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Job Record #16808
TitleImpact of flow deviation on the cooling of nuclear fuel rods
CategoryPostDoc Position
EmployerIRSN (French Safety Technical Organisation)
LocationFrance, Cadarache research center (south of France)
InternationalYes, international applications are welcome
Closure Date* None *
IRSN, Institut de Radioprotection et de Sûreté Nucléaire (see, is the technical support 
organization of the French regulator ASN for nuclear safety. The activities 
of the IRSN SEMIA department covers especially the assessment of safety 
studies of industrials and the corresponding research in the field of design 
basis accidents in nuclear power plants. This concerns the Loss of Coolant 
Accident scenario that corresponds to the consequences of a hypothetical 
pipe break in the primary loop of the plant.

During a hypothetical Loss of Coolant Accident within a nuclear power plant, 
the fuel rods within the core may balloon by creep and partially obstruct 
the coolant flow, potentially impeding their cooling. The flow deviation 
induced by the rods deformation has been experimentally studied in the mock-
up MASCARA [1] (see the illustration at the end of the document) using 
Reynolds analogy and MRI (magnetic resonance imaging), allowing to get a 
fine mapping of the flow velocity

The main objective of the work is to study the consequences of the flow 
deviation on the cooling of the fuel rods at the assembly scale. Based on 
the validation of the Code-Saturne CFD computational tool [2] on the MASCARA 
experimental results, models will be defined to describe the impact of 
ballooning on a simplified flow model used in the DRACCAR software [3], [4] 
that describes the hydrodynamics at a so-called sub-channel scale1.
The study can be divided in different tasks:

1/ CFD simulation of flow deviation
CFD calculation of the flow deviation induced by different geometrical and 
flow-rate configurations will be compared to experimental results in order 
to better understand the flow just downstream deformed rods, where the 
deterioration of heat transfer may be critical.

2/ Upscaling model of flow deviation
Cross-flows deduced from CFD in the region downstream deformed rods will be 
analyzed for prescribing models for a sub-channel scale analysis.

3/ CFD simulation of convective heat transfer
Thermal heat transfer between rods and flow will be studied thanks to CFD in 
order to identify the hot spots within the geometry and to relate their 
position to the previous hydrodynamics study. The fluid considered will be 
steam taking into account its thermal expansion that may induce an 
additional phenomenology.

4/ Upscaling model of single-phase heat transfer
Cross-flows and heat transfer intensity deduced from CFD in the region 
downstream deformed rods will be analyzed for prescribing models for a sub-
channel scale analysis.

5/ Toward other geometries
The hereinabove studies are limited to a set of configuration of an array of 
4x4 rods deformed within a 7x7 rods array. The ability of modeling the 
phenomena on a more generic fuel assembly geometry is required to study core 
geometry. Based on the previous analyzes, recommendation for the design of 
new experiments or for the performance of additional computations will be 
made. This work will be performed in interaction with both the experimental 
IRSN department SEREX [5] at Cadarache and the LEMTA lab at Lorraine 
University [6] where the MASCARA experiments have been performed.

6/ Two-phase flow heat transfer [optional]
In more realistic conditions, droplets flow within superheated steam act as 
an additional cooling source of the rods. Previous studies will be 
complemented by modeling their flow within the geometry based on an Euler-
Euler two-phase model with heat and mass transfer thanks to the Neptune-CFD 
software [7], [8].

[1] A. V. S. Oliveira et al., “Velocity field and flow redistribution in a 
ballooned 7×7 fuel bundle measured by magnetic resonance velocimetry,” Nucl. 
Eng. Des., vol. 369, p. 110828, Dec. 2020, doi: 
[2] “Code_Saturne is the free, open-source software developed and released 
by EDF to solve computational fluid dynamics (CFD) applications.” [Online]. 
[3] T. Glantz, T. Taurines, S. Belon, O. De Luze, G. Guillard, and F. Jacq, 
“DRACCAR: A multi-physics code for computational analysis of multi-rod 
ballooning, coolability and fuel relocation during LOCA transients. Part 
Two: Overview of modeling capabilities for LOCA,” Nucl. Eng. Des., vol. 339, 
pp. 202–214, Dec. 2018, doi: 10.1016/j.nucengdes.2018.08.031.
[4] “DRACCAR computer software.” [Online]. Available:
[5] “IRSN SEREX and corresponding experimental research lab.” [Online]. 
[6] “LEMTA, Laboratoire Énergies & Mécanique Théorique et Appliquée.” 
[Online]. Available:
[7] A. Guelfi et al., “NEPTUNE: A new software platform for advanced nuclear 
thermal hydraulics,” Nucl Sci Eng, vol. 156, pp. 281–324, 2007.
[8] P. Ruyer et al., “Two-phase flow across a partially damaged core during 
the reflood phase of a LOCA,” Nucl. Eng. Des., vol. 264, pp. 187–194, 2013, 
doi: 10.1016/j.nucengdes.2013.02.026.

Candidate :
The ideal candidate will have a PhD in physics or mechanical/thermal 
engineering. (expertise in nuclear area is not necessary). The position is 
reserved for foreign (non-frenchs) applicants. The appointment is for 18 
months (ths duration can be modulated) starting as soons as possible. The 
research will be performed at the Cadarache nuclear center located in the 
south of France close to Aix-en-Provence. It will be carried out under the 
direction of Pierre Ruyer expert in fluid dynamics and Herve Mutelle in 
charge of safety studies. Hiring is contigent upon eligibility to work in 
Contact Information:
Please mention the CFD Jobs Database, record #16808 when responding to this ad.
Email ApplicationYes
Cadarache - Bât. 288 porte 20
13115 Saint Paul Lez Durance
Record Data:
Last Modified13:13:34, Monday, October 19, 2020

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