SCORPIO-VVER Core Monitoring and Surveillance System for VVER-440 Reactors

J. Molnar, R. Vocka, Nuclear Research Institute Rez plc, Czech Republic

20th Symposium of AER on VVER Reactor Physics and Reactor Safety (2010, Hanasaari, Espoo, Finland)
Core Monitoring


The SCORPIO-VVER core monitoring system has proved since the first installation at
Dukovany NPP in 1999 to be a valuable tool for the reactor operators and reactor physicists.
It is now installed on four units of Dukovany NPP (EDU, Czech Republic) and two units of
Bohunice NPP (EBO, Slovak Republic) replacing the original Russian VK3 system. By both
Czech and Slovak nuclear regulatory bodies it was licensed as a Technical Specification
Surveillance tool.
The monitoring system operates in two modes: in core follow mode and in predictive mode.
In the core follow mode, the present core state is evaluated by a method combining the
instrumentation signals and the theoretical calculation of the power distribution done by the
core simulator. This procedure is followed by an automatic limit checking, where
characteristics of the current state are compared to the Technical Specifications. The operator
obtains relevant information on core status through the dedicated Man-Machine Interfaces.
In the predictive mode, the operator can visualize the core characteristics during the transients
forecasted for coming hours or days. Quick forecasts realized by the strategy generator are
deeply analyzed by the predictive simulator. Similarly as in the core follow mode,
characteristics of the evaluated states can be compared against Technical Specifications.
Since it?s first installation, the development of SCORPIO-VVER system continues along with
the changes in VVER reactors operation. The system is being adapted according the utility
needs and several notable improvements in physical modules of the system were introduced.
The latest most significant changes were done in connection with implementation of a new
digital I&C system, loading of the optimized Gd2 fuel assemblies, improvements in the area
of core design (neutron physics, core thermal hydraulics and fuel thermal mechanics) and
improvements in the predictive part of the system (Strategy Generator).
The currently finished upgrades (Upgrade 2 at EBO 06/2009, Upgrade 5 at EDU 12/2009)
includes the adaptation of the system to up-rated unit conditions as well as further
improvements of methods applied in physical modules, especially as are the improvements of
3D power reconstruction methods by using the SPND detectors in fuel assemblies, as are the
changes in design and methodology of the limit checking and as is the implementation of the
on-line shutdown margin calculation to the system.

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