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March 30, 2022
First irradiation studies of RSBs at the Dalton Facility
Writing about web page https://www.dalton.manchester.ac.uk/research/facilities/cumbria-facilities/
Last week was a first in the field of Radiation Dense Materials in that samples of Reactive Sintered Borides (RSBs) and cemented Tungsten Carbide (cWC) were irradiated for the first time by proton beam and gamma irradiation at the Dalton Cumbrian Facility in the Westlakes Science Park during some truly beautiful springtime weather.
Much work on simulating the radiation response and attenuating properties of a cWC, cWC-RSB and tungsten boride shielding concepts has occured during the 2010s onward [C.G. Windsor et al 2015 Nucl. Fusion 55 023014,C.G. Windsor et al 2018 Nucl. Fusion 58 076014], however, data on the radiation response of cWCs [Shielding materials in the compact spherical tokamak https://doi.org/10.1098/rsta.2017.0443] is very sparse due to their recent adoption as candidate shielding materials. No data on radiation response exists for RSBs due to their novelty so this will be the first time any practical data will be obtained from irradiated RSB materials.
The planned experimental work at DCF fell into two main topics: Proton irradiation and gamma irradiation. Each type of radiation would take place at two different intensities and at two different temperatures.
Proton radiation most closely resembles the conditions at or near the plasma-facing component of a tokamak reactor and hence was to take place at ambient and at 600oC.
Gamma radiation will be significant at all parts of a tokamak reactor but particularly near the superconducting magnets. These irradiations were performed at -196oC (77K) and at ambient. Each experiment consisted of three samples: cWC, RSB and W metal alloy with eight different irradiation conditions with a 9th sample set to sit in the gamma irradiator for long-term irradiation studies.
So....how did the work go and what happened over last week? Read on.
The gamma irradiation mostly went to plan. Low dose gamma irradiation was set to 30 kGy for both the 77K and ambient irradiation. High dose gamma radiation samples was set to 240 kGY for ambient and 90 kGY for 77k. The lower dose at 77K is a result of the different sample positioning due to the dewar and the requirement to change the N2 the dewar every 5 kGy to prevent excessive ozone formation, which is an explosion hazard. All gamma irradiated samples except the long-term samples have been returned.
Proton irradiation was less straightforward. The high dose ambient proton irradiation was successful, with a steady state temperature of 125oC and a total dose equivalent to 1.66 x 1018 protons. Subsequent proton irradiation attempts were unsuccesful, mostly due to the plasma failing the strike and therefore enable the proton beam to irradiate the samples. However, these sample will be irradiated this week and sent by post.
This is one of the many hazards of experimental work in that failure is always an option but nevertheless this work on completion will provide an important first step in realizing the cWC-RSB concept as practical radiation shielding materials whatever the damage or lack of is present on analysis.
This work would not be possible without the dedication of the staff and researchers at the DCF who make this possible.