Session: 01-01: Robotics and Remote Handling and Viewing Technologies

Paper Number: 110426

110426 - Robotic and Remote Inspection of Dry Cask Storage Systems 

EPRI has supported collaborative development and demonstration of technologies for performing required inspections of dry cask storage systems. Robotic crawlers capable of traversing the overpack ventilation ducts and navigating around the surfaces of welded canisters stored within were developed, demonstrated, and deployed to inspect for aging degradation. Use of drones to conduct inspections of overpack vents for blockage was separately investigated. 

Aging management inspections of welded canister surfaces are typically required in Independent Spent Fuel Storage Installation license renewals. One of the potential canister aging degradation mechanisms is chloride-induced stress corrosion cracking (CISCC). EPRI collaborated with multiple partners to incorporate a video borescope with two different robotic platforms and demonstrate visual screening inspections capable of identifying CISCC precursors such as surface discoloration or corrosion. The systems can traverse through vents and navigate the annulus regions between the shielding overpack and the welded canister of various dry cask storage system designs, including both vertical and horizontal configurations. The annulus region is a moderately high temperature and high radiation environment.  The robotic platforms include a vacuum suction system that traverses the surface of horizontal canisters and a magnetic wheel system that travels through the annulus with the wheels on a vertical overpack liner. Feasibility studies have found that application of surface and volumetric technologies such as eddy current and ultrasonic testing can detect CISCC type flaws in canister materials. EPRI is beginning a project to further develop the CISCC flaw sizing capability of technologies that are compatible with the robotic platform. The ultimate goal of the project is to deliver equipment capable of detecting and sizing CISCC to the surface of a welded canister without removing it from the overpack.

EPRI is also adaptiing the robotic crawler technology to support enhanced cleaning efforts that may be needed to remove dust, deposits, and potential free iron with associated corrossion products from the surface of canisters to enable visual examination of the stainless steel canister welds and heat affected zones.

It is necessary to ensure that the overpack cooling air vents are not blocked. This is either accomplished with daily walkdowns to visually inspect the vents or with remote temperature monitoring. Use of drones to conduct periodic aging management inspections of the overpack structure is recognized as an established practice. EPRI completed a demonstration effort to investigate using drones to perform routine visual inspections of vents. Drones with cameras and thermal imaging equipment were evaluated for their capabilities to visually confirm that vents were not blocked and detect the temperature at the vents. Use of drones is feasible, however, the benefits associated with drone surveillance are currently limited. The use of automated flights and artificial intelligence to complete drone inspections would offer greater benefits. 
 

Presenting Author: Shannon Chu Electric Power Research Institute

Presenting Author Biography: Shannon Chu is responsible for research in support of used fuel extended storage. She led the effort to develop aging management guidance for welded dry storage canisters which may be subject to chloride-induced stress corrosion cracking (CISCC) and continues to support industry implementation of this guidance and related technical basis research.

Shannon previously supported the EPRI Materials Reliability Program (MRP) in projects to address stress corrosion cracking and thermal fatigue issues. Prior to joining EPRI, Shannon received an M.S. Nuclear Engineering degree from the University of California, Berkley and a B.S. Nuclear Engineering degree from the University of Michigan, Ann Arbor. She also spent one year training in the Region II office of the Nuclear Regulatory Commission as part of a graduate fellowship program.