Instrumentation for experiments on a fuel element mock-up for the study of thermal hydraulics for loss of cooling or coolant scenarios in spent fuel pools


Instrumentation for experiments on a fuel element mock-up for the study of thermal hydraulics for loss of cooling or coolant scenarios in spent fuel pools

Arlit, M.; Partmann, C.; Schleicher, E.; Schuster, C.; Hurtado, A.; Hampel, U.

After the Fukushima accident the focus in nuclear safety research has been extended to the spent fuel pool. In the consequence of a longer persisting station black out or loss of integrity of the pool, the cooling of the fuel elements can potentially not be guaranteed. Thus, the investigation of the thermal hydraulics of potential accident scenarios is of great scientific interest. The German national joint project SINABEL (SIcherheit NAsslager BrennElement-Lagerbecken) deals with the experimental investigation and the modelling of thermal hydraulics during the dry-out of a spent fuel pool in the consequence of a loss of cooling scenario. For this purpose a fuel element mock-up with electrically heated rods is constructed. During a dry-out scenario the water in the fuel element mock-up heats up to boiling temperature and evaporates. The water level decreases due to the continuing heating and the rods will be exposed to steam atmosphere. Parameters that have to be measured are the surface temperature of the rods, the height of the water level and the temperature as well as the velocity of the steam in the subchannels of the rod bundle.
The fuel element mock-up is designed according to the original dimensions of a BWR fuel element with pitch-to-diameter ratio- P/D = 1.24 and rod diameter D = 10 mm in a 10 x 10 square array. The housing consists of several metal boxes. To avoid heat sinks (adiabatic situation with no radial heat flow) the components are produced without flanges and are surrounded by a compact thermal insulation. The accessibility for instrumentation and other installations is reduced to the top side. The surface temperatures of the rods are measured by thermocouples and the water level by pressure transducers and electrical needle probes respectively.
For measuring both the temperature and the velocity of the steam in the small sub-channels no standard instrumentation is available. The applicability of established measurement techniques, such as Particle Imaging Velocimetry or Pitot tube, is not given due to constructional aspects of the test facility and the given flow properties (high temperatures, low velocities). Therefore, in this study a newly developed measurement system will be used. The experimental operating conditions are temperatures up to ϑ = 500 °C and very low local steam velocities down to v = 0.01 m/ s. Furthermore, the flow is expected to be laminar. The requirement for spatial resolution is to have one measurement point per subchannel in all subchannels of one rod bundle quadrant.
The presented solution is a thermal anemometry grid sensor TAGS, that is grid-type arrangement of special temperature-sensor elements measuring both, the temperature and the velocity nearly simultaneously. The sensitive elements are mounted on a ceramic grid-like structured substrate and connected to each other in a matrix arrangement. This sensor is connected to a special excitation and data acquisition electronics, applying the measurement technique of resistance thermometry for temperature measurement and thermal anemometry for velocity measurement. Within the paper a detailed description of the instrumentation of the fuel element mock-up in general and more specifically the TAGS are presented together with first results.

Keywords: Spent fuel pool; temperature measurement; thermal anemometry; grid sensor

  • Contribution to proceedings
    SWINTH-2016 (Specialists Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics), 15.-17.06.2016, Livorno, Italy
    Proceedings of SWINTH-2016
  • Lecture (Conference)
    SWINTH-2016 (Specialists Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics), 15.-17.06.2016, Livorno, Italia

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Publ.-Id: 23517