Reactivity Meter Research Articles

Estimating Temperature Reactivity Coefficients by Experimental Procedures Combined with Isothermal Temperature Coefficient Measurements and Dynamic Identification

A method to evaluate the moderator temperature coefficient (MTC) and the Doppler coefficient through experimental procedures performed during reactor physics tests of PWR power plants is proposed. This method combines isothermal temperature coefficient (ITC) measurement experiments and reactor power transient experiments at low power conditions for dynamic identification. In the dynamic identification, either one of temperature coefficients can be determined in such a way that frequency response characteristics of the reactivity change observed by a digital reactivity meter is reproduced from measured data of neutron count rate and the average coolant temperature. The other unknown coefficient can also be determined by subtracting the coefficient obtained from the dynamic identification from ITC. As the proposed method can directly estimate the Doppler coefficient, the applicability of the conventional core design codes to predict the Doppler coefficient can be verified for new types of fuels such as mixed oxide fuels. The digital simulation study was carried out to show the feasibility of the proposed method. The numerical analysis showed that the MTC and the Doppler coefficient can be estimated accurately and even if there are uncertainties in the parameters of the reactor kinetics model, the accuracies of the estimated values are not seriously impaired.

Feasibility of Continuous Sub-criticality Monitoring using a Digital Reactivity Meter to Overcome the Criticality Accident

In the foregoing studies, it has been proved that the digital reactivity meter can be used for not only sub-criticality measurement but also continuous sub-criticality monitoring during criticality approach. Based on these studies, we investigated the applicability of a digital reactivity meter for continuous sub-criticality monitoring to intervene before a criticality accident occurs that is similar to the Tokai-mura accident in 1999. In our mock up numerical simulation, there are three calculation steps that are (1) reactivity transient calculation, (2) neutron transient calculation and (3) sub-criticality monitoring calculation. The reactivity transient was calculated using two-group diffusion nuclear constants and the neutron transient was calculated using the one-point reactor kinetics. In sub-criticality monitoring, three algorithms for reactivity evaluation were compared. We have investigated which algorithm is the most suitable to use in an actual system. In practice, we also advise use of some filtering algorithm to reduce the neutron transient fluctuation and a warning reactivity to know estimated sub-criticality as earlier as possible.

Some Technical Issues on Continuous Subcriticality Monitoring by a Digital Reactivity Meter during Criticality Approach

It has been proposed that a digital reactivity meter can be used for not only subcriticality measurement but also continuous subcriticality monitoring during criticality approach. In this study, a mock up numerical simulation was carried out to investigate some technical issues that still exist. These are sampling interval, time lag of estimated subcriticality due to filtering effect as well as due to the error contribution to the initial reference subcriticality and the way to avoid time lag of estimated subcriticality from safety point of view. It was found that there is influence of sampling interval on the reactivity fluctuation. Filter can cause time lag of estimated subcriticality when a large filter time constant is used. In subcriticality monitoring, the error contribution to the initial reference subcriticality obtained by some design calculation should be investigated to detect accurately an unexpected criticality as earlier as possible. It was known that the negative error contribution to the initial reference subcriticality should be used from safety point of view. We have analytically obtained the relation between the error of the initial reference subcriticality, ramp rate of reactivity addition, warning subcriticality and the margin of the time interval for the counter action.

Subcriticality Measurement of Pressurized Water Reactors during Criticality Approach using a Digital Reactivity Meter

A mockup experiment of subcriticality measurement with a digital reactivity meter during criticality approach in a PWR was carried out using plant data. There are some difficulties in the direct application of a digital reactivity meter to the subcriticality measurement. Some treatments were needed in using the count rate of Source Range (SR) detector as input signal to the digital reactivity meter. To overcome these difficulties, we proposed a digital reactivity meter combined with a methodology of the modified Neutron Source Multiplication (NSM) method with the fundamental mode extraction. In this study, the neutron source strength was defined as a constant in terms of a known initial stable subcriticality and the neutron signal from a steady state condition. Even though initial stable subcriticality might be contained some errors, the errors of estimated subcriticalities do not depend on the error contribution of initial stable subcriticality when we normalize the estimated subcriticalities with exactly known reference subcriticality. It was proved that the digital reactivity meter could be used not only for the subcriticality measurement or control rod worth measurement but also for the continuous monitoring of the subcriticality during criticality approach.

Suberiticality Measurement of Pressurized Water Reactors during Criticality Approach using a Digital Reactivity Meter

A mockup experiment of subcriticality measurement with a digital reactivity meter during criticality approach in a PWR was carried out using plant data. There are some difficulties in the direct application of a digital reactivity meter to the subcriticality measurement. Some treatments were needed in using the count rate of Source Range (SR) detector as input signal to the digital reactivity meter. To overcome these difficulties, we proposed a digital reactivity meter combined with a methodology of the modified Neutron Source Multiplication (NSM) method with the fundamental mode extraction. In this study, the neutron source strength was defined as a constant in terms of a known initial stable subcriticality and the neutron signal from a steady state condition. Even though initial stable subcriticality might be contained some errors, the errors of estimated subcriticalities do not depend on the error contribution of initial stable subcriticality when we normalize the estimated subcriticalities with exactly known reference subcriticality. It was proved that the digital reactivity meter could be used not only for the subcriticality measurement or control rod worth measurement but also for the continuous monitoring of the subcriticality during criticality approach.

Some Technical Issues on Continuous Subcriticality Monitoring by a Digital Reactivity Meter during Criticality Approach

Some Technical Issues on Continuous Subcriticality Monitoring by a Digital Reactivity Meter during Criticality Approach

Subcriticality Monitoring with a Digital Reactivity Meter

Feasibility of subcriticality monitoring with a digital reactivity meter was experimentally investigated using a sub-critical assembly. In the experiment, neutron detectors were placed in the reflector region where the neutron flux multiplied by the difference of the multiplication factor from unity is almost constant. The significant fluctuation of the neutron signal was filtered with a smoothing and a low-path filter of first order delay. In the subcritical system above with a constant neutron source, it was confirmed through the experiment that a digital reactivity meter with noise filtering module could give real time subcriticality when the detector was placed at appropriate positions. Based on the experiment, we have proved that the reactivity meter can be used for monitoring the subcriticality on a real time basis.

Feasibility Study on Subcriticality Monitoring with a Digital Reactivity Meter

A conventional digital reactivity meter is based on a simple principle to solve inverse point reactor kinetics equations and it can monitor reactivity continuously on a real time basis. Then, feasibility was studied for a conventional digital reactivity meter to be used as a subcriticality monitor. It was necessary to overcome some problems; for example, the applicability of the point reactor kinetics equations must be verified for the system where neutron distribution is dependent on the subcriticality. We showed that the problems can be solved or can be taken into account. The subcriticality calculated by the reactivity meter might not be accurate for the measurement of the actual value of the subcriticality itself, however, it is accurate enough for the purpose of subcriticality monitoring. We believe that the monitoring on a real time basis is more important for subcriticality monitoring than the accuracy of the value of the monitored subcriticality. Based on the study, we proposed that a digital reactivity meter can be used as a subcriticality monitor.

Feasibility Study on Subcriticality Monitoring with a Digital Reactivity Meter.

A conventional digital reactivity meter is based on a simple principle to solve inverse point reactor kinetics equations and it can monitor reactivity continuously on a real time basis. Then, feasibility was studied for a conventional digital reactivity meter to be used as a subcriticality monitor. It was necessary to overcome some problems; for example, the applicability of the point reactor kinetics equations must be verified for the system where neutron distribution is dependent on the subcriticality. We showed that the problems can be solved or can be taken into account. The subcriticality calculated by the reactivity meter might not be accurate for the measurement of the actual value of the subcriticality itself, however, it is accurate enough for the purpose of subcriticality monitoring. We believe that the monitoring on a real time basis is more important for subcriticality monitoring than the accuracy of the value of the monitored subcriticality. Based on the study, we proposed that a digital reactivity meter can be used as a subcriticality monitor.

Reactive power and energy measurement in the frequency domain using random pulse arithmetic

There is not a universally recognised definition of reactive power which can be applied under non-sinusoidal conditions. In general, a 90/spl deg/ voltage shift is used by reactive meters. A new electronic shifter based on stochastic signal processing is proposed taht allows for simple and cost-effective digital implementation of a reactive power and energy meter. The proposed stochastic arithmetic is able to solve the algebraic equations involved in the calculations of reactive power and energy in the frequency-domain approach.

Errors in the Estimated Neutron Source and Gamma Source Strengths for Reactivity Measurement and the Influence on the Measured Reactivity

A new method has been proposed to estimate both neutron source and gamma source strengths to be taken into account for reactivity measurement using a digital reactivity meter. The method is based on a transient analysis with addition of known reactivity, p. In the analysis reactivity (pm) is calculated using the neutron detector signal (N) including both the unknown strengths of neutron source (S) and gamma source (γ). It is used to calculate the value (pm-p)N/l, which is equal to S-7gamma;p/l, a constant, where l is the neutron life time. With two values of known reactivity, both S and γ can be estimated in a short time. The key parameter of the method is the known reactivity. When the values of the known reactivity have some errors, the estimated S and γ have errors, respectively. The errors influence the measured reactivity which is corrected by the estimated S and γ From this point of view we studied on the estimation errors of S and γ due to the given reactivity error. And the afterwards reactivity measurement error caused by the estimation errors is also discussed. It is shown that the measured reactivity error caused by the erroneous correction can be quite larger than the error in the correction when the neutron flux level becomes low.

Analysis on Calculated Reactivity Error Caused by Inaccuracy of Sampling Intervals

Recently personal computers are widely used in various instrumentation systems. However some operating system does not have enough accuracy for controlling timer. When there are deviations between the absolute time of the natural phenomena and the time controlled by the operating system, error might be introduced. In a digital reactivity meter, inverse kinetic equations are solved for reactivity. When the sampling interval deviates from the intended interval, the calculated reactivity includes some errors. From this point of view we evaluated errors introduced in the reactivity calculation by a digital reactivity meter. It is found that the error characteristics are different with the added reactivity shape such as constant, sinusoidal, saw tooth shape or ramp. In this paper the results of quantitative error evaluations and some counter measures are discussed.

Analysis on Calculated Reactivity Error Caused by Inaccuracy of Sampling Intervals.

Recently personal computers are widely used in various instrumentation systems. However some operating system does not have enough accuracy for controlling timer. When there are deviations between the absolute time of the natural phenomena and the time controlled by the operating system, error might be introduced. In a digital reactivity meter, inverse kinetic equations are solved for reactivity. When the sampling interval deviates from the intended interval, the calculated reactivity includes some errors. From this point of view we evaluated errors introduced in the reactivity calculation by a digital reactivity meter. It is found that the error characteristics are different with the added reactivity shape such as constant, sinusoidal, saw tooth shape or ramp. In this paper the results of quantitative error evaluations and some counter measures are discussed.

Digital realization of frequency insensitive phase shifter for reactive Var-Hour meters

The paper describes a digital realization of a circuit for an additional phase shift of /spl pi//2 between two input signals, with a constant amplification nondependent on frequency. The circuit is intended for measuring the reactive power and energy of electric networks. The solution is based on a coupled digital integrator and differentiator and the microcontroller application. The results of simulation and experiments show that the solution is applicable in standard (classes 2 and 3) and precise reactive meters (class 0.2).

Errors in the Estimated Neutron Source and Gamma Source Strengths for Reactivity Measurement and the Influence on the Measured Reactivity.

A new method has been proposed to estimate both neutron source and gamma source strengths to be taken into account for reactivity measurement using a digital reactivity meter. The method is based on a transient analysis with addition of known reactivity, p. In the analysis reactivity (pm) is calculated using the neutron detector signal (N) including both the unknown strengths of neutron source (S) and gamma source (γ). It is used to calculate the value (pm-p)N/l, which is equal to S-7gamma;p/l, a constant, where l is the neutron life time. With two values of known reactivity, both S and γ can be estimated in a short time. The key parameter of the method is the known reactivity. When the values of the known reactivity have some errors, the estimated S and γ have errors, respectively. The errors influence the measured reactivity which is corrected by the estimated S and γ From this point of view we studied on the estimation errors of S and γ due to the given reactivity error. And the afterwards reactivity measurement error caused by the estimation errors is also discussed. It is shown that the measured reactivity error caused by the erroneous correction can be quite larger than the error in the correction when the neutron flux level becomes low.

A high accuracy reactive power and reactive energy meter

A high accuracy instrument for reactive power and reactive energy measurements in a single phase power network is described in the paper. The measurement principle is in accordance with IEC recommendation. Test results show that in the range of 1 to 100% of the input current the accuracy of the meter is better than 100 ppm for frequency variations of ±5% around the nominal frequency. The instrument could be used as a single-phase reactive power and reactive energy standard. A three phase version of the instrument could be used as a standard or as a revenue meter because of its high accuracy, simple design and anticipated low cost.

Ｈ∞最適推定器による反応度計と逆動特性による反応度計の比較検討

Reactivity estimation using the neutron flux signal has been carried out mainly by two methods, inverse kinetics equation method and Kalman filtering method. Recently a new estimation method has been proposed. The method is based on the H∞ optimal estimation theory and can improve rather slow time response of the Kalman filtering method.The previous studies on these methods, however, have been reported independently. Hence, the information required to select the most suitable method seems to be insufficient, especially for those who plan to design a new reactivity meter. From this point of view, we carried out a comparison study on the important characteristics for reactivity measurement, noise filtering and time response, between H∞ estimator and the inverse kinetics equation method derived by neglecting the time derivative of neutron flux.The comparison results show that the two types of reactivity meters have similar characteristics. Also some findings are shown for the tunig guidance of a parameter(γ) which determines the characteristics of H∞ estimator to be designed.

反応度測定のための中性子源ならびにガンマ線強度の評価法

A new method has been studied for estimating both neutron source and gamma source strengths to be taken into account for reactivity measurement using a digital reactivity meter. Normally such correction is not necessary because appropriate neutron flux level is selected for the measurements. However when the neutron flux level is to be lowered than the appropriate level the corrections of neutron source and gamma source must be made. It is shown from the study that the value(ρm-ρ)N/l equals to S-γρ/l, a constant, where ρm is the reactivity calculated by the reactivity meter without the corrections, ρ is a known reactivity, N is the sum of neutron and gamma signals, l is neutron life time, S is the neutron source and γ is gamma source. Based on this fact S and γ can be estimated when two different reactivities are given and the corresponding constants are known. Theoretically this constant can be obtained as soon as the reactivity is given so that it is not required to wait the transient effect to die out. Thus this method can estimate both neutron source and gamma source in a very short time.

A survey of North American electric utility concerns regarding nonsinusoidal waveforms

50 utilities in the United States and Canada responded to a questionnaire survey regarding concerns about nonsinusoidal waveforms in the electric distribution network. Responses regarding instrumentation, apparent and reactive power definitions, meter errors, rates, and trends are presented and discussed.

Real Time Measurement of Large Negative Reactivities by a Modified Digital Reactivity Meter

An experimental study was carried out to measure large negative reactivities such as -10%δk/k using a modified digital reactivity meter. Conventionally such large negative reactivities have been measured by the multi-channel scaler (MCS) method. In the present study both of the methods were used and the two results agreed quite well. Thus our new method of utilizing a digital reactivity meter for the measurement has been proved to be useful.