The tower BS is now closed and the evacuation has been started.
In the past days we have carried out various activities on the IVC with the aim of locating and mitigating its leaking defect:
- The leakage has been localized in correspondence of the bottom joint, where the IVC chamber rests on the flat viton seal (by visual localization + He-test in 'sniffer mode' with He via V82), see fig.1.
- The mitigation/repair has been attempted by adding a second seal (a viton cord of diameter 3 mm) for a lenght of about 1.5 m, or 1/3 of the seal circumference (see sketch in fig.2).The seal is held in position by slight pulling the cord itself + a few spacers.
- in addition, a viton o-ring of the IVC (the one of the base of the pipe at bellows level) was found not well positioned and it was redone
Notes:
- figs.3,4 pictures of the BS IVC , of the concerned area with the viton cord not yet in place
- the IVC has not been opened nor raised
The 'amended IVC leak' will be tested again once under vacuum in the next few days.
Other recordings: leak test activity performed in the preceding days on BS tower under vacuum:
Testing for external leak presence = no significant external leaks detected
- He-test upper rings joints: leak rate < 1E-8 mbar.l/s
- He-test lower flanges: leak rate < 1E-8 mbar.l/s