The WWR-M is an 18 MW pool-type reactor with a hexagonal core containing 145 fuel elements of WWR-5M design that are enriched in uranium-235 to 90 percent (Figure 2-6). Although this reactor entered ser­vice in 1959, it is still operating very effectively and has achieved several increases in power and flux densities since it was commissioned. It is now the highest power reactor of its type in existence.

Initial studies have been carried out to assess the feasibility of convert­ing this reactor to 36 percent enriched and 19.75 percent enriched fuel. It was observed that as enrichments decrease, burnups, thermal neutron flux densities, and fast neutron flux densities also decrease. These studies indi­cate that fuel having a uranium density of 8.25 gU/cm3 would be required to convert this reactor without sacrificing needed consumer characteristics. However, fuels with this density are not available at present.