- 22 -


such as these. However, since the reactor is very thermal, it is reasonable to expect that diffusion theory methods will suffice for survey and comparison calculations. In a parametric study of gaseous core reactors using both transport and diffusion theories, Plunkett (23) has demonstrated that multigroup diffusion theory is adequate for calculations of this type. In the present study, the effects of elevated temperatures and the resulting exaggerated nuclear motion will be treated within the framework of multigroup diffusion theory. This approach leads to the development of calculational methods which are designed specifically for application to diffusion theory codes. Such methods may be directly applicable to transport theory codes. If not, it will be necessary to include the effects of nuclear motion by reduction of equation (2.3) to a form which can be solved numerically.


Diffusion Approximation to Boltzmann Equation

        The previous discussion of -the plasma core reactor has considered the zero power reactor which contains no hydrogen. A power producing plasma reactor will operate with a high velocity hydrogen coolant plasma surrounding the uranium plasma. In this case the exaggerated motions of both absorbing fuel nuclei and scattering coolant nuclei become important. The inclusion of these effects will