Non-destructive testing helps nuclear plants identify problems with concrete structures

Assessing the integrity of concrete structures located on-site at nuclear facilities is critical to safe operation. Even more so when these structures are located in nuclear containment areas. However, taking a plant out of production by invasively testing concrete structures that provide containment isn’t practical because it requires the physical destruction of structures to locate a problem before any corrective actions can be taken.

“Non–destructive testing techniques are vital to a nuclear power plant’s maintenance and safety.”

Non-destructive testing (NDT) methods are playing an increasingly important role in the power generation industry. NDT services are not only used during the construction phase of a plant, but they are also vital to maintenance and safety. As more advanced testing methods are developed, NDT procedures are becoming more precise. This means being able to locate structural defects more accurately, and in a more efficient and timely manner.

Nuclear power plants have been in operation for about 50 years. Non-destructive testing techniques have become the primary method for operators to minimize plant downtime and promote enhanced performance of production assets.

Concrete testing
NDT techniques that evaluate the structural integrity of concrete have been used in other civil engineering cases, such as testing of roads and bridges. But in recent years, these non-invasive methods have become more common on nuclear facilities.

In 2013 the German Federal Institute for Materials Research and Testing issued a report about non-destructive testing and examined techniques that could be used on concrete structures in nuclear power plants. The report broke down the various situations in which non-destructive testing could be used. Researchers used such techniques to:

• Locate tendon ducts and determine the condition of the grout materials. Radiography, ultrasonic and active thermography have shown good results in such cases.
• Detect inclusions of different materials or voids adjacent to the concrete side of the containment liner. The methods used to detect cracking, voids, delamination and honeycombing are also used here.
• Detect cracking, voids, delamination and honeycombing in concrete structures. Ultrasonic methods, impact echo, ground-penetrating radar, acoustic emission and fiber-optic sensors are used to complete these tests. Pattern recognition using a camera is also used.
• Location of steel reinforcement in concrete and determine its cover depth. Magnetic, ultrasonic and inductive methods are often used in this case. A combination of radar and magnetic methods were found to be effective for determining cover depth.
• Identify corrosion on the concrete side of the containment liner. Electrochemical methods have been used most often in these instances.

Non-destructive testing technologies are an effective and accurate means for determining if certain asset components are at risk for structural flaws.  Because concrete is a durable material and can survive decades before any kind of deterioration occurs, precise and performance-enhancing testing is a valuable tool for plant operators and maintenance.

By Jerry Harper