Review of the historic neutron noise behavior in German KWU built PWRs

The behavior of low frequency neutron noise during the 30 years of operation of German KWU built PWRs is reviewed. The role of various factors influencing neutron noise such as sub-cooled boiling, power and enrichment uprates, fuel type and mechanical fuel assembly design is discussed. Simulation results of temperature driven neutron noise with Studsvik's S3K dynamic core simulator are shown and compared to measurements. Hypotheses for recent increases and decreases of low frequency neutron noise are compared with evidence from operating history.