CORRELATION BETWEEN THE EFFECTIVE DIFFUSION COEFFICIENT AND THE POROUS STRUCTURE IN NUCLEAR GRAPHITE. Project DRAGON.

In Part 1 a new method for the experimental determination of effective diffusion coefficients in porous graphites is described. For the measurements the self-diffusion or ortho- and parahydrogen is used; the partial pressure difference in the porous sample is maintained by the conversion of para- to orthohydrogen. Experiments were carried out with nuclear graphites Type G5 and HX12 at different degree of burn-off. The effective diffusion coefficient of hydrogen was measured as a function of pressure at different temperatures. In Part 2 a pore model containing two parameters (tortuosity factor x and shape factor alpha) is assumed, to correlate the diffusion coefficients with the pore size distribution of the graphite. From the experimental values the two parameters X and alpha are calculated as a function of burn-off. These values are discussed in more detail. (auth)