Robotic spent fuel inspection trials bring commercial use closer

U.S. researchers have completed eight field trials of robotic dry cask storage inspection and are widening drone testing from containment structures to fuel pads, Jeremy Renshaw, Program Manager - Used Fuel and High-Level Waste at the Electric Power Research Institute (EPRI), said.

As nuclear plants age and dry cask storage capacity grows, cost-effective storage inspections are required to support ageing management and license extensions.

Over 2,800 dry cask storage systems (DCSSs) are in operation in the U.S. and around 200 systems are added every year.

EPRI has been working with industry and research groups to develop new robotics and non-destructive evaluation (NDE) systems that will lower spent fuel maintenance costs and improve safety.

DCSS inspections are challenging, requiring detailed examinations amid high temperature and radiation levels past confined entry and exit pathways and internal obstructions.

To meet this challenge, EPRI and its research partners have successfully combined the latest robotics and probe designs with high sensitivity NDE techniques, Renshaw said at the Nuclear Decommissioning and Used Fuel strategy Summit on October 1.

"We are able to get really high-sensitivity to relatively small flaws so we are very excited about this and where this is going," he said.

Field trials have been completed at eight U.S. nuclear plant sites, including a blind DCSS inspection demonstration at Pacific Northwest National Laboratory (PNNL), Renshaw said.

"We are making lots of progress with these field trials, we've gotten lots of very good data and improved the state of where the robotics and inspection systems are," he said.

Further field trials are planned, including testing in a fuel-loaded canister at Entergy’s 620 MW Vermont Yankee plant, shut down in December 2014, Renshaw said. The Vermont Yankee Independent Spent Fuel Storage Installation (ISFSI) hosts 58 Holtec dry storage casks and spent fuel transfer was completed in August.

Fit for purpose

EPRI and industry partners have developed robots which can perform visual inspections, surface temperature measurements, radiation dose measurements, surface cleaning, and surface sampling. Some 23 component and system mock-ups have been developed for industry use.

In particular, the researchers have made significant advancements in NDE techniques over the last several years.

Four of these techniques --Visual (VT), eddy current testing, ultrasonic testing and EMAT/Guided Waves (GW)-- have already met requirements on temperature and radiation resistance, sensitivity, compatibility for DCSS inspection, and short-term deliverability, Renshaw said.

"We are ready to go with a capable technique that fits the application needs," he said.

In parallel, researchers have been adapting robotic technology to the different DCSS designs available.

Robots designed for Holtec and NAC storage casks have completed field trials and have fulfilled almost all of EPRI's development objectives, Renshaw noted.

"We are getting close-we are not there yet, but we continue to march down that path," he said.

            US Independent Spent Fuel Storage Installations (ISFSI)

                                                       (Click image to enlarge)

Source: NRC, August 2018.

Nuclear operators are increasingly turning to robotics solutions to reduce costs and improve safety. 

Canada's Bruce Power has used specialised digital robotic systems to shorten inspection of reactor systems such as fuel channels during planned maintenance outages.

France's EDF and environmental services group Veolia recently agreed to co-develop robotics solutions for dismantling graphite-moderated gas-cooled reactors.

Robotics have already been deployed at the decommissioning of Chooz A, EDF's first PWR decommissioning project. Westinghouse, the turnkey contractor for the reactor dismantling at Chooz A, is using a robot called ‘Predator’ to segment 25,000 bricks in the reactor vessel.

EPRI has also been developing integration of robotics advancements with more efficient cutting technologies to reduce dismantling costs.

Drone flights

EPRI has also been testing Unmanned Aerial Vehicles (UAV), or drones, with image analysis technologies for remote monitoring applications.

Manual inspections of large nuclear structures and systems can be time-consuming and costly, involving scaffolding, ropes and greater safety risks.

Drones fixed with the latest high-resolution cameras and thermal-based imaging can provide high-quality fault detection data.

EPRI and its research partners have been using different drone technologies to inspect containment structures. Shortlisted designs have been submitted to blind testing scenarios.

The tests show that drones can perform these inspections in less than half the time of manual inspections and at less than half the cost, Renshaw told the conference.

"It's a great technology platform that we can use very efficiently," he said.

Future projects

EPRI will soon test the use of drones for regular inspections of ISFSIs and other component monitoring and plant security applications.

By the end of 2018, EPRI is to perform an autonomous “walk-down” of an ISFSI site, Renshaw said.

Regular ISFSI inspections could be performed “better, faster and more safely by a drone," he said.

Going forward, EPRI plans to examine wider applications of drone and robotics technology, incorporating the latest data analytics advances including real-time image processing, Renshaw said.

“We are really excited about where this is going…There is a lot of innovation going on in nuclear right now," he said.

Nuclear Energy Insider