A conversation with Pablo Adelfang, Head of the IAEA´s Research Reactor Section:
What type of reactor is housed at Vinca? What type of fuel did it use and who supplied that fuel?
The research reactor at the Vinca Institute of Nuclear Sciences was a 6.5 MW heavy water reactor. It was a Soviet designed and supplied reactor. The fuel was also supplied by the Soviet Union, and was 80% Highly Enriched Uranium (HEU), although the reactor used 2% enriched uranium as well. The reactor and fuel were not of a very common design.
What type of activities were carried out in the Vinca reactor? How many years did it operate, and when was it shut down?
The reactor first went critical in 1959 and was shut down in 1984. While it was operational, it was used to carry out physics experiments, dosimetry work, some material irradiation, and radioisotope production.
What happened to the nuclear fuel when the reactor was shut down?
The spent fuel was stored at the reactor site in a spent fuel pond. However, by the mid-1990s, it was clear that this was not a viable long-term storage solution. On one fact-finding mission, the IAEA discovered that there was no water purification system in the pool, so the spent fuel elements were deteriorating and losing integrity. With repeated measurements, we saw the radioactive contents of the pool water rising. There were concerns that the fuel assemblies would lose all integrity and further complicate clean-up efforts. There was also some leftover fresh (unirradiated) fuel on site; one of our first actions in 2002 was to ship these fresh fuel elements back to Russia.
Why did Serbia decide to repatriate the fuel? What role did the IAEA play in their decision process?
The Institute had three problems with the deteriorating fuel. First, it had a problem with long-term storage of spent fuel, because the facility wasn´t set up to store fuel for long periods of time. Second, an environmental problem was brewing, as the fuel assemblies continued to corrode and contaminate the pool, although there was no evidence of a leak or release to the environment. And third, there was a nuclear security problem, because there was HEU in the spent fuel pool. So this combination of issues led Serbia to turn to the IAEA for assistance in repatriating the fuel to Russia.
Since Serbia was a fairly new IAEA Member State in 2002 (having recently become independent of the former Yugoslavia), it lacked many political and legal resources, such as a Nuclear Regulatory Authority, that are needed to run such a large project. It also lacked the physical infrastructure and finances to carry it out. So the IAEA was involved in every phase of this project, from assisting with legal and financial planning and coordinating donor support, to getting contracts signed and advising on spent fuel repackaging and shipment.
What steps were taken to start the project? How did it progress from there?
In 2002, all of the fresh nuclear fuel (material that had not yet been in the reactor, and so was not irradiated) was shipped back to Russia. This shipment was actually the first repatriation of fresh fuel to Russia under the present programme, and it helped lay groundwork for an entire programme of fuel repatriation to Russia.
After that, intense planning began for repackaging the corroded spent fuel elements. We carried out several studies of the fuel and the surrounding fuel pond. The fuel was stored in two types of containers: aluminium barrels, and fuel channel holders. Both had been stored in water of poor quality in the pool for years.
We knew that re-packing the fuel would be difficult, because it needed to be done underwater to protect operators from being irradiated and to avoid dispersion of radioactivity during the process. So we knew that we needed to bring in a lot of purpose-designed equipment to help out with the repacking. We also knew we´d need large numbers of transportation casks for the fuel.
Our next goal was finding the money to take on such a big project. The Nuclear Threat Initiative (NTI) paid for the shipment of fresh fuel back to Russia, and gave additional funds to start implementing the spent fuel project. Funds were also given by the US Department of Energy´s National Nuclear Security Administration. In the end, the European Union, the Serbian government, the Czech Republic, and other donors also contributed - everyone chipped in to make this international project happen.
We received bids from several companies to lead the project; the IAEA helped Serbia analyze these bids and select the best option. Ultimately, a consortium of Russian companies was selected to carry out the work, and in 2006, a tripartite contract between the IAEA, the Vinca Institute, and Sosny-Mayak-Tenex was signed.
Before the contract was signed, the IAEA had helped to draw up the regulations that Serbian nuclear authorities would use and to carry out studies to determine the condition of the fuel assemblies and water. The IAEA had also given advice on the technical and legal details of bids for the fuel repackaging and assisted with the technical negotiations surrounding the contract itself.
After the contract was signed, the contracted companies started repackaging the spent fuel. This involved opening all the barrels underwater, repackaging the spent fuel into new containers and baskets, and then loading the baskets into shipping casks. The loaded casks were vacuum dried, checked for contamination and air tightness.
The final contract called for the permanent disposal of the high-level waste that would be generated after reprocessing of the spent fuel, since Serbia didn´t have the facilities to take back the waste after Russia recovered the still-usable uranium components of the spent fuel.
How long did the entire project take? How much material was shipped back to Russia?
The entire project has taken about 8 years - from the first shipment of fresh fuel in 2002, to the final shipment ending in December 2010.
The Institute shipped 8 030 fuel elements - some 2.5 tonnes of material. Approximately 17 percent of those fuel elements contained HEU.
What will happen to the material now?
It will be reprocessed. The highly enriched uranium will be "downblended" to lower enrichment levels and used as nuclear power reactor fuel, thereby changing the material into a form that presents a substantially lower security risk.
The high-level waste is expected to be vitrified and stored in Russia.
How many research reactors still use HEU? Why can't they just switch to LEU?
Many research reactors - around 200 in the world - still use HEU fuel, so there´s a lot of work to be done on this front. Many of these reactors can switch to LEU fuel using existing fuel, but others need to have their LEU fuel tested and approved before they can use it. Some reactors need a special high-density fuel that´s still being developed, so converting them will take time.
Are similar repatriation projects taking place or planned?
Several other countries that have either shut down their reactors or converted them to LEU fuel have shipped HEU fuel back to Russia under this programme, so progress is being made on this front, and it´s encouraging.
What is the IAEA doing to implement or assist these projects?
We assist countries with any part of their fuel repatriation or reactor conversion, from legal issues and contract negotiations to carrying out technical studies and assisting with technical issues. In the case of Serbia, we were involved with every part of the project, from advising and planning to transportation of the re-packaged fuel. There are other repatriation projects where we only advise on a single part of the process, or are only tangentially involved. The essential message to be delivered is that the IAEA stands ready to assist Member States, upon their request, with all research reactor spent fuel issues.