Assembly thermo hydraulic model ASHYMO improvement for VERONA in-core monitoring system
19th Symposium of AER on VVER Reactor Physics and Reactor Safety (2009, Varna, Bulgaria)
Core Surveillance and Monitoring
Developments performed lately at Paks NPP – such as power up rate, application of fuel assemblies with increased pin pitch or containing burnable poison ? caused power distributions within the assemblies differing significantly from the present ones. In-core measurements and preliminary calculations pointed that our codes modelling the coolant flow in the assemblies are not sufficient accurate and can not describe the processes detailed enough. This paper describes the caused problems and their nature and after that their solution by applying a new appropriate sub channel and thermocouple model. Both of them are simple and fast enough to be built in the online core monitoring system but yet they serve sufficient accurate results.