Until now the IAEA’s collection of simulators included a generic 1300MW BWR (revised in 2008 to include a containment model), a generic two-loop and advanced PWR (both about 600MWe), a PHWR and advanced PHWR and a VVER. The simulators operate on personal computers and are provided for a broad audience of technical and non-technical personnel as an introductory educational tool. The preferred audience, however, are faculty members interested in developing nuclear engineering courses with the support of these hands-on educational tools. Although they are not intended to be used for plant-specific purposes such as design, safety evaluation, licensing or operator training, the application of these PC-based simulators is limited to providing general response characteristics of selected types of power reactor systems. The IAEA’s aim is to accurately model the behaviour of the various types of reactors while being somewhat generic and staying away from specific vendor or designer names whenever possible.
Some of the simulators currently in the collection have been donated to the IAEA by the original developers/owners. Other simulators have been developed from scratch at the request of the IAEA. In this second case, the IAEA has hired the services of experienced programmers to develop the software.
Although the simulators are normally provided together with their associated manuals, the Agency periodically organizes courses and workshops primarily for nuclear engineering faculty to teach their behaviour more in depth.
The entire collection of simulators can be obtained, free of charge, by relevant organizations in any of the IAEA member states by filling out the request form on the IAEA website (see: www.neimagazine.com/iaeasim). This request needs to be endorsed by the proper national authorities prior to being forwarded to the IAEA. In exchange for this free service, the IAEA asks the users to provide the agency with feedback and suggestions for improvement.
The passive BWR simulator
The new BWR with passive safety systems simulator has been developed by Cassiopeia Technologies Inc. (CTI) of Canada in 2008-2009 to meet IAEA’s objectives of technology training and education. The development of this simulator was a joint effort by the developer, agency staff, and a BWR thermal-hydraulics expert. All simulator responses have been reviewed and tested, and improvements based on the expert’s comments were incorporated.
Like the other simulators in the IAEA collection, the advanced BWR simulator can operate essentially in real time on a personal computer. The simulator is capable of dynamic response with sufficient fidelity to simulate typical passive BWR plant responses during normal operation and accident situations. It also has a user-machine interface that mimics the control panel instrumentation, including the plant display system. More importantly, it allows user interaction with the simulator during the operation of the passive BWR plant.
The interaction between the user and the simulator is established via a combination of monitor displays, mouse and keyboard. Parameter monitoring and plant operator controls are represented in a virtually identical manner on the simulator. Control panel instruments and controls, such as push-buttons and hand-switches, are shown as stylized pictures, and are operated via special pop-up menus and dialogue boxes in response to user inputs.
The simulation development used a modular approach: the basic models for each type of device and process are represented as algorithms and developed in FORTRAN. These basic models are a combination of first order differential equations, logical and algebraic relations. The appropriate parameters and input-output relationships are assigned to each model as demanded by a particular system application. These models are described in detail in the user’s manual provided together with the simulator.
The manual provides, in addition to detailed instructions to operate the simulator, a list of simulator exercises. These examples include normal operation exercises, such as a startup or a shutdown, as well as other power manoeuvring sequences. The manual also includes a total of 18 types of malfunction scenarios, encompassing a loss of feedwater accident to a load rejection event, and loss of inventory events such as a LOCA or a stuck-open safety relief valve.
The passive BWR simulator has nine interactive display screens that cover plant overview, control loops, power/flow map & controls, reactivity & setpoints, scram parameters, turbine generator, feedwater & extraction steam, containment and cleanup/shutdown cooling system. The top of each screen contains 21 plant alarms and annunciators that indicate important status changes in plant parameters that may require operator action. The bottom of each screen shows the values of the following major plant parameters: reactor neutron power (%), reactor thermal power (%), turbine generator output power (%), reactor pressure (kPa), core flow (kg/s), reactor water level (m), balance of plant (BOP) steam flow (kg/s), feedwater flow (kg/s) and average fuel temperature (ºC). The bottom left hand corner allows the initiation of two major plant events: ‘reactor trip’ and ‘turbine trip’ that correspond to hardwired push buttons in the actual control room.
The plant overview screen displays key parameters in the reactor dome, reactor core, outside of the reactor pressure vessel (RPV) (such as main steam isolation valves) and outside the containment (such as the turbine).
It is a well-known and well-documented phenomenon in the BWR that oscillations in neutronic and thermal-hydraulic parameters can occur during operation in the conditions of low flow – high power region. Since for a natural circulation reactor the highest power to flow ratio occurs at the rated conditions, a large stability margin was incorporated into the design.
Research has shown that such oscillations are characterized by density wave oscillations. From a physical point of view, the removal of thermal power by boiling water in a vertical channel, in a closed or open loop configuration, may cause instability in the operation due to the propagation of density changes and various thermal-hydraulic feedback mechanisms. Since the coolant is also a neutron moderator, an oscillation in the coolant density (void content) is reflected as a variation of the thermal neutron flux, which in turn, via the heat flux, affects the void. This may cause a coupled neutronic/thermal-hydraulic oscillation under certain power and core flow conditions. Although somewhat simplified, the IAEA advanced BWR simulator includes models that adequately model these phenomena for the case of a BWR with passive safety systems.
Author Info:
Sama Bilbao y León, technical head, water reactor technology development, Department of Nuclear Energy, IAEA, Wagramer Strasse 5, PO Box 100, A2569 1400 Vienna, Austria. The author thanks Dr. Lam of Cassiopeia Technologies Incorporated (CTI), for his support, and acknowledges Dr. Bereznai of the University of Ontario Institute of Technology, Dr. Po of Microsimulation Technologies and Dr. Tikhonov of Moscow Engineering and Physics Institute for permission to republish user manual content.
Omitted references are available on www.neimagazine.com/simu
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