Leak monitoring system

Positive indication of valve leakage will be provided in the control room. Monitoring will be provided by an Acoustic Leak Monitoring System (ALMS) consisting of an accelerometer (acoustic sensor) mounted downstream of each valve. A plant annunciator alarm will be provided to alarm if the valve is not fully closed. The ALMS is part of the NSSS Integrity Monitoring System (see Section 7.7.1.6.2 for a detailed description). 

Indication of safety valve leakage is provided by the Acoustic Leak Monitoring System (ALMS). The signal from the accelerometer sensor is monitored continuously, along with the RMS value of the signal computed. These signals are compared to a pre-established baseline value and alarmed in the main control room via the Nuplex 80+ Data Processing System (DPS) and Discrete Indication and Alarm System (DIAS) displays (See Section 7.7). 

Another part of the NRC effort to develop a resolution to this issue was work performed by Argonne National Laboratory to develop an advanced acoustic leak monitoring system. This work, reported in NUREG/CR-5134 (Reference 5), indicated that such a system appears capable of locating as well as quantifying pipe leaks. 

The System 80+ Standard Design incorporates a NSSS Integrity Monitoring System, which is a system that detects deterioration of the NSSS pressure boundary. A description of this system is documented in CESSAR-DC, Section 7.7.1.6. The system has three subsystems the Internals Vibration Monitoring System (IVMS), the Acoustic Leak Monitoring System (ALMS), and the Loose Parts Monitoring System (LPMS). 

Permeability of Liners with Leak Monitoring Systems.438... 

HDPE geomembranes can be combined with various other components (leak monitoring system, geosynthetic clay liners of high durability, polymer amended sand-bentonite-mixtures, capillary barriers) to form alternative composite liners as reliable and cost effective capping systems (Simon and Muller 2004). Such alternative capping systems are tested and increasingly applied for landfills and for the containment of contaminated sites. 

In the following, leak monitoring systems for geomembranes will be considered (Muller and Seeger 2002). There are various possible options, but three main types of control methods can be distinguished ... 

Leak monitoring systems that enable measurement of electrical anomalies due to a hole. The idea here is that geomembranes are impermeable not only for liquids but also for electric current. It could be said that virtual electrical holes or electrical leak paths are measured which only form potential leak paths for water flow. 

Considering these different types of leak monitoring systems in more detail it will become clear that in most cases only electrical systems are practically capable of providing adequately accurate control for large-area geomembrane liners. Therefore only the requirements on these systems will be analysed in more detail in later sections of this chapter. 

The first type of leak monitoring system requires sensors applied beneath the geomembrane which exhibit specific reactions to changes in the subgrade due to water input through a hole. This concept has been used by various manufacturers of which three examples will be briefly discussed. 

Fig. 11.6. This picture of a prepared subgrade shows another version of a leak monitoring system. The electrodes are distributed regularly over the subgrade and each electrode has its own connecting cable...

All leak monitoring systems discussed so far are permanently mounted and therefore capable of reliable long-term liner monitoring if their compo-... 

The approach described in Sect. 11.1 for permanently installed electrical leak monitoring system can be used to undertake a leak detection survey as a CQA measurement on geomembranes already covered with a layer of soil (the soil-covered geomembrane system). Typically, the layer thickness has to be less than 1 metre to obtain the appropriate efficacy and spatial resolution (Laine and Darilek 1993 Laine and Miklas 1989). However, in some cases leaks might be detected even under a much greater thickness of cover (Colucci et al. 1999 Laine et al. 1997). Instead of using an electrode... 

Long-term Behaviour and Handling of Leak Monitoring Systems... 

Even the schematic diagrams of Figs. 11.1a and b indicate that a leak monitoring system comprises components for which various durability requirements are valid. Buried cables and sensors under the geomembrane can only be repaired at very great expense if at all. Cables and sensors... 

Notwithstanding that requirement the leak monitoring system should also exhibit a high degree of redundancy with regard to the sensors failure of a few sensors should not be allowed to lead to the collapse of the whole system. 

The leak monitoring system must therefore be supplied with equipment which can divert voltage surge on the buried components and protect people and the control and assessment system. An independent expert inspector must have examined and reported on the lightning prevention equipment. 

Installation of the leak monitoring system must be integrated into the liner construction technology. The manufacturer s installation procedure must be adapted to these conditions. In the appendix of the recommendation document, the AK DKS Working Committee has published sample drafts for the additional technical contract conditions and the performance list for an invitation to tender for leak monitoring systems plus a quality assurance plan for their installation. It is first advisable to pilot the leak monitoring system in a test field of a minimum area of 1000 m, which may be part of the liner itself The structure of the test field should be iden-... 

Table 11.1. Survey of the occurrence of frequencies of faults found with electric leak monitoring systems on 94 installation sites totalled one million square meters (Nosko 1998)...

---