Nuclear Power Technology Development

IAEA Coordinated Research Projects (CRP)

Prediction of Axial and Radial Creep in Pressure Tubes


Pressure tube deformation is a critical aging issue in operating Heavy Water Reactors (HWRs). According to the service year, horizontal pressure tubes have three kinds of deformation: diametral creep leading to the flow bypass and the penalty to critical heat flux for fuel rods, longitudinal creep leading to the interference of feeder pipes and/or with fuelling machine, and sagging leading to the interference with in-core components and potential contact between the pressure tube and calandria tube.

Since the first pressure tube was produced in the 1960’s, manufacturing processes have been evolving. Many of the manufacturing changes were adopted to reduce the risk of pressure tube failures resulting in loss of coolant accidents. The effects of the these changes on the longer term dimensional changes due to irradiation creep have only been realised after many years of reactor operation through various monitoring programs. In fact each pressure tube has unique behaviour even within a specified manufacturing envelope. The deformation behaviour of an individual pressure tube is therefore subject to so-called extrinsic effects (the operating conditions) and intrinsic effects (the material characteristics dictated by the manufacturing process).

Predictive models have been developed to determine the diametral creep, elongation and sag rates of pressure tubes based on the extrinsic conditions and these are used to provide assurance that adverse conditions will not develop in the projected operating period for the fuel channel. Predictive models that capture the effect of the extrinsic operating conditions (fast neutron flux, temperature and pressure) are directed at an average tube. The intrinsic material effects leading to large variations in the pressure tube behaviour for a given set of operating conditions have not been targeted to the same degree as models that capture the effect of the operating conditions.

The R&D community is still not at the point where the deformation behaviour of Zr-2.5Nb pressure tubes used in HWR reactors is fully understood. Further information is required to develop improved predictive models for in-reactor deformation. The gaps in our knowledge could be addressed through collaborative R&D programs with various international organisations.

Overview of the CRP

The CRP scope includes the establishment of a database for pressure tube deformation, microstructure characterization of pressure tube materials collected from HWRs currently operating in Member States and development of a prediction model for pressure tube deformation.

Planned activities within the CRP include:

  • Assess the existing databases and make agreement on the ownership, scope of data to be included, database holder, and maintenance scheme for new database. Determine the structure of database and template for data collection.
  • Establish and test the database. Collect measured data from all participants and complete the database. Identify the best PT performance based on the database.
  • Prepare guidelines for channel selection, standard examination methods, and qualification procedure for microstructure characterization.
  • Prepare samples and specimens for microstructure characterization. The first examination by a designated laboratory and then the second examination of specimens by the home institutes.
  • Assess and improve the prediction model using the database and the microstructure characterization for pressure tube materials.
Flowchart for major CRP tasks and relationship

Flowchart for major CRP tasks and relationship

The expected outcomes from this CRP are:

  • Improved understanding of pressure tube creep mechanism by studying the effect of intrinsic (material response) as well as extrinsic parameters (operating conditions)
  • Improvement of material characterization technology
  • Recommendation for manufacturing to achieve optimal PT performance
  • Improvement in the prediction of pressure tube creep
  • Improvement in aging management procedure


The following institutions are participating in this CRP:

Atomic Energy National Commission (Argentina), Atomic Energy of Canada, Ltd. (Canada), China Institute of Atomic Energy (China), Third Qinshan Nuclear Power Co., LTD (China), Bhabha Atomic Research Centre (India), Nuclear Power Corp. of India Ltd. (India), Korea Atomic Energy Research Institute (Rep. of Korea), Institute for Nuclear Research (Romania)

Research Coordination Meetings

The first Research Coordination Meeting (RCM)
Scheduled on 2-4 July 2013 at IAEA Headquarters, Vienna, Austria

Please contact NENP Technology Development Section - Contact Point if you have any questions.