Analysis of Phenix Core Response to Inlet Sodium Temperature Increase During One of the EOL Tests
NURETH-14 - 2011 September 25-30

Presented at:
2011 September 25-30
Toronto, Canada
Session Title:
E6-1 Safety Analysis of Sodium Cooled, RBMK and VVER Reactors

Aurelia Chenu (PSI, EPFL)
Konstantin Mikityuk (Paul Scherrer Institut)
Robert Adams (PSI, ETHZ)
Rakesh Chawla (PSI, EPFL)


This work presents the analysis, using the TRACE code, of the Phénix core response to an

inlet sodium temperature increase. The considered experiment was performed in the frame of

the Phénix End-Of-Life (EOL) test program of the CEA, prior to the final shutdown of the

reactor. It corresponds to a transient following a 40°C increase of the core inlet temperature,

which leads to a power decrease of 60%. This work focuses on the first phase of the transient,

prior to the reactor scram and pump trip.

First, the thermal-hydraulic TRACE model of the core developed for the present analysis is

described. The kinetic parameters and feedback coefficients for the point kinetic model were

first derived from a 3D static neutronic ERANOS model developed in a former study. The

calculated kinetic parameters were then optimized, before use, on the basis of the

experimental reactivity in order to minimize the error on the power calculation. The different

reactivity feedbacks taken into account include various expansion mechanisms that have been

specifically implemented in TRACE for analysis of fast-neutron spectrum systems. The point

kinetic model has been used to study the sensitivity of the core response to the different

feedback effects.

The comparison of the calculated results with the experimental data reveals the need to

accurately calculate the reactivity feedback coefficients. This is because the reactor response is

very sensitive to small reactivity changes. This study has enabled us to study the sensitivity of

the power change to the different reactivity feedbacks and define the most important

parameters. As such, it furthers the validation of the FAST code system, which is being used

to gain a more in-depth understanding of SFR core behavior during accidental transients.

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