RD&D-Programme 2004 - SKB

13 Overview – safety assessment and research
The long-term safety of a deep repository for spent nuclear fuel is evaluated by means of safety
assessments. These assessments essentially consist of first carefully describing the repository’s
initial state, for example at closure, then analyzing possible long-term changes, and finally
describing the consequences for man and the environment. The safety assessment uses scientific
methodology and obtains knowledge concerning long-term changes from research.
SKB’s research on final disposal of spent nuclear fuel can be divided into three fields:
• Long-term safety
• Social science
• Alternative methods
These fields are described in general terms in this chapter and in greater detail in subsequent
chapters. The greatest attention is given to research on long-term safety. The purpose of this
research is to underpin SKB’s safety assessments of the deep repository for spent fuel, and one
purpose of the safety assessment is to establish priorities for the research. Processes of importance
for long-term safety are discussed below and a rough estimate is made of the research
need during the coming three-year period.
Social science research is a relatively new field for SKB, at least on the scale that is now
planned. The focus is on questions that need to be addressed in conjunction with the environmental
impact assessment, EIA.
When it comes to alternative methods for disposing of spent fuel, SKB keeps track of the results
of research on two selected methods: Partitioning and Transmutation (P&T) and Very Deep
Holes (VDH).
The research on low- and intermediate-level waste (LILW) is presented in Chapter 25.
13.1 Safety assessment
The most important safety assessment projects during the period are SR-Can and SR-Site. The
purpose of these projects is to produce safety assessments for applications for permits to erect
an encapsulation plant and a deep repository. SR-Can is currently under way. An important
milestone is the interim report, which presents the methodology that will be used /13-1/.
Many of the models which the safety assessment needs to calculate e.g. groundwater flow, the
chemical evolution of the buffer and the evolution of ice sheets etc. are arrived at by research
on geosphere, buffer, climate and so on. A vital task of the safety assessment is to utilize these
models, but also to develop modelling tools for integrated modelling. A system model has been
developed consisting of submodels, each of which describes a process in the repository. In
this way, different sets of input data can be quickly tested and probabilistic calculations can be
performed if necessary, see section 14.2.1.
Numerical calculations of radionuclide transport are made with the aid of the software package
Proper. In addition, development is under way of an alternative software package, Tensit, which
can be run on a personal computer. The commercial codes Matlab and Simulink are used to a
great extent within Tensit, which will greatly facilitate the future work of maintaining the codes
and preserving knowledge about them. The near-field calculations and biosphere calculations
are already fully implemented in Matlab and Simulink. The biosphere model included in Tensit
has, incidentally, undergone considerable development, see section 14.2.2. Proper and Tensit
will both be used for SR-Can.
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