Leak detection isolation

Suitable redundancy in components and features, and suitable interconnections, leak detection, isolation, and containment capabilities shall be provided to ensure that for on-site electric power system operation (assuming off-site power is not available) and for off-site electric power system operation (assuming on-site power is not available) the system safety funct i on can be accompIi shed, assum i ng a single failure. 

The next step is to apply a number of loss control credit factors such as process control (emergency power, cooling, explosion control, emergency shutdown, computer control, inert gas, operating procedures, reactive chemical reviews), material isolation (remote control valves, blowdown, drainage, interlocks) and fire protection (leak detection, buried tanks, fire water supply, sprinkler systems, water curtains, foam, cable protection). The credit factors are combined and appHed to the fire and explosion index value to result in a net index. 

Leaks in process vessels and devices such as valves are a serious problem in many industries. A variation of vibration monitoring and analysis can be used to detect leakage and isolate its source. Leak-detection systems use an accelerometer attached to the exterior of a process pipe. This allows the vibration profile to be monitored in order to detect the unique frequencies generated by flow or leakage. 

As you can see, this process is aided or thwarted by vacuum system design. Temporary isolation of the various parts of any vacuum system may be impossible by bad design. Therefore, be forewarned If you are designing a vacuum system, provide a stopcock at every branch of the system to aid in leak detection (section isolation not only helps in leak detection, but creates a more robust vacuum system allowing greater control and protection). 

Imagine a room full of people. Now imagine you want to find the one(s) named Bill. If there was no way to easily identify the Bills, the process would become significantly laborious. However, if you called out and asked all those named Bill to please raise their hands, the task of identification becomes easy. The helium leak detector has the ability to isolate and count the helium atoms from a vacuum system full of many other atoms and molecules. In reality, the helium leak detector is nothing more than a customized mass spectrometer. The mass spectrometer was developed in the 1920s, but became a leak detection tool in the 1940s when the need for ultra-vacuum systems became critical on the Manhattan project. ... 

Specifically, for GDC 54, the lines penetrating the containment are provided with the required isolation and testing capabilities. Each line has two containment isolation valves in series, and test connections are provided to allow periodic leak detection tests to be performed. 

Errors in modeling may arise if due eare is not taken in developing fault/event tree models or identifying appropriate failure meehanisms. For an example, let us consider an area that has two toxie gas deteetors, either of whieh ean close an emergency isolation valve. In the fault tree, both deteetors would have to fail for leak detection failure to oeeur and the events would be ANDed together. The fault tree should be described down to the power supply level. This would ensure that the Boolean solution to the fault tree would capture the case... 

A sodium leak detection system provides early warning of any sodium-to-air leaks from the IHTS piping. In the event of an SG tube leak, the sodium-water reaction pressure relief subsystem (SWRPRS) provides overpressure protection of the IHTS and IHXs. The SWRPRS consists of a safety-grade rupture disk, a sodium dump tank, a cyclone/separator tank, a vent stack, and a hydrogen igniter. To separate the reactants, the SWRPRS also initiates the water-side isolation of the SGS and pressure relief. 

The nuclear heat supply system generates heat in the reactor core and produces steam in the IHTS. The IHTS SG is composed of a helical coil counterflow heat exchanger, startup recirculation tank and pump, leak detection system, and isolation valves. Intermediate sodium flows on the shell side of the helical coil tubes, through which water flows to produce superheated steam. Two reactor SGs feed one turbine island to form a power block. 

The fill connections and cylinder valves should be inspected for leaks during the filling process. Leaks can be detected by using a leak detection solution or leak detection instrument. A valve that leaks should be marked and isolated for repair. When the correct pressure (temperature compensated) is attained, the manifold supply valve and each cylinder valve is closed. The vent valve is opened to release manifold pressure and each cylinder is disconnected from the manifold. A leak check of each cylinder valve including the outlet and pressure relief device is again performed. 

Upon receipt of any gas or gas mixture, the user must become familiar with emergency procedures to be taken by reading the MSDSs provided. Gas mixtures that can pose serious hazards to personnel or property if they were to be released should be isolated from the area of use as much as possible. Where this is impractical, monitoring or leak-detecting equipment should be installed, calibrated, and maintained on a routine schedule. In the event of a leak or release, thorough knowledge of the properties of... 

Watch for signals from leak detection systems. For H2S-containing systems that focus directly on the measurement of H2S, pressure changes can indicate a leak, while temperature changes can be a sign of a loss of containment and potential fire. Signals from these detection systems can start a well shut-in or isolation of sections of pipehne, so it is important to know the features of the system you are working with. 

The potential for release of activity from a break or leak in the chemical and volume control system is minimized by the location of the purification subsystem inside containment and the design and test of the isolation valves. Chemical and volume control system leakage inside containment is detectable by the reactor control leak detection function as potential reactor coolant pressure boundary leakage. 

Leak Duratioa The Department of Transporation (1980) LNG Federal Safety Standards specified a 10-min leak duration other studies (Rijnmond Public Authority, 1982) have used 3 min if there is a leak detection system combined with remotely actuated isolation valves. Other analysts use a shorter duration. Actual release duration may depend on the detection and reaction time for automatic isolation devices and response time of the operators for manual isolation. The rate of valve closure in longer pipes can influence the response time. Due to the water hammer effect, designers may limit the rate of closure in liquid pipelines. 

Figure 6.14 shows the various components of the protective system for an SGU and secondary sodium circuit. Isolation and dumping would be initiated by operation of the rupture discs or by receipt of signals in excess of pre-determined limits fi-om the leak-detection instrumentation shown in Figure 6.13. 

Interconnections and isolation capabihties and other appropriate design features (such as leak detection) shall be provided to fulfil the requirements of para. 6.33 with sufficient reliability, on the assumptions of a single failure and the loss of ofif-site power, and with the incorporation of suitable redundancy, diversity and independence. 

Design features (such as leak detection, appropriate interconnections and isolation capabilities) and suitable redundancy and diversity in components shall be provided in order to fulfil these requirements with sufficient reliabihty for each PIE, on the assumption of a single failure. 

A potential problem in the Reactor Core Isolation Cooling (RCIC) system circuitry of a particular BWR was identified. Within this particular RCIC control system, because of the design of the RCIC steam leak detection circuit, it is possible for a sneak circuit to occur and cause an unintended, nonrecoverable isolation of the RCIC pump in conjunction with a station blackout. There are at least three subtle design aspects which lead to the occurrence of this failure mode (1) the RCIC system contains an isolation circuit, (2) the isolation circuitry is deenergized given a loss of offsite power (i.e., the circuitry is not fed by a nonintemiptible, battery-backed vital AC power supply), and (3) the isolation circuit contains a seal-in circuit. 

Fluid systems that penetrate the containment envelope and extend outside the containment should be robust and should possess adequate devices for flow isolation that are capable of preserving the safety function and performance of the containment envelope. The section that penetrates the containment, up to and including the flow barrier, should be considered an extension of the containment boundary and should be designed to the appropriate levels of quality and performance in accordance with the applicable codes and standards. These systems, if they are not provided with the capability for prompt and reliable leak detection and rapid isolation, should be considered extensions of the containment boundary and should be designed accordingly. 

Provide isolation on detection of high flow, low pressure, or external leak... 

The leak could have been stopped as soon as it was detected if an emergency isolation valve (Section 7.2.1) had been fitted in the pump suction line. On the rebuilt plant such valves were fitted on the pump suction lines, more combustible gas detectors and more extensive insulation were installed, plastic pump bodies were replaced by metal ones, and spillages were directed to collection pits. The plant was built in 1972, when these features were not common practice many improvements had been made since then, but they did not go far enough. Most of those made after the fire could have been made beforehand. 

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... 

---