Electronic Personal Dosimeter went into Alarm during X-ray Radiography Operations
Radiographers were working in a cell in a redundant reprocessing facility, carrying out digital imaging of legacy crates using X-rays in order to identify their contents.
This cell is an area of known high background radiation containing ten legacy crates.
A previous health physics survey of the crates had identified radiation levels in nine of the crates between 0.5 mSv/h and 1.8 mSv/h gamma, with the other crate up to 20mSv/h gamma.
The work was carried out using an adjacent room, approximately 20 metres away, as a control point. The high dose rate crate is located at the rear of the cell with the high radiation field facing away from the X-ray generator.
Upon entry into the cell to reposition the digital imaging plate which was adjacent to a crate, the first radiographer's Electronic Personal Dosimeter (EPD) went into alarm at a dose rate of greater than 37.5 mSv/h.
This radiographer retreated from the cell and the alarm ceased.
The image was captured and then a second radiographer entered the cell to reposition the digital imaging plate to capture the last image on the crate.
After positioning the imaging plate, the second radiographer's EPD also went into alarm; he then retreated from the cell and the alarm ceased.
A reconstruction was carried out to determine the radiation dose rates around the live generator.
This concluded that radiation measured on the EPDs was due to the X-ray generator, rather than from ambient radiation levels in the cell, or originating from the crates in storage.
It was determined that neither of the radiographers received significant radiation doses.
There were shortfalls with adherence to safety procedures resulting in the potential for the operators to be exposed to very high (100s of Sieverts/hr) radiation levels.