Nuclear Security in Action: Mobile Hot Cell in Manila
The IAEA helps its Member States find long-term solutions for the safe and secure storage of disused sealed radioactive sources. This photo essay documents a successful source conditioning project in the Philippines.
Radioactive sources are used in a wide variety of devices in medical, industrial and agricultural facilities worldwide. These sources, such as cobalt-60, can treat cancer, measure materials used in industry and sterilise food and medical appliances. When the radioactive material decays, it is no longer usable for the original purpose and becomes 'disused'.
In March and April 2013 a team of experts from South Africa's Nuclear Energy Corporation (NECSA) successfully removed 16 highly radioactive disused cobalt and caesium sources from teletherapy and industrial devices and placed them into two secure, long-term storage shields. The six-week mission was financed by the IAEA's Nuclear Security Fund.
The devices had been in storage at the Philippine Nuclear Research Institute (PNRI) in Manila. For safety and security reasons they needed to be 'conditioned'. This means they are properly isolated from the environment and secured against loss and theft. If disused sources are not properly stored they can be a threat to human health and the environment and pose a security risk.
Due to the size of the operation, the IAEA arranged for a specialised facility known as a 'Mobile Hot Cell' to be deployed. This is a shielded radiation chamber that was conceived by the IAEA. It was manufactured by NECSA, which owns and operates the facility. Funds from the IAEA's Nuclear Security Fund were made available to develop and manufacture the mobile unit and it was ready in 2007.
The hot cell and all the equipment needed to erect, use and dismantle it fits into two shipping containers. The technical preparation and shipping to the site of operation takes around two months. It takes three to four days to erect the unit. The operation itself takes around one to three weeks, depending on the amount of sources to condition. The on-site work ends with the dismantling and packaging of the hot cell and shipping it back to South Africa or to the country of the next operation.
The conditioning of the devices begins with a stage known as 'pre-dismantling'. The NECSA team try to gain as much access to the source as possible, without putting themselves at risk of exposure to radiation.
Each device needs to be lifted into the hot cell with a crane. The mobile hot cell is the first of its kind in the world. But since it was introduced two further models have been developed, based on the IAEA design.
Once inside the hot cell a NECSA expert adjusts the position of the device for the subsequent remote handling. The space inside the hot cell is limited because between the thin steel plates, which form the walls of the unit, there is a gap of 1.5 metres. This is filled with sand that is acquired locally. This thick sand layer provides adequate shielding to protect the operators from the ionizing radiation emitted by the bare, high-activity sources after they have been removed from the shielded devices.
Once the device is securely in place, the complex part of the operation can begin. From outside of the hot cell the NECSA team needs to remove the source from the teletherapy head remotely, with the use of special manipulators. The sources cannot be removed outside of the hot cell because the high radioactivity would cause severe health damage to the operators.
The window, through which the operators can view all objects and manipulations inside the hot cell, must have the same shielding properties as the rest of the walls, but has to be fully transparent to provide good vision. A 1.5 metre long tube, closed by transparent end panels and filled with an aqueous solution of 50 per cent zinc bromide, provides both transparency and protection.
The NECSA team can also follow the action within the hot cell on a monitor, where live images captured by cameras inside the cell are displayed.
The team successfully extracts the source from the medical device. Usually the sources are stored in a kind of drawer, which needs to be extracted first and the cap covering the source has to be removed - this step alone can take up to two hours.
Due to the high levels of humidity in tropical Manila, most of the devices were badly corroded. This made the job of the NECSA team even tougher and caused delays. By the end of the mission NECSA managed to remove 16 sources. Sources from six devices could not be removed due to the extreme corrosion. These teletherapy heads were placed in steel boxes for long term storage.
A nuclear security expert and a radioactive waste specialist from the IAEA were sent to Manila to observe the mission. The proper storage of disused sources is important from both a nuclear safety and security perspective. Such sources are vulnerable to loss, abandonment, theft or misuse and could be used by criminals in a so-called 'dirty bomb'. They are also classified as 'category 1', meaning they are considered the most dangerous because they can pose a very high risk to human health and the environment if not managed safely.
A NECSA team member measures the dose rate with a telescopic monitor. NECSA takes all necessary precautions to limit the amount of radiation they are exposed to during a hot cell mission. Two radiation protection officers are present throughout the operation and all team members wear personal devices to monitor their exposure levels. In addition, radiation levels within and outside the hot cell are constantly monitored.
Once the sources have been removed they are placed into protective capsules within the hot cell. These are welded and checked to ensure they are air tight. One capsule can hold several sources.
The capsules are then slid through a passageway into a long-term storage shield. This kind of shield has inherent security and safety features. The IAEA provided the PNRI with two of these shields, manufactured by NECSA, for the Manila mission.
These shields are then placed into an additional metal container, secured further with a metal cage, locked and then placed in a long-term storage facility. At the end of the project the two long-term storage shields, containing the conditioned sources, were moved to a secure storage chamber at the PNRI.
