Duty Systems

Asphalt mastic is a heavy duty system that is shop-applied in thicknesses up to 1 in. (25.4 mm). Although asphalt mastics perform well, they are very costly. Their use is usually limited to river crossing and swamp areas. Coal-tar enamel has more than 50 y of successful performance underground, but it is subject to cracking when the temperature is below 20° F (-7°C), and there are environmental constraints. The EPA has shut down applicators in the middle of production because of air pollution. These problems rule out asphalt mastic and coal-tar enamel as feasible materials for most pipelines. In addition, coal-tar enamels are often ruled out because of long-term deterioration. Asphalt enamel is generally considered inferior to coal-tar enamel therefore, its use is limited. Polyvinyl chloride tape is becoming obsolete because of the superior performance of polyethylene tape. 

It is worth noting that the determination of hydrogen in bulk materials has great importance in many areas (NEA 2001), for example, hydrogen in metals and alloys causes structural weakness in the components of heavy-duty systems (aircraft, engines, missiles, pipelines of nuclear and chemical plants). Metal hydrides are applied in various fields of science and technology (electricity, propulsion, battery, food, nuclear fusion, etc.). 

Contact Duty system of pilots Bridge resource management Management of the ship Working relationship pUot/bridge team Hours of darkness/adverse weather... 

We have seen in the previous chapter that, as well as an obvious moral duty, systems designers and software engineers may have legal responsibilities under statutes such as the Health and Safety at Work Act to ensure that other people are not put at risk by their acts or omissions. Despite its apparently specific subject area, the general approach to safety matters contained in the Health and Safety at Work Act and associated regulations need not be confined to workplace safety. Indeed, the sequence— assess, control and monitor—found in the Control of Substances Hazardous to Health Regulations and the European regulations is capable of application to... 

For heavy-duty systems, the situation is less clear although significant research and development work have been performed over the past years. The benefit with... 

Removal of heat fi om the core is controlled by one of a range of plant duty systems if ac power is available or by automatically actuated passive safety systems, which are qualified against enviromnental conditions and hazard challenges within the design basis. These passive safety systems can be maintained without operator intervention for at least 72 hours. 

The safety of any nuelear power plant can be challenged by the hazards and faults it experiences throughout its hfe. Its abihty to withstand these hazards and faults is governed by the functionality of the duty systems and the safety systems included in its design. The safety function of any particular SSC is the specific role required of it in maintaining... 

The duty systems that can provide additional defence in depth protection against loss of KSFs for each fault, but that are not claimed in the design basis assessment. 

Immediately following reactor trip, which has in turn tripped the turbine and set the steam circuit to the turbine by-pass line, duty systems would be deployed as defence in depth to manage the fault by controlling reactor pressure, tempeiatuie and inventory, thereby avoiding actuation of the engineered safety features (ESFs). The duty systems are not claimed in the fault schedule - they are providing additional defence in depth. 

If the duty systems are unavailable, or are imable to control the ult, passive residual heat removal (PRHR) is initiated and the CMTs actuated to inject borated water into the reactor coolant system (RCS). In most cases this will be sufficient to manage the fault for at least 72 hours. 

Because the engineered safety features are passive systems or are actuated by the protection and safety monitoring system (with diverse actuation system (DAS) backup), whereas the plant duty systems are electrically powered and actuated by the plant control system (PLS), there is significant diversity between the duty and protection systems. 

In addition to the principal safety systems listed above, the fault schedule demonstrates that there is at least one safety measure (which may be a Class 1 system that is not claimed in the analysis, or a non-Class 1 system) available to enhance control over the KSFs. Because the non-Class 1 systems are, like the duty systems, electrically powered and actuated by the PLS there is diversity between the claimed safety systems and the defence in depth. 

The I C system must provide a reliable means of controlling duty systems to keep the plant within the permitted operating envelope during reactor start-up, critical operations and while shut down. 

In addition, the PLS provides control over a munber of supporting duty systems, as listed in Table... 

Table 6.7-1 PMS Signals Resulting in ESF Actuation and Duty System Isolation 1 of 2...

The ECS must provide power to the plant duty systems. 

The regulatory treatment of duty system features as developed and licensed with the NRC. This approach provides a graded safety classification system. This process uses PRA and... 

The Level 1 defence in depth features are the duty systems that control and monitor the plant during normal operation and during expected operational deviations. On the APIOOO, the following SSCs are in this category ... 

Nuclear safety for the APIOOO is less dependent than current plants on ihe duty systems (IAEA Level 1) and the systems that are deployed to control abnormal operation and detect failures (IAEA Level 2), because of the presence of robust safety measures (IAEA Level 3) that stop ihe loss of nuclear safety function these Level 3 safety measures are robust because they do not require support systems such as ac power, component cooling water and service water. The five IAEA levels of protection are discussed in more detail in Section 8.2.1 of this PCSR. 

The plant control system provides the fimctions necessary for normal operation of the plant, from cold shutdown through to full power. This system controls the duty systems in the plant, which are operated from the main eontrol room or remote shutdown woikstation. The plant control system contains the control and instmmentation needed to change reactor power, control pressuriser pressure and level, eontrol feed water flow, turbine control and perform other plant fimetions associated with power generation. 

The DAS is not claimed as a safety measure by the fault schedule. However, it does provide defence in depth, and as such it possesses two out of two voting logic to prevent spurious actuation, and it is designed to higher quality standards than normal duty systems. 

The main control room accommodates an operator console, a supervisor s console, safety consoles, the wall panel information system large screen displays and the DAS panel. The operator console provides the displays and controls to start up, manoeuvre, and shut down the plant, and it is designed to be staffed by one to six operators. The operator interfaces are the duty system control displays, soft controls, alarm presentation system displays, computerised procedures displays, as well as the VDU monitors, keyboards and mice. The supervisor s console is a smaller version of the operators console, and is designed to be staffed by one or two personnel. The primary dedicated safety panel and VDU-based safety system workstations are located at the centre of the operator console, with a secondary safety panel located in close proximity to the supervisor s console. The DAS panel is located at a sidewall in the main control room. The main control room also includes communication devices, document lay down areas, printers and storage space. A meeting table is provided and equipped with a VDU-based workstation to allow access to the duty control system by, for example, a technical advisor or shift manager, without disrupting control room operations. In close proximity to the main control room are the shift supervisor s office, the operations staff area, an operations woik area, restrooms, and kitchen facilities. 

The start-up feed water pumps and their associated pipes and valves is the duty system for decay heat removal from the reactor coolant system. If it operates correctly, it obviates the need for its counterpart IAEA Level 3 safety measure, the passive residual heat removal heat exchanger. 

The safe operating envelope of the APIOOO is defined by the operational parameters within which it can be safely operated, and by the protective safety measures that must be available in case a duty system fails. The limiting operational parameters are the boundary conditions assumed by the transient analysis for each fault in the design basis fault schedule (see Section 5.2 of this PC SR). The conditions placed on the availability of protective safety measures are based on the required reliability of providing the nuclear safety function, given the postulated frequency and consequences of each fault. 

From the results of the measurements just described it is clear that quantitative measurements on delamination under an intact coating are not possible with impedance measurements as long as the impedance of the systems remains high, which is often the case for thicker heavy-duty systems. In terms of equivalent circuits that are used to explain impedance measurements, this implies that the corrosion... 

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