Part II: The International Security of Medical Isotope Supply: Assessment of Potential Technologies

Mohamed Zakzouk       
Economics, Resources and International Affairs Division

(This is the second in a series of two HillNotes on The International Security of Medical Isotope Supply. Part one explores progress in Canada and abroad.)

The main technology options available to produce molybdenum-99 (99Mo) (or technetium-99m (99mTc) directly) can be grouped under two broad categories:

  • reactor-based technologies, which generally have a wide range of research and commercial uses, including the ability to produce different isotopes simultaneously; and
  • accelerator-based options, which tend to be more specialized.

Currently, reactor-based fission is the most well-established and commercially viable technology, supplying almost the entire global demand for 99Mo. According to the Nuclear Energy Agency (NEA), the alternative accelerator-based technologies appear promising, but their commercial viability for wide deployment remains unknown.

The following provides an overview of the technical, commercial and financial feasibility of different isotope-producing technologies, based on the most recent NEA review.

General Assessment of Technical and Commercial Feasibility of Reactor-Based Technologies

HEU Fission

High-enriched uranium (HEU) fission is the most widely used method of molybdenum-99 (99Mo) production. The technology is well-established, with high 99Mo–specific activity/purity, and the highest production yield of all options. While the world’s demand is met almost entirely using existing HEU facilities, most 99Mo-producing research reactors are old; thus, their reliability has been in decline. HEU targets are weapon-graded, and therefore, not proliferation-resistant and require heavy regulation from a security perspective. Furthermore, they produce highly radioactive waste that is not systematically recycled due to technical limitations.

HEU fission remains the most commercially attractive option today, and one capable of co-producing a wide range of radioisotopes, along with 99Mo.

LEU Fission

Low-enriched uranium (LEU) fission is a well-established technology, with high 99Mo–specific activity/purity and production yield (relative to other HEU alternatives). Compared to the HEU route, LEU targets are proliferation-resistant, and thus, safer, more available, and easier to transport and process from a regulatory perspective. On the other hand, they are less productive than their HEU counterparts because of their lower uranium content. That is, larger amounts of uranium are needed, with correspondingly increased volumes of waste, to produce the same yield. The productivity of LEU targets could be improved by increasing their uranium content.

LEU fission is compatible with the current global supply chain of 99Mo/99mTc (technetium-99m), and its irradiation capacity is comparable to that of HEU targets. Furthermore, LEU fission can co‑produce a wide range of radioisotopes, along with 99Mo.

LEU Solution Reactors Low-enriched uranium (LEU) solution reactors were built in several countries, mainly for criticality studies. Although they have been proven to produce pure 99Mo, no reactors are currently available for 99Mo production.

LEU solution reactors appear to have favourable characteristics in terms of yield, production rate, proliferation resistance and, potentially, cost. On the other hand, they have yet to reach full technological maturity and acceptance by regulators and users. Technically, they could be used to co-produce a wide range of radioisotopes, and their 99Mo yield could be shipped worldwide for global distribution.

98Mo Neutron Activation

The neutron activation of 98Mo in a research reactor is another way of producing 99Mo. The currently used process is technically feasible, and can be done using almost any research reactor (and even some power reactors). Furthermore, it is proliferation-resistant, safe, and produces almost no radioactive waste (unless enriched Mo is used). On the other hand, it has low specific activity (possibly too low for current 99mTc generators), and is 50 times less productive than the fission route. Productivity can be theoretically increased through technological upgrades, and by using highly enriched Mo to improve the quality of the yield.

Although currently used for small-scale commercial production in some non-OECD countries, neutron activation is not yet attractive for large-scale commercial users or power plant operators. It competes with their primary purpose (of generating power) and would require a detailed safety case and a potentially long approval process. Large-scale production is not envisaged in the near future.

Source: OECD Nuclear Energy Agency, The Supply of Medical Radioisotopes: Review of Potential Molybdenum-99/Technetium-99m Production Technologies, November 2010.

General Assessment of Technical and Commercial Feasibility of Accelerator-Based Technologies

Cyclotrons

Cyclotrons have been tested and proven to produce 99mTc directly. They have potential advantages in terms of cost, waste management (they produce almost no nuclear waste), proliferation resistance and ease of approval (they do not involve any hazardous, explosive or fissile materials). On the other hand, their yield, based on current technology, is significantly smaller than the fission route, and they require significant amounts of highly enriched molybdenum (100Mo).

Cyclotrons can only be used to supply local needs, and therefore, have limited compatibility with the current 99Mo/99mTc supply chain. Finally they can be used to produce other isotopes, but not simultaneously with 99Mo. (In Canada, recent advancements in cyclotron technology have been announced by TRIUMF and the Sherbrooke Molecular Imaging Centre.)

Photofission (electron accelerator)

Although electron acceleration using photofission has been tested experimentally, its use for the complete production of 99Mo has not been tested. The main advantage of this route is that it uses a similar process, with almost the same yield, as the reactor fission routes. It is also proliferation-resistant, and is considered safer than LEU fission. On the other hand, this technology is currently not mature enough for irradiation. Furthermore, the very high energy consumption of electron accelerators undermines the overall production efficiency of this option.

Photofission acceleration seems to have potential only as a small-scale producer of 99Mo. Finally, while electron accelerators could produce other isotopes, they cannot do so simultaneously with 99Mo production.

Photonuclear Reaction (electron accelerator)

The theoretical production yield of the photonuclear accelerator is considered high, although the technology is still at the stage of laboratory research. On the other hand, the specific activity of 99Mo output is not high enough for current 99mTc generators (the same challenge as the reactor-based neutron activation technology). Productivity could potentially be increased through technological upgrades and by using highly enriched Mo.

As an electron accelerator–based technology, this option has similar challenges to the photofission option: high-energy accelerators are energy intensive and not widely available, and they cannot produce other isotopes simultaneously with 99Mo. The potential commercial viability of this route remains unknown.

Other Other accelerator-based technologies, currently in a theoretical stage, could develop into commercially viable options in the long term, between 2025 and 2035.

Source: OECD Nuclear Energy Agency, The Supply of Medical Radioisotopes: Review of Potential Molybdenum-99/Technetium-99m Production Technologies, November 2010.

Financial Estimates for Different Technologies (based on global demand)

Technology Units Required to Supply the World Market Estimated Capital Costs to Satisfy Global Demand(normalized to 100% of the world’s estimated demand) Estimated Unit Cost of the Final Product(per 6-day curie of 99Mo)
High-enriched uranium (HEU) fission 5–10 reactors and processing facilities US$1.38 billion (Total world capital costs, based on OECD Nuclear Energy Agency [NEA] calculations) US$555–850
Low-enriched uranium (LEU) fission 5–10 reactors and processing facilities US$2 billion(Total world capital costs, based on NEA calculations) US$735–1,100
LEU solution reactor At least 13 solution reactors and processing facilities US$0.325 billion
(Although the costs associated with the technology development risk remain unknown)
US$410–970
Molybdenum-98 (98Mo) neutron activation 20+ reactors US$1.6 billion

US$3,740–3,960
(Unit cost could drop to US$510–850 through technical upgrades to current process)

Cyclotrons 200 cyclotrons US$2.3 billion (US$11 million for one cyclotron) US$900–1,230
Photo-fission (electron accelerator) Hundreds of high-power units (500 kW) N/A
(US$45 million for one accelerator)

N/A
(Expected to be very high)

Photo-nuclear reaction(electronaccelerator) 20 high-power units (500 kW each), or 100 units of 100 kW power US$0.9 billion for the facilities, plus additional costs for the target material (i.e., highly enriched molybdenum) N/A

Source: OECD Nuclear Energy Agency, The Supply of Medical Radioisotopes: Review of Potential Molybdenum-99/Technetium-99m Production Technologies, November 2010.

This is the second in a series of two HillNotes on The International Security of Medical Isotope Supply.  Part one explores progress in Canada and abroad.