Late phase fuel degradation in the Phébus FP tests

Abstract The aim of the experimental Phebus FP program was to study the degradation phenomena and the behaviour of the fission products during the progression of a severe accident. The present paper focuses on the late phase fuel degradation in these tests and more particularly on some phenomena that happened during this phase, which could explain the transition processes from the fuel bundle geometry to a debris bed or molten pool. One of the main results produced by the program is the evidence of the loss of the fuel rod geometry systematically in the same range of temperature, (2200 ± 200 °C), in spite of the different test conditions. The severe degradations at these temperatures appear linked to important chemical interactions between the fuel and structural materials, principally the Zircaloy cladding of the fuel rods and possibly with stainless steel oxides from the control rod guide tube (and with boron oxide in FPT3). The oxidation of fuel itself could lead to a lowering of the fuel rod relocation temperature. The irradiation effect was not clearly identified as important in these degradations.

[1]  C. Ronchi,et al.  Laser-Pulse Melting of Nuclear Refractory Ceramics , 2002 .

[2]  David A. Petti,et al.  Review of Experimental Results on Light Water Reactor Core Melt Progression , 1991 .

[3]  Marc Barrachin,et al.  Fission product release in the first two PHEBUS tests FPT0 and FPT1 , 2005 .

[4]  J. E. Sanecki,et al.  Fuel Relocation Mechanisms Based on Microstructures of Debris , 1989 .

[5]  Brent J. Lewis,et al.  Fission product release mechanisms during reactor accident conditions , 1999 .

[6]  C. Walker,et al.  Examination of melted fuel rods and released core material from the first Phebus-FP reactor accident experiment , 2000 .

[7]  L. Sepold,et al.  Behavior of a VVER-1000 fuel element with boron carbide/steel absorber tested under severe fuel damage conditions in the CORA facility. (Results of experiment CORA-W2) , 1994 .

[8]  M. Barrachin,et al.  Improvement of the European thermodynamic database NUCLEA , 2010 .

[9]  Dario Manara,et al.  Melting of Stoichiometric and Hyperstoichiometric Uranium Dioxide , 2005 .

[10]  Marc Barrachin,et al.  Phase diagram of the UO2-FeO1+x system , 2007 .

[11]  L. Sepold,et al.  Impact of absorber rod material on bundle degradation seen in CORA experiments , 1996 .

[12]  Sandro Paci,et al.  Thematic network for a Phebus FPT1 international standard problem (THENPHEBISP) , 2005 .

[13]  T. Haste,et al.  In-Vessel Core Degradation in LWR Severe Accidents: A State of the Art Report - Update January 1991 - June 1993 , 1993 .

[14]  R. Dubourg,et al.  Development of the mechanistic code MFPR for modelling fission-product release from irradiated UO2 fuel , 2006 .

[15]  Marc Barrachin,et al.  Early phase fuel degradation in Phébus FP: Initiating phenomena of degradation in fuel bundle tests , 2013 .

[16]  B. Cheynet,et al.  Progress in the thermodynamic modelling of the O–U binary system , 2002 .

[17]  David A. Petti,et al.  Results from the Power Burst Facility Severe Fuel Damage Test 1-4: A Simulated Severe Fuel Damage Accident with Irradiated Fuel Rods and Control Rods , 1991 .

[18]  G. Ducros,et al.  Lessons learnt from VERCORS tests.: Study of the active role played by UO2–ZrO2–FP interactions on irradiated fuel collapse temperature , 2005 .

[19]  R. E. Latta,et al.  Determination of solidus-liquidus temperatures in the uo2 + x system (−0.50 , 1970 .

[20]  Beverly A. Cook,et al.  Materials Interactions and Temperatures in the Three Mile Island Unit 2 Core , 1989 .

[21]  P Hofmann,et al.  Current knowledge on core degradation phenomena, a review , 1999 .

[22]  P. Hofmann,et al.  Liquefaction of Zircaloy-4 by molten (Ag, In, Cd) absorber alloy , 1994 .

[23]  G. Ducros,et al.  Overview of experimental programs on core melt progression and fission product release behaviour , 2008 .

[24]  Marc Barrachin,et al.  New modelling of the U–O–Zr phase diagram in the hyper-stoichiometric region and consequences for the fuel rod liquefaction in oxidising conditions , 2008 .

[25]  B. Cheynet,et al.  Progress in the thermodynamic modelling of the O–U–Zr ternary system , 2004 .

[26]  M. Oguma,et al.  Melting Temperature of Irradiated UO2 and UO2-2wt%Gd2O3 Fuel Pellets up to Burnup of about 30 GWd/tU , 1988 .

[27]  Martin Steinbrück,et al.  Core Loss during a Severe Accident (COLOSS). , 2003 .