Post-irradiation examination of plutonium-bearing fuel elements irradiated in LWR power plants. A European Community campaign

In the framework of the E.C. programme ''Plutonium Recycling in LWR'', a series of post-irradiation examinations were carried out on mixed-oxide fuel elements irradiated in LWR's. The examinations were performed in 10 campaigns on fuel irradiated in the following power reactors: Garigliano, Dodewaard, SENA, Lingen and BR3 as well as in the HFR. The paper subdivided in three parts describes first the extent of the R and D programme for five of these campaigns; that is the main characteristics of 95 examined fuel rods, their irradiation conditions and the examinations techniques involved. Then, the essential experimental results of the programme are summarized: clad deformations, fuel microstructure, fission gas release and gamma activity distributions. The second part of the paper is devoted to the analysis of these results, leading to a comparative description of the in-reactor behaviour of the uranium-plutonium oxide and the uranium oxide fuels. The last part of the paper summarizes the confrontation between the observed in-reactor behaviour and the predictions of the thermo-mechanical fuel behaviour using the COMETHE III-L code and the isotopic compositions anticipated using the ORIGEN-2 code. The campaign is not yet entirely completed but all results so far obtained allow to conclude that: in no case plutonium fuel has perturbed the normal operation of a power reactor; no rod failure due specifically to the behaviour of the mixed-oxide fuel could be detected; the behaviour of the rods, up to a burn-up typical for power LWR, has always been found to be at least as good as that of the traditional uranium oxide rods; the fuel behaviour under irradiation and the evolution of its isotopic composition can be predicted using existing codes with a very good accuracy. The correlation of fission gas release however is not so good for all the experiments. (author)