A unique technology of dilution and immobilisation of irradiated highly enriched uranium (HEU) fuel has been developed by specialists at the National Nuclear Centre (NNC) in Kazakhstan. In 2010, NNC, together with the US Battelle Energy Alliance undertook a large-scale project to convert research reactors IVG.1M and IGR to use low enriched uranium (LEU) fuel. The work was part of a global initiative to consolidate and eliminate stockpiles of HEU and transfer research reactors to low enriched nuclear fuel.

This also required solving the issue of disposing of irradiated graphite from the initial core of the IGR reactor, which had been stored for more than 60 years. NNC specialists developed their own conceptual technology for dilution and immobilisation. Subsequently, the technology was approved by specialists from the US Idaho National Laboratory, Sellafield in the UK and International Atomic Energy Agency (IAEA) experts.

“To address the issue of disposal of irradiated graphite fuel from the initial core of the IGR reactor, NNC specialists proposed their own conceptual dilution and immobilisation technology,” said NNC Director General Erlan Batyrbekov. “The essence of the technology lies in the dilution of highly enriched uranium fuel by grinding and mixing it with depleted uranium dioxide and its subsequent encapsulation in a cement matrix.”

In support of this technology, research was carried out, which confirmed the compliance of the developed matrix with the criteria defined by the rules and standards of Kazakhstan, as well as with the requirements of the IAEA. Based on the results of research and experimental testing, a technology was developed for the dilution and immobilisation of irradiated graphite HEU, which was sent to the IAEA for expert assessment.

After reviewing the positive conclusion was sent to the NNC. The Expert Opinion emphasises the uniqueness of the technology and its fundamental reliability. In addition, IAEA representatives noted that thanks to a well-planned and implemented research programme in support of the project framework for immobilising diluted HEU-IGR fuel, all the goals were achieved. Already, we can say that this technology can be used for similar fuels in other countries participating in the programme to minimise HEU.

Image: New technology for treating HEU fuel has been developed by the NNC in Kazakhstan (courtesy of Rosatom)