SimER: An Advanced Computer Code for the Simulation of Environmental Risks Associated with Site End Points

The SimER (Simulation of Environmental Risks) code was developed over a four-year period, and the first version was released in June 2004. It has been designed for application in assessments of environmental remediation and other end points associated with contaminated land, and performance assessments for radioactive waste disposal. SimER represents a major advance in safety assessment modelling. It offers a unique range of functionality that, until now, has not been available in any single safety assessment tool. For the first time in a single application, it is possible to define a fully probabilistic three dimensional physical representation of an evolving landscape and engineered features, compute water and gas flows, model chemical reactions, calculate contaminant transport and evaluate a wide range of impacts. The capability to represent environmental change explicitly is particularly important for problems where impacts to humans and the environment may not occur for extended periods. Modern computing power, coupled with efficient model algorithms, means that complex environmental systems can now be assessed for periods of thousands of years in a few tens of minutes.

SimER is a powerful Performance Assessment (PA) code developed for BNFL/Nexia Solutions Ltd. The SimER code was developed in line with the development of an integrated framework for site end point management.

The code has been developed to undertake assessments of both contaminated land and near-surface repositories. It therefore represents a major new tool to help address and assess issues on UK and other nuclear sites. Its main capabilities can be summarised as follows:

• The whole system can be modelled in a single code. This avoids the need for the output from one code to be used as the input to another. This greatly speeds up the assessment process and has major Quality Assurance advantages.
• Topographical details and geological structures can be represented.
• The evolution of the system with time is modelled explicitly.
• Groundwater flow and contaminant transport are represented using a 3D 'coarse' continuum approach.
• SimER has a multiple run capability. This enables both sensitivity studies and probabilistic assessments to be undertaken.
• Both radioactive and non-radioactive contaminants can be modelled.
• The code includes a groundwater flow component, enabling groundwater flows to be calculated within the code rather than having to be imposed.
• The inclusion of a groundwater flow component, enables groundwater flows to be calculated within the code rather than having to be imposed.
• All model parameters have associated units, and SimER checks that all expressions and algorithms that are used have consistent units. This checking provides a major contribution to the Quality Assurance of SimER calculations.
• The code uses file-based input and output and enables data libraries to be included in code input.
• Graphical spatial viewers and parameter charter visualisation tools allow inputs and outputs to be checked visually.

SimER uses an Executive to provide all of the capabilities that are needed to use the other components of the code. In particular, the Executive controls the solvers that are used by the other components to step the solution through time.

There are System Evolution components for representing the way the system changes with time, and Process components to represent the various processes that affect the behaviour of contaminants in the environment and potential impacts. It is possible to consider different conceptual models by using alternative components. In the first version of the code only a single option is available for each type of component, and these will be described in this paper.

SimER represents the System Domain, consisting of the engineered part of the system together with the features of the surrounding surface and sub-surface environment. As the system evolves so will the characteristics of the surface features. The code has Viewers to assist the user in developing a model, in particular to envisage the evolution of the system domain; information from the relevant Viewer can be used to check the input to a given component.

For further information about SimER, please see the following paper, or contact Philip Maul.

Maul P R, Benbow S J, Bond, A., Kwong, S., Paulley, A., Penfold J S S, Robinson P C, Walke R C, Watson C E and Watson S P, “SimER: An Advanced Computer Code For The Simulation Of Environmental Risks Associated With Site End Points” in Proceedings of the 9th International Conference on Environmental Remediation and Radioactive Waste Management ICEM05-1097 (2005).