A COUPLED NEUTRONICS-THERMOHYDRAULICS MODEL OF THE HOMOGENEOUS SLOWPOKE REACTOR FOR APPLICATIONS TO TRANSIENT STATES
4th International Technical Meeting on Small Reactors - 2016 Nov. 02-04


Presented at:
4th International Technical Meeting on Small Reactors
2016 Nov. 02-04
Location:
Ottawa, ON Canada
Session Title:
Parallel Session D - Research-Reactor Physics

Authors:
B. Limbeek (Royal Military College of Canada)
H.W. Bonin (Royal Military College of Canada)
P.K. Chan (Royal Military College of Canada)
J.W. Hilborn (AECL (retired))
  

Abstract

The primary application of the Homogeneous SLOWPOKE reactor, a design derived from the present heterogeneous SLOWPOKE-2 research reactor, is the production of radioisotopes for applications in industry and nuclear medicine, 99Mo and 99mTc in particular. A network of about 15 Homogeneous SLOWPOKE reactors dispersed throughout North America can replace the NRU reactor which is nearing its service life for the production of these two radioisotopes, with the advantage of the proximity of the radioisotope production sites to the hospitals and radiopharmacies. The Homogeneous SLOWPOKE reactor is designed on a liquid fuel core that enables these isotopes to be extracted much more easily. The Homogeneous SLOWPOKE reactor has been designed also as a replacement for the heterogeneous SLOWPOKE-2 reactors at universities, allowing the continuation of their teaching and research missions in neutron activation analysis and neutron radiography. The Homogeneous SLOWPOKE reactor was first simulated for a variety of transient states under several start-up and shut-down conditions, as well as abnormal situations. The neutronics calculations were performed using both MCNP 5 and WIMS-AECL codes, and the thermohydraulics calculations were performed using COMSOL Multiphysics. The results showed that natural convection was sufficient to ensure adequate reactor cooling in all situations. The most severe transient simulated resulted from a 5.87 mk step positive reactivity insertion to the reactor in operation at critical and at steady state. Peak temperature and power were determined as 83oC and 546 kW, respectively, reached after 5.1 s after the reactivity insertion. However, the power fell rapidly to values below 20 kW some 35 s after the peak and remained below that value thereafter. Both the temperature and void coefficients are significantly more negative than the corresponding coefficients in SLOWPOKE-2. The simulations of the reactor in transient states showed that the temperature and power levels attained never compromised the integrity of the reactor. The on-going research is now focussing on the development of an accurate computer model which dynamically simulates the interacting neutronics and thermohydraulics effects within the liquid core. This component of the development of the Homogeneous SLOWPOKE reactor is needed to address safety-related issues arising from the non-rigid core configuration. The proposed model uses the probabilistic code MCNP 6 for the neutronics calculations and COMSOL Multiphysics for the thermohydraulics computations. By using a mesh geometry that would be common in the two programs, and by writing programs to import, export, and format data, MCNP 6 and COMSOL may be coupled to iteratively determine accurate temperature, heat source, density, and neutron flux distributions within the core to be used in further safety analysis and refinement of the design. The codes will be used in an alternating fashion for each time step, creating a model that accounts for the actual configuration of the core as time progresses.

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