Power Release Estimation Inside of Fuel Pins Neighbouring Fuel Pin with Gadolinium in a WWER-1000 Type Core,

J. Mikus / NRI Řez plc / Czech Republic

16th Symposium of AER on VVER Reactor Physics and Reactor Safety (2006, Bratislava, Slovakia)
Core Operation, Experiments and Code Validation


The purpose of this work consists in investigation of the gadolinium fuel pin (FP) influence on space power distribution, especially from viewpoint of the values and gradient occurrence inside of neighbouring FPs that could result in static loads with some consequences, e.g., FP bowing. Since detailed power distributions cannot be obtained in the NPPs, needed information is provided by means of experiments on research reactors. As for the power release measurement inside of FPs, some special (e.g. track) detectors placed between fuel pellets are usually used. Since such works are relatively complicated and time consuming, an evaluation method based on mathematical modelling and numerical approximation was proposed by means of that, and using measured (integral) power release in selected FPs, relevant information about power release inside of needed (investigated) FP, can be obtained. For this purpose, an experiment on light water, zero-power research reactor LR-0 was realized in a WWER-1000 type core with 7 fuel assemblies at zero boron concentration and containing gadolinium FPs.
Application of the above evaluation method is demonstrated on investigated FP neighbouring a FP with gadolinium by means of the
• Azimuthal power distribution inside of investigated FP on their fuel pellet surface in horizontal plane and
• Gradient of the power distribution inside of investigated FP in two opposite positions on pellets surface that are situated to- and outwards a FP with gadolinium.
Similar information can be relevant from the viewpoint of the FP failures occurrence investigation.

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