CSNI1025 PHEBUS/B9+.

1. NAME OF EXPERIMENT:  PHEBUS/B9+.

3. DESCRIPTION OF TEST FACILITY

PHEBUS SFD test facility operated at the CEA Research Center CADARACHE consists of a test stringer with a pressurized gas supply, a condenser and a storage tank
- 21 nuclear fuel rod bundle, coupled to a separate nuclear driver core
- active length 0.8 m, flat cosine axial power profile
- pre-pressurized fresh fuel rods
- controlled fluid-dynamic conditions at the bundle inlet (high temperature mixture of steam/hydrogen or helium)
- multi-layer insulating shroud consisting of an inner liner, a porous ZrO2 layer (24,5 mm) surrounded by a dense ZrO2 layer (1mm) and a stainless steel tube (8mm) to limit heat losses to the surrounding structures

4. DESCRIPTION OF TEST

Parameters offered for Comparison:
- fuel temperatures of several fuel rods at various elevations
- fuel cladding temperatures of several fuel rods at various elevations
- local fuel temperatures
- liner and shroud temperatures
- oxidation, UO2 and ZrO2 dissolution profiles
- hydrogen production rates
- axial distribution of relocated core materials
  
The exercise showed the existing capabilities of advanced codes for the prediction of the main degradation phenomena, although test-specific but unavoidable uncertainties existed
- predictions using specified conductivity function overestimated the rod temperatures by underestimating the heat losses through the shroud
- generally, results point on the needs for more verification and validation for severe fuel damage computer codes
- most important limitation concerned simultaneous UO2-ZrO2 dissolution by molten Zr and the relocation of molten materials
- specific features of testing degraded core conditions would require more code versatility to allow a correct analytical simulation of the experimental atypicalities (e.g., the shroud in case of the PHEBUS SFD test B9+)

6. PHENOMENA TESTED

PHEBUS Test B9+ was devoted to predict phenomena occurring during a severe fuel damage (SFD) accident in a PWR with specific emphasis on
- cladding oxidation
- dissolution of UO2 and ZrO2 by molten zircaloy
- relocation of the melt
- mechanical behaviour of the external zirconia layer of the cladding containing molten zircaloy

- B. Adroguer, A. Commande, C. Rongier, M. Mulet:
OECD/NEA/CSNI INTERNATIONAL STANDARD PROBLEM ISP 28,
PHEBUS-SFD B9+ Experiment on the Degradation of a PWR Type Core
Comparison Report Vols. I and II (NEA/CSNI/R(92)17; December 1992)
- S. Aleza et al.:
Contribution to ISP-28 by the Polytechnical Universtiy of Madrid with the
MELCOR Code (Theoretical Analysis of PHEBUS CSD B9+ Experiment
CTN-78/90 (December 1990)

11. TEST DESIGNATION:  B9+.

15. ESTABLISHMENT:  
CEA/CEN-Cadarache,
IPSN/DERS/SEAREL, France

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