An analysis to select a new, modern core monitoring system replacement for twin Westinghouse Pressurized Water Reactors (PWR) is presented. The reactors, Kernkraftwerk Beznau (KKB), are located in Switzerland and operated by Nordostschweizerische Krafwerke AG (NOK). KKB was one of the first PWR reactor sites in the world to use a fuel vendor on-line core monitoring system starting in the early 1990’s. Core monitoring for KKB is even more challenging than for most reactors due to over 25 years of operational experience using MOX fuel.
The objective of the investigation was to assess the merits of available core monitoring systems to determine if operational performance could be further improved. (KKB already demonstrated excellent operational performance, so this was no small task).
The investigation was motivated in part through the realization that the existing core monitoring solution used at KKB was built for an earlier era, constrained by the price/performance limitations of computational hardware of that time as well as the accuracy limitations of physics models developed for such hardware. Often, accuracy of the physics models employed was sacrificed for computational performance in the core monitoring system.
The selection of a new core monitoring system to replace the existing one was driven by the following criteria:
- Improve operational performance by reducing uncertainties of calculated parameters associated with thermal margin (e.g., radial pin power peaking factors, LHGR, etc.)
- Improve operational performance by implementing a pin-based PCI model
- Improve operational performance by implementing on-line DNBR calculations based on plant-specific DNB correlations
- Provide the reactor operators and reactor engineers a reliable, intuitive tool to assist them in evaluating unexpected operational conditions
- Eliminate tedious and expensive cycle initialization procedures
- Reduce costs for hardware and software support for the core monitoring system
- Minimize impact on plant process computer
After a one-year evaluation period, KKB chose Studsvik’s GARDEL core monitoring system. GARDEL is based on Studsvik’s well-established in-core fuel management code system, consisting primarily of the lattice code, CASMO, and the core physics model, SIMULATE. The Studsvik physics modeling software has been used in analysis of every commercially available light water reactors (PWR and BWR) fuel and core design in the world.
In addition to the Studsvik physics model, GARDEL includes a highly automated core physics model update throughout the cycle, triggered by monitoring changes of plant process computer signals. All data is archived in a flexible, highly efficient database system.
GARDEL also includes a flexible, configurable, graphical user interface as well as international language support. All data - both calculated parameters, as well as collected plants signals - are easily accessed via the user interface for analysis or via included automatic reporting functions. Multiple users can use the system simultaneously (e.g., an engineer can perform an operational maneuver forecast of control rod position vs. time to control axial flux imbalance, and an operator can access and view the projected results as the plant begins the maneuver).
GARDEL is unique in modularity and flexibility, as it runs on a variety of hardware systems (e.g., UNIX, Windows, and Linux PCs) with no proprietary hardware required. Furthermore, GARDEL’s modular design allows for plant-specific network configurations, meeting strict data security requirements. Different levels of user access can be controlled administratively.
It is important to note that GARDEL does not run on the plant computer. No modifications to the plant computer are required for GARDEL. A simple query of the plant computer data archive is periodically conducted (typically every one minute) and data is passed to the GARDEL server.
During the evaluation period at KKB, considerable improvement to the accuracy of thermal margin related quantities, both at steady state and during transient conditions, were observed. This performance led to the decision to replace the existing core monitoring system with Studsvik’s GARDEL as the official core monitoring system for KKB.