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Message ID: 24     Entry time: Wednesday, August 24, 2011, 16:35
Author: Bevan Moss 
Category: South Hot-Cell 
Type: Repair 
Module: TM1 
Target/Number: UCx#2 
Subject: Move, inspection and repair 

 On August 22nd TM1 was vented with Argon in the conditioning station. It had been pumping with just the roughing pump over the weekend so the UCx#2 target would not be exposed to oxygen. The move went without incident and took roughly an hour to complete. Once at the hot cell the panel was removed by Tom Lyth and a leak check completed with Bevan, David Wong, Grant Minor, and Tom Lyth present. The connections to source tray were checked starting at the top. Each connection was checked on either side of the VCR and at the center through the hole in the nut. For both connections on the source tray there was no response from the leak cart which was at a pressure of 0.0 x 10^-4 T and had a baseline leak rate of 0.0 x 10^-9 atm cc / sec. The leak check then proceeded to VCR connections on the Target. A leak was found on the upper VCR connection of the target and was repeatable. This leak was detected at the hole of the VCR nut connection by priming the line with helium and placing it next to the hole in the VCR connection. Response time was between 5 and 10 seconds to a maximum of 2.6 x 10^-8 atm cc / sec. The lower connection also appeared to have a small leak rate of 4.4 x 10^-9 atm cc/ sec but could be a result of helium drift. Unfortunately the target is not design to be repaired with manipulators and required the target to be removed from the south hot cell and repaired in the anteroom. The anteroom was prepared for the target by lining much of it with plastic so to prevent the spread of contamination. Once the target was in the anteroom it was leak checked again, the base pressure was 0.0 x 10^-4 and the base leak rate was 0.0 x 10^-9. A response from the upper connection again was detected in the 10^-8 range but no leak was found in the lower connection. It was attempted to tighten the joint to stop the leak but this caused it to increase to the 10^-7 range. This increase in leak rate is as expected from past experience because copper gaskets are used rather than silver plated ones. The heat shield cover was loosened and the gaskets from from both joints were replaced with the silver plated ones. The target was then leak check and passed with no response once again with a full pump down. The target was had an electrical checked with the megger and was within spec. The target was then placed in an argon bag and returned to the hot cell. The bag was damaged went placing it in the hot cell and there were not any acceptable options for leaving the target over night. The target was removed and and placed in 2 bags filled with argon for over night.

On August 23rd the target was removed from the argon bags that were still inflated and returned to the hot cell. The target was re-installed on the target module by Grant Minor, Tom Lyth, an Bevan Moss. One VCR gasket fell off during the first attempt and it appeared that the right target leg may have been slightly bent at some point. Other than that the installation went smoothly but slowly. The heat shield line was then leak checked once again by Grant, Tom, David, and Bevan and no response was detected from the source tray or target VCR connections, the base leak rate and pressure once again achieved the minimum detectable levels. The target module passed the electrical check with the megger, this test was completed by Bevan and Pierre Bricault. The module was then moved from the south hot cell to the conditioning station. Roughing was started at 3:00 and the turbo pumps were turned on at 3:45. The module was left to pump over night.     

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