Equipment protective system shutdown

Equipment Protective System Shutdown Systems that are usually provided for the protection of centrifugal pumps, rotating and reciprocating gas compressors, gas expansion and combustion gas turbines (CGTs), electric motors, generators, and forced or induced draft air fans. 

Automatic systems have a detection system that should automatically activate fire protection systems, significantly reducing the chance of a larger fire. The disadvantage is the potential for nuisance activations that can damage the equipment being protected, shutdown production, and require the fire protection systems to be recharged. 

The PPIS receives signals from the ex-vessel detectors of the NCSS or other protection system sensors and interprets these signals to determine appropriate protective actions. In all DBEs except DBE-2, the control rod drives are tripped and their function is completed in the very early stages of the event. For DBE No. 2, which Includes shutdown by the reserve shutdown control equipment, the shutdown action (release of the reserve shutdown material) is delayed for a brief interval (i.e., minutes). However, if the shutdown action should take place after considerable delay (i.e., several hours), the RSCE is designed to withstand the most severe environment to which it might be exposed prior to completing the required action. 

A system important to safety, i.e., provided to ensure the safe shutdown of the equipment or otherwise control an operation or to limit the consequences of anticipated operational occurrences and design basis incidents. Safety systems consist of the protection system, the safety actuation systems, and the safety system support features. Components of safety systems may be provided solely to perform safety functions, or may perform safety functions in some plant operational states and non-safety functions in other operational states. Safety system support features are considered the collection of equipment that provides services such as cooling, lubrication, and energy supply required by the protection system and the safety actuation systems. 

The reactor protection system protects the reactor and associated equipment by tripping the reactor, when certain plant parameters exceed their respective set points. Two independent reactor shutdown systems are provided in PHWRS. These systems introduce a neutron absorbing material into the reactor core to decrease reactivity and therefore shutdown the reactor. The two shutdown systems are physically separate and diverse in function. The features of the shutdown systems are brought out in Section 5.9.2.3.3. 

The PIUS plant is also provided with instrumentation systems, protection, logic, and actuation systems for reactor shutdown, residual heat removal, containment isolation, etc. in a similar way as present-day LWR plants. Their importance for ensuring safety is significantly reduced in a PIUS plant. The equipment of these instrumentation, monitoring, protection, and actuation systems is separated from that of other systems and located in separate, physically well protected compartments at the bottom of the reactor building. The reactor protection system (RPS), with a two-out-of-four coincidence logic, has the task of initiating power level reduction, reactor shutdown or reactor scram when reactor process parameters exceed set limits, in order to prevent further departure from permissible conditions. 

Figure 12.29 A chemical process operator relies on a furnace fuel shutdown system for personnel protection and equipment protection.

The environment in which the power-conditioning system operates will have a significant effect on reliability. Extremes of temperature, altitude, humidity, and vibration can be encountered in various applications. Extreme conditions can precipitate premature component failure and unexpected system shutdown. Most power-protection equipment is rated for operation from 0 to 40°C. During a commercial power failure, however, the ambient temperature of the equipment room can easily exceed either value, depending on the exterior temperature. Operating temperature derating typically is required for altitudes in excess of 1000 ft. 

The action functional component represent all the possible predetermined response actions which should occur upon reaching apredetermined alarm/action setpoint. Response actions could include activation of audible and/or visual alarms, annunciation of specific alarm conditions and locations, hardcopy of past and present gas concentrations or environmental conditions, notification of local and remote emergency response personnel, activation of emergency safety control systemsl l through relays such as gas supply source and equipment shutoffs, HVAC system shutdown with 100% exhaust, or one-pass cleanroom air flow operations. The predetermined response actions should follow established emergency response procedures and policies of your organization and all applicable environmental, health, and safety regulations to protect both personnel and the environment and minimize the extent and effect of any hazardous situations. 

This section should provide relevant information on the instrumentation and control systems as described in paras 3.65-3.70. The reactor instrumentation senses the various reactor parameters and transmits appropriate signals to the control systems during normal operation and to the reactor trip systems and engineered safety features and systems during anticipated operational occurrences and in accident conditions. The information provided in this section should emphasize those instruments and their associated equipment that constitute the protection systems and those systems rehed upon by operators to monitor plant conditions and to shut the plant down and maintain it in a safe shutdown state after a design basis accident. Information should also be provided on the non-safety-related instrumentation and control systems used to control the plant in normal... 

Whenever possible, the safety interlock system should be used to shut down equipment as part of a planned shutdown in order to test the protective system. 

The requirements for most protective actions are such that automatic initiation of the actions wiU be necessary. In addition, a capabiUty for manual initiation of reactor shutdown and for the initiation of system level action such as containment isolation should be provided. This does not preclude intervention by the operator in a more detailed manner. Where manual actuation is provided for, it should be independent of the equipment of the automatic protection system to the extent practicable. 

Rack 1 (first from the left standing in front of the console) is the Safety Display and Command Rack, which belongs to the reactor protection system. In all its engineering aspects, it is equivalent to rack three in the main console hardwired, functionally and electrically independent, its indicator panel implements the Safety Parameter Display Unit, its command panel includes the manual triggering, interlock and reset pushbutton of the protection and active-safety systems. This rack in the secondary console includes all the equipment that is required to shutdown the reactor and to keep the reactor in a safe shutdown condition... 

Car-Sealed Closed Valve - In certain cases it may be advantageous to use car sealed closed valves, such as in a bypass around a fuel gas control valve used for furnace flameout protection. The bypass is provided so that the automatic shutdown system can be periodically checked for operation. Where CSC valves are used for other purposes, they are also limited to appUcations where inadvertent opening of the CSC valve would not overpressure the equipment by more than 1.5 times design pressure. 

As long as pressure, level, and temperature control devices are operating correctly, the safety system is not needed. If the control system malfunctions, then pressure, level, and temperature safety switches sense the problem so the inflow can be shut off. If the control system fails and the safety switches don t work, then relief valves are needed to protect against overpressure. Relief valves are essential because safety switches do fail or can be bypassed for operational reasons. Also, even when safety switches operate correctly, shutdown valves take time to operate, and there may be pressure stored in upstream vessels that can overpressure downstream equipment while the system is shutting down. Relief valves are an essential element in the facility safety system. 

Assume that two levels of protection are adequate. Experience in applying FMEA analysis to production equipment indicates that in many cases only one level of protection w ould be required, given the degree of reliability of shutdown systems and the consequences... 

Accident Mitigation 28 Detection of leaks/ruptures 29 Emergency shutdown switch locations 30 Accessibility of isolation valves 31 Potential for fire/explosion in unit affecting other equipment 32 Critical controls, mitigation, communication, and fire protection sy stems functional and accessible after initial explosion or release 33 Back-up power supply/redundant feeds for critical electrical systems 34 Water supply for fire fighting 35 Routing of utilities... 

Alterations to protective equipment systems, such as changes to critical settings for alarm, interlock, or shutdown systems or changes involving safety relief or vent systems. 

---