[en] As an introduction to the subject I propose not to offer one or other specific method, but rather to discuss general questions such as the need for method, its objective and the relationship between the model, the methodology and the objective. Method is defined as a special form of procedure especially in any branch of mental activity, and methodology as an orderly arrangement of ideas. This is an English definition. I like it, as it is important to get the ideas right before embarking on a lengthy exercise on paper. It is possible to embark on an exercise of risk comparisons over selected ranges of energy and risk, and to a varying degree of precision or depth, i.e. first, second or third order of ranking. The study might start by listing the energy systems; the system phases; the estimation sequence; parties at risk; types of consequences; methods of estimating probability and consequences - the selected criteria and types of risk evaluation and produce a chart. Some exercises have taken a sample selection under the various headings