OECD/NEA Rig of Safety Assessment (ROSA) Project

The key objectives of the OECD/NEA ROSA project are to:

1. Provide an integral and separate-effect experimental database to validate code predictive capability and accuracy of experimental thermal-hydraulic models. In particular, phenomena coupled with multi-dimensional mixing, stratification, parallel flows, oscillatory flows and non-condensable gas flows are to be studied.
2. Clarify the predictability of codes currently used for thermal-hydraulic safety analyses as well as other advanced codes presently under development, thus creating a group among the OECD member countries who share the need to maintain or improve the technical competence in thermal-hydraulics for nuclear reactor safety evaluations. The experimental programme is defined to provide a valuable and broadly usable database to achieve these objectives.

When evaluating the safety of light water reactors, computer codes are used to simulate their behaviour during design basis events and beyond-DBE transients. This involves complex multi-dimensional single-phase and two-phase flow conditions, which can include non-condensable gas in many cases. Although current thermal-hydraulic safety analysis codes have a very high predictive capability (especially for one-dimensional phenomena such as flows in piping at high flow rates) there is a need for experimental work and code development and validation for these complex flow conditions. Given the increased use of best-estimate analysis methods in licensing, which is replacing traditional conservative approaches, the validation and quantification of uncertainties in the simulation models and methods is required.

Many experimental facilities have contributed to the thermal-hydraulic databases available today. However, most of current data are insufficient for future codes that incorporate multi-dimensional simulation capabilities, mainly because the spatial resolution of measurement is not enough to assess the simulation models and methods. The ROSA project will seek to address these issues.

The project consists of the following six types of ROSA large-scale experiments:

• temperature stratification and coolant mixing during emergency coolant injection;
• unstable and disruptive phenomena such as water hammer;
• natural circulation under high core power conditions;
• natural circulation with superheated steam;
• primary cooling through steam generator secondary depressurisation;
• two open tests defined by participants (one on pressure vessel upper-head break loss-of-coolant accident (LOCA) and another on pressure vessel bottom break LOCA, combined with accident management measures with symptom-oriented operator actions).

The programme contemplates a total of 12 tests, of which eight have been carried out so far. Four tests were performed in 2007, one on temperature stratification, one on water hammer and two on primary cooling through depressurisation. The remaining four tests were discussed by the project steering bodies, which defined the test initial and boundary conditions. They will be conducted in 2008 and in the first part of 2009. Project members also discussed the issues to be addressed in a possible follow up of the project, which is scheduled for completion in March 2009.

Project participants

The project is supported by safety organisations, research laboratories and industry from the following countries: Belgium, the Czech Republic, Finland, France, Germany, Hungary, Japan, Republic of Korea, Spain, Sweden, Switzerland, the United Kingdom and the United States.

Project period

April 2005-March 2009

Budget

US$ 1 million/year

Related links

• Overview of joint projects

• NEA Nuclear Safety Programme

• NEA contacts: Carlo Vitanza (carlo.vitanza@oecd.org)

Last updated: 27 March 2007