The extracted proton beamline (EPB) in ISIS TS1 is what channels the protons from the synchrotron to the neutron-producing target. It also contains the secondary intermediate target: a thin graphite sheet that is used to produce muons. As a side product of the muon production, other particles are produced that cause this area to be much more radioactive than other sections of the EPB.
During the last run cycle, a water leak was detected in one of the collimators used to focus the beam. Replacing this collimator then became an important project that needed to take place during the current long shutdown. The project will require access to the area to dismantle a number of highly radioactive beamline components. Preparation of the risk assessment and procedures for the project requires detailed information on radiation levels in the area. Ordinarily, this would involve a Health Physics survey entering the area to carry out radiation monitoring. However, even with an extended shutdown period allowing some decay of the radioactivity over time, the radiation levels in the area remain too high for anything other than very controlled, short term occupancy. It was therefore important that the time staff spent working in the area was minimised.
The team led by Adrian Hooper, with advice from radiation protection adviser, Mark Bradley, thought they would try something new. Inspired by a recent gift, they bought a drone fitted with a camera, and added an electronic dosimeter. Using this they were able to measure the radiation levels at specific points, without sending anyone into hazardous areas.
“We have been able to map the radiation levels in the area in detail," explains Adrian Hooper; “and also conduct reconnaissance flights to get information on features that were unclear from the original drawings."
This visual information about the intricacies of the collimator assembly, as shown in the video below, has enabled the team to begin building a mock up to test the replacement before it is installed, reducing the time spent in the active area. The radiation information collected has also been extremely useful for Mark during preparation of the radiological risk assessment for the work.
He explains; "the information that the drone has been able to acquire remotely is priceless. It has solved the problem of obtaining essential information from an area too radioactive for people to spend sufficient time to obtain it. The “limitless" unmanned access has enabled the development of control measures that will limit the length of time people will ultimately need to spend in the area; significantly reducing their potential exposures when completing the work."
The use of the drone came with its own challenges: the in-built collision prevention system stops it getting into very small spaces, and occasionally it has complained about a lack of GPS signal inside the shielded tunnel! These have been overcome and, during discussions with other teams at ISIS, it seems that the drone has plenty of applications beyond EPB1.
“There are other areas where this sort of radiation mapping would be really useful, including in the synchrotron," adds Adrian. “It could also be used for other visual inspections of areas that are hard to get to, for example, the roof or pipework that is high up on the walls or ceilings."