Nuclear mattersHandling nuclear materials for less

Published 16 March 2009

During this century, nuclear plant decommissioning in the United Kingdom will likely produce thousands of waste packages that will be retrieved, conditioned, and stored for no less than £40 billion; BNS develops new way to reduce storage and handling costs of radioactive material

The United Kingdom could halve the storage space needed for low- or intermediate-level radioactive waste retrieved from decommissioned nuclear power stations using a new processing technique that can handle multiple kinds of hazardous material. The patented technology from Babcock Nuclear Services (BNS), the nuclear arm of Babcock International, encapsulates solid and sludge radioactive waste in a cement mixture within cube-shaped containers. The containers, which measure 1.6m3 and hold tons of material, can then be transported to nuclear-waste storage facilities.

Siobhan Wagner writes that the technique, which is the key feature of BNS’s Versatile Encapsulation Plant (VEP), differs from current technology that must handle solid and sludge waste in two separate plants. Encapsulation technology traditionally involves mixing low- and intermediate-level radioactive waste with a cement material to effectively reduce its radionuclie mobility. The waste materials generally behave as additives and become chemically or physically incorporated into the cement material, which is commonly blast-furnace slag.

With current technologies, cement powders are added to slurried waste in a drum and mixed with a paddle. The BNS technique, however, encapsulates the waste and cement in the cube-shaped container without a paddle. Doug Kirk, technical consultant at BNS and inventor of VEP, said the system does this by first concentrating the sludge, which is generally diluted so that it can be retrieved from the reactor.

The sludge is settled and concentrated in a tank for twelve hours before transferring to one side of an inline mixer. Kirk described the inline mixer as a 50mm-diameter tube containing a set of static veins designed to agitate and mix the sludge. “It’s a perfectly standard piece of technology used a lot in the oil and gas industry,” he said. “We have used it previously for blending different types of resins but it has not been used in this application before.”

Kirk said the other side of the inline mixer is fed with a wet blast-furnace slag grout mixture. “Those two streams are mixed together as they pass through the inline mixer so what comes out at the end is a grout, sludge mix,” he said. “The advantage of that is when it leaves the inline mixer, the job is done so it doesn’t matter what shape of container you are actually allowing the fluid to collect in.”

Kirk noted that the cubed container increases storage volume by 25 percent compared to a spherical drum with paddle. “The other advantage is because there