FracAffinity has been developed by Quintessa for the Japan Atomic Energy Agency (JAEA, formerly JNC) to model saturated and unsaturated flow in fractured (stochastic and/or deterministic discrete features) and/or permeable geological media. It is being applied within the Japanese high-level waste disposal programme.

The FracAffinity code is being used by JAEA in their on-going work for the Mizunami Underground Research Laboratory. FracAffinity is part of the GEOMASS system which utilises EarthVision for geological modelling and couples this to FracAffinity for flow modelling.

FracAffinity was originally developed to model saturated flow in complex geological settings, where flow occurs through the rock itself and through fractures. It uses a hybrid medium approach to handle the porous and fractured systems together, allowing for both deterministic and stochastic fracture features.

FracAffinity has been enhanced so that it can deal with unsaturated conditions near to the surface and near to excavations (such as shafts). It can handle steady-state conditions and model the transient evolution of the flow system, for example during shaft excavation.

FracAffinity has been used to understand the head distributions measured in exploratory boreholes around the Mizunami Underground Research Laboratory site, enabling the key role played by large-scale sealing faults to be explored. It is being used to predict the draw down of the water table in the vicinity of a large shaft excavation.