Study of Operator Actions in the Event of Failure to Close the BRU-A in the Event of a Large Number of SG Tube Ruptures

In this paper, a large loss of coolant is discussed from primary circuit to the secondary side in the horizontal steam generator (SG) type in the Nuclear power plant (NPP). The study continues the work connected with investigation of NPP behaviour of primary to secondary (PRISE) side large leakage of coolant including the operator actions. The analysis validates the applicability of NPP strategy's "bleed and feed" using the symptom-based emergency operator procedures (EOPs). The study discusses the results of the analysis of operator actions in the event of a large number of guillotine break of SG pipes leading to the opening of the steam dump control valve to the atmosphere (BRU-A). As input data for this analysis, previously published results for such an event were used, in which the guillotine double ended rupture of the 270 steam generator tubes leads to a rapid increase in pressure on the secondary side of the steam generator to the set opening point of the steam release through BRU-A. Assuming a failure of BRU-A to close, all emergency cooling water for flooding the reactor core will be loose in a very short time. The purpose of the presented analysis is to demonstrate the possibility of significantly delaying this loss of emergency water for providing time for the implementation of actions that can ensure the restoration of the plant's operability or to ensure its long-term maintenance in a safe state. The analysis is performed with an integral computer code RELAP5 mod3.3 using the input model for NPP with a VVER 1000 reactor developed at Institute for Nuclear Research and Nuclear Energy (INRNE-BAS). The referent NPP is the Kozloduy NPP equipped with a VVER 1000/V320 reactor types.

Keywords: PRISE, Loss of Coolant, RELAP5, SB EOPs, Reactor Core Heat up.