The FSA food chain models were initially developed in the early 1980s.  In 2001, Quintessa was contracted to update the conceptual models and their software implementation in order to:

• Take account of developments in radioecological understanding;
• Provide a probabilistic modelling capability; and
• Make use of advances in software-user interactions and computing power.

Probabilistic versions of the pre-existing FSA food chain models were developed and implemented in a software tool, PRISM, which provides a custom built graphical interface to the underlying soil, plant and animal models, enabling users to define simple or complex atmospheric source terms with a broad range associated agricultural scenarios.

The PRISM interface draws information from an underlying Microsoft Access database, whilst providing users with the ability to modify the default assumptions to reflect specific cases. Calculations are then undertaken via the interface, populating and driving template models by running AMBER in the background. Results are presented via the PRISM interface, whilst users have the capability to fully explore the supporting calculations in AMBER.

PRISM has the capability to represent short-term (down to seconds) exposure situations, as well as longer-term (multi-year) scenarios. It uses kinetic soil, plant and animal models rather than equilibrium models, the latter being more appropriate to long-term assessments.

The initial phase of work was followed by a significant review and update to the underlying soil, plant and animal models and data, which were implemented in Version 2 of PRISM in 2005. In collaboration with the Centre for Ecology and Hydrology, use was made of a substantial body of research data on the biokinetic behaviour of radionuclides in animals to validate the animal models.

Further development work has continued, notably to incorporate updated models for H-3 and C-14, resulting in Version 3 of PRISM in 2006. Subsequently, PRISM has been continuously maintained including an update to the database to take account of the output from the EMRAS programme documented in IAEA Technical Report Series 472. Work has also been undertaken, in collaboration with Imperial College to make use of 17 years of soil column and lysimeter study data to evaluate the performance of the soil-plant uptake model within PRISM.

PRISM now represents the FSA’s primary tool for assessing radionuclide behaviour in agricultural systems following atmospheric release and dispersion. The models and supporting data are fully documented in a Technical Report and a Data Report, which are available from the Food Standards Agency. Quintessa continues to maintain PRISM and to support FSA's use of PRISM.