Preliminary assessment for dust contamination of ITER in-vessel transporter

Saito, Makiko; Ueno, Kenichi; Maruyama, Takahito; Murakami, Shin; Takeda, Nobukazu; Kakudate, Satoshi; Nakahira, Masataka*; Tesini, A.*

Fusion Engineering and Design, 89(9-10), p.2352 - 2356, 2014/10

https://doi.org/10.1016/j.fusengdes.2014.02.023

After plasma operation of the ITER reactor, irradiated radioactive dust will accumulate in the vacuum vessel (VV). The In Vessel Transporter (IVT) will be installed in the VV and remove the blanket modules for maintenance. The IVT will be carried back to the Hot Cell Facilities (HCF) after exchanging the blanket, and the IVT itself also needs maintenance. It is considered that the maintenance workers will be exposed to the irradiated radioactive dust attached to the IVT surface. In this study, dust contamination of the IVT is evaluated to assess exposure during maintenance work in the HCF. The IVT contamination scenario is assumed in the ITER project. From plasma shut down until maintenance is performed on the IVT will take 345 days under the ITER project assumption. Under this scenario, the effective dose rate from irradiated radioactive dust was calculated as an infinite plate for each nuclide. As a result, W-181 and Ta-182 were the dominant nuclides for the effective dose rate. If all dust is W-181 or Ta-182, the effective dose rate is about 400 Sv/h and 100 Sv/h respectively. Nevertheless, using the dose limit determined by the ITER project and the estimated maximum maintenance time, the effective dose rate limit was calculated to be 4.18 Sv/h under these limited conditions. To satisfy the dose rate limit, decontamination processes were assumed and the dose rate after decontamination was evaluated.

Rail deployment operation test for ITER blanket handling system with positioning misalignment

Takeda, Nobukazu; Aburadani, Atsushi; Tanigawa, Hisashi; Shigematsu, Soichiro; Kozaka, Hiroshi; Murakami, Shin; Kakudate, Satoshi; Nakahira, Masataka; Tesini, A.*

Fusion Engineering and Design, 88(9-10), p.2186 - 2189, 2013/10

https://doi.org/10.1016/j.fusengdes.2013.02.086

R&D for rail deployment equipment was performed for the ITER blanket remote handling system. The target torque for the automatic operation was investigated. The result shows that the 20% of the rated torque is adequate as the torque limitation for the automatic operation. A schedule for the procurement of the blanket remote handling system, which will be delivered to the ITER in 2020, was also shown.

Verification test results of a cutting technique for the ITER blanket cooling pipes

Shigematsu, Soichiro; Tanigawa, Hisashi; Aburadani, Atsushi; Takeda, Nobukazu; Kakudate, Satoshi; Mori, Seiji*; Nakahira, Masataka*; Raffray, R.*; Merola, M.*

Fusion Engineering and Design, 87(7-8), p.1218 - 1223, 2012/08

https://doi.org/10.1016/j.fusengdes.2012.02.108

The current design of the ITER blanket system is a modular configuration and a total of 440 blanket modules are to be installed in the ITER vacuum vessel. Each blanket module consists of the first wall (FW) and the shield block (SB). The FW receives a high heat load from the plasma. The SB shields components from the neutrons generated by the nuclear fusion reaction. The FW will be damaged by the heat load and neutrons, so it requires scheduled replacement. For the FW replacement, cutting/welding tools for the cooling pipes must be able to conduct the following operations: access and cut/weld the pipe from the inside of the cooling pipe. The cutting tool for the pipe end is required to cut flat plate circularly from the surface side of the FW. This paper describes the current status of R&D of the cutting tools for maintenance of the cooling pipe of the FW.

Design progress of the ITER blanket remote handling equipment

Nakahira, Masataka; Matsumoto, Yasuhiro; Kakudate, Satoshi; Takeda, Nobukazu; Shibanuma, Kiyoshi; Tesini, A.*

Fusion Engineering and Design, 84(7-11), p.1394 - 1398, 2009/06

https://doi.org/10.1016/j.fusengdes.2009.03.006

Invessel components of ITER have to be maintained by remote handling (RH) equipment due to high radiation level in the vacuum vessel (VV) after D-D operation. Blanket module (BM) is maintained by a manipulator mounted on a vehicle traveled through an articulated rail deployed inside the VV. Towards the construction, the BLRH equipment design has been improved and developed in more detail. The overview of design results are introduced in this paper. The design of rail deployment system of the BLRH has been updated to enable the rail connection in the transfer cask in order to minimize occupation space. For this purpose, design works have been performed for concept, sequence and typical simulation of BL replacement in the VV and rail deployment of the RH equipment in the cask, including cask docking. The technical issues of the rail connection in the cask are (1) tight tolerance of a pin at a hinge, (2) limited space of the connection inside a cask and (3) tight positioning accuracy. This paper summarizes the idea to solve these issues and a result of the design work. The paper also introduces a new cable handling equipment, rail support equipment and BL receiver/transporter.

A Proposal of ITER vacuum vessel fabrication specification and results of the full-scale partial mock-up test

Nakahira, Masataka; Takeda, Nobukazu; Kakudate, Satoshi; Onozuka, Masanori*

Fusion Engineering and Design, 83(10-12), p.1578 - 1582, 2008/12

https://doi.org/10.1016/j.fusengdes.2008.08.009

The structure and fabrication methods of the ITER vacuum vessel have been investigated and defined by the ITER international team. However, some of the current specifications are very difficult to be achieved from the manufacturing point of view and will lead to cost increase. This report summarizes the Japanese proposed specification of the VV mock-up describing differences between the ITER supplied design. A series of the fabrication and assembly procedures for the mock-up are presented in this report, together with candidates of welding configurations. Finally, the report summarizes the results of mock-up fabrication, including results of non-destructive examination of weld lines, obtained welding deformation and issues revealed from the fabrication experience.

Progress of R&D and design of blanket remote handling equipment for ITER

Kakudate, Satoshi; Takeda, Nobukazu; Nakahira, Masataka; Matsumoto, Yasuhiro; Shibanuma, Kiyoshi; Tesini, A.*

Fusion Engineering and Design, 83(10-12), p.1850 - 1855, 2008/12

https://doi.org/10.1016/j.fusengdes.2008.08.029

The design of in-vessel transporter (IVT) including vehicle manipulator has been updated according to the design changes such as blanket segmentation and structure, taking account of the interface between modules and vehicle manipulator. In particular, the updated design of the vehicle manipulator and rail has been carried out in order to avoid the interference between modules and vehicle manipulator. According to the updated design, the vehicle manipulator has been reduced by about 30%, compared with the reference design. In parallel with design activities, the R&D to clarify the specifications of the IVT design in detail is also performed, i.e., simulation system to provide the visual information during maintenance, dry lubricant to prevent the lubricant oil from spreading in the VV. The rail connection and cable handling in the transfer cask, which are critical issues for IVT system, are under preparation of the demonstration tests to finalize the design of the IVT system. Connection of the rail joint and cable handling test facilities are planned and under fabrication now. These test facility will be installed by the end of March 2008, and the performance tests will be carried out from April 2008.

Performance test of diamond-like carbon films for lubricating ITER blanket maintenance equipment under GPa-level high contact stress

Takeda, Nobukazu; Kakudate, Satoshi; Nakahira, Masataka; Shibanuma, Kiyoshi

Plasma and Fusion Research (Internet), 2, p.052_1 - 052_4, 2007/12

https://doi.org/10.1585/pfr.2.052

In the present paper, a Diamond-Like Carbon (DLC) coating was assumed as a candidate of solid lubricants for the transmission gears of the ITER blanket maintenance equipment instead of liquid lubricant. The seizure tests using "pin-on-disk" method were performed with the disks of SCM440 and SNCM420 coated by the soft, layered and hard DLC. All cases satisfied the required allowable contact pressure, 2 GPa, and lifetime, cycles and thus, the feasibility of the DLC coating was validated. Among the three types, the soft DLC showed the best performance.

Design and rescue scenario of common repair equipment for in-vessel components in ITER hot cell

Kakudate, Satoshi; Takeda, Nobukazu; Nakahira, Masataka; Shibanuma, Kiyoshi

JAEA-Technology 2006-038, 38 Pages, 2006/06

JAEA-Technology-2006-038.pdf:1.64MB

Transportation of the in-vessel components to be repaired in the ITER hot cell is carried by two kinds of transporters, i.e., overhead cranes and floor vehicles. The access area for repair operations in the hot cell is duplicated by these transporters. Clear sharing of the respective roles of these transporters with the minimum duplication is therefore useful for rationalization. The overhead crane has an adapter for change of the end-effectors, which can be easily changed, to grasp many kinds of components to be repaired. The floor vehicle, which is equipped with wheel mechanisms for transportation, is just to pass through the components between cells with only straight (linear) motion on the floor. Rescue scenarios and procedures in the hot cell are also studied in this report. The proposed rescue crane has major two functions for rescue operations of the hot cell facility, i.e., one for the overhead crane and the other for refurbishment equipment such as workstation for divertor repair. Especially, for the rescue of the workstation, the rescue crane consists of a telescopic manipulator (maximum length of 6500 mm) with rescue tool such as wrench for operation of the faulty driving mechanism through the redundant mechanism in order to release the activated component.

Applicability assessment of plug weld to ITER vacuum vessel by crack propagation analysis

Omori, Junji; Nakahira, Masataka; Takeda, Nobukazu; Shibanuma, Kiyoshi; Sago, Hiromi*; Onozuka, Masanori*

JAEA-Technology 2006-017, 134 Pages, 2006/03

JAEA-Technology-2006-017.pdf:15.96MB

In order to improve the fabricability of the vacuum vessel (VV) of International Thermonuclear Experimental Reactor (ITER), applicability of plug weld between VV outer shell and stiffening ribs/blanket support housings has been assessed using crack propagation analysis for the plug weld. The ITER VV is a double-wall structure of inner and outer shells with ribs and housings between the shells. For the fabrication of VV, ribs and housings are welded to outer shell after welding to inner shell. A lot of weld grooves should be adjusted for the outer shell weld. The plug weld can allow larger tolerance of weld groove gaps than ordinary butt weld. However, un-welded lengths parallel to outer shell surface remain in the plug weld region. It is necessary to evaluate the allowable un-welded length to apply the plug weld to ITER vacuum vessel fabrication. For the assessment the allowable un-welded lengths have been calculated by crack propagation analyses for the load conditions, conservatively assuming the un-welded region is a crack. The analyses have been carried out for typical inboard straight region and inboard upper curved region with maximum housing stress. The allowable cracks of ribs are estimated to be 8.8mm and 38mm for the rib and the housing, respectively, considering inspection error of 4.4mm. Plug welding for welding between outer shell and ribs/housings could be applicable.

Research and development of remote maintenance equipment for ITER divertor maintenance

Takeda, Nobukazu; Kakudate, Satoshi; Nakahira, Masataka

JAERI-Tech 2004-071, 85 Pages, 2005/02

JAERI-Tech-2004-071.pdf:4.81MB

To facilitate easy maintainability, the ITER divertor is divided into 60 cassettes, which are transported for replacement using the remote equipments. The cassette of 25 tons has to be transported and installed with a positioning accuracy less than 2 mm in the limited space under the intense gamma radiation field. Based on these requirements, the following design and tests were performed. (1) Link mechanism was studied to apply to the transportation. A compact mechanism with links is designed through the optimization of the link angle taking account of space requirement and force efficiency. The lifting capacity of 30 tons has been demonstrated. (2) Compact link mechanism was also studied to apply for locking of the cassette. The final positioning accuracy of 0.03 mm for installation from the initial positioning error of 5 mm has been demonstrated. (3) Sensor-based control of the remote equipment was tested using simple sensors. It is found that the positioning accuracy of 0.16 mm has been achieved and this value is sufficient.