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Flow nucleate boiling is characterized by a high heat transfer. It is of relevance for the design of heat exchangers, boilers and nuclear fuel assemblies. Nevertheless, the heat transfer is limited by a corresponding maximum heat flux at the beginning of a boiling crisis or transition which is called critical heat flux (CHF). The CHF is indicated by a sudden rise of the surface temperature (e.g. of the fuel rod) due to the drop of heat transfer from the surface to the fluid. This means a strong limitation of the overall heat transfer performance and leads to larger and more expensive structures or functional or power limitations. CHF can not be predicted by pure analytical modelling.

Testing of heat transfer performance and CHF at water, steam and two-phase flow conditions eliminates modelling uncertainties and ensures safety margins. 

Our Heat Transfer, CHF and Cooling Limit Testing Services include:

  • Boiling water reactor (BWR): full fuel assembly CHF performance measurements, with a strong focus on the dry-out mechanism
  • BWR: Natural circulation stability tests
  • Pressurized water reactor (PWR): Strong focus on departure of nucleate boiling (DNB)
  • Quenching, flooding and anticipated transient without scram (ATWS) tests – focused on rewetting scenarios
  • Severe accidental heat removing tests with complex geometries
  • Non-nuclear performance measurements for heat recovery boiler and other conventional boiler up to supercritical (pressure) conditions
  • Investigation of direct solar steam generation.

All of the above tests can be conducted in our world leading thermo-hydraulic test loops KATHY and BENSON.

KATHY: Thermo-Hydraulic Fuel Testing Loop

Performance specification:

  • Electrical power: 20 MW (DC)
  • Max. current: 85 kA
  • Max. pressure: 185 bar
  • Max. temperature: 360°C
  • Flow rate: 250 m3/h

The KATHY thermo-hydraulic test loop started operation in 1987 with more than 40,000 CHF test runs for more than 159 nuclear power plants (NPPs).

BENSON: Multipurpose Thermal-Hydraulic Test Loop

Performance specification:

  • Electrical power: 2 MW
  • Max. current: 15 kA
  • Max. pressure: 330 bar
  • Max. temperature: 600°C

The BENSON test loop has been in operation since 1975. More than 500,000 heat transfer measurements have been provided to over 50 customers all over the world.

Interested in Heat Transfer Performance Testing?

BENSON Loop and KATHY Loop for heat transfer performance and critical heat flux testing at water, steam and two-phase flow conditions (click to enlarge)