PAssive Systems: Simulating the Thermal-hydraulics with ExperimentaL Studies

Project Information

PASTELS

Grant agreement ID: 945275

DOI

10.3030/945275

Project closed

EC signature date 20 May 2020

Start date 1 September 2020

End date 31 August 2024

Funded under

• Euratom

Total cost

€ 3 801 457,50

EU contribution

€ 2 993 262,76

Coordinated by

ELECTRICITE DE FRANCE
France

Periodic Reporting for period 3 - PASTELS (PAssive Systems: Simulating the Thermal-hydraulics with ExperimentaL Studies)

Reporting period: 2023-09-01 to 2024-08-31

Summary of the context and overall objectives of the project

The PASTELS project aimed to significantly increase the knowledge of passive systems for European nuclear players. One of the main objectives of the project was to assess the ability of several CFD systems and codes, used in the nuclear community for design and safety demonstration, to accurately model key physical phenomena for passive systems such as natural circulation loops.
Given the increasing use of passive systems in non-European nuclear power plants, it was essential, particularly with the rise of small modular reactors (SMRs) which largely integrate these systems into their design, for the European nuclear community to adapt its reference numerical tools to the study of these promising technologies, with this adaptation being made on the basis of relevant experimental data representative of the passive systems concerned. The Safety Condenser (SACO) and the Containment Wall Condenser (CWC) were the two innovative passive systems selected for the project.
The project was based on existing combined effects test campaigns obtained in the PERSEO and HERO-2 test facilities (SIET, Piacenza, Italy), but also on new data obtained in full-scale test facilities operating under conditions close to industrial applications, which fill the gap in representative experimental data at European level: PKL (Framatome GmbH, Erlangen, Germany) for the SACO and PASI (LUT, Lappeenranta, Finland) for the CWC.
The numerical and experimental activities were carried out using a progressive approach. Through various benchmarks, PASTELS has studied improvements to the model and proposed new coupling methodologies to obtain the advantages of system and CFD scales in the same calculation.
In addition, important insights into the behaviour of SACO and CWC were gained by observing their behaviour during test campaigns.
All the results of the project have contributed to the development of detailed methodological guidelines and a roadmap for the licensing and implementation of these innovative passive system technologies in future European nuclear power plants.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project began its technical activities with bibliographical research into the phenomena associated with closed-loop natural circulation (D2.1). Then, during the numerical analysis of separate-effect (HERO-2, D2.2) and combined-effect (PERSEO, D2.3) tests, various system-scale and CFD numerical tools were used to assess the simulation capabilities of natural circulation phenomena. This study provided an initial assessment of code capabilities and guidelines for improving tests and models. A summary of the status (D2.4) of SET and CET code validation has been published (D2.4).
For the SACO activities, the project began by defining the specifications for the design and construction of this new passive system on the PKL test loop (D3.1). A first series of tests is dedicated to sensitivity analyses of the SACO boundary conditions (D3.2) and a second consists of a simulation of a transient scenario - the Station Black-Out (SBO) scenario - and additional sensitivity analyses dedicated to the impact of SACO tube filling on its performance (D3.4). The results of the phase 1 and phase 2 calculations were published in (D3.3) and (D3.5) respectively.
For the CWC, the PASI test matrix was also defined by the consortium (D4.1) and the test facility was modified to meet the needs of the test program - 10 tests described in (D4.2). A numerical analysis of the PASI pre-tests (D4.3) was carried out using the system codes for model calibration. The experimental analysis and the overall analysis of the numerical results of the CWC simulations are available in (D4.4) and (D4.5) respectively.
The lessons learned from the design of ODS and CWC and the ability of the codes to simulate these systems have been summarised in (D3.6) and (D4.6).
From a general point of view, the numerical analysis shows that the system codes can simulate the basic phenomena with correct accuracy. However, condensation modelling could be improved. CFD tools are still difficult to use to simulate large systems, mainly because of the much higher simulation costs, which limit the verification and validation processes. Nevertheless, they can be interesting for better understanding/characterising phenomena in parts of the domain subject to local 3D effects. Approaches based on coupled systems codes and computer-aided design codes are promising, but further research will be needed to reach conclusions.
The project proposed a dissemination and communication plan at the start of the project (D5.1) and has set up various media to communicate about the project, such as a public website (D5.2) a LinkedIn account, an educational video...
Some 20 papers have been presented to date at various conferences, such as SNETP 2021, NURETH-19 and FISA/EURADWASTE in 2022 and NURETH-20 and ICAPP in 2023 and 2024, for which the project received a “Best Paper Award”.
Two major public communication events were also organised: an end-user workshop at Framatome Erlangen (March 2023) and the project's final symposium at EDF Lab Paris Saclay (May 2024).
Some methodological guidelines resulting from the project were presented in (D5.5) and a list of priority tips/actions was proposed in (D5.6) concerning a roadmap for a European versions of SACO and CWC.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project made it possible to experimentally evaluate the performance of the SACO and the CWC. These 2 systems were able to operate with a degree of performance in line with their design. One area of concern was the management of non-condensable gases in the design of the SACO. The project has once again highlighted the importance of relying on tests that are as well controlled as possible in terms of pressure losses, heat losses, the rate and location of non-condensables, local measurements dedicated to CFD, etc., to be able to condition the code input decks correctly and simplify the subsequent numerical analyses. The working methodology used in the project also illustrated the need to carry out more blind tests to consolidate the validation of the calculation tools.
System codes have demonstrated their ability to reproduce most physical phenomena, but there are still gaps to be filled in to make further improvements. Modelling a complete passive system with a CFD code remains a challenge but can be useful for enriching the numerical analysis in certain parts with significant 3D effects. Coupling the CFD code with the system code is an interesting way of limiting simulation costs and integrating the CFD scale into complete simulations of system architectures.
Generally speaking, the project has confirmed the robustness of these systems in extracting energy at a good level and without being excessively disturbed by phenomena such as the presence of non-condensable gas (SACO) or with oscillating behaviour (CWC). These latest findings contribute to confirm their ability to fulfil their mission and add to the interest in promoting their implementation in future nuclear power plants.
One of the first effects of the project will be the integration of experimental data and reference input decks into the validation database for the codes used in the PASTELS project.
In addition, the PASTELS consortium regularly takes part in discussions with other European projects (SASPAM, EASI-SMR, etc.) to share the knowledge acquired during the project on passive systems from an experimental and numerical point of view.

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