Neutron-gamma flux distributions in cylindrical beam tubes of pool-type research reactor

Abstract

In nuclear reactor, a variety of ducts are equipped in the radiation shield. Beam tubes, used for experimental facilities for research and development are one of them. It is very important to estimate the neutron and gamma photon flux profile inside as well as at the exit of the duct. This is required from experimental as well as radiation protection point of view. One way to estimate these flux profiles is to use transport method and another way is to use semi-empirical formula which describes energy-space distributions of streamed neutrons and gamma photons in various beam tubes with different shapes. Deterministic transport methodology using discrete ordinates approximation cannot be accurately model the streaming problems. This is due to inability to incorporate sufficient number of angular mesh points in the direction of streaming paths, which leads to ray effect (Miller and Lewis in Computational methods of neutron transport, Wiley, New York, 1985). This ray effect arises in the problem (radiation shielding etc.) having very little scattering and localized sources. In such problems anomalies (unphysical oscillations in the computed scalar flux) likely to arise in the scalar flux distribution. As a result, considerable underestimation occurs. Monte Carlo transport methods seem to be the best method in dealing streaming problems. However, reliable results with small statistical errors are not necessarily obtained in reasonable computation time. So, the use of semi-empirical formula will give the result with suitable accuracy and in less time. In this paper, streaming of neutrons as well as gamma photons through the beam tubes has been calculated using semi-empirical formula and compared with Monte Carlo results. Here, we have considered cylindrical ducts and the results obtained by semi-empirical formula are comparable with those from Monte Carlo code. The results can be verified further when the neutron-gamma flux measurement is done.