Royal Military College of Canada

Energy and Nuclear Science

Experimental and Computational Determination of Radiation Dose Rates in the Slowpoke-2 Research Reactor

By: Dr. Hugues W. Bonin & Lt(N) G.B. Lamarre

The first SLOWPOKE-2 research nuclear reactor designed to use the Low Enriched Uranium (LEU) dioxide fuel was commissioned at the Royal Military College of Canada in September 1985. It is being used mostly for Neutron Activation Analysis (NAA), but there is an expansion of research involving irradiation of samples for which the dose accumulated must be known accurately. After several attempts in measuring experimentally the dose rates at various irradiation sites in the reactor and the pool, only those thermal flux measurements proved to have reasonable accuracy, since the various measuring instruments failed under the intense mixed radiation field in the SLOWPOKE-2 environment. The research project described here represents the latest effort to determine accurate dose rate distributions. Here, the lack of accurate experimental data for radiation other than thermal neutrons is filled by an intensive computer simulation of the reactor and its pool. A mix of commercial software and in-house developed software is used for this study, with the neutron fluxes determined with the code WIMS-AECL developed by Atomic Energy of Canada Limited, which reproduced the experimentally-determined distribution of the thermal neutron flux with an agreement better than 5%.

The gamma photon flux and dose rate distributions were calculated using the software Microshield 5 which was supplemented with an in-house written program for a more accurate determination of back scattering effects. Additional in-house written programs were then used to determine the fluxes and dose rates from other important ionising particles: recoil protons and energetic electrons. For typical work such as the irradiation of nitrocellulose samples, the samples are located using the "elevator" device in the reactor pool against the reactor vessel wall, at a position 32.0 cm from the core centre line and at mid-plane of the reactor core. At this position and at half reactor power, the total dose rate determined was 3.7 × 104 Gy h-1 distributed as follows among the ionising particles: 3.2 × 104 Gy h-1 (86%) for the electrons, 2.6 × 103 Gy h-1 (7%) for the gamma photons, 1.0 × 103 Gy h-1 (2.7%) for the recoil protons, and 5.0 × 102 Gy h-1 (1.4%) for the fast and thermal neutrons. Conservatively, high 40% error bars were attributed to these dose rates to account for large uncertainties in the various absorption and scattering cross sections for the various particles.

Slowpoke-2 Particle Dose Distribution

SAMPLE PUBLICATIONS:

  • G.B. Lamarre & H.W. Bonin, "Experimental and Computational Determination of Radiation Dose Rates in the SLOWPOKE-2 Research Reactor at the Royal Military College of Canada", 20th Annual Conference of the Canadian Nuclear Society, Session 2A, 30 May-2 June 1999, Montréal, Québec, Canada.
  • G.B. Lamarre, "Determination of fluxes of particles (Gamma, X-Rays, Thermal and Fast Neutrons, Electrons and Beta Particles) at the Irradiation Sites in the SLOWPOKE-2 Nuclear Reactor Facility", Master's degree thesis, Royal Military College of Canada, Kingston, Ontario, April 1999.