18.02.2010 Medical isotope supplies dwindle

Nuclear-reactor shutdowns will cripple global isotope production next month.

The world's shaky supply of a crucial medical isotope is about to dry up.

Next week, one of the main nuclear reactors used to make molybdenum-99 (99Mo) will be shut down for repairs — and for several days next month, none of the five reactors that currently supply hospitals will be making the isotope.

Molybdenum-99 decays to yield the short-lived isotope technetium-99m (99mTc), which is used in about 70,000 medical imaging procedures every day, including bone and heart scans.

Supplies of 99Mo have already been badly affected by the unplanned nine-month shutdown of the Canadian National Research Universal (NRU) reactor in Chalk River, Ontario, following a heavy-water leak in May 2009. The situation will get much worse on 19 February when the High Flux Reactor (HFR) in Petten, the Netherlands, is taken out of service for six months so that corroded pipework can be repaired.

Together, these facilities normally produce two-thirds of the global supply of 99Mo. The short half-lives of 99Mo and 99mTc mean that supplies cannot be stockpiled. Instead, the 99Mo is loaded into so-called 'moly cows', which over several days produce a stream of 99mTc that can be 'milked' on-site at hospitals.

The crisis has again raised questions about the wisdom of relying solely on a clutch of ageing nuclear reactors to provide hospitals with the 99mTc they need on a daily basis. Assuming that this round of repairs is successful, the 49-year-old HFR will keep running until the end of 2015; if the 53-year-old NRU is restarted, it could operate until 2016.

But repairs to the Canadian reactor have been hit by a series of delays. Its operator, Atomic Energy of Canada Limited, now hopes that it will be online sometime in April.

With both big producers out of action for the next six weeks or so, reactors in Belgium, France and South Africa have been called upon to fill the 99Mo pipeline (see map). These reactors are increasing their production and have coordinated their operating cycles, but there will still be a few days next month when no 99Mo is produced.

"All reactors have to shut down on a regular basis for quality control and periodic maintenance," explains Marc Gheeraert, president of the Brussels-based Association of Imaging Producers and Equipment Suppliers, the body that is coordinating the week-by-week availability of 99Mo. "During the shutdown of the HFR and until the NRU is operational, the availability of the three remaining reactors has been optimized to minimize the impact on patients."

Companies that provide hospitals with 99mTc generators are already warning that orders might not be fulfilled. A spokesperson for Canadian isotope supplier MDS Nordion in Ottawa, Ontario, told Nature that the company expected to receive "little, if any" 99Mo before the NRU comes back online. Another major isotope supplier, Covidien of Hazelwood, Missouri, has announced that it will not be delivering any 99mTc generators on 20–23 March in Europe or on 21–25 March in the United States. It is also warning customers to expect "significant 99mTc shortages" from the end of February until mid-April.

A radioactive problem

Building replacement reactors that can produce 99Mo is both extremely costly and politically sensitive because the standard production pathway involves neutron-induced fission of weapons-grade uranium. The Nuclear Research and Consultancy Group (NRG) in Petten, which runs HFR, plans to replace the ageing reactor with a new one called PALLAS, which will be used for medical isotope production and research. However, the NRG is struggling to raise funds for the project and has recently halted its tendering process until the cash can be found, potentially delaying the project.

"The construction of PALLAS requires an investment of several hundreds of millions of euros. The timing of the availability of the financial resources will play an important role in the project planning and therefore the date that the reactor will enter into operation," the NRG said in a statement.

On 25 January, the US government announced that it was investing in alternative technologies to generate 99Mo. Two separate solutions — which together could supply 100% of the country's 99Mo needs — are being supported by the US energy department's National Nuclear Security Administration (NNSA). The NNSA has invested US$9 million in a joint project between reactor-construction firm Babcock and Wilcox of Lynchburg, Virginia, and Covidien to build a series of small nuclear reactors powered by a liquid core of low-enriched, non-weapons-grade uranium. Babcock and Wilcox expect the facility to be up and running in about five years.

A second NNSA grant of $2.25 million has been awarded to General Electric (GE) and its partner Hitachi, to develop a production cycle that would avoid uranium fission altogether. Instead, they would put 98Mo targets into existing commercial nuclear reactors to generate 99Mo. The GE Hitachi Nuclear Energy consortium has pledged to match the government funding, although further support will eventually be needed to meet the projected total development cost of $30 million. Isotope production would start "within the next couple of years", according to Ned Glascock, communications manager for GE Hitachi Nuclear Energy.