NTP Radioisotopes of South Africa is heading towards producing vital supplies of molybdenum-99 (Mo-99) from the Safari 1 reactor using only low-enriched uranium, both for fuel and for the target plates used to produce isotopes. And the secret to future reliable radioisotope supplies could simply come down to realistic economics.
South African Nuclear Energy Corporation (Necsa) subsidiary NTP is one of the world's major suppliers of reactor-produced Mo-99 and is now laying claim to be its only supplier of commercially viable quantities of the isotope produced solely from low enriched uranium technology, Necsa CEO Rob Adam told a special session of the World Nuclear Association's 35th Annual Symposium in London.
|Necsa's Rob Adam addresses the WNA Annual Symposium
Mo-99 decays to produce technetium-99m (Tc-99m), used in around 50 million medical diagnostic imaging procedures every year. With a half-life of only 6 hours, Tc-99m is too short-lived to be transported to hospitals but is produced where it is needed in generators containing Mo-99. As Mo-99 itself has a half-life of only 66 hours, the world relies on reliable, steady supplies of the isotope, most of which is made by irradiating uranium-235 contained in a solid target inside a research reactor.
Most of the world's Mo-99 comes from only five research reactors: Canada's NRU, the Netherlands' HFR, Belgium's BR-2, France's Osiris and South Africa's Safari-1. Australia's Opal reactor, which started up in 2007, has the capacity to produce up to half the world's Tc-99m demand but at present has only a small molybdenum processing facility and supplies only domestic demand.
With the exception of Opal reactor, all were originally built to use fuel containing highly enriched uranium (HEU) fuel. However, non-proliferation concerns have, over recent years, led a drive to convert research reactors to low-enriched uranium (LEU) fuel - that is, fuel containing less than 20% uranium-235 (U-235). Conversion of the 20 MW Safari-1 reactor at Necsa's Pelindaba facility to LEU fuel was completed in 2009. But at Safari-1, this proliferation proofing has been taken a step further, with the introduction of LEU-based targets for isotope production.
The use of target plates containing LEU instead of HEU is not without its downsides. Conversion to LEU means that a larger mass of uranium - 2 to 5 times as much - needs to be irradiated to obtain the same production yield as with HEU targets. This in turn poses problems for the Mo-99 extraction and purification process, with larger quantities of uranium needing to be processed, and for the quantity of waste produced. At best, the volumes of radioactive waste will increase, but any significant changes to the processing system could generate different waste streams, all with associated cost implications.
Conversion of Safari-1 to LEU targets has not been achieved without overcoming significant technical hurdles, Adam notes. Some of these hurdles have been associated with variable yields, and Necsa is working to overcome them, he explained to World Nuclear News
. For example, in order to achieve a sufficient mass of uranium in the targets, a powdered composite uranium-aluminium alloy has been developed and work is ongoing to optimise target plate configuration.
Mo-99 produced from LEU is around 20% more expensive than that produced from HEU, but South Africa is hopeful that regulatory systems in countries purchasing significant quantities of radioisotopes will respond by giving preferential treatment to LEU-origin products. The first radioisotopes produced at Safari-1 from LEU targets were shipped to international customers in July 2010, and the first major commercial shipment, to the USA, is due to take place on 29 September. The reactor is on course to reach full conversion to LEU targets within the year. Isotope crisis a market product?
The unscheduled outages of two of the world's major isotope production reactors, Canada's NRU and the Netherlands' HFR, in recent years resulted in a gross undersupply of Mo-99 on the world scale. The choice by many Mo-99 customers to rely on a single source of supply has led to reliance on a handful of ageing research reactors paid for by governments. Such government funding, far from being the noble gesture it may at first seem, effectively represents a subsidisation of a critical step in a pharmaceutical value chain. This has in effect placed Mo-99 outside a natural market system and this lies at the heart of the current supply crisis, Adam argues.
"It is unfortunate but true that a great many patients have not and will not receive diagnostic scans whilst the Mo-99 shortage persists. There is no doubt that a significant amount of suffering and even a number of deaths have resulted from the unavailability of Mo-99 and the associated Tc-99m generators," Adam said. The five reactors which can produce commercial quantities of Mo-99 are all over 40 years old, but the market price of radioisotopes has not been high enough for investors to justify the expenditure on the construction of new isotope production reactors.
As things stand, Safari-1 is itself due to close in 2022. Replacement with a multi-functional research reactor with radioisotope production as just one of its functions could, given the artificially depressed market price of radioisotopes, prove prohibitive. A solution for South Africa could be the construction of a pared-down reactor with isotope production as its sole function. With such a reactor up and running, Safari-1 could then be refurbished and enjoy a new lease of life concentrating on other research functions, Adam told World Nuclear News
A newly released report by the OECD Nuclear Energy Agency (NEA) concurs with Adam’s views on the radioisotope market. The current economics of the Mo-99 supply chain are not adequate for supporting new investment, according to The Supply of Medical Radioisotopes: An Economic Study of the Molybdenum-99 Supply Chain. Without changes to address the market, policy and technology failures, the supply of Mo-99 and hence Tc-99m will continue to be unreliable, the agency warns.
For the supply chain to be economically sustainable, remuneration for reactor irradiation services and processing services needs to be based on the full costs of production, according to the report. This would likely result in higher market prices but the impact on the final cost of medical diagnostic procedures would be small, says the agency.
The report is the first of a series being prepared in support of the NEA High-level Group on the Security of Supply of Medical Radioisotopes (HLG-MR).
Researched and written
by World Nuclear News