An electron linac, fitted with a standard x-ray converter, can produce high neutron yields in materials with low photonuclear threshold energies, such as D and %e. This paper discusses the preliminary MCNP modeling of a therapeutic thermal neutron source driven with a repetitively pulsed electron linac operated in the CW mode. Preliminary results indicate that a IO MeV, 10 kW electron linac can produce in excess of 3x101* nlsec in a 9.42 L tank of heavy water. Current modeling results are discussed.