Implementing a test facility in reduced scale for analysis of boron dispersion in a pressurizer of an integral compact and modular reactor
Introduction
Small Modular Reactors (SMRs) are projected with modular technology, reducing expenditures on series production and allowing the fabrication in a short period of time. SMRs designs include a range of technologies, some of them are variants of the Generation III systems (Carelli et al., 2010). Many small modular reactor designs with distinct characteristics have been proposed or are being developed. These designs vary in their power output, physical size, fuel type, refueling frequency, siting options, and status of development (Carelli et al., 2010, Small Modular Reactors, 2015). Some of the advanced SMRs, as NuScale, mPower and W-SMR, share a common set of design principles like the incorporation of the primary system components in only one single vessel, the consequent increase of the primary reactor vessel, the promotion of more effective heat removal, the increase of the pressurizer volume, the relocation of components in the vessel, that facilitate the core cooling by natural convection. These features, also adopted by IRIS reactor, use the passive safety systems, guaranteeing the optimization of the installations’ safety and its better operation and on the global economy aspects (Ferri et al., 2012).
Generally, the pressurizer is located at the reactor vessel top in an iPWR. This configuration involves changes on the techniques such as the fabrication of a larger system, without any additional costs (Barroso et al., 2003). Coolant mixing inside the nuclear reactor is the most important inherent safety mechanism against power peaks or overcooling transients (Rohde et al., 2007). Therefore, it is necessary to study the mixing and homogenization of boron in the pressurizer liquid volume as a function of movement mechanisms, which is being considered in the development of an integral modular nuclear reactor.
For the analysis of the mixing process in the pressurizer of a small modular reactor with integrated primary system, an experimental facility was built at the Centro Regional de Ciências Nucleares do Nordeste (CRCN-NE). This facility should allow variation of the various parameters of design and operation so that they can optimize the mechanisms of homogenization. As a contribution to the consolidation of this experimental facility, this work shows the preliminary research results about boron concentration in the surge orifices to simulate one in-surge and one out-surge in a facility, scaled 1:200, that represents one-fourth in volume of the pressurizer.
Section snippets
iPWR pressurizer
The pressurizer geometrical configuration of the small modular reactor iPWR is represented in Fig 1.
The saturated water in pressurizer is separated from the reactor primary sub-cooled water by an internal structure with an “inverted hat shape”. The function of this structure includes: (a) preventing the head closure flange and its seals from being exposed to the temperature difference between the reactor and pressurizer water, thus reducing thermal stresses and maintaining sealing tightness;
The test facility
The test facility built for experimental investigations of boron dispersion in the pressurizer of the iPWR is located at the Northeast Regional Nuclear Sciences Center (CRCN-NE). The main parameters of test facility were determined through the combination of Fractional Scaling Analysis and local scaling (Silva et al., 2011). The construction in reduced scale guarantees the similarity of phenomena with reduction in time and costs.
The general configuration of the test facility is shown
Concentration measurement
The simulation of boron mixing was accomplished by using sodium chloride (NaCl) as the tracer element. To verify the dependence of the electrical conductivity as a function of NaCl concentration, samples were prepared with a concentration varying from 100 to 3000 ppm. The conductivity measurement was determined with the CELTEC conductivity meter, model FA2104 N. The temperature correction is automatic. Before the data acquisition, the conductivity meter was calibrated using a standard solution. A
Boundary conditions of the experiment
Three experiments were conducted to evaluate the potential of the test facility to determine the concentration of the injected tracer element at the inlet/outlet of the test section. The experiments were executed without heating. Thus the valves V-9 and V-10 remained closed, and the heat exchanger (TC) was not used. Initially all pipes were carefully filled with distilled water.
Parameters used in the experiments
The characteristics that defined the execution of experiments, and the core values that have characterized the results are presented in the Table 2.
Experiment 1
The representation of a borating scenario conducted in the experimental setup allowed the identification of the behavior of salt concentration at the inlet and outlet of the test section for a period of 180 min. Fig. 8 shows the results at ST outlet. Each point is the average of three successive readings and the error bars show the experimental standard deviations. The continuous line is the fit of a first order exponential function.
The function that fits the experimental data is shown in Eq. (1)
Conclusion
The project for the test facility aimed to provide relevant data for boron homogenization phenomena in the pressurizer of a compact modular reactor. Three experiments were conducted at the experimental setup, all at room temperature and using only an input and an output of the test section. After the execution of the experimental setup and the experiments, it was possible to prove the feasibility of using the experimental installation, reliably, for values that constitute boration and
Acknowledgments
The authors are grateful for the financial support provided by CRCN/NE (Centro Regional de Ciências Nucleares do Nordeste), CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior), CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), FINEP (Financiadora de Estudos e Projetos) and INCT-RNI (Instituto Nacional de Ciência e Tecnologia – Reatores Nucleares Inovativos).
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