World first: synroc plant on site

The world's first synroc plant is being built on site and will be operational within the next three years. Construction of the plant, which will transform liquid molybdenum-99 radioactive waste into synthetic rock, is now underway. “Synroc technology will be used to turn waste from ANSTO’s medical radioisotope production into a structure that mimics rock in nature, forever trapping the radioactive products inside,” explained Dr George Collins. “Just like in nature, where some minerals trap radioactive elements such as uranium and thorium in their crystal structure, synroc is designed to trap radioactive waste,” said George. “This will ensure radioactive waste stays safely locked away until radioactive levels have died away, a process  that can take thousands of years.” Synroc was developed in the late 1970s at the Australian National University and later at ANSTO by a team of scientists. The technology to build the on-site plant was developed over ten years and has become a reality thanks to the work of husband and wife scientist- engineers Dr Erden and Dr Devlet Sizgek and a team of ANSTO engineers.

Erden's first step was to develop the technology to produce the precursor powders to be mixed with the radioactive waste before heat pressing into synroc. "This powder-making process is called solgel," Erden explained. "A 'sol' being a colloidal suspension of solid particles in a liquid medium which turns into a 'gel' when particles link-up to form a semi-solid." According to Erden, the sol-gel process is similar to how yogurt and cheese are made. "Milk consists of minute particles of fat and protein suspended in water, then a microbial reaction involving yeast causes the suspended particles to gel into a homogeneous mass," he said.

Devlet joined the effort at the next stage: developing the full-scale equipment required to mix the powders and waste. Although Devlet arrived at ANSTO nearly three years after her husband, she was already very familiar with his work. She led the project during the technology development phase. "Being married and working together had its pros and cons, but the pros outweighed the cons," Devlet explained. "Our strong commitment  to the project may not have existed had we not been so closely linked." “ANSTO engineers have also played a key role in building the plant and making new equipment, it is a real team effort,” concluded George.

The team have almost completed a fullscale mock-up synroc plant which is required to test custom-built equipment needed to process the radioactive material. “The equipment must be tested and be in working order before it can be placed in a ‘hot’ cell which is specially shielded to handle radioactive material,” said George. Once synroc is produced it is placed in cans and safely stored in a waste repository either above or below ground. Although the radioactive molecules are locked away in the synroc and cannot get out, the rock still emits radioactivity.