Thermal Hydraulics (THS)

Thermal hydraulics for fission reactors

The team focuses on applying thermal hydraulics expertise to improve nuclear power plant safety. We use computer codes, support plant operations, assess uncertainties, and contribute to code development through international collaboration.

In the field of thermal hydraulics, the R&D activity has been focused on technology transfer to the industry and administration.

 Experience in:

  • Improvement of the safety of nuclear power plants using TH system computer codes (e.g. RELAP5, TRACE)
  • Support to plant operation and engineering
  • Assessment of uncertainties
  • Contribution to code maintenance and assessment by participating in international benchmarks
  • Transfer of Knowledge

THS has a long cooperating experience (expanding for more than 20 years) with Ascó and Vandellòs II nuclear plants, giving support to operation and plant engineering through thermal-hydraulic (TH) analysis using TH codes distributed by the Consejo de Seguridad Nuclear, (CSN, Nuclear Safety Council, the Spanish regulatory body). In this sense, THS members have large expertise in the use of codes like RELAP5 and TRACE.


More than 400 Nuclear Power Plants are currently operating in the world. The safe operation of such plants is an important issue and a concern for citizens. Science contributes to it by developing a deep and reliable knowledge of plant behavior under normal and abnormal conditions.

Simulating such behavior is the main goal of the thermal-hydraulic section of ANT (THS). To predict and master this behavior, important know-how in thermal-hydraulics is required as well as other skills like neutronics, material performance, and controls.

Nuclear safety experiments constitute an essential part of thermal-hydraulic R&D. These experiments are performed in non-nuclear lower-scale facilities designed to reproduce accidental scenarios. The facilities are rather expensive and so usually maintained through international efforts.

THS  participates in several OECD projects, in facilities located in Germany, Japan, and Korea involving a large number of participants from several countries. The main interest of these experiments is that parameters that are relevant from the safety point of view can be measured and analyzed later on so that we can understand what happened and simulate it.

Simulating a full-size power plant is a complex task that requires experienced users. A validation process is unavoidable.
Within ANT, we have developed a novel methodology to scale up simulations of integral experiments up to the full plant size. In this way, we can predict the behavior of nuclear reactors in hypothetical accidental scenarios with a high degree of confidence.

Group Leader: Jordi Freixa