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https://doi.org/10.1016/b978-0-12-822054-2.00002-7
Copy DOIJournal: Pressurized Heavy Water Reactors | Publication Date: Oct 11, 2021 |
Citations: 2 |
CANDU nuclear reactors have been operating reliably for over 40 years providing an invaluable understanding of the factors responsible for the observed shape changes occurring in the fuel channels during service. Pressure tubes (PTs) are the pressure vessel in the CANDU reactors. These tubes are subjected to fast neutron irradiation, to high temperatures and internal pressures, as well as corrosion from the heat transport fluid. As a result of these operating conditions PTs experience substantial shape changes. The in-reactor deformation of cold-worked Zr-2.5Nb PTs during operation has been comprehensively studied by means of in-reactor testing and the gauging of the tubes. The acquired operating experience has resulted in an extensive database, which was used to develop models that allowed for the safe operation of existing units and the design of new reactors. The observed in-reactor deformation is considered to be due to three main components: thermal creep of irradiated material, irradiation growth due to the fast neutron flux but in the absence of external loading and irradiation creep as a result of the fast neutron flux and external loading. Irradiation growth is considered the best understood component of the observed shape change, whereas in-reactor creep is not yet well understood. The least understood component is the transition between thermal creep and irradiation where the fast neutron flux appears to either suppress or enhance the creep rate. This work reviews the metallurgical factors that affect the in-reactor deformation of PTs, the basic mechanisms that are consistent with the measured shape changes and the models that have been used to ensure their fitness during operation. It should be noted that this work has been based on many previous publications by a number of authors who studied this topic extensively.
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