Thermal Parametric Studies for Radioactive Waste Management
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D. MANZONI*, S. LE BONHOMME*, B. SOULIER**, Y. GUILLOUX*** *EDF, DNpartement TTA, 6 Quai Watier, 78401 Chatou, FRANCE **ENS de Cachan, 61 av du Pdt Wilson, 94235 Cachan, FRANCE ***ANDRA, 1-7 rue Jean Monnet, 92298 Chftenay-Malabry, FRANCE
ABSTRACT
The objective of this study is to optimize the storage system with respect to thermal constraints. Due to a large number of 3D calculations, a simple temperature model based on an Design Of Experiment method has been developed. The most significant parameters have been exhibited by an extensive parametric study. A satisfactory agreement is observed between polynomial model and 3D approach. INTRODUCTION
A radioactive waste disposal is characterized by various essential factors: cooling time, number of waste packages by tunnel, rock and buffer characteristics, drift spacing etc...This system have to verify some thermal limits, in particular in the buffer, so that the degradation of the clay and the canister corrosion will be moderated. In order to confirm and optimize the Initial Option of Storage, EDF and ANDRA carried out thermal parametric studies. A Design Of Experiment method has been performed to organize the calculations and to build a simplified model of the maximum buffer temperature. 1. DESIGN DESCRIPTION
This study considers a storage concept of tunnels filled with spent fuel UOX 33 GWd/MTU Burnup. The current container design is made of 10 cm of carbon steel. The spent fuel is stored directly inside the containers. 4 PWR assemblies are disposed in the container, as shown on figure 1" 0 1000 mm
5505 mm
0 800 m
........
0 1000 mm
Figure 1 Characteristicsof the container Figure 2 shows the fuel decay heat curves per container and per assembly for UOX 33 GWD/MTU Burnup. The material properties of the different materials are given in table 1. However, temperature dependent material properties can be taken into account to improve the modeling.
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Mat. Res. Soc. Symp. Proc. Vol. 608 0 2000 Materials Research Society
2000 I assembly UOX 33
1750
-!
1500 1250
MWd/MTU .... One container of 4 assemblies
z 1000
-
®750_ 500
"-..
250 020
. . . .
60
100
140
180
220
260
300
-.. - ------------....
340
380
420
460
500
Time (years) Figure2 : Spentfuel UOX 33000 MWd/MTU
Thermal conducticity
(W.m-1x-1)
Steel Concrete Air Buffer Clay
II
Density (kg.m-3)
Heat capacity (J.kg-'.K')
7850 2300 1.16 2200 2360
500 1000 1017 1050 775.5
35 1.75 0.025 k= 1.3 kx =k=1.8;k,=l.4
Table I : Thermal-Physicalproperties of the variousmaterials 2. THERMAL CALCULATIONS WITH AFINITE ELEMENT MODEL The materials temperatures are evaluated with the EDF thermal code called SYRTHES. It deals with conduction and radiation (limited to transparent medium) for transient problems in three dimensions. The solid structure is discretized by an unstructured grid made of around 300 000 nodes, and the radiation mesh is a surface grid. The grids are completely independent but still respect the same geometrical boundary. The tunnel geometry and all the heat transfers taken int
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