Nuclear Production of Hydrogen, Fourth Information Exchange ...

PRESENT STATUS OF HTGR AND HYDROGEN PRODUCTION DEVELOPMENT IN JAEA
SO 2 + I 2 + 2H 2 O = 2HI + H 2 SO 4 (1)
2HI = H 2 + I 2 (2)
H 2 SO 4 = H 2 O + SO 2 + 0.5O 2 (3)
H 2 O = H 2 + 0.5O 2 (4)
Reaction (1), known as the Bunsen reaction, proceeds exothermically as the SO 2 gas absorption
reaction by iodine-water mixture. The HI and H 2 SO 4 produced can be separated by liquid-liquid phase
separation of sulphuric acid and HIx solution found by the researchers of General Atomics. Reaction (2)
is slightly endothermic and can be carried out in gas phase using catalysts. Reaction (3) proceeds in
two steps, i.e.:
H 2 SO 4 = H 2 O + SO 3
SO 3 = SO 2 + 0.5O 2
The first reaction takes place spontaneously at temperature range of 300-500°C, while the second
takes place at temperature range of 750-850°C in the presence of catalyst. Here, the HTGR is uniquely
qualified to produce the nuclear heat necessary to drive the intensive endothermic high temperature
reactions of H 2 SO 4 decomposition to completion.
Hydrogen
Figure 5: Thermochemical IS process
Nuclear Heat
Oxygen
1
H 2 O O2
2
2
400 C
900 C
1
H O 2
2
2
+
2HI
Rejected
+
I 2 Heat 100 100 C
SO 2 +H 2 O
H 2 SO 4 SO 2
I 2
I (Iodine)
Circulation
2H I
+
I 2
+ H 2 O
+
H 2 O
H 2 SO 4
SO 2 +H 2 O
S (Sulfur)
Circulation
+
H 2 O
Hydrogen iodide (HI) Water
Sulfuric acid (H 2 SO 4 )
decomposition Bunsen decomposition
reaction
Present status of R&D on IS process in JAEA
JAEA has developed the IS process step by step as shown in Figure 6. The closed-cycle water-splitting
was verified in 1997 with a lab-scale apparatus at a hydrogen production rate of 1 L/h for 48 hrs
(Nakajima, 1999). Further tests were conducted using a glass-made bench-scale apparatus equipped
with an automatic control system. In June 2004, continuous hydrogen production was successfully
achieved with a hydrogen production rate of about 30 L/h for one week (Kubo, 2004, 2005). These tests
were carried out under atmospheric pressure (0.1 MPa) with electric heating.
At present, the process engineering study is underway for industrial scale up. Figure 7 shows a
main flow diagram of IS process plant driven by a sensible heat of high-temperature (up to 880°C) and
high-pressure (4 MPa) helium (He) gas, which simulates the HTTR secondary He gas temperature and
pressure. As the IS process constitutes a very corrosive environment, it is very important to develop
components made of corrosion resistant materials. One of such key components is the sulphuric acid
decomposer, with which H 2 SO 4 solution with concentration of more than 90 wt.% is evaporated and,
simultaneously, H 2 SO 4 is decomposed into gaseous SO 3 and H 2 O under high-temperature conditions of
NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010 51