Nuclear Fuel Cycle and Materials Section
Nuclear Power Reactor Fuel Engineering
Promoting good fuel performance and operating practice for current fuel types in water cooled power reactors
Objective: To understand, maintain and improve in-pile characteristics of UO2 and MOX fuels and fuel performance codes for ensuring nuclear fuel cycle; to assist countries embarking in nuclear power and countries operating Russian design reactors in validation and improvement their national fuel performance codes.
Responsible Officer: Victor INOZEMTSEV
Details Nuclear fuel performance and reliability are becoming ever more important as markets for electricity are deregulated. Fuel should be cheap, reliable, robust and operate at high burnups, longer fuel cycles and higher thermal rates. To cope with this, in-pile fuel behaviour (e.g. fuel creep, swelling, fission gas release, pellet-cladding interaction, fuel failure mechanisms, specifics of MOX fuel, etc) at normal, transient and accident conditions are to be studied and understood. Knowledge obtained has to be implemented in more adequate fuel design and performance codes and recommendations to fuel designers and technologists. IAEA is involved in both types of these activities, including analysis of information on fuel performance and validation and improvement of national fuel performance codes, especially used in countries embarking in nuclear power and countries operating Russian design reactors.
A new CRP on “Improvement of Models used for Fuel Behaviour Simulation ” (FUMEX II) was undertaken with the major objective to assist Member States in improvement of the predictive capabilities of codes used in fuel behaviour modelling for extended burnup. Organizations from 19 countries and 2 international organizations (EC and OECD/NEA) took part in this project and participated in the 1st RCM held in December 2002. Compare with the first CRP on this subject (FUMEX I, 1993 - 1996), the focus is placed on fuel thermal performance, fission gas release and pellet to clad interaction at burnup above 50 MWd/kg HM. In addition, the CRP will address the performance of codes used for transient analysis such as RIA and LOCA at extended burnup. FUMEX-II CRP takes the form of co-ordination between a Code Improvement Exercise and the NEA/IAEA International Fuel Performance Experiments (IFPE) Database. This Inter-Agency co-operation, with the link between the FUMEX-II CRP and the IFPE as a practical example, was judged to be very useful by the participants of the IAEA-NEA activities.
The state-of-the-art in water reactor fuel design, fabrication, performance and utilization was discussed at 2002 meeting of the TWGFPT. Status report and recommendations of the TWGFPT on major directions of future work in the area are given in Annex 1.
To address fuel performance at present, very demanding operation conditions, the IAEA held a Technical Committee meeting on “Causes and Mitigation of Fuel Failures in Water Reactors: Causes and Mitigation”. Meeting confirmed failure rate reduction in practically all countries operating NPPs, reaching now 10-5 (or 10 ppm) or lower values. However, every case of fuel failure worsens fuel cycle economics and requires longer outages for system cleaning. Side by side with “traditional” failure causes, like manufacturing defects, debris, improper fuel handling and pellet-cladding interaction, flow-induced vibration (FIV) has been a major cause of PWR fuel failure during last decade, see Fig. 2. FIV includes different mechanisms and conditions like: baffle jetting, enhanced cross flow at core periphery, enhanced cross flow at core bottom (vessel flow anomaly), mixing vane distribution and orientation in the grids, etc. It was strongly recommended to utilities and fuel vendors in case of every failure to carry out detailed inspection/post-irradiation examination of affected fuel, analysis of reactor specifics and circumstances, loop tests, modelling and simulation experiments and some others.
For summary report of the 2002 TWGFPT Intermediate Meeting please click.