| 1. |
- Andersson, Tell, et al.
(författare)
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Development and application of core diagnostics and monitoring for the Ringhals PWRs
- 2003
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Ingår i: Progress in Nuclear Energy. - 0149-1970. ; 43:1-4, s. 35-41
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Tidskriftsartikel (refereegranskat)abstract
- Noise analysis and reactor diagnostics have been applied at the Ringhals PWRs for a long time. Through a collaboration with the Department of Reactor Physics, Chalmers University of Technology, methods for treating new problems were elaborated, and known methods were developed further to make them more effective or to suit specific applications. All these methods were tested in real measurements, and many of them have been used routinely afterwards. In this paper two particular new methods are described in detail: 1) the determination of the axial position of control rods from the axial shape of the neutron flux with neural network methods, and 2) the use of gamma thermometers for the determination of the MTC and for core flow estimation.
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| 2. |
- Demaziere, Christophe, 1973, et al.
(författare)
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2-D 2-group neutron noise simulator and its application to anomaly localisation
- 2001
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Ingår i: Proc. Int. Mtg. Mathematical Methods for Nuclear Applications (M&C2001). - 0894486616
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Konferensbidrag (refereegranskat)abstract
- This paper presents a so-called neutron noise simulator, essentially an algorithm to calculate the dynamic transfer function, and its use in a procedure allowing to locate a noise source from the neutron detector readings. The noise simulator relies on the two-group diffusion approximation in 2-D. Benchmarking of this calculator versus analytical solutions showed that the finite difference discretisation scheme used in the simulator was accurate in case of homogeneous cores and a central noise source. The localisation algorithm was found to give correct results as long as one single noise source exists in the core and when the transfer function from the removal cross-section noise to the thermal neutron noise was used. Applying this localisation procedure to the Forsmark-1 BWR (Sweden) when a local instability event occurred (cycle 16) pointed out, via the use of an appropriate set of detectors, a region close to where an unseated fuel element was discovered.
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| 3. |
- Demaziere, Christophe, 1973, et al.
(författare)
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A phenomenological model for the explanation of a strongly space-dependent Decay Ratio
- 2003
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Ingår i: Proc. Int. Mtg. Nuclear Mathematical and Computational Sciences (M&C2003). - 0894486748
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Konferensbidrag (refereegranskat)abstract
- It is commonly believed that the Decay Ratio (DR), a parameter characterizing the stability of Boiling Water Reactors (BWRs), is a space-independent parameter of the reactor, i.e. it is independent of which Local Power Range Monitor (LPRM) is used in the core to perform the evaluation. This paper shows that the presence of several simultaneous types or sources of instability with different stability properties and different space dependence renders the DR also space-dependent, and even strongly space dependent. Two cases were investigated: the case of a local instability (i.e. one induced by a local noise source) coexisting with a global instability (in-phase oscillations), and the case of two local instabilities (noise sources). The results of these calculations were compared to the Forsmark-1 channel instability event, where strongly space-dependent decay ratios had been found in the measurements. Good adequacy was found between the DR model applied to the Forsmark-1 event and the corresponding measured DR. The fact that one single noise source in the core does not allow explaining a non-homogeneous DR suggests that in the case of Forsmark-1, at least two types or sources of instability had to be present in the core at the same time. According to the results obtained in this paper, these could be either a local and a global instability, or two local ones.
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| 4. |
- Demaziere, Christophe, 1973, et al.
(författare)
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Analysis of an MTC noise measurement performed in Ringhals-2 using gamma-thermometers and in-core neutron detectors
- 2003
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Ingår i: Progress in Nuclear Energy. - 0149-1970. ; 43:1-4, s. 57-66
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Tidskriftsartikel (refereegranskat)abstract
- A noise measurement in the Swedish Ringhals-2 PWR was performed in January 2002 by using twelve gamma-thermometers and two in-core neutron detectors, all located on the same axial level in the reactor. The gamma-thermometers are very versatile tools since they allow estimating the core-averaged moderator temperature noise throughout the core. This core-averaged temperature noise was then used to estimate the MTC by noise analysis, via a new MTC noise estimator. It was shown that whatever the location of the neutron detector might be, the MTC is always correctly estimated by this new MTC noise estimator, without any calibration to a known value of the MTC prior to the noise measurement. For the purpose of comparisons, the MTC was also estimated by using a single gamma-thermomemeter and a single core-exit thermocouple, together with an in-core neutron detector. In such cases, the WC was systematically underestimated, with a stronger bias for the core-exit thermocouple than for the gamma-thermometer. This shows that the main reason of the MTC underestimation by noise analysis in all the experimental work until now was due to the radially non-homogeneous temperature noise throughout the core. The resulting deviation from point-kinetics of the reactor response has a negligible effect.
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| 5. |
- Demaziere, Christophe, 1973, et al.
(författare)
-
Determination of the MTC by noise analysis methods
- 2003
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Ingår i: Proc. Annual Mtg. Nuclear Technology 2003 (JK2003).
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Konferensbidrag (refereegranskat)abstract
- Determination of the moderator temperature coefficient (MTC) in pressurised water reactors has been the matter of interest for a long time. The MTC should be within certain limits at all times; it should be negative, but its absolute value should not exceed a certain limit either. Since the MTC changes continuously during the fuel cycle with burnup and the corresponding change in the boron concentration in the water, a monitoring of its value is necessary. The traditional methods that are used to measure the MTC are time consuming and expensive. The noise based methods are more flexible but so far they were rather inaccurate with a systematic underestimation of the MTC. In recent work we have pointed out that the main weakness of the noise based method is the poor knowledge of the driving source, by measuring the temperature fluctuations only in one radial point whereas those fluctuations are highly spacedependent. The problems of the noise method can be eliminated or largely improved if the core average temperature is used instead of the local temperature, leading to an improved noise estimator. This fact was confirmed by us in detailed numerical simulations. The new estimator was also tested in measurements at an operating plant. In the Swedish Ringhals-2 PWR, 12 strings of gamma thermometers are permanently installed. In the frequency range of interest to the MTC, i.e. within 0.1 - 1 Hz, these sensors act as pure noise thermocouples, measuring the temperature fluctuations of the cold junction which is in the coolant. With the signals of the gamma thermometers the fluctuations of the core averaged temperature can be estimated accurately. A full measurement was performed in 2002 with gamma thermometers taken in all 12 radial points at one axial elevation, 2 in-core neutron detectors, and one core exit thermocouple. The purpose of the present paper is to report on these measurements. It was shown that with the suggested noise estimator, based on the core average temperature fluctuations, the correct value of the MTC was obtained, by comparison to SIMULATE calculations. It was seen that using only one in-core gamma thermometer the estimated value of the MTC was in significant error, and using one single core exit thermocouple yielded a yet larger error. The performance of the new MTC estimator was also investigated in view of some parameters of the evaluation such as the FFT procedure used and the neutronic weight function used in the core averaging of the temperature. Some further improvement of the method is also touched upon.
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| 6. |
- Demaziere, Christophe, 1973, et al.
(författare)
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Development of a method for measuring the MTC by noise analysis and its experimental verification in Ringhals-2
- 2004
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Ingår i: Nuclear Science and Engineering. - 0029-5639 .- 1943-748X. ; 148:1, s. 1-29
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Demaziere, Christophe, 1973, et al.
(författare)
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Development of a method for measuring the MTC by noise analysis and its experimental verification in Ringhals-2
- 2002
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Ingår i: Proc. Int. Mtg. New Frontiers of Nuclear Technology: Reactor Physics, Safety and High-Performance Computing (PHYSOR2002). - 0894486721
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Konferensbidrag (refereegranskat)abstract
- This paper deals with the estimation of the Moderator Temperature Coefficient of reactivity (MTC) by noise analysis. Previous experimental investigations showed that the MTC was systematically underestimated by a factor of two to five compared to its design-predicted value. In these measurements, the MTC was always determined by cross-correlating the neutron noise provided by a single in-core neutron detector with the local temperature noise given by a single core-exit thermocouple located at the top of the same fuel assembly, or of a neighbouring fuel assembly. It is shown in this paper via a noise measurement performed at the Swedish Ringhals-2 Pressurised Water Reactor (PWR) that the moderator temperature noise is radially strongly heterogeneous. Such a non-homogeneous temperature noise is proven theoretically to explain why the MTC was always underestimated in the previous experimental work when only the local temperature was used. A new MTC noise estimator, relying on the core-averaged moderator temperature noise, is thus proposed. This new estimator is demonstrated to provide an accurate MTC evaluation, as long as the radial structure of the moderator temperature noise can be measured. In the case of Ringhals-2, such in-core temperature measurements are carried out by Gamma-Thermometers (GTs), which in the frequency range of interest for the MTC investigation by noise analysis are working as ordinary thermocouples. This method, which is non-intrusive and free of calibration, can therefore be applied to monitor the MTC throughout the cycle.
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| 8. |
- Demaziere, Christophe, 1973, et al.
(författare)
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Estimation of the Moderator Temperature Coefficient (Analysis of an MTC measurement using boron dilution method)
- 2000
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Ingår i: Proc. Int. Topl. Mtg. Nuclear Plant Instrumentation, Controls, and Human-Machine Interface Technologies (NPIC&HMIT 2000).
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Konferensbidrag (refereegranskat)abstract
- The boron dilution method is analyzed, which is widely used for Moderator Temperature Coefficient (MTC) measurement in Pressurized Water Reactors (PWRs). Data were taken from the measurement of the at-power MTC at the PWR Unit 4 of the Ringhals Nuclear Power Plant (Sweden) during fuel cycle 16 at 300 ppm. Detailed calculations were made to estimate all reactivity effects. Calculations were performed with the static code SIMULATE-3, and error limits were also estimated. The analysis showed that the contribution from the Doppler correction was almost negligible, whereas the reactivity correction due to effects other than the Doppler and the boron effects were surprisingly significant. It was found that the uncertainty associated with the boron dilution method could be larger than previously expected.
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| 9. |
- Demaziere, Christophe, 1973, et al.
(författare)
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Evaluation of the boron dilution method for Moderator Temperature Coefficient measurements
- 2002
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 140:1, s. 147-163
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Tidskriftsartikel (refereegranskat)abstract
- A measurement of the at-power moderator temperature coefficient (MTC) at the pressurized water reactor Unit 4 of the Ringhals Nuclear Power Plant (Sweden) during fuel cycle 16 is analyzed. The measurement was performed when the boron concentration decreased under 300 ppm in the reactor coolant system, by using the boron dilution method. Detailed calculations were made to estimate all reactivity effects taking place during such a measurement. These effects can only be accounted for through static core calculations that allow calculating contributions to the reactivity change induced by the moderator temperature change. All the calculations were performed with the Studsvik Scandpower SIMULATE-3 code. Analysis of the measurement showed that the contribution of the Doppler effect (in the fuel) was almost negligible, whereas the reactivity effects due to other than the Doppler fuel coefficient and the boron change were surprisingly significant. It was concluded that due to the experimental inaccuracies, the uncertainty associated with the boron dilution method could be much larger than previously expected. The MTC might then be close to -72 pcm/oC, whereas the main goal of the measurement is to verify that the MTC is larger (less negative) than this threshold. The usefulness of the boron dilution method for MTC measurements can therefore be questioned.
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| 10. |
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