Shutdown sequences system

Most fuel cell units have an error code display alert that will tell you what is wrong with the system if it is not working properly, and an automatic shutdown sequence if there are gas leaks or other problems that require immediate action. 

SIS documentation consistent with installed system SIFs perform as specified with invalid process variables Proper shutdown sequence activated Proper alarm and display by SIS Correct computations included in SIS Bypass and manual shutdown function correctly Reset of SIS functions as per SRS Proof test interval included in maintenance procedure Diagnostic alarm performs as required SIS performs as required in case of loss of power SIS goes to desired state on power resumption SIS EMC immunity as per SRS... 

The mode of action has been a subject for research for a number of years. While it was originally thought that maleic hydrazide replaced uracil in the RNA sequence, it has been deterrnined that the molecule may be a pyrimidine or purine analogue and therefore base-pair formation is possible with uracil and thymine and there exists the probabiHty of base-pair formation with adenine however, if maleic hydrazide occurs in an in vivo system as the diketo species, then there remains the possibiHty of base-pairing with guanine (50). Whatever the mechanism, it is apparent that the inhibitory effects are the result of a shutdown of the de novo synthesis of protein. 

The fact that batch processes are not carried out at steady state conditions imposes broad demands on the control system. The instrumentation and control system have to be selected to provide adequate control for a wide variety of operating conditions and a wide variety of processes. In addition, basic process control and shutdown systems have to deal with sequencing issues. This chapter presents issues and concerns related to safety of instrumentation and control in batch reaction systems, and provides potential solutions. 

The Primary LOCA sequences. result from expansion joint breaks (51/59) and large break LCXZAs (8/59). Response to LOCAs in the primary system involves shutdown, emergency injection makeup of... 

The OWR protective systems were modeled with event tree diagrams for the time sequence following an initiating event to fuel damage or safe shutdown. Fault trees were used to find the probability of failure of each protective system in a particular event tree. 

Bums and Hazzan demonstrated tlie use of event tree and fault tree analysis in tlie study of a potential accident sequence leading to a toxic vapor release at an industrial chemical process plant. The initiator of tlie accident sequence studied is event P, the failure of a plant programmable automatic controller. Tliis event, in conjunction willi the success or failure of a process water system (a glycol cooling system) mid an operator-manual shutdown of tlie distillation system produced minor, moderate, or major release of toxic material as indicated in Fig. 21.4.1. The symbols W, G, O represent tlie events listed ... 

Inspecting and maintaining the interlock system is a vital function. It is required to ensure general safety and to avoid risks of boiler explosion. Interlocks provide for the safe sequence of boiler startup and shutdown procedures. 

Control systems will play a key role in future distributed plants ]139,145]. As a rule of thumb, plants will be smaller and simpler, but the control systems will be much more advanced, of a standard not known today. Plant personnel for operation and managing will ultimately no longer be required, except for start-up, shutdown, and services. This is a shift from a regulatory to a servo role, supported by a sophisticated sequence control. Control is needed for safety issues, operability, and product quality control. Sensors have a central role to provide the information needed for control and modeling and simulation is needed for process models. 

Mitigating events or mitigating factors act to impede the accident sequence, resulting in less severe consequences. Examples include detection and activation of emergency shutdown systems, operator intervention, spill containment, equipment spacing, natural dispersion, and reducing the... 

The unit is equipped with devices such as remote switches to alleviate problems such as missing the pickup of a test tube or pipette tip. In a sequence of events, the robot would pick up a test tube and move to a location that has a remote switch. It would then press down the switch which would send a response to the controller. The Zymate program and the response from the switch location would indicate whether the robot had picked up the test tube. If the response was positive it would continue with the assay. If negative, it would take other actions that might be programmed into the system. These actions might include another attempt at picking up the test tube or a system shutdown. These actions thus allow safety checks on system operation or status. 

By connecting the leakage monitoring system signals to the ventilation system via an interlock sequence, the shutdown of ventilation system can be achieved within two minutes after detection even for small or medium scale leakage. 

The number and location of the top entry control rods and the diverse reserve shutdown control have been specified to assure that the reactor thermal power is controlled both for normal and off-normal conditions. The radial thickness of the active core annulus was specified on the basis of assuring that the control rod worths of the reflector-located rods would meet all shutdown and operating control worth requirements. The choice of reflector control, coupled with the choice of a control system withdrawal sequence and safety classification was made to assure that the control rod integrity is maintained during passive decay heat removal. 

Any spray dryer control system can be run either automatically or semiautomatically. A fully automatic control system is recommended when the product quality should meet very stringent requirements and when lower operating costs are essential. A timing device starts up the dryer in a predetermined sequence. In case of failure in the control equipment it is always possible to employ manual control and to continue production without interruption. The shutdown and cleaning operations are programmed and controlled by means of timing equipment. The ACS must include a control system for fire detection, a system for fire or explosion prevention, and a programmable system for countermeasures. 

The PSA should set out to identify aU the fault sequences which contribute to risk determine if there are weaknesses in the design or operation of the plant and assess the need for changes to reduce the safety significance of such weaknesses. If the analysis does not address aU the contributions to risk (for example, if it omits external events or shutdown states) then conclusions made about the level of risk from the plant, the balance of the safety systems provided and the need for changes to be made to the design or operation to reduce the risk may be incorrect. 

Accidents must be shown to have acceptable consequences, not only if the safety systems work, but also if any safety system is unavailable or impaired. For example, in most other reactors, a loss-of-coolant accident coupled with prolonged unavailability of the emergency core cooling system, would result in melting of the reactor fuel. In CANDU this sequence would lead to damaged fiiel but no meltdown. This overall safety approach is achievable because there are at least two ways of providing the safety functions of shutdown and decay heat removal. 

This report examines the severe accident sequences and radionuclide source terms at the Sizewell pressurised water reactor with a piestressed concrete containment, the Konvoi pressurized water reactor with a steel primary contaimnent, the European Pressurised water Reactor (EPR) and a boiling water reactor with a Mark 2 containment. The report concludes that the key accident sequences for European plant designs are transient events and small loss-of-coolant accidents, loss of cooling during shutdown, and containment bypass sequences. The most important chemical and transport phenomena are found to be revaporisation of volatile radionuclides from the reactor coolant system, iodine chemistry, and release paths through the plant. Additional research is recommended on release of fission products from the fuel, release of fission products from the reactor coolant system, ehemistry of iodine, and transport of radionuclide through plants. 

---