Some results of noise measurements in a PWR NPP

doi:10.1016/0149-1970(85)90063-0

Progress in Nuclear Energy

Volume 15, 1985, Pages 387-393

https://doi.org/10.1016/0149-1970(85)90063-0 Get rights and content

Abstract

A shift of low frequency peak in pressure oscillation measured during the commissioning of a PWR is explaned as the result of changes of the water level in the pressurizer. Simple calculational model based on equivalence of electric circuit with Helmholtz equation gives a sensible interpretation of the phenomenon.

In the second part a new approach is suggested for estimation of reactivity coefficients in power reactors via noise measurement. The method has been used to evaluate pressure coefficient ϖϱ/ϖp during a fuel campaign.

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There are more references available in the full text version of this article.

Cited by (16)

Development and overall testing of the traditional MTC estimation based on noise diagnostics at all four units of the Paks NPP
2011, Nuclear Engineering and Design
Moderator Temperature Coefficient (MTC) of reactivity is an important parameter of nuclear reactors and its value should be in a specific range during the reactor operation. Determining MTC with traditional methods is performed through deviating the reactor state from the normal operation. Noise diagnostics has the potential to provide an MTC estimation method during normal operation without changing the reactor state.
This paper overviews the developments made on the traditional noise based estimators and the steps of their application in VVER-440 type reactors. Modifications were made to consider the effect of propagating perturbations through geometry and coolant velocity and to compensate the frequency response of the slow thermocouples. Frequency dependence of H₁ was calculated in high resolution which involved the revision of the method applied for reading the MTC value earlier (see the details in Kiss et al., 2010a, Kiss et al., 2010b).
Investigations were performed at all four units of the Paks NPP to verify the dependence of the results on specific core features (e.g. on core loading patterns) and instrumentation of the individual units. For a better comparison of the results, a common frequency range of the evaluation was chosen for all units, thus this range was made narrower and its weight went closer to the frequency range affected by power feedback. Absolute values of the estimated MTC are smaller than the reference value due to the effect of feedback and low coherence. During the investigated fuel cycles estimations were quite close to the reference for two units (the deviation was around 10%), while the agreement was only moderate for the other two units (here the deviation was around 40%).
Monitoring MTC using cold leg thermocouple and background neutron detector noise signals in a VVER-440 reactor during a whole fuel cycle
2010, Annals of Nuclear Energy
Monitoring of the Moderator Temperature Coefficient (MTC) was performed from the noise signals of cold leg thermocouples and background neutron detectors in a VVER-440 type reactor during a whole fuel cycle. A modified traditional noise based estimator was applied: the estimator was extended in order to take into account the effects of measurement geometry, coolant velocity and the relatively long time constant of the thermocouples. A systematic evaluation of measurement settings and evaluation parameters was carried out in order to determine optimal parameters. Optimal evaluation parameters were determined by considering the frequency dependence of the estimator, and by minimizing the statistical and systematic errors of the results. It can be concluded that the modified estimator provides adequate results which are close to the MTC given by the core design code calculations. It was found that relatively long FFT window sizes are needed to obtain correct results. The method needs long but industrially acceptable measurements for robust operation.
MTC estimation based on neutron noise and propagating temperature perturbation in VVER-440 reactors
2010, Annals of Nuclear Energy
Moderator Temperature Coefficient (MTC) is an important parameter characterizing inherent safety in PWRs. Noise diagnostics provides a theoretically well established method to estimate its value without changing the reactor state with using fluctuation of the temperature and neutron flux measurements in frequency domain. However, several difficulties arise when determining the core average neutron and temperature fluctuation from the real measured signals, due to the specific instrumentation of each reactor type. Coolant temperature fluctuations originate from inhomogeneities traveling with the coolant flow and the treatment of this phenomenon requires an approach using the theory of propagating perturbations. Traditional MTC estimation methods do not consider these effects and they result in substantial under- and overestimations.
This paper investigates MTC estimation in VVER-440 type reactors. For the evaluations the traditional H₁ estimator was used in a modified form: it was extended with factors taking into account the effects of propagating perturbations through geometry and coolant velocity. The 0.1–1.0 Hz frequency range of the traditional MTC evaluation was narrowed, as well, because of the relatively slow thermocouples and to decrease the effect of feedbacks. With these advancements results were quite close to the calculated values provided by reactor physics.
Theoretical investigation of the MTC noise estimate in 1-D homogeneous systems
2002, Annals of Nuclear Energy
In this paper, the accuracy of the noise-based determination of the moderator temperature coefficient (MTC) is investigated theoretically and quantitatively. It is known from earlier work that the noise method systematically underestimates the MTC. In this paper, it is found that the main reason for the underestimation lies with the radial incoherence of the temperature fluctuations. The deviation of the reactor response from point-kinetics is another possible reason, but it was found to play a quite insignificant role. The theory of neutron noise, induced by spatially random perturbations is elaborated and by its help the inaccuracy (bias) of the noise based MTC estimation was quantitatively investigated. It was found that a relatively short correlation length of the temperature fluctuations, which is in agreement with experimental evidence, can explain the observed underestimation of the MTC by the noise method.
Logic based feature detection on incore neutron spectra
1993, Annals of Nuclear Energy
Monitoring temperature reactivity coefficient by noise method in a NPP at full power
1987, Annals of Nuclear Energy

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Operational experience—ISome results of noise measurements in a PWR NPP

Abstract

Progress in Nuclear Energy

Report on measurements made during the commissioning Paks NPP Unit 1

OKKFT A/11-1.1.1

Pressure fluctuations inside PWR pressurizers

Interpretetion of the low-frequency pressure fluctuations in PWR-s

Frequency response Testing in Nuclear Reactors

Theoretical investigation of the lowfrequency pressure fluctuation in PWR-s

Operational experience—I
Some results of noise measurements in a PWR NPP