Speaker
Description
Shipping of ITER Vacuum Vessel (VV) Sector #6 was successfully carried out on 26 June 2020 at MIPO
port in Korea. Shipping completion means manufacturing completion of the 1st ITER VV Sector for the
last 10 years. The interim manufacturing progress was presented via several papers since 2010 [1~5].
Each step of the manufacturing process has been challenging as a First-of-a-Kind (FOAK). There are three
main challenges to be overcome that are nuclear safety process as a French nuclear pressure vessel, 100 %
volumetric inspections, and tight tolerance requirements.
The first one requires that all applicable documents shall be approved prior to actual application from
Korea Domestic Agency (KODA), ITER Organization (IO) and Agreed Notified Body (ANB). It requires
several qualifications, demonstrations, and certifications based on essential nuclear safety requirements.
Fundamental requirement is maintains traceability for all activities as nuclear pressure vessel. All of
manufacturing activities have been officially inspected and recorded with approved formats of
documents. One of the most representative quality control is controlled with Manufacturing Inspection
Plan (MIP) that describes all manufacturing activities and recorded main sequences with quality control
plans. Each of manufacturing step has been inspected by 7 residence inspectors from Vacuum Vessel
Project Team (VVPT) and ANB for manufacturing of 4 Sectors. ANB engages to review/approve all
nuclear safety related documents and inspect all nuclear safety related manufacturing activities. A total
of 45,000 inspection points were performed and 500 manufacturing documents, including reports, have
been developed during ITER sector #6.
The second one, 100 % volumetric examination, which promises very reliable quality and simultaneously
most technical challenges for this double wall full welded structure with very complicated 3 dimensional
geometry that has been achieved eventually. Taking all assembly activities on sector #6 into account, the
Hyundai Heavy Industries (HHI) team estimates the total length of full penetration welds at 995 meters.
In order to achieve these challenging activities, total 20 welding procedure specifications, and 60 special
scanning techniques of phased array ultrasonic test (PAUT) have been developed.
The third one is tight tolerances requirement. Regarding to the tight tolerances, critical manufacturing
steps is final assembly. The manufactured each poloidal segment (PS) is assembled all together, and then
form the D-shape structure. Final assembly is one of the most challenging work because the precise
handling for final assembly is very difficult due to each PS is heavy double walled structure and it has
own accumulated deformation during each PS manufacturing stage. In order to satisfy the strict tolerance
requirements after final assembly, HHI team in collaboration with the Vacuum Vessel Project Team
(VVPT) performed in advance a fitting virtually using actual dimensional inspection data after
completion of each segment manufacturing, required dimensions for welding and expected welding
deformation during final assembly via engineering analysis. Through this virtual fitting, 3 dimensional
target position has been defined for each fiducial post on PS before start of actual final assembly. Fit-up
for each PS has been performed on the assemble platform according to defined target position and the
final assembly has been completed including upper port stub extension and lower port stub extension.
In order to complete these challenging activities, new welding technique was prepared which can
perform even 5~21mm wide gap configuration, and special scanning techniques of phased array
ultrasonic test (PAUT) have been developed.
The qualification of the VV sector vacuum performance with respect to its safety function is a Protection
Important Activities (PIA), thus Helium leak test is a part of Final Acceptance Test (FAT) of the ITER
Vacuum Vessel Sector.
In general, 200 °C baking was considered to be essential to achieve the low background leak rate which
make the test possible, especially considering probable contamination of the VV Sector. However, there
were many risks associated with the baking, and final decision was to perform the leak test without
baking. KODA/HHI checked the feasibility of the leak test by pre-pumping the VV interspace, which
discovered that the background leak rate as well as the total pressure is low enough to perform the leak
test. The leak test procedure which incorporated the result of pre-pumping was developed in a prompt
way, and after successful completion of the Pneumatic Pressure Test with 5 bar of Nitrogen gas, which is
also a part of the FAT, Helium leak test followed immediately. VV Sector as a test object is enclosed by
tracer Helium gas, and the VV interspace is continuously pumped and evacuated gas is monitored by a
mass spectrometer. If leak paths are present, Helium would penetrate through the paths and the mass
spectrometer senses the change of the amount of Helium in the evacuated gas. Test was performed on 5
April, 2020, and the result was successful. The calculated leak rate (6.08x10-9 Pa∙m3∙s-1) satisfied the
acceptance criteria, which is 1x10-8 Pa∙m3∙s-1. It is a criterion for the clean, unbaked stainless steel.
The Sector #6 was packed with double hermetically sealed using special sealing material after
dimensional inspection.
ITER VV Sector #6 transportation activities are also classified as PIA according to French nuclear order.
Therefore, transportation plan including quality plan and inspection plan were prepared and approved
from VVPT and ANB before implementation. Inspection by VVPT and ANB inspectors was performed for
the major operations based on approved documents.
After long sea transport, the Sector #6 was unloaded on 22 July 2020 at FOS in France and delivered to
ITER site on 7 August 2020. Unpacking and site acceptance test including Helium leak test are going on
without major issue at IO Site Assembly Hall according to the site assembly schedule.
Disclaimer: This research was supported by National R&D Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning. The views and
optional expressed herein do not necessarily reflect those of the ITER organization.
[1] B.C.Kim et al., “Fabrication progress of the ITER vacuum vessel sector in korea”, Fusion Engineering and Design
88 (2013) 1960-1964.
[2] C.H.Choi et al., “Status of the ITER vacuum vessel construction”, Fusion Engineering and Design 89 (2014) 1859-
1863.
[3] J.M.Martinez et al., “ITER vacuum vessel structural analysis completion during manufacturing phase”, Fusion
Engineering and Design 109-111 (2016) 688-692.
[4] H.J.Ahn et al., “Manufacturing progress on the first sector and lower ports for ITER vacuum vessel”, Fusion
Engineering and Design 109-111 (2016) 718-723.
[5] G.H.Kim et al., “Qualification of phased array ultrasonic examination on T-joint weld of austenitic stainless steel
for ITER vacuum vessel”, Fusion Engineering and Design 109-111 (2016) 1099-1103.
| Affiliation | National Fusion Research Institute, Korea |
|---|---|
| Country or International Organization | Korea, Republic of |
