Abstract
A new device for puncturing of irradiated fuel rods in commercial power plants has been designed by Fuel Research Department of CEA Cadarache in order to provide experimental data of high precision on fuel pins with various designs. It will replace the current set-up that has been used since 1998 in hot cell 2 of STAR facility with more than 200 rod puncturing experiments. Based on this consistent experimental feedback, the heavy-duty technique of rod perforation by clad punching has been preserved for the new bench. The method of double expansion of rod gases is also retained since it allows upgrading the confidence interval of volumetric results obtained from rod puncturing. Furthermore, many evolutions have been introduced in the new design in order to improve its reliability, to make the maintenance easier by remote handling and to reduce experimental uncertainties. Tightness components have been studied with Sealing Laboratory Maestral at Pierrelatte so as to make them able to work under mixed pressure conditions (from vacuum at 10-5 mbar up to pressure at 50 bars) and to lengthen their lifetime under permanent gamma irradiation in hot cell. Bench ergonomics has been optimized to make its operating by remote handling easier and to secure the critical phases of a puncturing experiment. A high pressure gas line equipped with high precision pressure sensors out of cell can be connected to the bench in cell for calibration purposes. Uncertainty analyses using Monte Carlo calculations have been performed in order to optimize capacity of the different volumes of the apparatus according to volumetric characteristics of the rod to be punctured. At last this device is composed of independent modules which allow puncturing fuel pins out of different geometries (PWR, BWR, VVER). After leak tests of the device and remote handling simulation in a mock-up cell, several punctures of calibrated specimens have been performed in 2016. The bench will be implemented soon in hot cell 2 of STAR facility for final qualification tests. PWR rod punctures are already planned for 2018.
Highlights
Fission gas release from fuel under irradiation and the resulting pressure increase are key parameters influencing the behaviour of a nuclear Pressurized Water Reactor (PWR) fuel rod in nominal and accident conditions
Many improvements have been introduced in the design of the new rod puncturing device and the puncturing experiment procedure has been upgraded as well
Its reliability has been improved for evaluating the quantities of interest as well as for assessing the rod gas composition
Summary
Fission gas release from fuel under irradiation and the resulting pressure increase are key parameters influencing the behaviour of a nuclear Pressurized Water Reactor (PWR) fuel rod in nominal and accident conditions This data is obtained experimentally at the CEA Cadarache centre by a device that has been used in hot cell 2 of the STAR facility since 1998. As metallic seals could not be used in this case, it was crucial to find an elastomeric seal material resistant enough to permanent gamma irradiation in a hot cell and suitable for our working conditions This is why different kinds of elastomers were tested in the MAESTRAL Laboratory [3] at the CEA Pierrelatte centre to characterise leak-tightness and mechanical behaviour after several months of gamma irradiation in hot cell.
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