this isotope for medical use and are affecting the continuity of patient care in the United States and elsewhere.
The supply of Mo-99 to the United States is fragile over a number of different timescales. This fragility occurs because:
Mo-99 is highly perishable owing to its short (66-hour) half-life.
It is produced in a small number of reactors, all of which are shut down periodically for planned and unplanned maintenance. There is limited excess capacity when a major reactor is shut down for extended periods (weeks) or more than one reactor is shut down simultaneously even for shorter periods.
It is produced in reactors that are about 40–50 years old and have uncertain additional remaining lifetimes.
It is not produced domestically.
It is produced with HEU, which could be restricted in the future.
There are long supply lines from some producers in Europe and South Africa to users in the United States.
There can be difficulties involved in moving radioactive materials across international borders, especially by air.
As demonstrated by the 2007 NRU reactor outage and 2008 HFR outage, the sustained shutdown of reactors used by either MDS Nordion or Mallinckrodt would result in the substantial disruption of supplies to the United States and worldwide, as would the simultaneous shutdown of reactors used by both companies even for short periods.
AECL’s May 2008 announcement that it will discontinue development work on the Maple reactors is a blow to worldwide supply reliability and increases U.S. vulnerability to supply disruptions.
Reliability of Mo-99 supply is likely to become a serious problem for the United States in the early part of the next decade without new or refurbished reactors: The operating license for the NRU reactor expires in 2011 and substantial investment and refurbishment will apparently be required to obtain a license extension; moreover, the European replacement reactors (Jules Horowitz and Pallas) will not yet be operational. HFR and NRU can probably continue to meet incremental growth in Mo-99 demand if those reactors can remain operational, but continued operations are not assured through the next decade. There is enough surge capacity at existing reactors to cover shortages caused by the shutdown of a single reactor, but such surges can not be maintained indefinitely.
Conversion from HEU-based to LEU-based production of Mo-99 would improve supply reliability because it would remove uncertainties associated with the continued availability of HEU for Mo-99 production.