The high-temperature test reactor (HTTR) finished construction in 1996 (Figure 14.5). The power rating was 30 MWt and first criticality was achieved in 1998. This reactor includes the annular prismatic fuel design. The core outlet temperature is currently 850°C but may be increased by 100°C following design optimisation. This reactor is one of kind envisaged for process heat applications and, therefore, includes an intermediate heat exchanger with the purpose of supplying process heat.

Research is being conducted at JAERI on the high-temperature engineering test reactor (HTTR) for heat utilisation (Miyamoto et al., 1998). This is the first high-temperature gas reactor (HTGR) to be constructed in Japan. The design is for a 30-MW thermal output and outlet coolant temperature of 950°C. After a satisfactory demonstration period, a hydrogen production system will be fitted. The process will involve steam reforming of natural gas (Hada et al., 1996). It has been demonstrated in out-of-pile tests at 1/30 scale carried out by the Science and Technology Agency (Inagaki et al., 1997).

Nuclear heat of 10 MW at 950°C is supplied from the HTTR to a heat exchanger in a primary helium loop. A secondary helium loop then transfers heat to the steam reformer, which converts steam and methane to hydrogen and carbon monoxide. To provide stability

Steaa

Secondary hetiurn Feed water

Figure 14.5. HTTR hydrogen production system. Source: Miyamoto et al. (1998).

in the event of disturbances in the steam reforming process, a steam generator is installed at the downstream of the steam reformer to keep the helium gas temperature at the steam saturation temperature.

To reduce carbon emissions, further studies are in progress on hydrogen production by water splitting, via a thermochemical iodine sulphur process first proposed by the General Atomic Company (Norman et al., 1982). This is foreseen as an improved potential heat utilisation and hydrogen production process for the HTGR.

In addition to hydrogen production, there are other high-temperature applications being proposed, including the production of gases such as styrene and ethylene.

14.10.1 Generation IV Systems These have been considered in Chapter 12.