Verification of a real-time interactive transient simulator for Dalat Nuclear Research Reactor

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  1. Nuclear Science and Technology, Vol.10, No. 4 (2020), pp. 08-15 Verification of a real-time interactive transient simulator for Dalat Nuclear Research Reactor Cao Thanh Long*, Truong Hoang Tuan, Huynh Dong Phuong, Nguyen Hoang Nhat Khang, Ho Manh Dung Center for Nuclear Technologies, 217 Nguyen Trai Street, District 1, Ho Chi Minh City *Corresponding author’s email address: (Received 28 October 2020, accepted 17 December 2020) Abstract: A PC-based real-time interactive transient simulator of Dalat Nuclear Research Reactor (DNRR), namely DalatSim, based on the best-estimate thermal-hydraulic code RELAP5/MOD3.3 has been currently building at Center for Nuclear Technologies (CNT). This paper presents the study on developing the physics core, control module, and human-machine interface (HMI) of DalatSim. The nodalization of DNRR used for DalatSim was based on the reported numerical model in the Safety Analysis Report (SAR) in 2012. DalatSim can simulate operational procedures and several hypothetical transient accidents of DNRR. A curve of real operational power of DNRR was used to compare with calculation power results from DalatSim to verify its capability. The verification results are presented and discussed. Keywords: Simulator, Dalat Nuclear Research Reactor, RELAP5/MOD3.3, physics core, human- machine interface. I. INTRODUCTION maneuver, and shutdown [2]. The Korea Atomic Energy Research Institute (KAERI) Nuclear reactor simulation systems play developed a real-time simulation system for an important role in operator training, research High-flux Advanced Neutron Application on safety analysis, thermal-hydraulic, Reactor (HANARO) in Korea and Jordan automatic control, and protection system Research and Training Reactor (JRTR) in design. In addition to full scope simulators Jordan for operator training in 2014 [3]. They describing the entire real systems, basic also studied to construct a web-based nuclear principle simulators have also been designed reactor simulator using the best-estimate and developed for educational purposes. These nuclear system analysis code RELAP5 as the simulators, which can operate on personal core program and LabVIEW for the real-time computers, provide efficient tools for learning interactive interface in 2007 [4]. Moreover, the fundamental physical processes, the basic Dalton Nuclear Institute at the University of operation of complex systems, and the general Manchester, UK provided a simple nuclear operating procedures of various nuclear reactor reactor simulator on their website allowing types [1]. Numerous scientific, educational and students and internet users to access, training organizations in the world have familiarize, and understand nuclear reactor developed basic principle simulators for operation [5]. nuclear research reactor studies. Ricardo Pinto de Carvalho and José Rubens Maiorino built a In Vietnam, there are many activities of simulation system for Brazil's IEA-R1 nuclear learning and utilizing nuclear reactor research reactor in 2006, which allows simulators. These simulators, however, are simulation in real-time of start-up, power mainly for nuclear power plants and supplied ©2020 Vietnam Atomic Energy Society and Vietnam Atomic Energy Institute
  2. CAO THANH LONG et al. from other countries. The applications of the module, and a human-machine interface (HMI) real-time OPR 1000 core simulator and the module. The control module simulates the VVER-1200 nuclear power plant simulator reactor control and protection system of installed at Dalat University and Nuclear DNRR. The HMI module includes graphical Training Center (VINATOM), respectively, are interfaces that help users to interact with such examples. The development of a DalatSim. Besides, an auxiliary “realism” simulation system for DNRR is an essential module is required to prepare and process input task to support the operational training and data for the physics core, retrieve and display educating students from universities. the calculation data from the physics core Furthermore, it also helps to preserve valuable module to the HMI module in real-time, knowledge and experience gained from simulate the actual three monitoring channels research and operating activities on DNRR. of DNRR, etc. The research to build the first real-time The application of Hypertext Transfer transient simulator for DNRR in Vietnam is Protocol (HTTP) [6] was used to exchange being performed at CNT. This simulator is calculation parameters between the physics expected to simulate operational procedures in core and the driver module. The driver module, normal condition and several hypothetical as a client, sends requests for necessary control transient accidents of DNRR. The next section or display parameters to the physics core. The presents the methodology used to develop the physics core, as a server, will return the simulator. The computational capability of the required calculated parameters for further simulator was verified with actual operational simulation performance. power data of DNRR. The verification results The physics core, control, and HMI are also presented and discussed. modules are described in more detail in the next subsections. II. SIMULATOR DEVELOPMENT A. Physics core module The real-time interactive transient simulator for DNRR (in short DalatSim) The physics core was built based on consists of two main modules: a physics core RELAP5/MOD3.3 code. RELAP5 is a best- module and a driver module. The modules estimate thermal-hydraulic system analysis exchange necessary data together to build a code used extensively as the engine in many complete simulation program. Figure 1 real-time reactor simulators [4, 7-9]. The displays their functions and data transfer. code validation of thermal-hydraulic and core dynamic characteristics of DNRR was - The physics core module solves confirmed by comparing the analytical necessary neutron kinetics and thermal- results with the experimental data [10]. hydraulic problems for each time step required However, necessary work was implemented by the driver module for both steady-state and to investigate computational characteristics transient processes of DNRR. It provides the and capability of the code to develop our required parameters for the driver module for physics core module. Although RELAP5 is control and display functions of DalatSim. a very good tool for reactor simulation, - The driver module is responsible for some features need to be modified and controlling the execution of DalatSim and enhanced to meet the design requirements of comprises two main modules: a control a simulation system. 9
  3. VERIFICATION OF A REAL-TIME INTERACTIVE TRANSIENT SIMULATOR Firstly, RELAP5/MOD3.3 code does not The hot channel represents the hottest have the capability of real-time simulation. The channel in the core corresponding to a transient calculation control subroutine (tran) cooling channel with maximum heat flux. of the code was customized to ensure this The average channel represents the rest of feature. Secondly, users basically can not the cooling channels. Each channel was interact with the code in real-time besides modeled as three fuel element plates and preparing input files, running the code, and four coolant flow gaps according to the analyzing its printed output files. It is design of VVR-M2 fuel assembly. The impractical to prepare input files to describe all piping of the primary cooling system and operational states of DNRR. Therefore, an reactor pool was divided into volumes with interface written in C++ language was similar dynamic characteristics. designed and coupled with RELAP5/MOD3.3 Finally, a bug occurs inside the which was written in FORTRAN77 language embedded point reactor kinetics module of to solve this problem (Figure 1). This interface RELAP5/MOD3.3 resulting in nonphysical was able to directly access the memory of reactor power curves when applying small RELAP5/MOD3.3, retrieve and change all calculation time steps [12]. To solve that calculation variables. Data transfer from the problem, the embedded module was replaced physics core to other modules of DalatSim with SUNDIALS solver [13]. It has been would be easier with this coupling method. verified with benchmarks and proven to The nodalization of DNRR was based produce up to nine-decimal-place accurate on the reported numerical model in the results [14]. The coupled code, so-called Safety Analysis Report of DNRR in 2012 RELAP/SUNDIALS, not only helped us to [11]. The reactor core was divided into two prevent the bug but also enhanced the channels: hot channel and average channel. calculation accuracy of the physics core. Fig. 1. Design diagram of the real-time transient simulator for DNRR (DalatSim) B. Control module RELAP5/MOD3.3 code, the control module Instead of using the limited “control of DalatSim was built with many flexible variable” and “trip” card features of capabilities. This module processes all the 10
  4. CAO THANH LONG et al. required control and protection logic of was used for the interpolation. In terms of DNRR during the simulations. The module reactor protection features, the control was designed based on the logic circuit of the module can simulate the generation of actual reactor control and protection system warning and emergency signals of reactor of DNRR. It was written in C# language overpower, fast period, or abnormal using object-oriented programming with technological parameters in accordance with .NET Core technology, a new open source safety system settings of DNRR. and cross-platform framework from C. HMI module Microsoft [15]. Windows Presentation Foundation For simulation of control rods, i.e. (WPF), which is a powerful Microsoft's user shim rods, safety rods, and automatic interface framework, was chosen to develop regulating rod, a linear interpolation method was used to calculate insertion reactivity the HMI due to its flexible graphical based on the current position of each control programming features [16]. This technology rod in the reactor core. An excess reactivity has not been ever used to construct front ends lookup table for DNRR’s core configuration for nuclear reactor simulators in the world. The on December 28, 2011 was used as known HMI was designed to be as identical as data points. Another linear interpolation was possible to the real control panel of DNRR. All also applied to the module for feedback design formats and functions of each reactivity calculation due to the Xenon component were retained on the HMI for poisoning effect. Calculation and fidelity. Figure 2 displays a portion of the experimental data of reactivity module. The module consists of several compensation of Xenon poisoning effect submodules as follows: Fig. 2. The control panel and two parameter monitors of HMI module 11
  5. VERIFICATION OF A REAL-TIME INTERACTIVE TRANSIENT SIMULATOR - A control panel section allows users to - Raising reactor power to the power level perform operation actions such as reactor of 0.5% using manual mode of automatic start-up, maneuvering control rods as well as regulating rod; reactor shutdown when accidents occur - Maintaining reactor power at the power (Figure 2); level of 0.5% using automatic mode of - Three parameter monitors display automatic regulating rod; important operational, technological - Raising reactor power to the power level parameters and status of signals of the reactor of 50% by the steps below. control and protection system (Figure 2); - A panel of threshold setting for operative Setting the set points of emergency change of set points of emergency and warning power to 10% higher than the required protection by power; preset values of power power level; and period for automatic control; Setting the automatic control values of - A monitor displays trend histograms of power to the required power level; important operational parameters for further Controlling automatic regulating rod in analysis purposes; manual mode to raise reactor power to the - A monitor allows users to select and required power level so that reactor period is launch normal operational and accident not lower than 70 seconds; scenarios exercises; Maintaining reactor power at the - A monitor for user manual. required power level using automatic mode of automatic regulating rod; III. SIMULATOR VERIFICATION - Waiting for the reactor to work for 5 To assess the capability of DalatSim, the minutes at the power level of 50%; verification was performed by simulating a - Raising reactor power to the power level start-up process of DNRR. The start-up process of 80% by performing similar steps above; includes changing the reactor from subcritical to critical state; raising the reactor power to - Waiting for the reactor to work for 10 required levels of 0.5%, 50%, 80%, and finally minutes at the power level of 80%; 100% of nominal power (500 kW). All - Raising reactor power to the power level operations during the simulation were carried of 100% by performing similar steps above. out according to the start-up procedure for DNRR as follows [17]: The calculational power result given from DalatSim was compared with a set of - Withdrawing two safety rods in operational data of reactor power for a real sequence to the top of the reactor core; start-up process of DNRR. The operational - Setting the automatic control values data was extracted from a module called of power and period to 0.5% and 70 archiving, diagnostic, and recording (ADR) seconds, respectively. equipment of the reactor control and protection - Changing the reactor from a deeply system of DNRR. The start-up process of subcritical to the critical state by withdrawing interest lasted 3290 seconds, started from shim rods; 8:00:10 A.M to 9:00:00 A.M on June 10, 2019. 12
  6. CAO THANH LONG et al. IV. RESULTS AND DISCUSSION Figure 3 also shows that the reactor power curves are not exactly the same but their The comparison between calculational shapes are similar. That demonstrates the real- reactor power results obtained from DalatSim time simulation of a start-up process of DNRR and operational data for the start-up process is can be achieved with DalatSim. The simulator presented and discussed in this section. Table I can automatically maintain the reactor power at shows differences in the time to acquire each each required power level as expected as required power level. Table II presents the illustrated clearly in Figure 3. waiting duration at the power level of 50%, 80% of nominal power. Figure 3 illustrates the Table I. The time (in second) to acquire required power levels curves of reactor power from the simulation and operational data. Power level 0.5% 50% 80% 100% Simulation 1400 1800 2160 2820 The time to reach each required power result (s) level and the waiting duration at power levels Operational 1610 2165 2590 3036 of 50%, 80% of nominal power depend on the data (s) operator’s experience. In reality, the operator operated the reactor with higher reactor period Table II. The waiting duration (in second) at for safety purpose that results in longer time to required power levels reach the power levels as shown in Figure 3. In Power level 50% 80% our simulation, the simulator was manipulated Simulation result 300 600 with lower reactor period but still higher than (s) 70 seconds, which obeys the start-up procedure Operational data 333 371 for DNRR. (s) Fig. 3. The comparison between simulation result and operational data V. CONCLUSIONS simulation of DNRR. The verification also demonstrates DalatSim can be a suitable tool to The verification result shows that the effectively support the operator training and computational capability of DalatSim can meet nuclear education for trainees from VINATOM the requirement of real-time transient 13
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