Reactor Physics

ANSWERS supplies a range of Reactor Physics Software, including:

WIMS - A general purpose reactor physics program for core physics calculations.

WIMS can provide simple pin cell calculations of reactivity to whole core estimates of power and flux distributions.

The user can benefit from the flexibility of using predefined calculational routes or providing customised methods of solution using diffusion theory, discrete-ordinates, collision probability, characteristics or Monte Carlo methods.

PANTHER - A leading neutron diffusion and thermal hydraulics code for the analysis of any thermal reactor core.

PANTHER performs all types of reactor calculation, fuel management, safety transient analysis and on-line operational support using full consistent models with reference accuracy. Users can benefit from a modern software package which has been developed over the past 10 years by EDF Energy.

FISPIN - A Code for Nuclide Inventory Calculations.

FISPIN calculates the changes in the numbers of atoms of the nuclides of various species – heavy isotopes or actinides, fission products, and structural or activation materials – as a sample of nuclear fuel element is subjected to periods of irradiation and cooling.

FISPIN is developed in collaboration with NNL.


We have considerable experience in a wide range of reactor physics applications to support the operation, safety analysis and design of a large variety of nuclear plant. This expertise has been successfully applied to solve a wide range of customer problems.

Our assessment work on reactor physics includes:

  • Fuel Management Cycles
  • Steady-state Reactor Operation
  • Plant Operation Under Non-Standard Conditions
  • Transient Analysis

Fuel management calculations have been performed to investigate a wide range of fuel cycles and to choose the optimum for economic operation within the safety constraints.

Detailed analysis of steady-state operation have been performed to provide information on, for example, reactor power distributions, can temperatures, gas outlet temperatures, PWR dryout margins, source distributions for vessel embrittlement, spent fuel inventories and criticality.

In non-standard conditions accurate predictions of reactivity coefficients have been made to study issues such as xenon power oscillations, loss of coolant accidents, reactor cooldown and subsequent recriticality. Transient calculations have been performed to assess the effects of reactivity induced power excursions. These calculations, which include rod ejection studies, were carried out as part of safety submissions.

Models of nuclear plant operation can be made for plant through start-up, during operation, at shutdown and in possible accident scenarios.

The major codes used for reactor physics Consultancy are WIMS, PANTHER, TRAIL and FISPIN.


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