Test using ROV and lifter for recovery waste of HASWS wet waste

Sano, Kyohei; Tameta, Yuito; Akuzawa, Tadashi; Kato, Soma; Takano, Yugo*; Akiyama, Kazuki

JAEA-Technology 2024-018, 68 Pages, 2025/02

JAEA-Technology-2024-018.pdf:4.73MB

High Active Solid Waste Storage Facility (HASWS) at the Tokai Reprocessing Plant (TRP) is a facility for storing highly radioactive solid waste generated from the reprocessing operation. Wet cells in HASWS store hull cans that contain fuel cladding tubes (hull) and fuel end pieces remained after the spent nuclear fuel shearing and dissolving, as well as used filters and contaminated equipment. Dry cells in HASWS store analytical waste containers that contain waste jugs and the other waste generated from analytical operation of samples in TRP. Since HASWS does not have waste recovery equipment from the cells, it is considered that recovery equipment to be installed. In the wet cells, methods of recovery wet-stored waste are being considered that utilize a ROV, which has been used in decommissioning in the UK, and a lifter, which is used in the marine industry to float and transport items sinking to the bottom of the sea. To confirm the feasibility of the recovery method that combines the functions of the ROV and the lifter, tests for removing waste were conducted in steps that came closer to the real environment: a "unit test" to confirm the functions required of each of the ROV and the lifter, a "combination test" to combine the ROV and the lifter to move waste underwater, and a "comprehensive test" to retrieve waste in an environment simulating the hull storage facility. Through this test, the ROV and the lifter were able to perform a series of tasks required to recovery waste - cutting the wires attached to the waste, attaching a lifter to the waste, moving the waste to under the opening, and attaching the recovery device to the moved waste - in series, confirming the feasibility of the method for recovery wet-stored waste using the ROV and the lifter.

Effect of temperature on escape behavior of Cl ion concentrated in metal crevices

Soma, Yasutaka; Kato, Chiaki

Dai-68-Kai Zairyo To Kankyo Toronkai Koenshu (CD-ROM), p.205 - 206, 2021/10

This study investigates the effect of temperature on dissipation behavior of Cl ion within the crevice of stainless steel. Concentration of Cl ion was evaluated by conductivity measured by using sensors installed at crevice specimen. At 50 and 80 C, Cl ions within the crevice of PEEK and Pt dissipated in accordance with concentration diffusion. On the contrary, dissipation speed of Cl ions inside the Type-304L stainless steel were much lower than those anticipated by simple concentration diffusion. This behavior attribute to the anodic dissolution of stainless steel inside the crevice, therefore, to quantitatively understand the effect of temperature on the dissipation behavior, it is necessary to know the anodic dissolution rate and occurrence of localized corrosion. Numerical analysis taking the effect of concentration diffusion and migration into account is also needed.

Research and development of thick rubber bearing for SFR; Aging properties tests of semi full-scale thick rubber bearing

Watakabe, Tomoyoshi; Yamamoto, Tomohiko; Fukasawa, Tsuyoshi*; Okamura, Shigeki*; Somaki, Takahiro*; Morobishi, Ryota*; Sakurai, Yu*; Kato, Koji*

Nihon Kikai Gakkai Rombunshu (Internet), 83(850), p.16-00444_1 - 16-00444_14, 2017/06

https://doi.org/10.1299/transjsme.16-00444

A seismic isolation system composed of a thick rubber bearing and an oil damper has been developed for Sodium-Cooled Fast Reactor. This paper focused on the aging properties of thick rubber bearings, such as basic mechanical properties and ultimate strength. Aging of the rubber bearings was reproduced using thermal degradation based on Arrhenius law.

Development on rubber bearings for sodium-cooled fast reactor, 4; Aging properties of a half scale thick rubber bearings based on breaking test

Watakabe, Tomoyoshi; Yamamoto, Tomohiko; Fukasawa, Tsuyoshi*; Okamura, Shigeki*; Somaki, Takahiro*; Morobishi, Ryota*; Sakurai, Yu*; Kato, Koji*

Proceedings of 2016 ASME Pressure Vessels and Piping Conference (PVP 2016) (Internet), 8 Pages, 2016/07

http://doi.org/10.1115/PVP2016-63105

A seismic isolation system composed of a thick rubber bearing and an oil damper has been developed for Sodium cooled Fast Reactor. One of the advantages of the isolation system is employing the thick rubber bearing in order to realize the longer vertical natural period of a plant, and it leads to mitigation of seismic loads to mechanical components. Rubber bearing technology has progressed based on many past studies, but test data regarding an aging effect is not enough. Also, there is no data of linear strain limit and breaking behavior for the thick rubber bearing after aging. This paper focuses on aging properties of the thick rubber bearing, such as basic mechanical properties and ultimate strength. An aging promote test of the thick rubber bearing was performed by using 1/2 scale and 1/8 scale rubber bearings. Aging of the rubber bearing was reproduced by thermal degradation, where the target aging period was 30 years and 60 years. The load deflection curves of the thick rubber bearing after aging were obtained through the horizontal and vertical static loading tests, and the aging effect was evaluated by comparing with the initial mechanical properties.

Multilayered surface oxides within crevices of type 316L stainless steels in high-temperature pure water

Soma, Yasutaka; Kato, Chiaki; Yamamoto, Masahiro

Corrosion, 70(4), p.366 - 374, 2014/04

https://doi.org/10.5006/1106

Surface oxide layers were formed within crevices of type 316L stainless steels in pure water at 288C and 8 MPa. Cross-sectional structures of the surface oxides were analyzed using transmission electron microscopy. In the condition of dissolved oxygen concentration of 2 ppm, the properties of the surface oxide layer changed with position and dual or triplex layered oxides were formed at a certain distance from the crevice mouth. The multilayered oxides were composed of Fe-based oxide in the core and a high-Cr content in the outer layer, which had not been observed on a boldly exposed surface. On the contrary, in deaerated condition, the surface oxide layers were composed of a FeO-based outer and a Cr-enriched inner oxide layer, regardless of the crevice position. Electrochemical condition within the crevice was identified by using E-pH diagram. It was suggested that, at 400m distance from the crevice mouth, the potential lowered at the early stage of exposure and then, shifted to noble direction with decrement of pH. Consequently, even within a narrow crevice with a gap size of a few m, the uniqueness of the crevice electrochemistry, characterized by the position and time dependence of both the potential and the pH, has been exhibited.

Growth behavior of surface oxide layer on SUS316L stainless steel at the early stage of exposure to 288C water

Soma, Yasutaka; Kato, Chiaki; Yamamoto, Masahiro

Materials Transactions, 53(1), p.195 - 200, 2012/01

https://doi.org/10.2320/matertrans.M2011200

Surface oxide layer on SUS316L stainless steels exposed to 288C pure water with 2ppm dissolved oxygen (DO) for 1100h were analyzed using Focused Ion Beam and Scanning Transmission Electron Microscope equipped with EDS to understand the early stage of surface oxide layer formation. At 1h exposure, double oxide layer which is composed of compact inner oxide layer and outer oxide layer with Fe-rich and Ni-rich oxide particles was formed. At the outermost region of the SUS316L substrate, Ni and Cr were enriched. At 100h exposure, growth of the inner oxide layer was suppressed and the Ni and Cr enriched region at the alloy substrate was preserved underneath the Ni-rich outer oxide particles. At 1h exposure, most of the outer oxide particles were composed of Fe-rich ones, at 10h exposure, another Ni-rich outer oxide particles were nucleated and grew faster than Fe-rich ones. Consequently, a part of pre-formed Fe-rich outer oxide particles were covered with Ni-rich ones.

Surface oxide layer within crevices of 316L stainless steels in 561K pure water

Soma, Yasutaka; Kato, Chiaki; Yamamoto, Masahiro

no journal, , 

Surface oxide layers were formed within crevices of type 316L stainless steels in pure water at 561 K and 8 MPa. Cross-sectional structures of the surface oxides were analyzed using transmission electron microscopy. Under the condition of a dissolved oxygen concentration of 2 ppm, the properties of the surface oxide layer changed with the crevice position and dual or triplex layered oxides were formed, which had not been observed on a boldly exposed surface. The thickness of the inner oxide layer showed a local maximum at a certain distance from the crevice mouth. These oxide characteristics suggest the presence of locally varying electrochemical conditions. Potential-pH diagrams of the multilayered oxides suggest that the potential decreased at the early stage of exposure and then re-increased, accompanied by weak acidification.

Effect of impurities in steel and ppb level of chloride in bulk water on electrical conductivity of stainless steel's crevice solution in high temperature water

Soma, Yasutaka; Komatsu, Atsushi; Kato, Chiaki

no journal, , 

In this study, the effect of impurities in steel and ppb level of chloride in bulk water on electrical conductivity of stainless steel's crevice solution (K) has been studied. Crevice specimens were made of as-polished Type-316L stainless steel (standard-SS), standard-SS exposed to 60% nitric acid to dissolve sulfur containing inclusions (acid-picked SS), and 316EHP steel in which sulfur and phosphorous concentration was decreased compared to standard-SS (EHP-SS). These crevice specimens were immersed into 561 K, 8 MPa water the K values were measured as a function of time with stepwise increase in dissolved oxygen levels. In addition, effect of 50 ppb Cl added to bulk water was investigated using standard-SS crevice. The all of the standard-SS, acid-picked SS, and 316EHP showed similar K vs time curves. It can be concluded that impurities dissolved from the steel itself do not significantly contribute to the increase of K. The effect of 50 ppb Cl on K vs time curve was obvious because maximum K value became more that 2 times larger than the solution without Cl addition. This indicate that small concentration of impurities can be migrated into the crevice.

Effects of potential on the electrical conductivity of a solution within a crevice of stainless steel in high-temperature water

Soma, Yasutaka; Komatsu, Atsushi; Kato, Chiaki

no journal, , 

This study investigates the effects of potential (electrochemical corrosion potential (ECP)) on the water chemistry within a crevice of stainless steel in 288C water containing Clmajor anionic impurities. In situ measurements of the electrical conductivity of a solution within a 15 m gap crevice () were conducted using small sensors installed at different crevice depths. The ECP at the external surface of the crevice specimen (Eext) was controlled by the dissolved oxygen concentration in the bulk water. An increase in Eext from approximately -0.49 V (versus a standard hydrogen electrode at 288C) to -0.12 V resulted in an increase in from 12 to 160.3S/cm at 21 mm from the crevice mouth. FEM analysis taking into account the electrochemical reaction quantitatively reproduced this behavior. Cl was considered to be the major anionic species transported into the crevice in this potential range. A further increase in Eext up to 0.3 V led to a decline in . An increase in the flux of oxidizing (O and hydrochromate ion) and alkalizing species (OH) into the crevice was considered the cause of this behavior.

Study of steel plate reinforced concrete containment vessel for JSFR, 3; Experimental research on SCCV out-of-plane bending property

Kato, Atsushi; Hara, Hiroyuki*; Takami, Shinji*; Somaki, Takahiro*

no journal, , 

Japan Sodium-cooled Fast Reactor (JSFR) adopts a new concept of a containment vessel called steel plate reinforced concrete containment vessel (SCCV). The SCCV is considered to be effective to shorten construction schedule thanks for elimination of rebar work at a site compared with applying the reinforced concrete CV. JAEA has been investigating its characteristics under high thermal load to adopt the SC structure to a CV. This paper mainly describes the experimental study on SCCV out-of-plane bending property.