Session: 07-02: Experiments and Analyses - I

Paper Number: 133058

133058 - Pre-Test Analysis of a Plofa Scenario for the Circe-Thetis Facility by Means of Coupled Sth/cfd Calculations. 

Abstract: 

In the context of GEN IV fission reactors, the LMF reactor stands out as a highly promising solution due to its improved thermal efficiency, safety, and radioactive waste management with respect to the GEN III NPPs. Therefore, numerous projects have been launched over the past few decades to support the development of these reactor concepts. In the frame of EU PATRICIA project, thermal-hydraulics aspects of liquid metal pools are investigated by means of both experimental and numerical tools. Particularly, an experimental campaign is planned at the ENEA Brasimone R.C. for the CIRCE-THETIS facility, aiming at investigating the consequences of postulated PLOFA scenarios. The main purpose is the investigation of the capabilities of safety systems providing DHR during a failure of the main circulation system; their effectiveness in Natural Circulation (NC) conditions will be investigated as well. During the experimental campaign, 4 different PLOFA will be considered, each one characterized by different combinations of cooling strategies. 

 

This paper focuses on the pre-test numerical analyses for the Protected Loss Of Flow Accident number 1 (PLOFA1) foreseen during the campaign. During this test, the capabilities of the steam generator acting as DHRs will be investigated. The Main coolant pump failure is assumed, meanwhile the SCRAM is simulated reducing the power supplied to the electrical heater. At this point the feed water mass flow rate is reduced and the SG acts as DHRs.

 

A preliminary evaluation of this transient was done by a stand-alone STH approach. In addition, the geometry of the pool was also reproduced in the CFD domain, and BC for the CFD were derived from the final steady state of the STH evaluation. A code-to-code comparison was performed, and the results highlighted that STH tends to underestimate the HT mechanism of the pool environment.   

Considering the poor capabilities of the CFD model in dealing with two-phase flow and of the STH one in dealing with the pool thermal-hydraulics, a coupled STH/CFD model was developed trying to overcome the limits of both the applications while keeping the observed advantages. CFD simulates the pool and loop environment while STH provides information about thermal power removed from the secondary side. The model was deeply examined to ensure the most accurate representation of reality, aligning with the preliminary evaluations provided by the experimentalists.  

Preliminary results from the coupling simulation are presented and compared with STH standalone calculations. The result highlights the effects of the heat transfer underestimation between loop and pool environment by the STH code, especially in the first part of the transients, where the temperature peak is higher than in the coupled simulation.  The coupled STH/CFD calculation should thus provide improved predictions with respect to the stand-alone ones. Coupled STH/CFD predictions for all the foreseen PLOFA cases are expected to start soon at the University of Pisa.

Presenting Author: Pietro Stefanini University of Pisa

Presenting Author Biography: Pietro Stefanini is a dedicated PhD student enrolled at the University of Pisa, specializing in Nuclear Engineering. Possessing a Master of Science in the same field, he has good capabilities in Computational Fluid Dynamics (CFD) and System Thermal-Hydraulic (STH) codes. His primary research focus lies in the domain of thermal hydraulic analyses of Liquid Metal Reactors.
Stefanini's work is centred around the exploration of a multi-scale approach and the development of coupling procedures for the thermal hydraulic examination of emerging reactors. Noteworthy among his recent endeavours is the initiation of work on the coupling scheme for the forthcoming experimental facility, CIRCE-THETIS, scheduled at the ENEA Brasimone RC. He has produced compelling pre-test results, indicating the depth of his contributions to this innovative research.

Authors:

Pietro Stefanini University of Pisa
Andrea Pucciarelli University of Pisa
Nicola Forgione University of Pisa
Ivan Di Piazza ENEA