RD&D-Programme 2004 - SKB

Recently, simplified analytical versions of the near- and far-field transport models have been
developed /14-6/. These models use the same input data as the corresponding numerical models
and doses are calculated by means of ecosystem-specific dose conversion factors. The models
can be executed probabilistically and yield results in good agreement with the deterministic
and probabilistic calculation cases in SR 97. A single realisation with the analytical models
runs in about 0.1 second on a 2 GHz personal computer, making them well suited for extensive
probabilistic calculations. The analytical models will be used as a complement to the numerical
models in coming safety assessments, in particular for early scoping calculations and for
complementary probabilistic calculations.
The following sections briefly describe the platforms for the numerical radionuclide transport
calculations and the numerical models of the near-field, the far-field and the biosphere.
Platforms for radionuclide transport calculations
Radionuclide transport calculations in SKB’s safety assessments have been performed with the
Proper package (SKB 91, SR 95 and SR 97). The Proper package, written in Fortran 77, consists
of a number of sub-modules that handle the transport calculation, see Figure 14-2. The nearfield
transport calculation is handled by the Proper sub-module Comp23 /14-7/, the far field
by Farf31 /14-8/ and the biosphere by Bio42. The Proper environment not only has centralized
communication between the different modules, but also routines for performing deterministic
simulations and libraries with tools for numerical calculations (Numlib). In addition, the environment
contains sub-modules for communication with the groundwater flow model, weighting
and summation of time series (Sum41) and communication with ASCII files outside Proper
(TS01 and Pick51).
As a complement to the Proper package, an alternative software package, Tensit, that runs on
a desktop PC is under development. Tensit can be used in parallel with the Fortran77/Unix
version of Proper in the safety assessment calculations. The PC version, which is based on
the same conceptual models as the Proper package, has been developed separately from the
Fortran77/Unix version and is written as a Matlab program. Matlab is a widely used tool in
numerical calculations and offers a wide selection of mathematical functions, a script language
and a graphical environment, Simulink, where models can easily be built and where different
sub-modules can be connected together in a simple and intuitive way. Both Matlab and
Simulink are widely used, both in the university world and in industry, which is helpful since it
means personnel with the necessary programming know-how and skills are trained and leads to
continuous maintenance of the code. A large number of users should also increase the likelihood
that any errors in the code’s computational routines will be discovered. Simulink’s graphical
interface enables the total quantity of program code to be reduced. This, in combination with
Matlab’s built-in numerical calculation routines, simplifies review and development of the
different models (especially for persons outside the development group).
At present the near-field calculation has been fully implemented in Matlab and Simulink,
which means that calculations equivalent to those handled by the Comp23 sub-module can be
run in Tensit. A ported version of the Fortran77 code that is used in Proper, with an interface
that enables the code to be used as a Matlab function, is used for migration calculations in
the far-field. The biosphere module has been developed into a considerably more versatile
tool. While the Proper module uses dose conversion factors calculated by an external code,
the Matlab version can either calculate dose conversion factors in advance or perform timedependent
biosphere calculations as part of a probabilistic computational chain.
In addition to the Matlab package, the PC version can use the commercially available risk
analysis code @Risk for probabilistic analyses. @Risk can generate a large number of probability
distributions, perform probabilistic simulations and run external programs like Matlab.
Moreover, the combination Matlab/@Risk provides a transparent environment for safety
assessment calculations.
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