The hot spot locator

27 March 2019

Decontaminating an area containing nuclear waste is complicated due to the intangible nature of radiation. But the use radiation imaging systems can help, as Innovative Physics has demonstrated in Fukushima.

IN 2011, THE CATASTROPHIC EARTHQUAKE and tsunami that devastated Fukushima Daiichi created an urgent need for aids to decontamination.

Innovative Physics’s market research found a requirement for equipment that could rapidly identify radiation hotspots in a contaminated environment. Using its knowledge of imaging processing algorithms, IPL produced a platform that allowed users to visualise contamination.

David Prendergast, chief technical officer, says workers “were painstakingly removing the top few centimetres of soil and putting this into long term storage bags. This was incredibly slow and an inefficient way to decontaminate. What was needed were devices that could not only identify but also locate radioactivity in a more efficient manner than those that were currently available on the market.” The Innovative Physics team worked with its Japanese partners to design and develop a portable device capable of showing hot spots of radioactivity and known as the Hot Spot Locator (HSL). After 6 months, a working prototype was tested and within 12 months the first unit was sold. Since this, IPL has been refining the HSL product range, whilst creating newer, different solutions to radiological barriers.

The HSL uses data from a coded aperture (used in telescope technology) and a high-energy radiation sensor and combines it with an image from a video camera. Merging these, using bespoke deconvolution software created in-house at IPL, an image of radioactive hotspots is displayed in real time. This makes the radiation visible to users handling the device and shows where there are higher levels of contamination.

The HSL uses IPL’s dynamic imaging mask (DIM), which reduces background interference not emitted from the gamma source located in the field of view. This allows the coded aperture to adjust, allowing different patterns of radiological data and eliminating false hotspots.

Traditional handheld radiation detectors allow the user to know radiation is present but not where it is located; workers then need to use the detector to search for the source of radiation, which is time-consuming and costly.

Using technologies such as IPL’s, around 20% of the 1000km2 Fukushima exclusion zone has been scanned; continuing at this pace, the clean-up effort will conclude five to ten years earlier than was originally planned.

Applications such as the Hot Spot Locator are likely to play an increasing role in equipping those working in the nuclear industry, as well as helping provide reassurances to those who work in or live near nuclear plants.

IPL has been invited to demonstrate the HSL Lite variant at a contaminated piggery farm in Tomioka, South East of Fukushima Daiichi. The HSL Lite was operated in three different scenarios (see below).  

Surveying radioactive waste bags

Contaminated waste bags were manually checked, with a survey meter to categorise and sort them, with their disposal location determined by the dose rate. Checking by hand would have proved both time- consuming and costly (see Figures 1 & 2 opposite).

Surveying the farm for hot spots

IPL undertook a survey of the pig pen using an HSL Lite tripod setup.

Parts of the piggery were largely untouched because of the background and hot spot dose rates. IPL overcame this challenge by making the HSL Lite mount customisable to fit onto a robot/Unmanned Ground Vehicle/Unmanned Air Vehicle and utilise its wireless communications to undertake remote surveys (see Figures 3 & 4 opposite).

Checking vehicular contamination

Vehicles leaving the exclusion zones around Fukushima Prefecture have to be checked for contamination. When this is done manually with survey meters, it can lead to traffic build up which can affect the thoroughness of the checks. Using three to four HSL Lite units set up at different angles, quick visual measurements enabled those performing the checks to quickly and accurately locate any contaminated areas (see Figures 5 & 6 opposite).

The three photos above show David Prendergast, chief technical officer at Innovative Physics, demonstrating the Hot Spot Locator in Japan
Figure 1: Survey taken of a waste bag containing contaminated soil. The HSL was placed 4.6m from the bag and took 4 minutes 44 seconds to acquire an image. Background ~4.2µSv/hr, with a hotspot recorded above 30µSv/hr @1cm
Figure 2: Survey taken of a waste bag containing contaminated soil raised 1m above the ground. The HSL was placed 6.07m from the bag and took 2 minutes 59 seconds to acquire an image. Background 3.1µSv/hr, with a hotspot recorded above 30µSv/hr @1cm
Figure 3: Survey taken externally of the pig pen. The HSL was 8.6m from the pen and took 14 minutes 1 second to acquire an image. Background 7.3µSv/hr, with a hotspot recorded above 30µSv/hr @1cm
Figure 4: Survey taken at the bottom of a drain pipe on the pig farm where soil had been collected. The HSL was placed at 1.64m from the drain at acquired a hotspot within 9 minutes 13 seconds. Background 5.1µSv/hr with a hot spot of 28.2µSv/hr @1cm
Figure 5: Survey taken from the rear of a car to be decontaminated before leaving the area. The HSL was placed 2m from the car and acquired an image within 3 minutes 39 seconds. Background 0.8µSv/hr, with a hot spot recorded at 0.9µSv/hr @1cm
Figure 6: Survey taken from the front of the car, being checked for decontamination before leaving the area. The HSL was placed 3m from the car and acquired an image within 5 minutes 7 seconds. Background 0.8µSv/hr, with a hotspot recorded at 1.7µSv/hr @1cm

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