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CONCEPTUAL DESIGN OF THE HTTR-IS NUCLEAR HYDROGEN PRODUCTION SYSTEM
Introduction
Japan Atomic Energy Agency (JAEA) has been conducting R&D on both high-temperature reactors and
hydrogen production technologies. Concerning reactor technology, an HTTR was constructed at Oarai,
Japan and successfully delivered 950°C heat outside its reactor vessel (Fujikawa, 2004). Regarding
hydrogen production technology, JAEA has been conducting R&D for a thermochemical water-splitting
iodine-sulphur process (IS process), and achieved a continuous hydrogen production of 31 NL/h for
175 hours using a bench-scale apparatus in 2004 (Kubo, 2004). Followed by pilot plant experiment,
JAEA plans to construct a hydrogen production system with the IS process utilising heat from the HTTR
(HTTR-IS system), which is expected to be the world’s first demonstration on hydrogen production
utilising heat directly supplied from a nuclear reactor (Sakaba, 2007).
One of the key issues for the nuclear hydrogen demonstration is the IHX tube rupture scenario
(IHXTR). In case of the HTTR design, the secondary cooling system is included in the containment
vessel (CV), and cooling ability is sufficient by secondary pressurised water cooling system during the
scenario. Hence, there is no significant impact on either reactor safety or public exposure. In contrast,
the secondary cooling system of HTTR-IS system penetrates the CV and reactor building in order to
provide heat to the hydrogen production plant. Thus the containment isolation valves should be
automatically closed detecting an appropriate signal from engineered safety features actuation system
in order to reduce radionuclide transportation from primary to secondary cooling system. Furthermore,
core cooling and component integrity should be reinvestigated due to the procedure change in IHXTR.
This paper summarises the HTTR-IS nuclear hydrogen production system and discusses detection
method of heat transfer tube rupture of IHX and system analysis results during IHXTR.
Conceptual design of the HTTR-IS system
A tentative flow diagram of the HTTR-IS system is shown in Figure 1 and the major design specifications
are shown in Table 1. The HTTR-IS system consists of the reactor, primary cooling system, secondary
cooling system and IS process. At rated operation of the HTTR-IS system, primary pressurised water
cooler (PPWC) and IHX are used in parallel and remove the heat of the reactor core. The heat produced
by the reactor core transfers to the secondary cooling system at the IHX. Secondary cooling system
penetrates CV and flows through the inner tube of the concentric hot gas duct in order to provide heat
to the IS process. At the IS process, secondary helium gas provides heat to process heat exchangers,
etc., such as a H 2 SO 4 decomposer, a HI decomposer, and a re-boiler of the HI distillation column.
Downstream of the IS process, a steam generator and a helium gas cooler are installed as a thermal
buffer. Finally, the helium gas is compressed by a secondary helium circulator and flows through the
outer tube of the concentric hot gas duct and flows back to the IHX.
Figure 1: Flow diagram of the HTTR-IS system
Containment vessel
Containment
isolation valves
Auxiliary
cooling
system
Reactor
IHX
Concentric
-hot gas
duct
IS process
Steam
generator
PPWC
Secondary
helium
circulator
Helium
cooler
388 NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010