Nuclear Reactor Vessel in-service inspection using ROVs

Amanda Coulas | October 15th, 2012

Strong Teamwork Makes Thermal Sleeve Inspection Great Success

October 15, 2012

During the Unit 2 10-Year Reactor Vessel In-service Inspection (ISI), the Safety Injection (SI) thermal sleeve on the 2A1 Cold Leg was found rotated and partially dislodged. And, the 2B1 SI Cold Leg Nozzle Thermal Sleeve was found completely dislodged at the bottom of the vessel annulus -- a space between concentric circles -- against the core support barrel skirt. The conditions were identified with a systematic underwater inspection using a submersible submarine camera. Several plants with the same design have experienced the same condition.

To address the condition, a team was assembled to analyze the acceptability of operating without the 2B1 sleeve as well as the potential risks of operating with a rotated sleeve. The analysis concluded that operating without the 2B1 thermal sleeve is safe. But, a concern was raised regarding ongoing suitability of the 2A1 rotated sleeve.

The team decided to conduct a Safety Injection Tank (SIT) dump test through the 2A1 pipe and nozzle to assess the integrity of the rotated sleeve. This would require a post-test underwater in-pipe inspection of the sleeve with a robotic submarine camera, similar to what had been used in the previous initial inspection. But, the initial quotes for the second submarine inspection were very high.

Let us help find the right ROV for your inspection projects and applications

Project Manager Rusty Hurt said, “The submarine vendor that we decided to use for the project, Deep Trekker, saved a large percentage of money compared to other vendor proposals. Deep Trekker also generously offered hands-on technical assistance. They even agreed to provide a spare backup sub for the inspection, and shipped a prototype sub that came equipped with a gripper attachment that could be used to retrieve the 2A1 sleeve, should it become dislodged from the SIT dump test. All of this was at no additional cost. We are very grateful for their generosity.”

Project team member Dennis Isom said, “This experience was one to be remembered. The vendor support we received from Deep Trekker was second to none. The representative, Sam Macdonald, sent to our site was very knowledgeable on the physical operation of the sub and the design and function of all aspects of the equipment.

“Radiation Protection was also very supportive during the evolution. Barry Robertson did an excellent job setting up the video and recording equipment and getting the feed out of containment.

“And, Engineering made themselves available to monitor the inspection real time to verify we captured all critical views of the sleeve prior to removing the sub from the reactor cavity. This eliminated any possible rework and/or re-entry into the cavity with the sub.

“The preparation and mock-up testing performed was a large part of the project’s success. The project was well thought out and executed.”

On Tuesday, October 2, the SIT dump test was performed, and the project team immediately mobilized to perform the remote inspection. Within 30 minutes of performing the SIT dump test, the sub was deployed, motored into the RCS piping to the 2A1 nozzle and began transmitting a live video feed of the sleeve out to the inspection analyst, Mark Joseph, in Juno Beach via the FPL intranet.

Based on the live camera observation, it was determined that the sleeve had not perceptibly moved, and that it could be used as-is with no further actions required. The sub was withdrawn, secured by Radiation Protection and the team demobed.

Rusty said, “Because of excellent planning, close vendor support, and interdepartmental cooperation, the project was successfully implemented in less than 60 minutes.

As a major bonus, the final cost of performing, including the cost of purchasing the sub was a fraction of the projected cost from the original inspection contractor.

This team demonstrated the great successes we can achieve when we live our Nuclear Excellence Model core principle of Strong Teamwork.”