Around the clock monitoring16 January 2018
Coltraco Ultrasonics explains why continuous monitoring of fire protections systems is critical at nuclear facilities and how it can be achieved.
Continuous improvements and maintenance are required of the fire safety systems at nuclear power plants due to the safety critical nature of the site. Accidents in nuclear plants around the world have continued to demonstrate the vulnerability of safety systems to fire and its effects.
The International Atomic Energy Agency states clearly in its standard, Fire Safety in the Operation of Nuclear Power Plants, that the effects of a single failure in fire safety systems, such aa a system not performing its required function, can be detrimental.
The Chernobyl disaster is an example. Inherent reactor design flaws, and reactor operators arranging the core in a manner contrary to a test checklist, eventually resulted in uncontrolled reaction conditions that flashed water into steam, generating a destructive steam explosion and a subsequent open-air graphite fire. The fire produced considerable updrafts for about nine days, which lofted plumes of fission products into the atmosphere. The radioactive inventory released during
this very hot fire phase was similar to the airborne fission products released in the initial destructive explosion. Over 30 years later investment into the site is still required. Flamgard Calidair provided fire shut-off dampers to the site, as part of an €1.5 billion multinational engineering project.
Fires still occur at nuclear power plants – in 2017 an explosion at the Flamanville nuclear plant in France was deemed “very serious” by industry experts. A significant technical issue led to a blast in the turbine hall in the unit. Although there was no radioactive leak, a thorough investigation is being conducted into the event.
Going beyond standard compliance
Coltraco Ultrasonics provides continuous monitoring to the gaseous extinguishing systems at power plants, going above and beyond existing standards. The International Atomic Energy Agency’s standards are clear in their demands:
“2.13: Effective procedures for inspection, maintenance and testing should be prepared and implemented throughout the lifetime of the plant with the objective of ensuring the continued minimisation of fire load, and the reliability of the installed features for detecting, extinguishing and mitigating the effects of fires.”
Three of the fire protection measures stated in the standards that should be regularly inspected, maintained and tested are:
- passive fire rated compartment barriers and structural components of buildings, including the seals of barrier penetrations,
- a supply and distribution pipe,
- gaseous and dry powder fire extinguishing systems.
Gaseous extinguishing systems
Gaseous extinguishing systems protect important infrastructure against special hazards, and are fundamental for the safeguarding of critical facilities. Gaseous extinguishants have a specific design purpose, as an effective medium for extinguishuing flammable liquid fires and fires in the presence of electrical and ordinary Class A hazards. However, it should not be forgotten, in planning comprehensive schemes, that there may be hazards for which these media are not suitable, or that in certain circumstances or situations other dangers may require special precautions. The appropriate fire authority, the health and safety authorities and insurers all have valuable input to the consideration of these, as do the prevailing national standards and statutory regulations.
Gaseous extinguishing systems are highly pressurised: 29-48bar for CO2, and up to 300bar for Inergen and nitrogen. The risk of the agent contents leaking and discharging is widely accepted by the industry and this is shown in the regulations for their upkeep, because it is accepted that gaseous extinguishing systems are dynamic and not passive or static.
Cylinders accidentally discharge. CO2 can cause fatalities if it does. Around 1% of pressure gauges fail and 25% of valves do too. In Germany they constantly monitor at the cylinder’s weakest point – the cylinder neck. This is a haphazard approach to the complex engineering world that a dynamic pressurised fire system has to serve.
In ISO 220.127.116.11 the regulations explain that the storage container contents shall be checked at least every six months as follows:
a) Liquefied gases: for halocarbon agents, if a container shows a loss of agent in quantity of more than 5% or a loss of pressure (adjusted for temperature) of more than 10%, it shall be refilled or replaced.
b) Non-liquefied gases: for inert gas agents, pressure is an indication of agent quantity. If a container shows a loss of agent quantity or a loss of pressure (adjusted for temperature) of more than 5%, it shall be refilled or replaced.
Essentially, it is known in regulations that the gaseous systems leak and have to be maintained. Given that the gaseous systems are designed specifically to the individual need of the room or building, a 5% loss of agent may mean that they would not fully extinguish a fire.
Manually weighing a cylinder is costly and dangerous. The neglect of continuous monitoring – of the fundamental protection provided by the gaseous extinguishing systems – is to the peril of the lives of occupants of the premises and at the risk of crippling financial and reputational loss to the facility.
A holistic approach
Clean agent fire suppression systems rely on holding the agent in the room for the correct amount of time, so it is concentrated enough to extinguish the fire. This is part of the total flooding principle, on which inert gases and halocarbon agents both function.
Room integrity tests are imperative to determine the hold time and peak pressure needed for successful fire suppression. The level of leakage is carefully monitored to ensure the correct concentration is achieved; room integrity must be ‘tight’ enough to ensure sufficient retention time, according to NFPA or ISO, yet remain ‘loose’ enough to prevent enclosure damage at discharge.
The testing of room integrity is necessary for adherence to standards and requirements outlined by the NFPA 2001: Standard on Clean Agent Fire Extinguishing Systems and ISO 14520: Gaseous Fire-Extinguishing Systems, established concerning enclosure design and testing.
Leakage reduces room integrity and will change the hold time and peak pressure, placing room contents and potentially wall structures at risk. Retention time is more often a challenge for small rooms with chemical agents than large data halls protected with inert gases, where several hours of agent retention are possible (and might also be necessary for business continuity purposes).
Finding and addressing leakage is therefore important. Leakage paths include gaps and cracks, and penetrations, as well as fabrications constructed from porous materials. The more airtight the construction of the enclosure boundary the better for system performance. Whilst leakage is required for the pressures generated through the discharge, it should be purpose- engineered in the form of pressure relief vents; natural leakage is undesirable. The predicted retention time must meet the minimum required by the stakeholders and regulators; typically, this will be a minimum of 10 minutes.
Solutions for 24/7 monitoring
Faced with this problem, Coltraco Ultrasonics and commissioned the first Permalevel in 2003. Coltraco has now developed the Permalevel® Multiplex, a fixed fire suppression monitoring device, designed for permanent contents verification. It ensures that fire suppression systems are always fully operational and that no accidental discharge has occurred.
The system offers adaptability for purpose, 24/7 remote access to the systems status, an interruptible power supply and remote real- time monitoring. The UK’s Atomic Energy Authority asked Coltraco Ultrasonics to tailor-make it a solution to constantly monitor a special application using the Permalevel® Single Point for over ten years.
The Portascanner® 520 provides precise data concerning leak locations and aperture. It complements Coltraco’s range of equipment for testing fire extinguishing systems.
It works with door fan testing to meet the total requirements for fire safety regulations and ensure the continuous fire protection of rooms using clean agent fire suppression systems. As door fan testing is a reliable and trusted method of room testing, it is expected that its will continue to be the dominant method. The Portascanner® improves the final stage of room integrity testing – the search for leak sites in the case of a leakage excess – where we believe it can vastly improve accuracy and operational efficiency. A device such as this has never been used before in this industry, and is the first to place emphasis directly on this important aspect of room integrity testing.