Woodruff School of Mechanical Engineering

NRE 8011/8012 and MP 6011/6012 Seminar

Nuclear & Radiological Engineering and Medical Physics Programs


Axial Offset Anomaly in Pressurized Water Reactors






Thursday, April 7, 2016 at 11:00:00 AM


Boggs Building, Room 3-47




High power density Pressurized Water Reactors, such as Southern Nuclear’s Plant Vogtle, are susceptible to a phenomenon known as Axial Offset Anomaly (AOA) or Crud-Induced Power Shift (CIPS). Various metals in solution in the primary coolant deposit on fuel rod surfaces undergoing subcooled nucleate boiling, forming a porous layer known as “crud.” As the crud thickens, a boron-lithium compound may form within the crud layer. The boron-lithium compound acts like a neutron poison coating, affecting the axial flux distribution. The ability of the control rods to shut down the reactor with the excess reactivity margin required by Technical Specifications, known as shutdown margin, may be affected negatively. Operational transients may cause the boron-lithium compound to come out of the crud or even cause the crud itself to come off the fuel rods, resulting in changes in the axial flux distribution which would not be expected in the absence of CIPS. The crud layer can have a thermal blanketing effect which can cause cladding damage in extreme cases. Extensive research has significantly improved the understanding of CIPS since the phenomenon was first identified in the early 1990’s. A coordinated multi-disciplinary approach involving core designers, reactor engineers, plant chemists, and operations is required to minimize and mitigate the impact of CIPS on reactor operation. This presentation will give an overview of the CIPS phenomenon and actions to mitigate it.


Susan Hoxie-Key is a Consulting Engineer in the Nuclear Fuel Department at Southern Nuclear. In this role she works on multi-disciplinary technical projects relating to nuclear fuel. She has extensive experience in PWR core design and fuel-related licensing. Immediately before moving into her current role, Susan was Nuclear Fuel Services Manager where she was responsible for nuclear fuel procurement, nuclear fuel fabrication oversight, in-reactor fuel performance, and spent fuel support activities for the Southern Nuclear fleet. Susan joined Southern Nuclear as a senior engineer in 1990. Prior to joining Southern Nuclear, she spent eleven years in various technical roles supporting reactor operations at the Department of Energy’s Savannah River Site. Susan is one of six elected members of the World Nuclear Fuel Market Board of Governors. She is chair of the Nuclear Energy Institute’s Utility Fuel Committee and a member of the North Carolina State University Nuclear Engineering Department Undergraduate Curriculum Subcommittee. In 2008, Susan was awarded the American Nuclear Society’s Mary Jane Oestmann Professional Women’s Achievement Award for her technical accomplishments. Susan holds a BS in Nuclear Engineering from Mississippi State University and an MS in Nuclear Engineering from Georgia Tech. She is a Registered Professional Engineer in Alabama and Georgia. Susan and her husband, John, reside in Birmingham, AL, and are the proud parents of two grown children, including a 2011 GT grad.