Dry Casks 101: What Do Robots Have to do With Dry Cask Storage?

Darrell Dunn
Materials Engineer

CASK_101finalCutting-edge robot technology is making it easier to inspect inside spent fuel dry cask storage systems.

You may remember from past blog posts that most spent fuel dry cask storage systems, or casks, consist of stainless steel canisters that are welded shut to safely contain the radioactive contents. The canisters are in turn placed inside thick storage overpacks to shield plant workers and the public from radiation. As these casks remain in use for longer time frames, the ability to inspect canister surfaces and welds will become an important aspect of the NRC’s confidence in their safety.

To be clear: techniques for inspecting canister surfaces and welds have been used for decades. These techniques are collectively known as nondestructive examination (NDE) and include a variety of methods, such as visual, ultrasonic, eddy current and guided wave examinations.

img2 (002)Where do robots come in? They are a delivery system. Robots are being developed to apply these NDE techniques inside casks. Not just any robot will do. These robots need to fit into small spaces and withstand the heat and radiation inside the cask. The state-of-the-art is evolving quickly.

To date, the Electric Power Research Institute and cask manufacturers have successfully demonstrated robotic inspection techniques to NRC staff three times: at the Palo Verde plant in Arizona (Sept. 2-3, 2015), at the McGuire plant in North Carolina (May 16-19, 2016), and just last month, at Maine Yankee (July 12-13, 2016).

At Palo Verde, the robot was used to deliver eddy current testing instrumentation inside a cask. Eddy current testing detects variations in electromagnetically induced currents in metals. Because it is sensitive to surface defects, eddy current testing is a preferred method for detecting cracks. The inspection robot was used to examine part of the mockup canister fabrication weld. An EPRI report provides a detailed description of the Palo Verde test. Future reports are expected on the McGuire and Maine Yankee demonstrations. These demonstrations are helping to refine the robots’ designs.

Cutaway Cask Mockup with Robot (002)The Maine Yankee demo was conducted in July 2016 on a cask loaded in 2002. The demo involved a robot maneuvering a camera with a fiber optic probe, which meets the industry code for visual examinations, inside the cask. The probe was able to access the entire height of the canister, allowing the camera to capture images of the fabrication and closure welds. The welds showed no signs of degradation. The canister was intact and in good condition.

The robot was also able to obtain samples from surfaces of the cask and canister. These samples are being analyzed for atmospheric deposits that could cause corrosion.

Ultimately, if degradation is identified, cask users would select their preferred mitigation and repair option.  They would have to meet the NRC’s safety requirements before implementing it.

Cask inspections are important to ensure continued safe storage of spent nuclear fuel and robots will continue to be a helpful tool in this important activity.

When Plans Change — Discontinuing Some Rulemaking

Leslie Terry
Team Leader
Office of Administration

NRC does its job with regulations contained in the Chapter I of Title 10 of the Code of Federal Regulations. These regulations cover everything from commercial 10cfrreactors to nuclear materials used in a variety of settings, to storing and disposing of nuclear waste.

A year ago we explained how we keep our rules up to date and unveiled a web page to provide periodic updates on our rulemaking activities. To recap, we identify the rules already under development and any new rules that need to be written. We then rank by priority every rule, regardless of the regulatory area. This way we ensure we’re focusing our resources on the high priority rules that most contribute to the NRC’s key strategic goals of safety and security. We also monitor the progress of our rulemaking activities and develop budget estimates for preparing new rules.

Sometimes our rulemaking plans change. Our Commissioners voted recently to approve a staff recommendation to discontinue eight rulemaking activities that were in the early stages of development.

During our most recent review, the staff identified several rulemakings that were in the early stages of development, but staff believes are no longer needed to meet the NRC’s key strategic goals of safety and security. The staff wrote a paper requesting Commission approval to discontinue nine activities, and discussed a 10th rulemaking the Commission had already decided to discontinue. The Commission agreed to discontinue seven of the nine rulemakings the staff proposed.

The discontinued rulemakings covered a variety of topics, and the basis to discontinue is different for each rulemaking. For example, we have a rulemaking underway to better define the requirements for reactors that have permanently shut down and are decommissioning. We felt that rulemaking was an appropriate place to address decommissioning options, including entombment for power reactors, so we are discontinuing a separate rulemaking on entombment.

We also feel the current case-by-case framework is sufficient for reviewing the limited number of requests we’ve received for alternate disposal pathways for waste with very low activity. So we’re discontinuing a rulemaking to set generic requirements, which had already been on hold for a number of years. Instead, we’ll take another look at the issue as part of an assessment of low level radioactive waste disposal, and if we decide that a rulemaking is necessary, we’ll ask the Commission to revisit the issue.

We encourage you to read more about the Commission’s vote and the staff’s proposal on our web site. You can also check our prioritization web page for future updates on our rulemaking activities.