Unit 5 of the Zaporozh’ye Nuclear Power Plant (ZNPP5), equipped with a VVER-1000/320 4-loop reactor, has been modelled in detail using the RELAP5/MOD3.2 thermal-hydraulic system code (Ref. 1). The 4-loop model affords a fidelity with ZNPP5 in terms of the system geometry such as the point of emergency core cooling (ECC) injection, for example. Both the reactor vessel and steam generators were nodalized in a quasi 3-dimensional (3-D) fashion thus allowing to capture asymmetric effects in the main reactor system components and realistic heat transfer distribution in the steam generators. Besides its use for accident analysis, the present model is intended to closely simulate operational events such as pre- and post calculations of anticipated transients and tests. At present, the model is used to support justification of the new — symptom-oriented — set of emergency operating instructions. ZNPP5 makes use of both digital and analog controls. They have been modelled in the RELAP5 model allowing to analyse in detail workings of various plant equipment. The present model was validated using three ZNPP5 transient events.

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