Nuclear Production of Hydrogen, Fourth Information Exchange ...

EXECUTIVE SUMMARY
safety assessments often define design and performance specifications that critical components and
structures as well as lead to process improvements or new process designs to assure the safe
operation of a nuclear hydrogen production facility.
A panel of experts representing nuclear regulatory agencies (US NRC), government national
laboratories and agencies (DOE/ANL and JAEA) and universities [Purdue University (USA), National
Autonomous University of Mexico, and Kyushu University (Japan)] was convened to present advances
in understanding the safety aspects of nuclear hydrogen production.
William Reckley (US NRC) presented a description of the methodology that the NRC may employ
to develop the framework required for licensing a nuclear reactor at a hydrogen production facility.
The NRC is currently developing the needed infrastructure and knowledge base to prepare to license
high-temperature gas-cooled reactors, which are being developed as part of the US Department of
Energy’s (DOE) Next Generation Nuclear Plant (NGNP) programme. The NRC will then build upon
existing guidelines related to hazards posed by nearby industrial facilities and the use of hazardous or
flammable materials at the nuclear site when reviewing license applications for nuclear hydrogen
plants. Tools such as phenomena identification and ranking tables (PIRT charts) will be used to
identify issues, assess safety significance, and define research and development needs for developing
the licensing guidelines.
Nicholas R. Brown (Purdue University) presented the development of transient control volume
models for the sulphur-iodine (SI) and the hybrid sulphur (HyS) cycles in his paper titled, “Transient
modelling of sulphur iodine cycle thermochemical hydrogen generation coupled to pebble bed modular
reactor.” These models are based on heat and mass balances in each reaction chamber coupled to the
relevant reaction kinetics (in the case of the HyS cycle, the Nernst equation is used for the reaction
model). The models indicate that the rate-limiting steps are hydrogen iodine decomposition for the S-I
cycle and the sulphuric acid decomposition for the HyS cycle. Brown then uses the transient control
volume model for the S-I cycle coupled to a THERMIX model of a 268 MW pebble bed modular reactor
(PBMR-268) and a point kinetics model to evaluate the impact of various component failure scenarios
on the nuclear reactor in his paper entitled “Proposed chemical plant initiated accident scenarios in a
sulphur iodine cycle plant coupled to a pebble bed modular reactor.” Component failure scenarios in
the chemical plant such as intra-reactor piping failure, inter-reactor piping failure, reaction chamber
failure, and heat exchanger failure, can be reduced to two types – discharge rate limited failures related
to the SO 3 decomposition reaction and discontinuous reaction chamber failures. It is concluded that a
reaction chamber failure, such as a rupture, will result in an increase in the average and maximum
fuel temperatures of the nuclear reactor coupled with a decrease in power.
H. Sato (JAEA) presented a paper discussing detection methods and system behaviour assessments
for a tube rupture of the intermediate heat exchanger (IHX) for a sulphur-iodine based nuclear
hydrogen plant. A rupture could be detected by monitoring the secondary helium gas supply using a
control system that monitors the differential pressure between the primary and secondary helium gas
supply. Isolation valves would be used to reduce the helium flow between the primary and secondary
cooling systems. The study showed that the maximum temperature of the reactor core does not
exceed its initial value and that system behaviour did not exceed acceptance criteria.
Alexander Mendoza-Acosta (National Autonomous University of Mexico) presented the use of
probabilistic safety assessment (PSA) as a tool for evaluating the impact of accidental releases of
highly toxic chemicals, such as sulphuric acid, used in the S-I cycle on the health and safety of both
the plant operators and residents in the vicinity of the plant and then designing safety systems to
mitigate the consequences of such releases. In this presentation, the impact and mitigation of a toxic
gas cloud resulting from the uncontrolled leakage of concentrated sulphuric acid from the second
section (Bunsen reaction) of the General Atomics S-I cycle was investigated. Mitigation systems based
on the isolation of the leak followed by neutralisation and flushing of the sulphuric acid leak were
proposed and analysed using PSA. A toxic cloud mitigation system was proposed which consisted of a
system for isolating and neutralising the leakage coupled with a secondary electrical backup system
which will reduce the frequency of cloud formation to less than 1 × 10 –9 events per year.
Satoshi Fukada (Kyushu University) expounded upon a chemical heat pump system employing
hydrogen-absorbing alloys comprised of Zr-V-Fe to more efficiently use heat and produce hydrogen in
a nuclear hydrogen production facility that couples a high-temperature gas-cooled reactor integrated
with a sulphur-iodine thermochemical cycle (HTGR-IS). The objective of this research is to increase
NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010 17