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The potential use of a pulsed neutron source (PNS) to measure reactivity during nuclear fuel loading as a means to prevent core loading errors has been studied at the GUINEVERE facility. This facility couples the deuteron accelerator GENEPI-3C to the fast neutron subcritical reactor VENUS-F at the Belgian Nuclear Research Center SCK·CEN. The 14-MeV neutrons are produced in the reactor core center via T (d , n) 4 H e fusion reactions. PNS experiments were performed in five reactor configurations corresponding to the different loading steps of VENUS-F. The evolution of the neutron flux during these PNS experiments was measured by several 235U fission chambers in various positions in the inner and outer reflector and analyzed using the area-ratio method. The results show that, despite strong spatial effects, a strong correlation between the reactivity values given by the area-ratio method and some reference reactivity values remains throughout the reactor unloading. Monte Carlo simulations were first validated by comparison with the data and then used to investigate the sensitivity of the method to a core loading error. First results show that some loading errors could be experimentally detected using a PNS. [ABSTRACT FROM AUTHOR]

• The reactivity is usually determined by solving the inverse point kinetic equation, which is an integral equation that depends on the nuclear power variation history. • New method to calculate the reactivity through the solution of an ordinary differential equation that does not depend on the nuclear power variation history. • New formulation is accurate and allows the prompt recovery of the reactimeter in case of loss of the nuclear power data acquisition or malfunction of such equipment. The reactivity that represents the percentage departure of a nuclear reactor from its criticality condition is perhaps the most important individual property since it is directly related to the nuclear reactor's safe operation. Control systems are used to limit the rate of increase in reactivity. The development of systems for monitoring the reactivity, from the nuclear power data acquired from the plant's onboard electronics, requires a constant improvement of the nuclear kinetic models. The transient situations that emerge in nuclear reactors can be predicted from the changes in the neutron flux and, therefore, it is possible to make a sufficiently accurate prediction about the consequences of the disturbances relating to the magnitude of the neutron flux, which varies over time, by using the integral parameters that represent the nuclear reactor core. The point kinetic equations relate these parameters and, in this way, allow the transient situations that can occur in a nuclear reactor to be studied. The reactivity is usually determined by solving the inverse point kinetic equation, which is an integral equation that depends on the nuclear power variation history. In this paper, we present a method to calculate the reactivity through the solution of an ordinary differential equation that does not depend on the nuclear power variation history, then allows the prompt recovery of the reactimeter in case of loss of the nuclear power data acquisition or malfunction of such equipment (Zarei, 2022; Ansari, 1991). The presented paper is organized as follows: Section 1 contains the basic concepts of point kinetics equations and the integral formalism for the reactivity calculation. The mathematical formalism that leads to the differential equation for the reactivity is presented in Section 2. The prompt recovery of the reactivity using the proposed method is discussed in Section 3. The results are shown in Section 4 and the conclusion is presented in Section 5. [ABSTRACT FROM AUTHOR]

Highlights • The "current-to flux" method for monitoring ADS subcriticality was successfully tested experimentally. • Spatial effects affecting the reactivity estimation can be corrected with Monte Carlo simulations. • The robustness and precision of the correction technique is demonstrated. Abstract In this article, we evaluate the quality and robustness of a method envisaged for the on-line monitoring of the subcriticality of an ADS, called the "current-to flux" (CTF) method. For this evaluation, we performed a dedicated experiment at the GUINEVERE facility. It is hosted at the SCK-CEN and consists of the subcritical VENUS-F reactor coupled to a continuous external neutron source provided by the GENEPI-3C accelerator. During this experiment, the reactor control rods were moved in various patterns, and the subsequent dynamical evolutions of the reactor reactivity were monitored using nine fission chambers (FCs). The space-energy effects that bias the reactivity values are corrected using a procedure based on simulations computed with the Monte Carlo neutron transport code MCNP. We investigate the precision of this correction procedure by comparison with a reactivity value extracted with the beam interruption technique and we demonstrate its insensitivity to the simplifications made on the VENUS-F reactor modeling and to a simulation key parameter such as the boron carbide density filling the control rods. [ABSTRACT FROM AUTHOR]

• One of the most frequently methods used for the continuous calculation of reactivity relies on the classic formulation of point kinetics. • New formulation for inverse point kinetics that produces a non-linear differential equation for the calculation of real-time reactivity. • New formulation is accurate and allowing the recovery of the reactivity calculation at any time without the loss of precision, after some unexpected interruption of a reactimeter, making power history unnecessary. This paper presents a new formulation for inverse point kinetics that produces a non-linear differential equation for the calculation of real-time reactivity, without the need of the nuclear power history. A non-linear differential equation (NLDE) results from a process of integration by parts of an existing integral in the classic inverse point kinetics equation and from the use of the prompt-jump approximation. The use of a NLDE has been shown to yield a significant gain in relation to the classic methods found in the literature, as the use of the nuclear power history became unnecessary, allowing the recovery of the reactivity calculation at any point in time without the loss of precision, after some unexpected interruption of a reactimeter. Apart from this, the formulation proposed favored a sampling of the data on nuclear power with a minimum 1-second time interval, to allow the calculation of reactivity in real time. [ABSTRACT FROM AUTHOR]

A recently developed method for the continuous reactivity monitoring in nuclear reactors and in subcritical source-driven systems is applied for the interpretation of flux measurements carried out in the KUCA facility. The scope of the work is to validate the method using real experimental data. The method is based on general mathematical properties of the differential equations constituting the point kinetic model. Several pulsed experiments performed in different system configurations and using different source target materials are analysed. The results are compared with the classic area ratio method. A good agreement is obtained when the space-energy transient following the source shut-down dies out and when the system sets on a point-like evolution. The results prove the suitability of the proposed method for application to the reactivity monitoring of source-driven systems. [ABSTRACT FROM AUTHOR]

Abstract: The development of a reactivity monitoring system for subcritical reactors is a major task prior to industrial scale accelerator driven system (ADS) construction. Within the 6th European Framework Program, the IP-EUROTRANS project has performed a series of experiments at the Yalina-Booster subcritical assembly located at the Joint Institute for Power and Nuclear Research (JIPNR) of the National Academy of Sciences of Belarus, using a continuous (D, T) (fusion) neutron source in pulsed and continuous mode with short interruptions (beam trips). In this paper, the implementation and results of three different monitoring techniques intended to operate with continuous neutron sources will be presented, namely the source-jerk technique, the prompt decay constant technique and the current-to-flux technique. The results will be compared with the values of the reactivity obtained using the pulsed source in PNS experiments, discussed in detail in another paper. [Copyright &y& Elsevier]

Abstract: The prompt decay constant method and the area-ratio (Sjöstrand) method constitute the reference techniques for measuring the reactivity of a subcritical system using Pulsed Neutron Source experiments (PNS). However, different experiments have shown that in many cases it is necessary to apply corrections to the experimental results in order to take into account spectral and spatial effects. In these cases, the approach usually followed is to develop different specific correction procedures for each method. In this work we discuss the validity of prompt decay constant method and the area-ratio method in the Yalina-Booster subcritical assembly and propose a general correction procedure based on Monte Carlo simulations. [Copyright &y& Elsevier]

An air monitoring program is in place at a wafer fab to characterize outdoor air quality and its potential impact on manufacturing processes. Airborne molecular contamination (AMC), and specifically acid contamination, was of particular concern as the facility incorporated 90-nanometer (nm) manufacturing technology. Impinger ionic analysis, passive and real-time reactivity monitoring, and litmus paper hue readings were among the techniques used to assess air quality. Historical data for each monitoring technique was evaluated and compared to determine the applicability of each monitoring technique for these purposes. Data from this monitoring program also offered an opportunity to evaluate the performance of chemical filters installed in makeup air handling units for their ability to remove AMC. This study presents the results of air monitoring, detailing outdoor air quality and how that air quality compares to established specifications; comparison of different monitoring techniques used in the study; performance of installed chemical filter systems; recommendations for improving acid contamination control and evaluation of selected options; and recommendations for overall AMC monitoring and control programs. [ABSTRACT FROM AUTHOR]

Abstract: In the framework of nuclear waste management, highly radiotoxic long-lived fission products and minor actinides are planned to be transmuted in a sub-critical reactor coupled with an intense external neutron source. The latter source would be created by a high-energy proton beam hitting a high atomic number target. Such a new system, termed an accelerator-driven system (ADS), requires on-line and robust reactivity monitoring. The ratio between the beam current delivered by the accelerator and the reactor power level, or core neutron flux, is the basis of one method which could give access to a core reactivity change. In order to test reactivity measurement technique, some experimental programs use 14-MeV neutrons originating from the interaction of a deuteron beam with a tritium target as an external neutron source. In this case, the target tritium consumption over time precludes use of the beam current for reactivity monitoring and the external neutron source intensity must be monitored directly. A range telescope has been developed for this purpose, consisting of the assembly of a hydrogenous neutron converter and three silicon stages where the recoiling protons are detected. In this article, the performances of such a telescope are presented and compared to Monte-Carlo simulations. [Copyright &y& Elsevier]

Abstract: In the context of the world energy demand growing and of greenhouse effect concern, new nuclear power options are extensively studied, especially systems dedicated to high activity waste incineration. It is the case of fast accelerator driven subcritical systems which are the subject of several projects among which the recently completed MUSE programme. From the coupling of a fast subcritical mock-up to a pulsed neutron source, various methods leading to the measurement of the reactivity level and kinetic parameters, which are of prime interest for safety, were investigated. An analysis of pulsed neutron source time spectra taking into account the full distribution of the time intervals between two consecutive fission events – the k p method – was developed and is recalled in this paper. Complete results obtained during the MUSE experiment with this method are given and compared to reference measurements as well as to PNS measurement analysis like exponential fitting or area methods. The quality of the results led to the investigation of the applicability of the method in the case of a continuous source interruption and then in the case of a power ADS. In both cases, on the basis of simulations, no obstacles are found to get the prompt multiplication factor from this method. The aim of this paper is to give a complete overview of the k p method applications and limits. [Copyright &y& Elsevier]

• This paper presents a fast online procedure of background current elimination. • The test results show the superior performance under the actual measurement noise level. • The relative deviation between the result and the theoretical value is within 10%. The Dynamic Rod Worth Measurement (DRWM) is a fast and accurate method for measuring the value of control rods. During the process of DRWM, the minimum value of the detector current will reach the order of 10-11A. At this time, the impact of the gamma background current on the rod worth estimation is so big that the results of the reactivity calculation will deviate significantly from its true value. This paper presents a fast online procedure of background current elimination, with the verification results of the algorithm from the actual measured data of Tianwan Nuclear Power Plant 1# unit. The test results show that the algorithm displays the superior performance under the actual measurement noise level. The relative deviation between the result and the theoretical value is within 10%. [ABSTRACT FROM AUTHOR]