Analysis of Environmental Conditions for NPP Krsko DC Battery and Battery Charger Rooms Following SG Blowdown Processing System Line Break

This paper describes analysis of thermal-hydraulic conditions in NEK DC Battery and Battery Charger rooms after a postulated break of the SG Blowdown Processing System (SGBD) line. The calculation was performed in frame of Equipment Qualification Parameters determination for NPP Krsko. Such break can result in release of the SG water in NEK Intermediate Building which can endanger the safety related electrical equipment. Since this break cannot happen in the mentioned rooms the presence of HVAC (heating, ventilation and air conditioning) ducts must be taken into account, i.e., the HVAC duct can potentially be damaged under the pressure conditions in the rooms where the SGBD break can occur leaving the free path to the DC Battery and Battery Charger rooms. This analysis covers mass and energy release calculation (MER) due to SG blowdown line break (A), calculation of ventilation duct structural integrity (B), and the pressure and temperature response of selected IB rooms (C). A. The SGBD break is postulated in the Intermediate Building downstream the Containment Isolation valves and upstream of the Blowdown Heat Exchanger to conservatively predict the mass and energy release. This calculation was performed with RELAP5/MOD3.2.2 computer code. B. FEM (Finite Element Method) stress calculation using NISA II and ALGOR computer programs was performed for representative section of the HVAC duct in order to estimate pressure difference which can open the duct and connect battery rooms with the rooms where SG blowdown break was simulated. C. In order to take into account influence of possible damage of HVAC duct on TH conditions in IB rooms 011, 012, 014 and 015 (DC Battery and Battery Charger rooms) the GOTHIC code was used considering SGBD break in rooms IB009 and IB010. (author)