30 years on… and still providing ANSWERS

Wood’s ANSWERS Software Service has been at the forefront of radiation transport modelling for more than 30 years.

The ANSWERS codes are used to simulate nuclear processes, creating models which enable customers to solve problems in core design, fault studies, reactor shielding, dosimetry and transport flask assessments, waste management and decommissioning.

They are kept up to date with the help of techniques such as high performance computing, automated processing, advanced graphics and uncertainty quantification, thus ensuring that the software is extensively validated for current and future reactor designs.

Small Modular Reactors (SMRs)

Modelling of SMRs with ANSWERS takes advantage of experience gained from work on earlier small research and prototype reactors of varied relevant technologies. In particular this is true for modelling and operational experience. It also includes development work carried out for early UK SMR designs such as the Safe Integral Reactor. ANSWERS codes have been developed and validated against many small scale experiments and small reactors and are currently being used in the development of a latest technology UK PWR SMR core design, which is led by a consortium that includes Rolls-Royce and Wood.

Future naval propulsion plants

The development of a new ‘Whole Core 3D Reactor Physics Code’ for analysis of future naval nuclear propulsion plants is a multi-year collaboration between Rolls-Royce and Wood. The modelling development is based on the ANSWERS WIMS physics code including new 3-dimensional fine mesh whole core solution methods based on transport theory. The new code will provide improved accuracy and greater justifiable safety margins and core performance compared with current methods.

High Temperature Reactors (HTRs)

The UK has amassed a great deal of experience in gas reactor technology through experience of operating firstly the Magnox reactors and then secondly the Advanced Gas-cooled Reactor (AGR) fleets. Much of this experience is relevant to potential New Build HTR technology such as the micro-modular U-Battery reactor, which is being developed by a consortium including URENCO and Wood.

A goal for ANSWERS HTR activities has been to develop WIMS and MONK models for advanced HTR concepts. The reactor physics and fuel performance of HTRs is difficult to model and the ‘double heterogeneity’ geometry, i.e. small spherical TRISO fuel particles in a graphite matrix, within larger cylinders, presents unique modelling challenges.  Modelling ‘small reactors’ is also challenging as they are ‘leaky’, with neutron losses at the peripherals.

HTR pebbles, cylinders and plates are analysed using double-heterogeneity modelling. If necessary, a lattice calculation can then be used to model complicated assembly geometries. This allows equivalent cross sections to be generated for multigroup core diffusion theory calculations, or alternatively from a full 3D multi-group transport solution of the core.


Dr John Lillington, Wood

A longer version of this article appeared in Nuclear Engineering International www.neimagazine.com