3D simulation of a power ramp including fuel thermochemistry and oxygen thermodiffusion

Abstract

This paper presents 3D simulations of power ramps in pressurized water reactors with the fuel performance code ALCYONE, which is part of the computing environment PLEIADES. The code has been upgraded to couple the description of irradiated fuel thermochemistry already available with oxygen transport taking into account thermodiffusion. The impact of oxygen redistribution during a power transient on irradiated fuel thermochemistry in the fuel and on chemically reactive gas release from the fuel (I (g) , I 2(g) , CsI (g) , TeI 2(g) , Cs (g) , Cs 2(g) ) is studied. The simulations show that oxygen redistribution, even if moderate in magnitude, leads to the reduction of metallic oxides (molybdenum dioxide, cesium molybdates, chromium oxide) at the fuel pellet center and consequently to the release of a much greater quantity of gaseous cesium. Pellet-Cladding Interaction failure propensity is shown to decrease in consequence of the thermodynamically favourable reaction of iodine with released cesium in the free volume of the rod.

Determination of tolerance limits for fuel assembly fission gas release summary statistics

“…Currently it is possible to couple the thermomechanical behavior of nuclear fuel and thermochemistry using the elemental composition determined by neutronics calculations. Such couplings are demonstrated in, for example, [33,25,27] and Publications I, II and III. Piro et al [33] used a coupled thermomechanical, thermochemical and neutronic calculation to investigate the oxygen potential and chemical state of fission products in nuclear fuel, and Baurens et al [25] used a similar approach to investigate corrosive gas release.…”

“…Thermodynamic data is not available for all of these elements, and some of the elements occur in minute amounts. It has become commonplace to group elements into representative elements according to chemical similarity (see, for example, [25,26,27] and Publication II), and use the mole amounts of the representative elements in calculations. In table 2.2 the grouping used in Publication II is shown for all elements calculated to occur in the fuel by Serpent except boron, nitrogen and carbon.…”

“…Piro et al [33] used a coupled thermomechanical, thermochemical and neutronic calculation to investigate the oxygen potential and chemical state of fission products in nuclear fuel, and Baurens et al [25] used a similar approach to investigate corrosive gas release. This coupling has been further developed by Konarski et al [27] to investigate oxygen thermodiffusion and its effect on corrosive gas release.…”

“…The exact chemical composition is difficult to measure from nuclear fuel, whereas "oxygen potential" -when defined without the standard chemical potential of oxygen -can be measured with less difficulty. Therefore this definition of oxygen potential is a useful proxy for the chemical composition, which is of interest, and the oxygen content of the fuel in itself has effects on the performance of fuel: it has been shown that oxygen released from the pellet may prevent crack formation in the cladding [15] and influence the release of corrosive gases from the pellet [27].…”

An improved method to evaluate the “Joint Oxyde-Gaine” formation in (U,Pu)O2 irradiated fuels using the GERMINAL V2 code coupled to Calphad thermodynamic computations

“…In the past years, several groups have worked on implementing thermodynamic calculations inside fuel performance codes in order to improve predictive abilities. Baurens et al [9] and later Konarski et al [10] have coupled ANGE together with the ALCYONE (also in the PLEIADES simulation platform) in order to simulate, respectively, stress corrosion cracking and oxygen thermodiffusion. Simunovic et al [11] have coupled THERMOCHIMICA [12] to the mass and heat transport models of the BISON [13] fuel performance code.…”