Effect of statistical characteristics of fuel pin bundle on evaluation of temperature in the core of sodium cooled fast reactor

7/14/2014 2014 - #02 Physics and technology of nuclear reactors

Tikhomirov B.B. Poplavsky V.M.

https://doi.org/10.26583/npe.2014.2.14

The article is devoted to optimization of analytical models used for the evaluation of fast reactor (FR) fuel element cladding temperature with the aim to increase the fidelity of the results obtained.

The rated value of the fuel element cladding temperature at the core outlet in FR fuel subassemblies is basically determined by the coolant temperature. However, calculation of the coolant temperature in the channels surrounding the fuel elements requires knowledge of the model of the fuel pin bundle arranged in a triangular grid. Distribution of the local flow rates and, hence, coolant temperature rise values in the channels over the pin bundle cross section is fully dependent on the arrangement of the fuel elements in the fuel subassembly wrapper taking into account the technological fitting gap.

Various hypothetical bundle models adopted for the calculation were studied and their drawbacks were identified. The difference in sodium temperature rise values for the different models is over 30 °С. The models are static, so they do not allow taking into account to the full extent radial and, particularly, axial heat and mass transfer that would decrease non-uniformity of the fuel element cladding temperatures.

A bundle model was developed based on the results of experimental studies of fuel element arrangement in fresh fuel subassemblies. It is demonstrated that formation of channel dimensions at the stage of manufacturing subassemblies with fuel pin bundles is a stochastic process following statistical laws. The relationships between characteristics of the fuel pin bundle required for calculation and the value of the technological fitting gap in the fuel subassembly were obtained by processing statistic data using the Weibull distribution.

There are two pin bundle models created taking into account statistics, one of which allows using the most probable statistically average dimensions of different type channels instead of hypothetical dimensions in the calculation of the rated value of sodium temperature rise at the design development stage. The second option makes it possible to evaluate the random dispersal of temperature rise values in the pin bundle taking into account axial and radial heat and mass transfer. This significantly increases the fidelity of evaluating the working temperatures of the hottest fuel elements.

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sodium cooled fast reactors fuel subassemblies fuel element bundle models cladding temperature evaluation statistics-modified model inter-channel exchange

Link for citing the article: Tikhomirov B.B., Poplavsky V.M. Effect of statistical characteristics of fuel pin bundle on evaluation of temperature in the core of sodium cooled fast reactor. Izvestiya vuzov. Yadernaya Energetika. 2014, no. 2, pp. 128-139; DOI: https://doi.org/10.26583/npe.2014.2.14 (in Russian).