The design philosophy led us to some unique design features. The desire for inherent safety and minimum activation was a top priority. Material choices for the first wall, blanket, and shield were all influenced. The first wall consists of low-activation SiC composite. Both long-term and short- term activation is small, minimizing waste disposal problems and providing negligible decay heat. Li and LiPb were rejected for safety reasons in favor of a Pb wall protectant. Pb has toxicity and radioactivity concerns, but these were carefully estimated and minimized in the design. The blanket also uses SiC structure and reflector, with low-activation Li₂O breeder and He coolant. Care was taken to minimize the tritium inventory in the breeder. Use of He at relatively low pressure, together with mul-tiple containment barriers, makes blanket failures unlikely and the consequences benign. The shield material also was chosen to reduce activation. Instead of concrete, Prometheus uses an innovative, highly-effective shield consisting of Al structure, water coolant, and B₄C, Pb, and SiC absorbers.

While not all of the design choices use proven technologies, an attempt was made to minimize required R&D and technical risk by adopting near-term technologies that can be extrapolated from existing data. SiC composites are commercially available today, although some development will be required for use in a neutron radiation environment. Pb has been used as a coolant in the past and technologies for using liquid metal as a coolant are well-developed. Similarly, in the blanket, He cooling is an established technology and the data base for Li₂O is being rapidly developed for the MFE fusion program. The R&D needs are bounded and predictable, since the extrapolation from existing technologies is minimized.

*Work supported by USDOE contract #DE-AC02-90ER54101

Category #11

Please associate this paper with that of M. A. Abdou on the IFE reactor design study.