Abstract
The gap between fuel and cladding is initially pressurized to prevent unstable thermal behavior and to maintain cladding integrity. Helium is often chosen as the initial fill gas in nuclear fuel rods to improve the heat transfer through the gap between the fuel and the cladding. In light water reactors, this initial pressure ranges from 0.3 to 3.45 MPa and tends to increase throughout the life of the reactor as a result of expansion/contraction of the fuel and cladding, fission gas release, and so on. In some cases, the rod internal pressure approaches the external pressure or exceeds it. However, the pressure dependence of the thermal conductivity is neglected in nuclear fuel performance codes at present. Current codes use correlations that use only temperature and are calibrated to data at pressures below 0.1 MPa, but the pressure effect is significant on the thermal conductivity for the pressures above 1.0 MPa. Therefore, the use of the current models in nuclear applications, particularly in gap conductance calculations, is questionable. This is examined herein. Theories related to gas properties are presented, along with their validation against literature data for selected inert gases. Underlying assumptions are clearly described for each model, and their possible impacts on gap conductance calculations are discussed. It is concluded that the current approach in nuclear applications is only valid for helium; however, it is not valid in most gap conductance calculations once the gap is occupied mostly with either lower conductivity gaseous fission products or an initial fill gas other than helium.
Original language | English |
---|---|
Pages | 227-232 |
Number of pages | 6 |
State | Published - 2020 |
Event | 14th International Nuclear Fuel Cycle Conference, GLOBAL 2019 and Light Water Reactor Fuel Performance Conference, TOP FUEL 2019 - Seattle, United States Duration: Sep 22 2019 → Sep 27 2019 |
Conference
Conference | 14th International Nuclear Fuel Cycle Conference, GLOBAL 2019 and Light Water Reactor Fuel Performance Conference, TOP FUEL 2019 |
---|---|
Country/Territory | United States |
City | Seattle |
Period | 09/22/19 → 09/27/19 |
Funding
This research is supported by and performed in conjunction with the Consortium for Advanced Simulation of Light Water Reactors (http://www.casl.gov), an Energy Innovation Hub (http://www.energy.gov/hubs) for Modeling and Simulation of Nuclear Reactors under US Department of Energy Contract No. DE-AC05-00OR22725. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the US Department of Energy.