Crud Risk Assessment
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Crud Risk Assessment

Analysis Division Experience

Zachry’s Analysis Division personnel supported the development and analyses of the EPRI BWR crud deposition models and a risk assessment tool, CORAL, to predict tenacious crud deposition and assess the risk for crud-induced fuel cladding corrosion issues. Zachry’s Analysis Division personnel also supported the development and application of the EPRI Boron-induced Offset Anomaly (BOA) risk assessment tool to evaluate corrosion, physical chemistry, and thermal-hydraulic effects for the prediction of corrosion product release. Zachry currently maintains CORAL and BOA for EPRI.

Boron-Induced Offset Anomaly (BOA™)

A Crud and Boron Deposition Prediction Tool for Pressurized Water Reactors (PWR)

In some PWR’s, crud deposits have led to anomalous power distribution and core reactivity behavior (Axial Offset Anomaly or AOA, sometimes also referred to as Crud Induced Power Shift or CIPS). In a more limited number of PWR’s, crud deposits have also led to accelerated clad corrosion which resulted in fuel cladding failure (Crud Induced Localized Corrosion or CILC). Zachry participated in EPRI sponsored development of Boron-Induced Offset Anomaly (BOA), a computer code that is used to predict “crud” and boron depositions on fuel pins and development of an unanticipated neutron flux shift (AOA).


A Fuel Crud Deposition Assessment tool for Boiling Water Reactors (BWR)

Zachry participated in the EPRI-sponsored development of CORAL, a tool for assessing the effects of fuel duty and water chemistry variables on fuel crud deposition and fuel integrity risk in BWRs.

The CORAL code has been developed, and extensively qualified, for the prediction of crud deposition on individual fuel assemblies. CORAL will predict crud deposition at four circumferential positions at each of up to 80 axial nodes of every fuel rod within the evaluated fuel assembly. The crud deposition prediction includes:

  1. the total deposited mass
  2. separate quantification of the non-tenacious and tenacious deposited mass
  3. the tenacious crud layer thickness
CORAL will also estimate the potential for crud layer spallation, as well as the potential for autocatalytic corrosion failure risk of the fuel rod cladding due to the crud layer thermal resistance. With these capabilities, the CORAL model possesses the ability to evaluate fuel performance effects for several potential applications. Possible CORAL applications include:

  1. Water Chemistry assessment, such determining the FW zinc strategy
  2. Fuel Design assessment
  3. Core Design assessment
  4. Operating Strategy assessment
  5. System Design assessment, such as RWCU changes or power up-rates

Analysis Support

For more information on our Crud Risk Assessment analysis experience and how our experience can be applied at your plant, please contact Mike Howard. The Analysis Division contact list is here, including phone numbers.