Group constant generation and core design optimization methodology for the GEN IV ALLEGRO reactor

Bálint Batki, András Keresztúri, István Pataki, István Panka (MTA EK)

28th Symposium of AER on VVER Reactor Physics and Reactor Safety (2018, Olomouc, Czechia)
Advances in spectral and core calculation methods


The ALLEGRO gas-cooled fast reactor is currently under development. The current core design should be optimized to fulfil several criteria. The optimization from reactor physics point of view requires numerous full core calculations, thus nodal methods should be used. Reliable group constants should be determined to get precise nodal results, with special regard to thermal effect. The whole methodology should be verified.
In this paper, a group constant (GC) generation methodology is shown using the Serpent Monte Carlo code for the ALLEGRO reactor. Thermal effects, such as Doppler and thermal expansion effects were also investigated. These are particularly important since these phenomena are largely different in fast reactors than in thermal systems and play a significant role during transients. The obtained GCs were applied in the KIKO3DMG nodal code. The results of the nodal calculations including reactivity coefficients were verified through the comparison of the full core nodal and Monte Carlo results.
Using the KIKO3DMG code and the determined GCs, the ALLEGRO core was modified to fulfill the following criteria: enough reverse reactivity needed for the determined fuel cycle length; the number of fuel assemblies and the radial peaking factor should be set not to exceed the maximum allowed linear heat rate; displacement per atom quantity should be maximized for the experimental channels. For the above goals, the plutonium content of the fuel assembly was varied. The modified core should be further investigated from thermal hydraulics and reactor physics point of view to get a core, which fulfils all the required criteria.

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