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Fusion Science and Technology
Cs-137 sealed source lost in Western Australia
A rendering of the sealed source capsule’s appearance. (Image: DFES)
Authorities are searching 1,400 kilometers (870 miles) of Australia’s Great Northern Highway, between Perth and the remote town of Newman, for a lost sealed-source capsule containing cesium-137. The source was part of a density gauge used by mining company Rio Tinto at its mining operations in Western Australia.
The Department of Fire and Emergency Services (DFES) of Western Australia reported that the density gauge containing a 6-mm-diameter (0.24-inch-diameter) by 8-mm-height (0.31-inch-height) source capsule was sent by flatbed truck to Perth for repair, leaving Rio Tinto’s Gudai-Darri mine site in Western Australia on January 12 and arriving in Perth on January 16. The package containing the gauge, however, was not inspected until January 25.
Upon opening the package, it was found that the gauge was broken apart with one of four mounting bolts missing. The source itself and all screws on the gauge were also missing. It is assumed that vibrations from the truck broke the gauge apart and allowed the screws and capsule to fall through the bolt hole and away from the truck. DFES said they were notified of the loss on the evening of January 25.
Aljaž Čufar, Paola Batistoni, Sean Conroy, Zamir Ghani, Igor Lengar, Sergey Popovichev, Brian Syme, Žiga Štancar, Luka Snoj, JET Contributors
Fusion Science and Technology | Volume 74 | Number 4 | November 2018 | Pages 370-386
Technical Paper | doi.org/10.1080/15361055.2018.1475163
Articles are hosted by Taylor and Francis Online.
The fusion power output of fusion plasmas is measured using the neutron yield detectors due to its linear relation to the fusion yield. Absolutely calibrated neutron yield detectors are thus a crucial part of the plasma diagnostics system and the absolute accuracy of their calibration must be ensured.
The transition of the Joint European Torus’s (JET’s) first wall material from carbon (C) wall to ITER-like (Be/W/C) first wall was a significant change in the structure of the machine and recalibration of the main neutron yield detectors was needed to maintain the required measurement uncertainty of less than ±10%. The neutron yield detectors were thus recalibrated through two in situ calibrations to deuterium-deuterium neutrons in 2013 and deuterium-tritium neutrons in 2017 using 252Cf spontaneous fission source and a compact neutron generator, respectively.
We describe the extensive neutronics calculations performed in support of these latest calibration experiments. These analyses were performed using Monte Carlo simulations to better understand the calibration procedure, optimize the experiments, ensure personnel safety, and quantify the effects of the uncharacteristic circumstances during calibration experiments. This paper focuses on assessments of the effects of the uncharacteristic circumstances, e.g., the presence of the remote handling system in the machine due to its use in neutron source delivery, difference in the neutron emission spectrum, and differences in the neutron source shape. Lessons learned, findings, and relevance for calibrations of future large tokamaks are discussed.