needs, policy concerns and licensing approaches. A brief description of nuclear power plant licensing in the United States and a discussion of specific issues for using nuclear power plants for process heat applications are presented.

A transient control volume model of the sulphur iodine (S-I) and Westinghouse hybrid sulphur (HyS) cycles is presented. These cycles are some of the leading candidates for hydrogen generation using a high temperature heat source. The control volume models presented here are based on a heat and mass balance in each reaction chamber coupled to the relevant reaction kinetics. The chemical kinetics expressions are extracted from a relevant literature review.

In the sulphur-iodine (S-I) cycle nuclear hydrogen generation scheme the chemical plant acts as the heat sink for the very high temperature nuclear reactor (VHTR). Thus, any accident which occurs in the chemical plant must feedback to the nuclear reactor. There are many different types of accidents which can occur in a chemical plant. These accidents include intra-reactor piping failure, inter-reactor piping failure, reaction chamber failure and heat exchanger failure.

One of the key safety issues for nuclear hydrogen production is the heat transfer tube rupture in intermediated heat exchangers (IHX) which provide heat to process heat applications. This study focused on the detection method and system behaviour assessments during the IHX tube rupture scenario (IHXTR) in the HTTR coupled with IS process hydrogen production system (HTTR-IS system). The results indicate that monitoring the integral of secondary helium gas supply would be the most effective detection method. Furthermore, simultaneous actuation of two isolation valves could reduce the helium gas transportation from primary to secondary cooling systems. The results of system behaviour show that evaluation items do not exceed the acceptance criteria during the scenario. Maximum fuel temperature also does not exceed initial value and therefore the reactor core was not seriously damaged and cooled sufficiently.

Throughout the past decades, the need to reduce greenhouse gas emissions has prompted the development of technologies for the production of clean fuels through the use of zero emissions primary energy resources, such as heat from high temperature nuclear reactors. One of the most promising of these technologies is the generation of hydrogen by the sulphur-iodine cycle coupled to a high temperature nuclear reactor, initially proposed by General Atomics. By its nature and because these will have to be large-scale plants, development of these technologies from its current phase to its procurement and construction phase, will have to incorporate emergency mitigation systems in all its sections and nuclear-chemical “tie-in points” to prevent unwanted events that can compromise the integrity of the plant and the nearby population centres.

A chemical heat pump system using two hydrogen-absorbing alloys is proposed to utilise heat exhausted from a high-temperature source such as a high-temperature gas-cooled reactor (HTGR), more efficiently. The heat pump system is designed to produce H2 based on the S-I cycle more efficiently. The overall system proposed here consists of HTGR, He gas turbines, chemical heat pumps and reaction vessels corresponding to the three-step decomposition reactions comprised in the S-I process. A fundamental research is experimentally performed on heat generation in a single bed packed with a hydrogen-absorbing alloy that may work at the H2 production temperature. The hydrogen-absorbing alloy of Zr(V1-XFeX)2 is selected as a material that has a proper plateau pressure for the heat pump system operated between the input and output temperatures of HTGR and reaction vessels of the S-I cycle. Temperature jump due to heat generated when the alloy absorbs H2 proves that the alloy–H2 system can heat up the exhaust gas even at 600°C without any external mechanical force.

Control system studies were performed for the next generation nuclear plant (NGNP) interfaced to the high-temperature electrolysis (HTE) plant. Temperature change and associated thermal stresses are important factors in determining plant lifetime. In the NGNP the design objective of a 40-year lifetime for the intermediate heat exchanger (IHX) in particular is seen as a challenge. A control system was designed to minimise temperature changes in the IHX and more generally at all high-temperature locations in the plant for duty-cycle transients. In the NGNP this includes structures at the reactor outlet and at the inlet to the turbine.

High temperature creep in structures at the interface between the nuclear plant and the hydrogen plant and the migration of tritium from the core through structures in the interface are two key challenges for the very high temperature reactor (VHTR) coupled to the high temperature electrolysis (HTE) process. The severity of these challenges, however, can be reduced by lowering the temperature at which the interface operates. Preferably this should be accomplished in a way that does not reduce combined plant efficiency and other performance measures. A means for doing so is described. A heat pump is used to raise the temperature of near-waste heat from the PCU to the temperature at which nine-tenths of the HTE process heat is needed. In addition to mitigating tritium transport and creep of structures, structural material commodity costs are reduced and plant efficiency is increased by 1%.