Westinghouse adapted its fuel data management system to meet utility needs as well as changing industry and regulatory requirements. By Barry Cooney
The Westinghouse TracWorks® fuel data management system maintains fuel assembly and core component data within a single, broadly available, regularly updated resource. It is used by 17 utilities (87 reactors) in the USA and six plants in other countries. The system generates regulatory reports and it eliminates the need to maintain a separate special nuclear materials (SNM) database.
Users influence the system’s evolution through the TracWorks Advisory Council (TRAC). This user group reviews and prioritises new developments requested by utilities or needed to address regulatory reporting requirements.
The original TracWorks system had four interactive modules: reporting, inventory management, fuel properties tracking and move sequence tracking. Later, real-time movement and decay heat monitors were added.
The reporting module generates reports on fuel properties for regulators, isotopic data, non-fuel nuclear materials, operating history and discharge. From the start, reporting included the associated physical inventory documentation and move sheet creation.
Move sheets are a summary of a refuelling campaign and help to ensure that the criticality-based restrictions in the spent fuel pool are met. The SNM reporting capability requires fuel inventory information, isotopic data and movement updates, which are obtained from data in other modules.
The inventory management module tracks fuel assemblies and core components from receipt to their final disposal after depletion, whether they are in the spent fuel pool or in dry storage.
The fuel assemblies can be tracked as either a full assembly or pin.
For non-fuel components such as burnable absorbers, rod cluster control assemblies, thimble plugs, sources, fission detectors, fuel rod storage baskets, channels and load power-range monitors, TracWorks maintains a history of core locations, SFP locations and, as appropriate, host assemblies.
One of the original users of the TracWorks system requested that capability was added to provide decay heat calculations to support refuelling outage operations. As a result, the decay heat monitor was developed as an extension. This allows plant operators to calculate the decay heat in either the core or the spent fuel pool as a function of time, assuming either the current fuel configuration, a full core offload at a user-specified time, or the results of an anticipated move sequence.
In 2013, TRAC proposed extending the decay heat monitor to include a time-to-boil calculation in response to post-Fukushima monitoring requirements. To make this determination the decay heat monitor uses the decay heat load already available and information on the volumes, masses and specific heats of the spent fuel racks, fuel assemblies and core components to calculate the amount of water in the spent fuel pool, along with the heat capacity of the racks and water.
The fuel properties tracking module provides the isotopic data needed for nuclear materials reporting. It includes fresh fuel isotopic inventories and a running material balance. Utilities can evaluate fuel performance and calculate depreciation using assembly burnup and power history.
TracWorks also maintains pin data.
Personnel at one plant had to determine whether freshly discharged fuel assemblies had been placed close to the concrete wall, where
the high radiation dose causes damage to the concrete. To use the TracWorks system Inventory Management Module tracks all fuel assemblies and core components information available within the system it would have been necessary to query the database for the history of dozens of locations to determine if a fuel assembly had ever been placed adjacent to the concrete wall immediately upon removal from the core. Instead, Westinghouse was able to write a query against the underlying database.
The move sequence tracking module imports and updates location information as moves are made. It helps plan fuel moves and manage spent fuel pool criticality. Geometry limitations change depending on which assembly is placed into which location in the pool. Dynamic management avoids using empty cells as separators between different geometry configurations that are adjacent. The module accepts the geometries, burnup and enrichment limits, and, as each move in the spent fuel pool is planned, checks to confirm that criticality limits are maintained. If a movement violates the requirements, the module prohibits it.
Some utilities began using the module for real-time tracking of fuel moves during outages and made the resulting display available to
the outage control centre. The status of refuelling is instantaneously available to anyone that has access to the system and relevant reports can be generated as part of the process.
Utilities using the move sequence module also make use of the adjunct burnup credit acceptability monitor, which evaluates the current fuel arrangement in the spent fuel pool to confirm no assemblies violate burnup credit constraints. This monitor also supports re-evaluating the arrangement with selected assemblies removed helping determine the smallest number of changes needed to bring the pool into compliance with burnup credit requirements.
Utilities have been using data available within TracWorks to support the qualification effort to dispose of spent fuel and characterise fuel assemblies for dry cask storage. Assembly information is preserved in one database that has been collected during the life and use of the fuel.
About the author
Barry Cooney is a fellow engineer, Westinghouse Engineering Center of Excellence, Westinghouse Electric Company