The aim of the NOK M109 International Programme was to investigate MOX fuel performance at high burnup.
Eight fuel rods, fabricated by BELGONUCLAIRE, were irradiated during five cycles in the Swiss BEZNAU-1 Pressurized Water Reactor to reach a peak burnup of about 47 GWd/tM. Post-irradiation examinations were performed on the eight fuel rods at the Paul Scherrer Institute laboratory.
The main fuel rod fabrication parameters, the irradiation characteristics and the post-irradiation results of the MOX fuel rod, irradiated in position D3 of the full MOX assembly M-109 are summarised hereafter. This fuel rod has reached a peak pellet burnup of 46.6 GWd/Tm.
Fuel Rod Fabrication:
The fuel rod was manufactured by BELGONUCLEAIRE on the basis of the Westinghouse 14x14 fuel assembly design.
The cladding used for the rod fabrication is seamless Zircaloy 4 tube manufactured by Westinghouse Electric Corporation SMP (USA) from ingots provided by Western Zirconium Ogden, UT (USA).
The Zircaloy 4 cladding tubes were delivered to BELGONUCLEAIRE in one lot identified as BNT 104. All the tubes are annealed at 675 deg.C / 3 hours under vacuum before the final cold working and stress relieving.
The mixed oxide fuel pellets were manufactured by BELGONUCLEAIRE in its Dessel plant, using the MIMAS process (Micronized MASter blend process). Mixed oxide powder containing approximately 24 w/o plutonium was micronized and subsequently blended as master blend to free-flowing UO2 powder (AUC). The pellets were sintered at 1700 deg.C / 9 hours under argon + 5 v/o hydrogen.
The mixed oxide is composed of depleted uranium dioxide mixed with 4.24 % fissile plutonium. The O/M ratio was measured and yielded 1.995.
The M-109 assembly was irradiated for 5 consecutive cycles (cycle 18 up to cycle 22) in the BEZNAU-1 reactor.
Post-irradiation examinations performed on the D3 fuel rod at PSI include visual inspection of the rod, eddy current oxide thickness measurements, profilometry and length measurements, gamma scanning, gas puncture measurements, ceramographies and density measurements.