Automated burnup sequence

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Homogenized group constants form the input data for core-level fuel cycle and transient simulator calculations. The data is parametrized according to discrete state-points, which are defined by the local thermal hydraulic conditions together with reactivity control. The process of group constant generation must cover the full range of operating states within the reactor core, which often requires repeating the assembly-level calculation thousands of times. Since the local operating conditions inside a fuel assembly also affect how the materials are depleted, the state-points by which the data is parametrized are not completely independent either. The calculations are instead divided into:

  1. History calculations, i.e. burnup calculations representing a single combination of state variables, which takes into account operating conditions that persist for an extended period of time and affect how the fuel is depleted.
  2. Branch or calculations, which account for momentary changes in the operating conditions, for example, insertion of control rods or increase or decrease in fuel temperature.

In practice, the procedure involves burnup calculations covering all assembly types and history variations. Branch variations are accounted for by performing restart calculations for each burnup point, varying the local operating conditions accordingly.