Explicit transverse leakage treatment using an analytic basis function expansion

An explicit method for calculating the transverse leakage is presented in this paper. The method is based upon the use of analytic basis functions, which represent individual eigenfunctions of the neutron diffusion equation. The intranodal flux solution is expressed as an eigenspace, and can be solved by using the already calculated surface currents and flux moments as boundary conditions. The salient feature of the method, therefore, is that no ad hoc presumptions are made with regard to the leakage shape. The individual eigenfunctions are calculated based upon already calculated parameters from the flux solution and response matrix solution, and therefore no additional parameters are introduced into the problem, which could lead to an unwanted increase in computation time. The new transverse leakage method is implemented in PSU's NEM code and is tested against the OECD/NEA 3D C5G7 rodded MOX benchmark and the C3 benchmark. (author)