NEA Advanced Thermal-hydraulic Test Loop for Accident Simulation (ATLAS) Project

This project was referenced in the The Fukushima Daiichi Nuclear Power Plant Accident: OECD/NEA Nuclear Safety Response and Lessons Learnt report as one of the three new joint projects based on existing research facilities which address safety issues related to the accident.

The ATLAS project is aimed at topics of high safety relevance for both existing and future nuclear power plants.

It is important because the use of computer codes is required in safety evaluation of light water reactors (LWRs) in order to simulate plant behaviour during design basis accidents (DBAs) and design extension conditions (DECs). This involves complex multi-dimensional single-phase and two-phase flow conditions.

Although current thermal-hydraulic safety analysis codes have achieved very high predictive capability especially for one-dimensional phenomena, there is a strong need for experimental work and code development and validation for these complex flow conditions.

Further, the increased use of best-estimate (BE) analysis methods in licensing, which is replacing traditional conservative evaluation model (EM) approaches, require the validation and quantification of uncertainties in the simulation models and methods.

Many experimental facilities have contributed to the thermal-hydraulic databases available today which have been extensively used for the validation of EM and BE computer codes. However, most of current data are insufficient for future codes that are to incorporate multi-dimensional simulation capabilities, mainly because the spatial resolution of measurement is not enough to assess the simulation models and methods, especially in system-integral testing.

The main objective of the NEA ATLAS Project is to provide experimental data for resolving key LWR thermal-hydraulics safety issues related to multiple high-risk failures and highlighted in particular from the Fukushima Daiichi nuclear power plant accident, by using the ATLAS facility at KAERI. The facility is described below.

In particular, the ATLAS Project will focus on the validation of simulation models and methods for the following complex phenomena of high safety relevance to thermal-hydraulic transients in DBA and DEC.

  1. Generate system-integral and separate-effect experimental database to validate predictive capability and accuracy of computer codes and models. Thermal-hydraulic phenomena coupled with multi-dimensional flows that may include mixing, stratification, counter-current flows, parallel-channel flows and oscillatory flows will be the main focus of the investigations.

  2. Facilitate assessment of codes currently in use for thermal-hydraulic safety analyses, as well as advanced codes presently under development, including three-dimensional computer codes, through active involvement of the project partners, who will maintain and improve the technical competence in thermal-hydraulics for nuclear reactor safety (NRS) evaluations.

The experimental programme is intended to provide a valuable and broadly usable database to achieve the above objectives. In the ATLAS Project, a total of eight to ten tests at the ATLAS facility are proposed to be conducted in five different research topics.


The ATLAS project will be supported by the safety organisations and industry in the following countries:

Belgium, China, Finland, France, Germany, Hungary, India, Japan, Korea, Russian Federation, Spain, Sweden, Switzerland, United Arab Emirates and the United States. Discussions are ongoing with other countries.

Project period

April 2014 to March 2017


EUR 2.5 million

Related links

Last updated: 30 June 2016