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Jan 27:
T1-MK1 was moved to the storage pit in position #4. M9BB was moved to the hot cell for shutdown maintenance (o-ring replacement, air cylinder servicing, etc.).
When M9BB work is done, it will be returned to the target station and replaced with T2-MK1 for servicing (target exchange, measurement target installation, etc.).
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Jan 29:
Maintenance operations on the M9BB were completed on the hot cell.
- The air cylinders actuated and lowered smoothly, and at 42 psi as indicated in the instructions document.
- The felt wiper on the shaft seal was replaced.
- 3 o-rings were replaced on the bronze shaft seal bracket and lubricated with vacuum grease
- upper limit switch actuation was confirmed after reassembly
- BB returned to the adapter plate on the turntable and reoriented for pickup
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Feb 03:
M9BB returned to target station:
- o-ring groove on monolith cleaned,
- replacement o-ring with vacuum grease placed
- during return, we noticed pieces of 'scrap metal' on the bottom of the beamblocker, it was removed and when scanned registered a count that exceeded the radiation cave monitor's dial, this will be stored/disposed as active waste.
- M9 ASU still disconnected, could not 'push-down' M9BB with gas line connected, gas line left disconnected for now.
- T handle plate removed, limit switch rod returned
T2-MK1 moved from target station to hot cell roof, north hook used for flask, south hook used to adjust the position of the alignment frame:
- section of hot cell roof railing had to be removed for the flask to clear when handled by the north hook, there is also a similar functioning cutout on the wall by the storage pits
- peak fields are 1100 uSv/hr at the hot cell opening by the target.
T2-MK1 servicing started on hot cell roof:
- T2-MK1 water flush completed, ~1 min air purge cycles completed for all target positions, left at position 5 (plugged) for longer term air purging (~3 hours).
- A broken ceramic cap was found on the top of the target vacuum flange.
- 4 quarter circle segments from what looks like the old-style graphite targets were found on the base of the target ladder.
- The coupling between the potentiometer gearbox and the ladder drive screw has a rubber section, we will have to inspect it and decide whether to replace it with a metal coupling during this shutdown, if so, we should also replace the plastic ferrules and update the bulkhead plate to be more servicable.
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Feb 05:
T2 station was surveyed, peak fields were found by the blanked off T2 opening: 4mSv/hr. Immediately at the cover fields were around 16 mSv/hr.
No fallen pieces of suspected graphite target segments were found on the monolith, it may be a good idea to check inside the monolith hole with a remote viewing camera to make sure nothing is obstructing the locating feature on the base of the target ladder (to be included in the T2 return work permit).
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Feb 10:
The T2-MK1 target ladder underwent a water rinse and several days of air purging.
5 psi compressed air was run through each target position (including position 5 which is plugged) for several hours each. Then, the ladder was fully dried using the leak detector and cold trap on Feb 07.
The leak detector was calibrated with Vacuum Group's external source to 8.7e-8 mbar-L/s prior to operation. The leak detector and vacuum line up to the target service panel connections were checked to be leak tight prior to testing (0 leak rate and <1e-3 Torr pressure).
A single pump-down cycle was sufficient to get vacuum to establish within reasonable time:
- Total pump-down duration was ~55 minutes
- 60 seconds to go into 'fine vacuum' mode.
- 2 min 13 seconds to get to ~1e-3 Torr vacuum in ladder
- leak rate was initially ~1e-8 Torr-L/s and slowly dropped to 0.0e-10 Torr-L/s over the course of the pumpdown (48 minutes to bottom out)
- the ladder was left at the bottomed out leak rate for around 5 minutes prior to venting.
- approximately a 1cm thick, 10cm diameger puck of ice formed on the side of the LN2 vessel of the cold trap.
Upon closer inspection with Isaac Earle, the following were observed for graphite pieces on the T2-MK1 target ladder base:
- The surface finish on the chips strongly suggest that they are graphite target materials
- Curiously the graphite chips are all of different thicknesses, to our understanding, the graphite material used in the old targets are of consistent thickness.
- The rounded faces of the chips had no clear sign/evidence of brazing when compared to sample pieces that can be found in the Hot Cell Lab office.
- No clear signs of beam spots can be found on the flat faces of the chips, near the corner edge.
- No clear signs of brazing on the targets were observed.
The above observations suggest that the chips did not originate from an operational target that has seen beam. |