Development of a method for measuring the MTC by noise analysis and its experimental verification in Ringhals-2
Artikel i vetenskaplig tidskrift, 2004

This paper deals with the estimation of the moderator temperature coefficient of reactivity (MTC) by noise analysis. The current noise analysis-based MTC measurement, relying on the cross correlation between the neutron noise measured by a single in-core neutron detector and the local temperature noise given by a single core-exit thermocouple located at the top of the same fuel assembly, or of a neighboring fuel assembly, is not accurate. The MTC is systematically underestimated by a factor of 2 to 5 compared to its design-predicted value. A theoretical study shows that, in case of nonhomogeneous moderator temperature noise, the core-averaged moderator temperature noise should be used for the MTC estimation. The new estimation method can reach up to 3% accuracy as compared with the results of core calculations for the Swedish Ringhals-2 pressurized water reactor (PWR). We show via noise measurements performed at the Ringhals-2 PWR that the moderator temperature noise is actually radially strongly heterogeneous and loosely coupled. The new MTC noise estimator is demonstrated to provide an accurate MTC evaluation, with the core-averaged moderator temperature noise estimated via the use of many radial in-core gamma-thermometers. More important, different forms of weighting functions are suggested to calculate the core-averaged moderator temperature noise. This new MTC noise estimator, which is nonintrusive and free of calibration, can therefore be applied to monitor the MTC throughout the cycle.

correlation length

noise analysis

temperature noise (structure of)

core calculations

dynamic reactor transfer function

Moderator Temperature Coefficient (MTC)


Gamma-Thermometer (GT)

boron dilution method


Christophe Demaziere

Chalmers, Institutionen för reaktorfysik

Imre Pazsit

Chalmers, Institutionen för reaktorfysik

Nuclear Science and Engineering

0029-5639 (ISSN)

Vol. 148 1 1-29





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