Leak detection system reliability

WSRC, WSRC-RP-90-99, "Leak Detection System Reliability," March 9, 1990. 

The reports concluded that visual inspections of the K-Reactor tank have shown no unusual indications. The report also indicated that the operating. conditions do not adversely affect tank integrity and the material remains stable under normal load and credible accident conditions. These reports have been accepted by DOE however, recently WSRC reported that another report WSRC-RP-90-099, "Reactor Material Program-Leak Detection System Reliability" (Reference 15) will replace RP-SI-89-02. This item is a part of the ROMP DB-6.4, and has been reviewed and accepted in SER Section 6.7, System Integrity. 

If a leak does occur in the inner wall, a mechanism must exist to vent or drain the substance between the walls to a safe location. Connections must be provided to neutralize, clean, and hydrotest the annular space after a failure. The annular space must also receive preventive maintenance to assure its proper operation. Periodic checks of the integrity and reliability of leak detection systems should be required. 

For a leak-detection system that features fixed-point detectors to be reliable, it must be monitored and calibrated frequently. As discussed in Section... 

Another study for the SG safety is aimed for the FBR design concept which eliminates the secondary sodium loop. To support this conceptual feasibility study, double-wall SG design is proposed and examined. Since a reliable leak detection system is essential for this design, detailed investigation of tube failure detectability is performed. A helium gas system in the g of double-wall tube is used for detection. In case of an inner tube failure, steam in the helium system is detected. On the contrary, helium gas contents in sodium is detected in case of an outer tube failure. Both experimental studies and code development are in progress to validate this detection system. 

Apart from the prototype FBR MONJU, much research and development (R D) has already been performed to complete the design of the Demonstration FBR, sponsored by nine Japanese utilities, Electric Power Development Co., Ltd., and the Japan Atomic Power Company (JAPC). The R D included the development of new types of equipment for sodium cooled reactors such as highly reliable electromagnetic pumps and double-walled tube steam generators with leak detection systems for both sodium and water/steam. This new equipment is considered to become more important for the commercialization of sodium cooled reactors, and the 4S is adopting these technologies in its design. 

This has led to the need of improving the capability of the primary/secondary leak detection systems, to allow for a more accurate and reliable detection. 

WSRC has issued a summary report (Reference 42) that provides the basis for the capability, sensitivity, and reliability of the PWS leak detection system. As a result of the evaluation of this criterion, the staff concluded that there is reasonable assurance that online leak detection system will provide large margins of leak detection capability for SRS reactors. This conclusion is based on the fact that multiple diverse backup systems are installed to detect leaks. Procedures are also implemented to routinely detect leaks. The following is the evaluation of this criterion. 

There are three methods of release detection that are associated with modem tank systems.18,22 The first approach is to conduct an annual tank or line tightness test to detect small releases and to use more frequent monitoring by another method to detect large releases. All tank and line tightness tests must be performed at least once a year and must be able to detect leaks of 0.38 L/h (0.1 gal/h). In all cases where annual tightness tests are used, the regulation requires an additional form of leak detection in which tests on tanks are conducted at least monthly and those on pressurized lines at least hourly this ensures the detection of excessively large releases. For tanks, daily inventory records must be reconciled monthly, for pressurized lines, leaks of up to 11.4 L/h (3 gal/h) must be reliably detected. 

Failure of bellows can be detected by medium leaking via the bonnet vent. As this is not always evident and detection systems not always very reliable, people have become very inventive in trying to detect bellows failure by putting whistles on the bonnet vent in order to detect leakages from the bonnet vent. The bottom line, however, is that bellows are a very vulnerable but, for its correct operation, very critical part of a spring-operated SRV. Bellow balanced valves need more frequent maintenance or at least checking in order to assure proper operation. The system might have an SRV installed but with the bellows invisibly ruptured, the SRV has no purpose whatsoever. 

Chapter 6 addresses issues associated with postrelease mitigation, namely, the detection of a leak and the response of an organization to the event. Chapters 3, 4, and 5 cited numerous needs to detect releases and activate postrelease mitigation systems. In this chapter, the hardware that is available to perform this function, their operating principles, and maintenance requirements to ensure maximum system reliability are reviewed in some detail. 

In addition to the safety evaluation analyses of the IHTS for large leaks, R D work on sodium water reaction carried out to date includes small water leak experiments for the determination of a design base leak rate, development of reliable and real time detection system of water leaks using the acoustic signal as well as hydrogen detection, among others. Sodium fire characteristics and... 

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. 

The use of vibration analysis is not restricted to predictive maintenance. This technique is useful for diagnostic applications as well. Vibration monitoring and analysis are the primary diagnostic tools for most mechanical systems that are used to manufacture products. When used properly, vibration data provide the means to maintain optimum operating conditions and efficiency of critical plant systems. Vibration analysis can be used to evaluate fluid flow through pipes or vessels, to detect leaks, and to perform a variety of non-destmctive testing functions that improve the reliability and performance of critical plant systems. 

This system is ideal for thermoformed trays with porous lids and flexible pouches with one porous side. The test has been shown to detect leaks as small as 0.002 in. Guidmt and Medtronic have demonstrated the reliability of detecting leaks in blind tests and have quantified 100 percent of the purposely manufactured leaks in thermoformed trays (Hacked, 1996). In addition, there were no false positive readings in any of the unaltered packages. 

---