The severe-accident-free high-temperature gas-cooled reactor (SFHTR) is a prototype design for a next generation reactor. It is suitable for widespread deployment by virtue of its inherent safety features and very long refueling interval. Furthermore, its inherent safety features can be demonstrated by full-scale tests. Many of these features may be demonstrated in the High-Temperature Engineering Test Reactor (HTTR).

The SFHTR is designed to have the probability of a severe accident at least two orders lower than existing systems. The fuel will not exceed its failure temperature even in the event of complete loss of coolant or complete withdrawal of two control rods. A unique configuration of burnable poisons allows a fuel cycle of 16 yr and a burnup exceeding 120 GWd/t. This feature promises very high availability and good economics.

We have designed two SFHTR systems. The larger one, called the MSFHTR, has a 450- to 600-MW thermal capacity and is intended for the production of hydrogen and electricity. The smaller SFHTR (SSFHTR) is intended for remote areas, off the electrical grid, for simultaneous production of electricity and desalinated water. The SSFHTR can produce 23.5 MW(electric) plus 40 t/h of water with a net efficiency of 47%.

The HTTR is capable of conducting full-scale simulation testing of key SFHTR design features in order to confirm and extend the designs and as a first step in convincing the public and the licensing authorities of the validity of demonstrable inherent safety. Design features of a 50-MW SFHTR focusing on the safety concept, safety evaluation, and core design are described. In addition, an HTTR-based test-and-development program for the SFHTR is presented.