While wrapping up vacuum seal bearing replacement on the M20 beam blocker I found a piece of hard black material approximately 3x1x1cm on top of the hot cell turntable. Checked for contamination and found 480,000cpm on the Ludlum 44-2 probe, and off scale on the pancake monitor. This piece fell from the transport flask when it was opened above the hot cell after picking up the M20 beam blocker. Upon further inspection, more pieces were found inside the hot cell on the table. RPG was notified and currently has the sample for further testing.
It was determined that the piece was broken off what appears to be a shaft guide or bearing, which is mounted below the lowest shielding disc on the beam blocker. This is not part of the original beam blocker design, and is not documented in any drawings in the remote handling hot cell office, or the design office. The part appears to be made of plastic that has become brittle due to beam exposure, and is now getting crushed and destroyed as the shaft swings during actuation or beam blocker transportation.
This information will be presented at the operations meeting on Monday January 16th so we can determine if we should remove and replace the part now, which could delay BL1A shutdown activities by 2 - 10 days, or if it should be addressed during the next shutdown.
Possible concerns if the beam blocker is returned to the beamline before repair:
* falling material may get stuck between the blocker and the beam blocker tube in the monolith (only ~1/8" cleareance each side) and could interfere with movement of the beam blocker.
* because it is damaged and getting worse, the plastic bearing part may not perform its intended function properly (its intended function is still unknown)
* falling material may migrate to other areas in the beam line and cause problems with other equipment
* more material may fall unnoticed during transportation which poses a radiation hazard
See attached photos of shielding discs and damaged part.
(The sample was not available for photographs)
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