Final Works Acceptance of the JT-60SA gaseous helium storage vessels successfully completed

On 5 February the Final Works Acceptance tests of the six helium pressure vessels to be provided by Europe for the JT-60SA cryogenic system were successfully completed. The cryogenic system can be described as a large plant for cooling helium to very low temperatures with an equivalent refrigeration capacity of 9 kW at 4.5 K (-269 degrees C). The plant will provide helium at 80 K to the thermal shields, at 50 K to the current leads, at 4.4 K to the superconducting coils, and at 3.7 K to the cryopumps of the JT-60SA Tokamak. The JT-60SA Tokamak, is being constructed in Japan under the Broader Approach Agreement between Japan and Europe.

The Final Works Acceptance tests of the six vessels, which consisted of verifications to ensure that the components conform to international standards and to ensure that there are no defects, was carried out during a period of seven days each. Their completion is an important milestone and brings the operation of the JT-60SA machine one step closer.

In total, the six pressure vessels will store 3.6 tonnes of gaseous helium. Each pressure vessel is 22 metres long, has a diameter of 4 metres and a 250 m³ volume, and weighs about 73 tonnes. As the vessels will store pure helium, the tightness and cleanliness requirements are demanding.

If a fast discharge of the current in the superconducting coils is necessary, one of the vessels is also designed to receive cold helium (-254 degrees C) discharged from the coils through the cryogenic system quench line. F4E has performed a fluid dynamic study of the impact of this event on the quench line and this pressure vessel. The results have shown that the use of a special 18 metres long helium diffuser system and of a thermal barrier connector at the quench line flange avoids local chilling of the vessel wall below the minimum allowed temperature of the material. The procurement of these components has been added to the supply contract during the contract execution without impacting on its deadline.

The contract for the supply and transport to Japan of the pressure vessels and their equipment has been awarded by F4E to A. Silva Matos Metalomecanica SA (ASMM) (Portugal). Collaboration has been very efficient and successful – the project has run on budget and on time with the earliest delivery date (two months ahead of the contractual date), in spite of the very stringent schedule. In less than nine months from the kick-off meeting, the detailed design, manufacturing and testing of these large components have been completed according to the ASME VIII div. 1 rules (particular requirements standards with regards to quality control).

The six helium pressure vessels will now be shipped to Hitachi port in Japan. The last difficult operation will be the road transport of the vessels from the port to Naka and their installation on site, which is planned to be executed before the end of June 2015.