Accounting for the Inertia of the Thermocouples' measurements by Modelling of a NPP Kalinin-3 Transient with the Coupled System Code ATHLET-BIPR-VVER
18th Symposium of AER on VVER Reactor Physics and Reactor Safety (2008, Eger, Hungary)
Reactor Dynamics, Safety Analysis
Abstract
The ATHLET-BIPR-VVER coupled system code is applied for performing of safety analysis for different VVER reactors. During the last years its validation matrix is continuously being enlarged. The measurements performed during the commissioning phase of NPP Kalinin Unit #3 for the transient ?Switching-off of one Main Circulation Pump (MCP) at nominal power? are very well documented and have a variety of recorded integral and local thermo-hydraulic and neutron-physic parameters including the measurements? errors. This data is being used for further validation of the coupled code system ATHLET-BIPR-VVER.
In the paper are discussed the problems and our solutions by the correct interpretation of the measured thermocouples? records at NPP Kalinin-3 and the comparison with the predicted results by the coupled thermal-hydraulic/neutron-kinetic code ATHLET-BIPR-VVER. Of primary importance by such comparisons is the correct accounting of the fluid mixing process that take place in the surrounding of the measuring sensors and also the consideration of the time delay (inertia term) of the measuring devices. On the bases of previous experience and many simulations of the defined transient a method is discussed and proposed to consider correctly the inertia term of the thermocouples? measurements. The new modelling is implemented in the coupled system code ATHLET-BIPR-VVER for further validation.