PBNC

In conducting emergency exercises at its nuclear power plants, Taiwan Power Company (TPC) has for years used large transient analysis computer codes and training simulators to prepare the accident scenarios. Neither is convenient and meets full requirements of the task. Advancement in modern 32-bit microprocessors and Windows-based graphic user interface (GUI) has completely revolutionized the simulation technology. It becomes possible to automate the preparation work and actual exercise on a desktop computer. TPC has selected a PC-based simulation code PCTRAN [1,2] as the basis for its plant specific emergency exercise systems for the plant Maanshan, the twin Westinghouse 3-loop PWRs of 900 MWe each and the GE ABWR Lungmen Project in construction.

The source code of PCTRAN was converted into Microsoft Visual Basic 6.0. Operation of the GUI follows strictly the specifications of Microsoft Windows environment. Data input/output are in MS Office’s Access database format. Reports and data can be transferred conveniently through all Windows-based software products over the entire exercise network.

Maanshan has sophisticated automatic control systems. The control rod system and soluble boron control the core neutron flux. Pressurizer heater and spray control the primary system pressure. The Chemical and Volume Control System (CVCS) controls the primary coolant inventory and water chemistry. On the secondary side, steam output is controlled by the turbine control valve and steam dump system. Steam generator water level is controlled by the feedwater system. During the automatic control mode, they work in a synchronized way so that transition to stabilized conditions will be achieved smoothly. This has all been modeled in the PCTRAN software. Operation is defaulted to the automatic mode. Operator can take one of the control systems into manual operation by clicking the corresponding manual button ("M") and a window will pop-up. By entering a new set point, activating the manual action and closing the window, that system will then run in the manual mode.

In the attached Windows displayed mimic of the Maanshan model, a single loop is at the left side and the other two loops are combined at the right side. The mimic also represents the controllable systems as small panels with the important equipment shown as icons (i.e., pumps, valves, and heat exchangers). Design of the panels in the mimic is limited to those critical to operations and emergency functions. Other windows can be activated to display the radiological release pathways, source terms, trend curves, P-T diagram (for PWR subcooling margin), etc.

Important components such as the Power-Operated-Relief-Valves (PORV) and safety valves of the pressurizer and the steam lines, pressurizer spray valve and heaters, Main Steam Isolation Valves (MSIVs), Turbine Bypass (Steam Dump) Valves, main and auxiliary feedwater pumps and their isolation valves, Reactor Coolant Pumps, etc. are displayed locally. Their control is by point-and-click on the component using the mouse. A local window pops up for status control to on, off, fail-at-mid-position, or even greater than 100% (e.g. pump run-out). The status is indicated by color consistent with the control room panel.

Control rod motion is animated. Pipe breaks are shown dynamically by flashing sprays at the break location with the leakage flow digitally displayed. Emergency systems include High Pressure Safety Injection, Accumulators and Low Pressure Injection. Each one is automatically activated when the plant condition demands so. Operators can over-ride the automatic activation and manually control equipment anytime during the simulation.

Preparation of the input files, selection of the initial conditions, performing the transient analysis, graphic display of plant status can all be conducted interactively and on-line. This saves considerable time during preparation of an exercise and provides a "live" tool during the actual exercise.

In order to demonstrate that the PCTRAN system truly represents the Maanshan plant, verification benchmark analysis was conducted for all FSAR Chapter 15 events. Reasonable agreement has been achieved for each event. Success of the reactor physics and thermal-hydraulics model formulates a solid foundation to further expand into fission product transport.

The three major fission product barriers: cladding, reactor coolant system and containment are modeled in the transport model. Transport through various pathways such as containment leakage, steam generator relief valves, turbine offgas and auxiliary building vents are included. The radiological isotope iodine and noble gases at the four release points formulate the source term. It will be used as input to an offsite dose assessment model. The system uses actual meteorological data and Maanshan neighborhood 3-D terrain to make dose projection. Protection action guidelines such as food control, localized shielding or evacuation are then decided according to the dose projection.

An exercise scenario will be prepared by running the software in fast-time to find a most-challenging script. During actual exercise the Windows-based system will be re-run in real-time by the operations personnel following directions of the planner. It will be tested in the coming annual exercise at Maanshan.

References

1. L. C. Po, "Analysis of the Rancho Seco Overcooling Event Using PCTRAN", Nuclear Science & Engineering, 98, 154-161 (1988).
2. L. C. Po "IAEA Activities in Advanced Reactor Simulation", paper S1, the Fifth International Topical Meeting on Nuclear Thermal Hydraulics, Operations and Safety (NUTHOS-5), April 14-18, 1997, Beijing, China.

© 2007 Micro-simulation Technology