Control Rod Worth Measurements Research Articles

A practical subcritical rod worth measurement technique based on the improved neutron source multiplication method

The control rod worth is a key safety parameter required to be measured in commercial pressurized water reactors (PWRs). Conventionally, the control rod worth is measured after reaching the critical state, which occupies the considerable time in the zero-power physics test. In this study, an efficient control-rod worth measurement technique has been proposed based on the improved neutron-source multiplication method, which can be implemented with the source-range detector count rates in the subcritical states. Moreover, the noise reduction technique has been adopted to smooth the large fluctuation existing in the original signals. In order to verify the engineering performance of the proposed measurement technique, the measured source-range detector count rates during the rod withdrawal process before reaching critical state in a CNP1000 reactor have been employed. It demonstrated that almost all estimated results of control rod worth satisfy the engineering acceptance criteria, except one control rod with the relative difference over 10 %, which indicates the capability of the proposed method in estimating control rod worth.

Sensitivity of a control rod worth estimate to neutron detector position by time-dependent Monte Carlo simulations of the rod drop experiment

The control rod worth sensitivity to the neutron detector position in the rod drop experiment is studied by the time-dependent Monte Carlo (TDMC) neutron transport calculations for AGN-201K educational reactor and the Kyoto University Critical Assembly. The TDMC simulations of the rod drop experiments are conducted by the Seoul National University Monte Carlo (MC) code, McCARD, yielding time-dependent neutron densities at detector positions. The detector-position-dependent results of the total control rod worth calculated by the extrapolation, the integral counting, and the inverse methods are compared with the numerical reference using the MC eigenvalue calculations and the experimental results. From these comparisons, it is observed that the total control rod worth can be estimated with a considerable difference depending on the detector position through the rod drop experiment. The proposed TDMC simulation of the rod drop experiment can be applied for searching a better detector position or quantifying a bias for the control rod worth measurement.

Multi-parameter nuclear data adjustment for sodium fast reactor

This paper studies the application of nuclear data adjustment method in the physics calculation of sodium cooled fast reactor. Based on Bayesian theory, the multi-parameter nuclear data adjustment method is derived, and then the experimental screening rules are given. The verification based on 47 candidate experiments, including the critical measurement experiments, control rod worth measurement experiments and sodium void reactivity measurement experiments of ZPPR-9、ZPPR-10A、ZPPR-10B and ZPPR-10C zero-power experimental facilities, is then carried out. The numerical results show that the adjustment based only on keff has obvious limitations, it can only reduce the calculation uncertainty of keff, but the uncertainties of other physical parameters cannot be improved effectively. However, the multi-parameter nuclear data adjustment method effectively reduces the calculation uncertainties and errors of different physical parameters besides keff. In the meantime, the screening rules for experimental data are analyzed to avoid the improper adjustment of nuclear data.

NEUTRONIC MODELLING OF THE FFTF CONTROL ROD WORTH MEASUREMENTS WITH DIFFUSION CODES

This paper presents an assessment of three deterministic core simulators with the focus on the neutronic performance in steady-state calculations of small Sodium cooled Fast Reactor cores. The selected codes are DYN3D, PARCS and the novel multi-physics solver GeN-Foam. By using these codes, the multi-group diffusion solutions are obtained for the selected twenty control rod worth measurements performed during the isothermal physics tests of the Fast Flux Test Facility (FFTF). The identical set of homogenized few-group cross sections applied in the calculations is generated with the Serpent Monte Carlo code. The numerical results are compared with each other as well as with the measured values. The obtained numerical results, such as the multiplication factors and control rod worth values, are in good agreement as compared to the experimental data. Furthermore, a comparison of the radial power distributions is presented between DYN3D, PARCS and GeN-Foam. Ultimately, the power distributions are compared to the full core Serpent solution, demonstrating an adequate performance of the selected deterministic tools. In overall, this study presents a verification and validation of the neutronic solvers applied by DYN3D, PARCS and GeN-Foam to steady-state calculations of SFR cores.

Transient Reactor Test (TREAT) Facility Restart Heat Balance Calibration and Rod Worth Measurements

The Transient Reactor Test Facility has been restarted after more than 20 years in a safe standby condition. The plan to bring the reactor back into operation included a typical core characterization that was historically performed every time the core was reconfigured for a new experiment campaign. The core characterization included determining initial critical position of the control rods, a heat balance run for calibration of the nuclear instruments to enable the indication of reactor power, control rod worth measurements, and a series of three temperature-limited transients increasing in the amount of reactivity inserted as a step for the interpolation of set points for the reactor trip system and reactivity insertion limits. The heat balance and control rod worth measurements are discussed in this paper. After critical control rod position was determined, a heat balance operation was used to position the nuclear instruments for correct power indication. This was followed by control rod differential worth measurements to generate the control rod worth curves used by the automatic reactor control system for control of the reactor during transient operations. These restart evolutions are summarized here, and the results are compared to the historic measurements.

Application of dynamic rod worth measurement in a VVER

Abstract Control rod worth measurement is very important in physical experiments before every cycle of nuclear plants. The traditional method is boron dilution method. DRWM (for Dynamic Rod Worth Measurement) (Chao et al., 2000) is an advanced method developed by Westinghouse and Electric Power Research Center. The main idea is to record the current signals from reactors, which is converted as reactivity by using inverse dynamic method. Besides, corrections are needed to get a good result. In China, an advanced reactivity meter made by China Institute of Atomic Energy is applied in a VVER. VVER is the abbreviation of Vodo-Vodyanoi Energetichesky Reactor in Russian. It is one kind of PWR using hexagonal fuel assembly developed by Russia. This paper gives the application of dynamic rod worth measurement in a VVER in Jiangsu Nuclear Plants. The correction coefficient calculations, experimental details and results would be introduced.

Rod insertion method analysis – A methodology update and comparison to boron dilution method

The rod insertion method for control rod worth measurement is explained and past as well as recent developments are outlined. The original methodology is updated with a more consistent use of the flux redistribution correction, conversion from dynamic to static reactivity and a new procedure to account for the so-called reactivity overshoot. As an example, the procedure is applied to real measured data from Krško NPP. Resulting integral and differential worth curves are compared with reference measurements by the boron dilution method, where a previously unattainable match is observed. Additional research is presented in order to assess the remaining small deviations. Besides other advantages, the rod insertion method is demonstrated to produce results that are in excellent agreement with those of boron dilution method and can therefore be used as replacement.

Evaluation of Neutron Radiography Reactor LEU-Core Start-Up Measurements

Benchmark models were developed to evaluate the cold-critical start-up measurements performed during the fresh core reload of the neutron radiography (NRAD) reactor with low-enriched uranium fuel. Experiments include criticality, control rod worth measurements, shutdown margin, and excess reactivity for four core loadings with 56, 60, 62, and 64 fuel elements. The worths of four graphite reflector block assemblies and an empty dry tube used for experiment irradiations were also measured and evaluated for the 60-fuel-element core configuration. Dominant uncertainties in the experimental keff come from uncertainties in the manganese content and impurities in the stainless steel fuel cladding as well as the 236U and erbium poison content in the fuel matrix. Calculations with MCNP5 (Monte Carlo N-Particle version 5-1.60) and ENDF/B-VII.0 neutron nuclear data are ˜1.4% (9σ) greater than the benchmark model eigenvalues, which is commonly seen in Monte Carlo simulations of other TRIGA (Training, Research, Isotopes, General Atomics) reactors. Simulations of the worth measurements are within the 2σ uncertainty for most of the benchmark experiment worth values. The complete benchmark evaluation details are available in the 2014 edition of the International Handbook of Evaluated Reactor Physics Benchmark Experiments.

Measurements of control rod worth by modified inverse kinetic method

Results of control rod worth measurements on the Astra critical assembly at the Russian Research Centre Kurchatov Institute are presented. The measurements were carried out by the modified inverse kinetics method, which is based on the use of experimental information about the variation of neutron detector readings only after introducing a reactivity perturbation. Calculated corrections are not required. The results of measurements do not depend on the neutron detector position.

Feasibility Study for Evaluation of Control Rod Worth in Pressurized Water Reactors using Neutron Count Rate during a Control Rod Drop Testing

Applicability of the modified Neutron Source Multiplication (NSM) method with extraction of the fundamental mode to subcriticality measurement has been proposed. Following the feasibility verification in the previous study based on numerical analyses, its applicability has been proven in a more realistic situation; in a withdrawal sequence of control rod banks during the PWR startup. Subcriticalities with various control rod insertion configurations were estimated based on the modified NSM method. The subcriticality could be evaluated with a good accuracy even with the mockup experiment where any special treatments for accurate measurement were not taken into account and furthermore the insensitivity of measured signals by reactivity changes and their large fluctuations were seen. Based on this fact, we further investigated a feasibility to use neutron count rate data obtained during the control rod drop testing, which is carried out before the reactor physics tests at hot zero power condition. When it is proven that these data could be used for the estimation of each control rod worth, the following reactor physics tests could be performed with the advanced knowledge of each control rod worth and procedures for detailed control rod worth measurement could be simplified or eliminated from the reactor physics tests.

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.

Subcriticality Measurement of Pressurized Water Reactors by the Modified Neutron Source Multiplication Method

Applicability of the modified Neutron Source Multiplication (NSM) method with extraction of the fundamental mode to subcriticality measurement has been investigated. This concept can be applied to the control rod worth measurement that is performed during reactor physics tests at periodical inspection of commercial PWRs. Following the feasibility verification in the previous study based on numerical analyses, its applicability has been proven in a more realistic situation; Regarding a withdrawal sequence of control rod banks during the PWR startup as a mockup experiment, subcriticalities with various control rod insertion patterns were estimated based on the modified NSM method. The subcriticality could be evaluated with good accuracy even with the mockup experiment where any special treatments for accurate measurement were not taken into account and furthermore the insensitivity of measuring signals by reactivity changes and their large fluctuations were seen. Some vital treatments for accurate estimation were identified: The reference subcritical state must be as closer to zero as possible. It is necessary to wait long enough for the delayed neutron effect to attenuate after a reactivity change by control rod bank withdrawal. Gamma-ray contamination contained in the detector signals should be corrected.

Subcriticality Measurement of Pressurized Water Reactors by the Modified Neutron Source Multiplication Method

Applicability of the modified Neutron Source Multiplication (NSM) method with extraction of the fundamental mode to subcriticality measurement has been investigated. This concept can be applied to the control rod worth measurement that is performed during reactor physics tests at periodical inspection of commercial PWRs. Following the feasibility verification in the previous study based on numerical analyses, its applicability has been proven in a more realistic situation; Regarding a withdrawal sequence of control rod banks during the PWR startup as a mockup experiment, subcriticalities with various control rod insertion patterns were estimated based on the modified NSM method. The subcriticality could be evaluated with good accuracy even with the mockup experiment where any special treatments for accurate measurement were not taken into account and furthermore the insensitivity of measuring signals by reactivity changes and their large fluctuations were seen. Some vital treatments for accurate estimatio...

96/01535 Application of the rod-insertion method for control rod worth measurements in research reactors

96/01535 Application of the rod-insertion method for control rod worth measurements in research reactors

Application of the rod-insertion method for control rod worth measurements in research reactors / Bestimmung des Reaktivitätswertes von Absorberstäben in Forschungsreaktoren mittels der Stabeinfahr-Methode.

Details of the rod-insertion method as applied for control rod worth measurements in research reactors are presented. Sources of errors and corrections are discussed, particularly the effects of detector position, control rod interference, and flux redistribution. The analysis is supported by calculations to explain the physical phenomena involved. The method is applied to two TRIGA reactors, which differ significantly in the characteristics of their control rods. The results show that the rod-insertion method is very quick and simple to apply, and sufficiently accurate for practical purposes. The conclusions related to control rod interference and flux redistribution effects are also applicable to other methods for control rod worth measurements and to the calibration of the nuclear detectors.

TRIGA Mark II Benchmark Experiment, Part II: Pulse Operation

Experimental results of pulse parameters and control rod worth measurements at TRIGA Mark II reactor in Ljubljana are presented. The measurements were performed with a completely fresh, uniform, an...

Accuracy of the Modal-Local Method for Reactivity Determination

Control rod worth measurements through the inverse kinetics equation depend on accurate determination of the amplitude function from detector signals. The modal-local method introduced in a previou...

Use of Zero Power Plutonium Reactor Measurements as a Support of Criticality Prediction for the SNR-300

Evaluations of criticality measurements performed in various SNEAK and Zero Power Plutonium Reactor (ZPPR) cores are compared. The best available methods of calculations (including transport theory) are used. The ZPPR results support well the trend indicated by the SNEAK evaluations for clean cores and for cores with followers; for cores with absorbers partially inserted, the agreement is only rough. Evaluations of control rod worth measurements are therefore also compared, using the routine method of calculation for SNR-300 (diffusion theory). The control rod worths are largely underestimated in SNEAK (C/E = 0.89), but only slightly underestimated in the ZPPR (C/E = 0.97). The difference in the nature of core fuel (uranium in SNEAK, plutonium in the ZPPR) could be at the origin of this discrepancy.