Limits and conditions' as a guiding document for ensuring nuclear safety of nuclear power plants. Experience of employment in case of V-1 'Bohunice'' NPP operation

'Limits and conditions of V-1 nuclear power plant (V-1 NPP) safe operation' is a component of instruction manuals needed for the start and routine operation of V-1 NPP units. It consists of a set of principle administrative, engineering and technological conditions that ought to be followed during operation of each separate WWER-440 unit and V-1 NPP as a whole. The document contains the following categories of data: a) safety limits; b) reference values for protective systems; c)limits and conditions for normal operation regimes; d) check-out requirements. The experience of this document employment acquired during operation of V-1 NPP 'Bohunice' allows to consider it as satisfactory from the viewpoint of operating instruction structure. At the same time a number of unresolved problems owing to the natural development process is emphasized. So the application of the 'Limits and conditions...' is not quite clear in case of a loss-of-coolant accident (maximum design accident), when, with emergency pumps put into operation and the primary loop cooled down, the temperature of the reactor vessel can become lower than the embrittlement temperature (100-150 grad.C) atthe reactor pressure higher than 3.5 MPa, what is inadmissible. Besides this a basing is needed forthe table of marginal operation regimes with recommendations on the stationary operation regime corrections and suggestions on the ways of emergency conditions elimination. It seems to be necessary to develop a reference 'Limits and conditions...' in order to formulate invariably the volume, the profundity and the form of this document with the further concrete supplements and specifications for a given NPP. Czechoslovakian party is ready to prepare a draft of the reference 'Limits and conditions...' for NPPs with WWER-440 reactors