Data acquisition related to improving operability of ROVs for the retrieval of HASWS stored waste

Tameta, Yuito ; Sano, Kyohei ; Takano, Yugo*; Yamamoto, Masahiko  ; Nakazaki, Katsutoshi; Akiyama, Kazuki 

At the High Active Solid Waste Storage (HASWS) of Tokai Reprocessing Plant, high active solid waste generated from the reprocessing process is stored. In the wet cell, hull cans containing fuel cladding tubes (hulls) and end pieces are stored, along with used filters and contaminated equipment. It is being considered that utilizes a small underwater remotely operated vehicle (ROV) along with a lifter for recovering and transporting objects from the seafloor for the retrieval of the waste stored in the HASWS. Mock-up tests were conducted in FY2022 and FY2023 to verify the feasibility of retrieving waste using the ROV and the lifter. In this study, to achieve safer and more reliable waste retrieval, improvements were made to each component, including the ROV cable, waste gripping grab, lifting hook, lifter, and ROV monitoring camera, and data were collected to evaluate operational performance. For the ROV cable, attaching a float to the rear section of the ROV cable to reduce its weight facilitated forward-tilt operation and improved the ROV's attitude stability during wire-cutting. For the waste gripping grab, attaching a jig to the tips of the grab of the lifter (grabtype) enhanced the gripping stability of the hull can. For the lifting hook, setting the ring diameter of the lifter (hook-type) to 15 cm shortened the time required for grasping and improved accessibility to the hook. For the lifter, using lifters with modified internal structures enabled fine air-volume adjustment and reduced blockage of air passages, thereby improving the stability of air supply and exhaust. For the ROV monitoring camera, adding a light near the ROV monitoring camera in a dark environment ensured sufficient cell illumination and enhanced cable visibility.