Comparative modeling of stochastic versus regular arrangement of TRISO particles in HTTR

• Published in: Progress in nuclear energy (New series) Vol. 78; pp. 291 - 296
• Main Authors: Torabi Ardakani, A., Ghofrani, M.B., Ezzati, A.O.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2015
• Subjects: Compacts; Criticality calculation; Cubic lattice; Fuels; HTTR; Mathematical models; MCNPX; Nuclear engineering; Nuclear power generation; Nuclear reactor components; Nuclear reactors; Regular arrangement; Stochastic arrangement; TRISO; Regular arrangement; HTTR; TRISO; Stochastic arrangement; MCNPX; Criticality calculation
• ISSN: 0149-1970
• DOI: 10.1016/j.pnucene.2014.09.017

TRISO particles are the specific features of HTTR and generally HTGR reactors. Their heterogeneity and random arrangement in graphite matrix of these reactors create a significant modeling challenge. In this study, an algorithm is proposed for modeling random arrangement of TRISO particles in the fuel compacts of HTTR. The effect of this arrangement on criticality calculations, i.e. effective multiplication factor and critical position of control rods, is then compared with regular arrangement. Regular arrangement was modeled by positioning each TRISO as a fixed sphere in the center of a cubic lattice and subsequently, each fuel compact was filled with around 13,000 (approximate number of TRISOs in fuel compact) of these cubic lattices, depending on its packing factor. Stochastic arrangement was modeled by our algorithm, via distributing definite number of TRISOs in a cubic lattice and each fuel compact was then filled with this cubic lattice. The calculations have been carried out using MCNPX version 2.6 for three core configurations: thin annular core, thick annular core and fully loaded core. The comparison of criticality calculations between these two arrangements in different core configurations showed approximately 60–250 pcm difference. All simulations were benchmarked with different simulation results presented in the IAEA-Technical Document No.1382. It was observed that our estimation of critical heights of control rods was more consistent with the experimental data. •A method to adapt non-explicit MCNPX simulation code to model random arrangement of TRISOs in HTTR was tested.•Investigation of criticality results of stochastic and regular arrangements of TRISOs, in both sample fuel block and in the reactor core.•Comparison of stochastic and regular arrangements in different core configurations.•Very small differences between the results of regular and stochastic arrangements were obtained.•Benchmarking the simulation results with experimental data and IAEA-Tech Doc 1382.