One of the most essential tools in maintaining nuclear safety is the In-Service Inspection, or ISI, performed routinely during refueling outages. These inspections ensure that critical systems and components inside the reactor remain in safe, operable condition. They are required by regulatory bodies such as the Nuclear Regulatory Commission (NRC) and follow ASME standards.

The goal of these inspections is to identify, evaluate, and mitigate degradation mechanisms like corrosion, fatigue, cracking, and other age-related wear before they impact plant safety or efficiency. Preferred Engineering supports facilities with their ISI inspection by providing both professional guidance and high-quality nuclear outage equipment that enables Steam Generator (SG) inspections.

There are two primary methods for performing the SG inspection, using:

1. Loop plugs, or
2. A temporary reactor head

Preferred Engineering designs and manufactures both pieces of equipment. Let’s talk a bit more about these two methods.

Loop plugs method

Using loop plugs, plant operators can drain down steam generator loops, allowing simultaneous inspection work to occur both in-core and in the steam generator. This parallel work structure helps:

• Minimize critical path impact
• Shorten outage durations
• Increase overall outage efficiency

Temporary Reactor Head Method

A temporary reactor head (or temporary reactor pressure vessel cover) seals off the Reactor Pressure Vessel (RPV) while keeping the reactor cavity filled with water. This method enables the cavity to remain flooded while the RPV is drained. This provides:

• Greater flexibility in water management
• Improved shielding and safety
• Compatibility with modern outage procedures

Preferred Engineering ISI support

Our engineered solutions allow facilities to optimize outage schedules, manage radiation exposure, and ensure regulatory compliance during ISI activities. With decades of experience, we can help you get the job done safely and efficiently.

Check out the product pages for our Loop Plugs and Temporary Reactor Pressure Vessel Cover for more information.