GARDEL

Almost all boiling water reactors and many pressurized water reactors use a core monitoring system in the plant control room. These core monitor systems combine measured data and physics calculations monitor the compliance of fuel thermal limits according to the plant’s Technical Specification requirements. For a variety of reasons, these systems are frequently not available in the simulated control room, or are available only via a simplified emulation. This paper presents a product which allows rigorous core monitoring to be present in the control room. Further, this paper discusses the additional instructional capabilities offered by the usage of software of this nature.

Studsvik Scandpower has established its core monitoring system GARDEL as an advanced and reliable solution for PWR and BWR plants of different designs seeking high accuracy, availability, simplicity, and powerful core analysis and operational support tools.

This paper provides an overview of the most recent GARDEL implementations and of GARDEL’s functionality beyond that of traditional core monitoring systems.

The replacement of the core monitoring system for twin KWU Boiling Water Reactors (BWR) is presented. The reactors, Kernkraftwerk Gundremmingen B and C (KGG), are located in Germany. Core monitoring for KGG is more challenging than for most BWR reactors due to its core composition with about 30% MOX fuel assemblies.

The objectives of this paper are to discuss the specific MOX modelling aspects in CASMO-4/Simulate-3, the impact of the MOX fuel on several core monitoring aspects like the LPRM detector modelling and to present some core monitoring results since the beginning of GARDEL’s operation.

The available core monitoring results confirm the accuracy of the underlying physical methods.

The core monitoring system replacement att KGG was a common project of Studsvik Scandpower and NIS Ingenieurgesellschaft GmbH, where Studsvik Scandpower supplied its standard core monitoring system GARDEL and NIS was responsible for the computer hardware, system integration and plant specific add-ons.

Cooper Nuclear Station and Monticello Nuclear Generating Plant are General Electric single unit Boiling Water Reactors (BWRs) of 2381 MWt and 1775 MWt respectively. Since February of 2005, these plants have relied on Studsvik’s GARDEL system for core monitoring. Both plants have accumulated a full cycle (cycle 23 for both plants) of operating data and are in their second operating cycle using the GARDEL system.

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.

Almost all boiling water reactors (BWRs) and many pressurized water reactors (PWRs) use a core monitoring system in the plant control room. These core monitor systems combine measured data and physics calculations to provide operations assistance information. For a variety of reasons, these systems are frequently not available in the simulated control room, or are available only via a simplified emulation. This paper presents a product which allows rigorous core monitoring to be present in the control room. Further, this paper discusses the additional instructional capabilities offered by the usage of this software.

The Studsvik Scandpower in-core fuel management code system, CMS, is now extended to online core monitoring and reactivity management functions. This application, named GARDEL, is fuel vendor, reactor vendor, and in-core instrumentation independent.

GARDEL consists of the well established core design neutronics solution, SIMULATE, along with a highly automated core tracking system, database archive system, and user configurable graphical user interface which includes international language support. All plant measured signals and results from all neutronic calculations are automatically archived into the database facilitating rapid user access to important data.

GARDEL is unique in modularity and flexibility, running on a variety of hardware systems (e.g., UNIX, Windows and Linux PCs), and accessible to multiple users simultaneously. No proprietary hardware is required. Due to binary file compatibility of CMS, GARDEL can be deployed on both homogeneous and heterogeneous (mixture of UNIX and PC workstations) computing networks.

GARDEL is in use at a variety of operating reactor sites, demonstrating exceptional results at both steady-state and transient conditions. A system description, results from operating reactors and merits of the system are presented.

BWR core monitoring has traditionally been limited to systems that are only provided by fuel vendors. These systems are normally non-graphical based, use older methods, run on proprietary hardware, and are not readily extendable by the utility.

A common limitation in existing systems is that there is a separation between on- line core supervision and off-line core calculations. This separation typically requires manual data transfers between the two systems and results in a large effort to maintain the quality assurance of the two different models. Also, in current systems there are difficulties to analyze past events and to plan future operation because operational data may be scarce or not available for core analysis purposes.

Studsvik Scandpower has extended it strengths in in-core fuel management software to BWR online core monitoring in its GARDEL product, which removes all limitations listed above. GARDEL is a graphical based core monitoring system that is independent of fuel vendor, reactor type and uses non-proprietary and readily available modern computing hardware and operating systems.

This paper provides a description of the GARDEL system components and the calculational capabilities of the system.