Keywords: noise analysis, neutron noise, vibration, detector impacting, detector strings, spectral analysis, APSD, coherence, phase, wavelet analysis, boiling water reactors, BWR, noise measurement, fuel cycles, fuel assembly, nuclear reactors, nuclear energy, nuclear power, nuclear technology, Sweden
Investigation of detector tube impacting in the Ringhals-1 BWR
Neutron noise measurements were made in two consecutive fuel cycles in the Swedish BWR Ringhals-1 with the purpose of diagnostics of vibrations and impacting of detector strings. Two diagnostic tools were used, first a traditional spectral analysis and second a wavelet-based method. Both types of methods have been used in the past, but not simultaneously during one fuel cycle. In addition, a new method, wavelet-based coherence, was tested with success. Based on the results of the analysis, with emphasis on the traditional method, the detector tubes were divided into three groups with respect to the severity and likelihood of impacting. For the first series of measurements, these conclusions could be checked against visual inspection of the fuel assemblies during refuelling after the cycle, in order to find impacting damage. A good correlation between the prediction of the analysis and the inspection results was found.