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Godzilla is helping ITER prepare for tokamak assembly
ITER employees stand by Godzilla, the most powerful commercially available industrial robot available. (Photo: ITER)
Many people are familiar with Godzilla as a giant reptilian monster that emerged from the sea off the coast of Japan, the product of radioactive contamination. These days, there is a new Godzilla, but it has a positive—and entirely fact-based—association with nuclear energy. This one has emerged inside the Tokamak Assembly Preparation Building of ITER in southern France.
W. Breitung
Nuclear Science and Engineering | Volume 108 | Number 1 | May 1991 | Pages 1-15
Technical Paper | doi.org/10.13182/NSE91-A23804
Articles are hosted by Taylor and Francis Online.
Measurements of the total pressure from irradiated (U,Pu)-mixed oxide were analyzed with respect to the fission product release kinetics and availability for pressure generation in Bethe-Tait excursions. Two pressure sources acting on a millisecond time scale were identified: release of grain boundary fission products (gases and volatiles such as cesium) triggered by grain boundary separation and release of formerly intragranular fission products due to fuel boiling. The former process can provide pressures on a megapascal scale early, and the latter process, late in the accident progression. No fission product release was observed from nonboiling liquid fuel. Based on the experimental data, a model was formulated for the total pressure over irradiated (U,Pu)-oxide. Fuel vapor and gases interact by a suppression mechanism: pIF = max(pAG + pFP, psat). The total pressure over irradiated fuel pIF is equal to the pressure sum from ambient gas pAG and released fission products in the gaseous state pFP when this sum is greater than the saturation vapor pressure of fresh (U,Pu)-oxide psat. In this regime, fuel boiling is suppressed. At sufficiently high temperatures when psat > pAG + pFP, the oxide begins to boil and the total pressure pIF reaches the fresh fuel saturation vapor pressure psat. The switch-over in the controlling mechanism occurred at ∼5200 K.
