Systems which need energy and/or intelligence signals to operate. which are the contrary of active systems.

Structure, set of structures or of systems which contrast the uncontrolled release of radioactive material to the outside or to the inside of a nuclear plant. For the radioactivity connected to fission products, the plant design provides the following barriers: the fuel matrix, the fuel element claddings, the primary circuit(s), the containment system.

Best estimate approach to safety evaluation or best estimate codes are those which are based on a faithful representation of the plant behaviour; they should be used in a safety analysis in combination with a reasonably conservative selection of input data and a sufficient evaluation of the uncertainties of the results; this approach is accepted by regulatory bodies; it may also be acceptable to use a combination of a best estimate code and realistic assumptions on initial and boundary conditions. The best estimate approach is the opposite of a conservative approach.

Nuclear reactor where the steam is directly generated in the core (BWR = Boiling Water Reactor).

Conservative approach to safety evaluation or conservative code analyses are those where every assumption is chosen in a conservative way, in the light of the phenomenon to be evaluated. This approach is the opposite of the best estimate approach.

Set of systems forming the most external barrier(s) against the uncontrolled release(s) in the...