IRSN, Institut de radioprotection et de sûreté nucléaire

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Enhancing Nuclear Safety


Research programmes

Third PHEBUS FP test: FPT-2

The PHEBUS FP (Fission Products) had to purpose to improve the understanding of the phenomena occurring during a core meltdown accident in a light water reactor and to validate the computational software used to represent these phenomena in reactor safety evaluations. Five test have been realised. The FPT-2 test was realised in 2000 and had to main objective to watch degradation of non-irradiated fuel and the behaviour of the fission products with fission products release under a hydrogen melt.



Test conditions

This test supplemented the first two PHEBUS FP tests (FPT-0 and FPT-1) in 2000 by studying somewhat reducing (hydrogen-rich) conditions. The flow rate of steam injected at the test system inlet was much lower. The aqueous solution in the containment vessel was kept alkaline at a temperature greater than that of the gaseous phase so as to simulate an evaporative sump. Addition of boric acid to the coolant was also studied in this test.


Observations and results

When the flow rate of injected steam is lower, the steam is almost entirely consumed by oxidation of the cladding on the lower part of the fuel rods and depletion of steam is observed on the upper part, leading notably to a period of near-complete consumption of the steam by oxidation of the cladding. A slight overestimate of hydrogen production is noted in this case.

The fission products transported in the form of aerosols are the same as those in the first two PHEBUS FP tests (iodine, caesium and cadmium), but two elements, indium and tellurium, which represent more than half the total mass, are added to the list.


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Dates: 2000

Involved IRSN services: Severe Accidents Service (SAG), PWR Safety Service (SSREP)

PHEBUS FP programme

Test results

Further informations



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