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  4. Cable and Pipe Sealing in Operational Nuclear Plants

Cable and Pipe Sealing in Operational Nuclear Plants

by Karl Mosbacher, Global Segment Manager, Power.

Cable and Pipe Sealing in Operational Nuclear Plants

The global nuclear energy industry has faced a number of monumental challenges over the past several years. Natural disasters, rising operational costs, and competition from renewables and natural gas have left many in the industry wondering what the future holds. Plant age is also on the minds of many within the industry. In fact, Florida Power & Light’s Turkey Point Nuclear Power Plant will be 80 years old when it reaches the end of its most recent 20-year life extension (Natter, A. (2020). The U.S. May Soon Have The World's Oldest Nuclear Power Plants).  In the face of these difficulties one fact remains – nuclear is an energy source that will remain relevant for many years to come. However, the challenges, both real and potential, still exist. It is with this understanding that owners, EPCs, and maintenance personnel must work harder than ever to extend the life of nuclear plants and ensure operational reliability.

A small, but critically important, component to ensuring operational reliability is deciding how cable and pipe penetrations are sealed. Each operational nuclear plant on this planet contains thousands of cable and pipe penetrations. Building types such as reactor, fuel, and auxiliary all contain sensitive penetrations through walls, floors, electrical equipment, and underground infrastructure. These penetrations require protection ranging from fire, water pressure, electromagnetic interference, radiation, dust and debris, pests, and in many cases, a combination of these threats. Events such as Fukushima in Japan have driven the industry to take extra precaution when considering protection against catastrophic water pressure events in vulnerable plant areas. To put it plainly, mitigating these risks in order to preserve aging plants has never been more critical and more challenging.

Taken at face value, cable and pipe sealing seems to be an insignificant matter when facing the completion of a FLEX or life extension initiative. The truth is, selecting the right (or wrong) cable and pipe sealing solution can have a significant impact on your project’s success. While there are many cable and pipe sealing products available on the market today, Roxtec multi-cable cable and pipe transit seals are mechanical in nature and designed to meet the harshest of industrial environments in a plethora of applications.

Multiple demands

The very nature of how operational nuclear plants approach cable and pipe penetration seals is changing. Key penetration areas throughout a plant must withstand multiple threats at once, and hazards such as fire and water pressure are often combined whereas in the past they were treated as singular issues. Critical protection demands such as electromagnetic compatibility, EMC, shock and vibration, explosion, gas and vapor are paired with fire and water-related requirements. The necessity of multiple protection demands has increased dramatically since the Fukushima event. Key cable and pipe penetrations in critical areas of a plant are now being re-evaluated in order to meet fire and increased water pressure protection. Requirements such as the IAEA’s Safety Analysis Report (SAR) demand compartmentalization within site buildings to avoid the spread of not only fire, but also steam line breaks and moisture ingress. As seen in the diagram below, Roxtec cable and pipe seal products can accommodate several protection demands in almost any application.

The Roxtec system is resistant to:

Fire

Ensure certified fire protection. Prevent smoke from spreading.

Gas

Ensure complete tightness against air and gas pressure.

Water

Avoid water ingress. Prevent humidity, flooding and corrosion.

Pressure

Protect against catastrophic as well as constant pressure.

Electrical danger

Protect against EMI, EMP and lightning strike effects.

Particles

Take control of dirt, dust, chemicals and fumigants.

Pests

Keep snakes, insects and rodents out.

Blast

Protect against vibration, shock-waves and the risk of explosion.

Application types: Electrical equipment and enclosures

A core aspect of maintaining operational nuclear plants now and in the future is digitalization. Replacing decades-old electrical equipment with new switchgear, DCS, PLS, IO, and a variety of other equipment is becoming commonplace. While this offers nuclear plant operators an abundance of benefits, this digitalization brings about serious concerns of EMC. All of this equipment is susceptible to electromagnetic interference, which poses a risk to a nuclear plant’s operational reliability. This is why it is paramount to ground shielded cables in order to reduce or eliminate disturbances. Traditionally, this means labor-intensive installation of several grounding wires. With Roxtec EMC cable sealing solutions, shielded cable penetrations are not only environmentally sealed, but also protected from electromagnetic interference with the requirement of only one grounding wire per application (see figure 2). This provides superior protection along with a significant reduction in installation time. Roxtec also provides a number of non-EMC cable and pipe sealing solutions that provide environmental and IP protection while requiring only a small footprint of equipment space.

Application types: Walls and floors and underground structures

Wall and floor penetrations are common and numerous within the many structures that make up a nuclear power plant, but a “one-size-fits-all” cable and pipe seal will not always provide sufficient or correct protection.  

Water ingress

Take into consideration a below grade cable trench that penetrates the exterior wall of an auxiliary building. What is preventing a high water table or catastrophic flooding from filling the trench and subsequently entering the building? Roxtec cable and pipe seals are watertight up to 4 bar; that is over 133 feet of head pressure protection. This ensures that your building envelope is sealed and the exterior elements do not find ingress. This is also applicable to manhole and vault applications, especially when these structures ultimately lead to the interior of plant buildings (see figures 3a and 3b). 

Firestop and cable retention

Looking at a separate scenario, a cable spreading room is typically located directly below a control room and contains a large number of ceiling/floor penetrations. While the 1975 Browns Ferry fire demonstrated the dire importance of providing a proper fire barrier in this application, cable retention must also be taken into consideration. These large, heavy power cables are vertically run through the floor and into various pieces of equipment in the control room. If not properly supported, the weight of these cables can put strain on their ultimate terminations (see figure 4). In addition to offering significant fire ratings, Roxtec’s cable and pipe seals also provide robust cable retention through the mechanical compression that is inherent to the product.  

Product lifecycle and testing 

Roxtec invests greatly in testing of its cable and pipe sealing products. Tests involving fire, water pressure, EMC, shock and vibe, rodent mitigation and more ensure the highest level of protection is offered to nuclear plant customers (see figures 5a and 5b). Roxtec products also undergo accelerated aging testing to ensure the products stand the test of time. Due to the highly engineered quality of these seals, a product lifecycle of at least 25 years with no maintenance required can be expected. This also results in a positive impact from a site inventory standpoint. While many traditional, putty and foam sealants have a one year shelf life, Roxtec cable and pipe seals remain install-ready for several years. 

Functionality/installer experience

Roxtec’s multi-cable and pipe transit seals are designed with user experience in mind. The modular and mechanical nature of the product means that installation is quick and consistent. Full sealing is achieved through mechanical compression, not curing, which means requirements such as fire watching may be greatly reduced. As shown below in figure 6, Roxtec’s system also includes physical sealing indicators, which give inspectors a quick visual indication that the product is completely compressed and sealed. 

Consider Roxtec for your next project

The Roxtec sealing system was created for some of the harshest environments. This makes it an ideal fit for many applications within operational nuclear plants. To learn more about Roxtec’s products and services, visit www.roxtec.com to begin the process of ensuring operational reliability at your plant.

Author

Karl Mosbacher

Global Segment Manager Department Power and Process Industries
Karl Mosbacher