Maple cancelled

22 August 2008

On 16 May the Canadian Crown Corporation AECL announced that it was discontinuing work on its Maple (Multi-purpose Applied Physics Lattice Experiment) medical isotope production reactors, putting an end to more than 12 years of effort to establish a dedicated medical isotope production facility.

In its announcement, AECL said that the decision was based “on a series of reviews that considered, among other things, the costs of further development, as well as the time frame and risks involved with continuing the project.” AECL’s president and chief executive officer, Hugh Mac­Diarmid, said that despite the “tremendous efforts” that had been made to bring the Maple project into service, “the board of directors and senior management have concluded that it is no longer feasible to complete the commissioning and startup of the reactors.” AECL’s announcement also claimed that this decision would not affect the current supply of medical isotopes produced by the NRU reactor.

The federal government issued a joint statement from natural resource minister Gary Lunn and health minister Tony Clement to the effect that the Maple project underwent a number of tests between January and April, which all failed. Lunn also said that the government was “absolutely committed to ensuring the medical community has the isotopes it needs in the future,” and that private companies were proposing solutions to the long-term supply of medical isotopes but he did not specify either the companies or the solutions.

MDS Nordion, AECL’s sole customer for medical isotopes and a former partner in the project, said that it had not been consulted by AECL and expressed its “disappointment” with the decision to discontinue the Maple project. Subsequently, on 9 July, MDS announced that that it had served AECL with notice of arbitration proceedings and would be seeking an order to compel AECL to fulfil its contractual obligations under its 2006 agreement. If this order was not granted, then MDS would seek “significant monetary damages.” MDS noted that it had concurrently filed a court claim for C$1.6 billion in damages against AECL, for negligence and breach of contract, and against the government of Canada, for inducing breach of contract and for interference with economic relations.

Isotope production

Since its very earliest days, AECL has produced and (originally through its Commercial Products Division) marketed commercial and medical isotopes. The division was renamed the Radiochemical Company in the ’70s and then sold to MDS Nordion by the Progressive Conservative government in 1991. The principal sources for medical isotopes were the NRX and NRU reactors. These heavy-water moderated reactors were built for plutonium production and nuclear research, and were started up in 1947 and 1957 respectively. In the late ’80s it began to become clear that continued isotope production would require the construction of a new reactor to replace capacity lost by the closing of the NRX reactor in 1992, and the (then) planned closing of NRU in 2005. Discussions with MDS Nordion resulted in the decision to build a new facility dedicated to the production of medical isotopes at Chalk River Laboratories. According to MDS Nordion, an agreement was made with AECL in 1996 for the construction of two reactors and an associated processing facility to provide a 40-year supply of medical isotopes and to be completed by 2000. In the interim, isotope supplies were to be maintained by NRU.

Construction began at the end of 1997, and the two reactors were complete by 2000, with Maple 1 achieving criticality in February of that year. By 2003 it was apparent that delays in the Maple commissioning programme dictated continuing to operate NRU past the planned shutdown date of 2005, and AECL approached the Canadian Nuclear Safety Commission (CNSC) for approval to operate NRU beyond 2005 on the grounds that there was no available replacement for the reactor.

The delay in bringing the Maple reactors into service was principally the result of the discovery that the reactors’ power coefficient of reactivity was positive, not negative as had been predicted. The power coefficient of reactivity (PCR) is the change in reactivity per percent change in power and is the summation of the moderator temperature coefficient of reactivity, the fuel temperature coefficient of reactivity, and the void coefficient of reactivity. In a reactor with a negative PCR, reactivity will decrease as power increases while if the PCR is positive, the converse holds true. CNSC staff and nuclear safety professionals agree that a positive PCR by no means precludes safe operation, but they also agree that it is desirable that the reason for the discrepancy between prediction and reality be understood. So far that understanding has not been reached.

In a presentation to the CNSC in October 2005, AECL reported that Brookhaven National Laboratory had reviewed AECL’s own analysis of the Maple core and concluded that the work was in general thorough and of high quality. Also, AECL reported that work carried out by the Idaho National Laboratory, using independent models and code calculations had produced similar results to AECL’s own PCR predictions. In December AECL reported that the “PCR issue [is] poised for resolution following significant work by AECL and independent organisations.”

At this time MDS Nordion, facing a reported doubling of costs on a project already five years late, entered mediation with AECL to renegotiate its agreement. In 2006, agreement was reached whereby, according to MDS, AECL took over complete financial responsibility for the project, committed to have the reactors in service by October 2008, and agreed to provide MDS with a 40-year supply of isotopes.

In a September 2007 presentation to the CNSC in support of its licence renewal application, AECL reported that preliminary results from tests suggested the highly enriched uranium targets were a contributor to the positive PCR, however further testing was needed to assess the significance of other factors. An in-service date for the facility of 2nd or 3rd quarter of 2008 was predicted. On 25 October, the CNSC renewed the Maple project’s operating licence for a four-year period to “permit the completion of the commissioning activities and the operation of the Maple 1 and 2 reactors and the new processing facilities.”

Less than seven months later, the whole project has been cancelled. The extensive legal wrangling that can almost certainly be expected in the wake of the cancellation will only add to the substantial costs already incurred by the Canadian taxpayer – figures of up to C$700 million have been reported but not confirmed by any official spokesperson. The prospect of legal action has also, inevitably, stifled attributable timely, substantive comment on the matter from those most closely involved. Predictably, reaction from the Canadian Nuclear Society and some academics has been to roundly condemn the cancellation. A more interesting, and more thoughtful response came from a highly experienced Toronto-based nuclear safety consultant who told NEI: “Perhaps our real concern should be about our ability to predict reactor behaviour. Demonstrably there is a gap in our understanding and it could be rather important to find out what that gap is.”

Isotope supply future

At the moment the NRU reactor produces more than half the world’s supply of medical isotopes. While there is general agreement that the life of this veteran reactor may well be safely prolonged past the current licence renewal date of 2011, it is equally clear that extended shutdowns for repairs or modifications are not improbable events – it was just such an extended shutdown of NRU that triggered a medical isotope supply crisis in late 2007. It is not clear how the Canadian government will meet its clearly articulated commitment to maintain the security of medical isotope supplies.

Use of an accelerator rather than a reactor for isotope production is one possibility. A senior official from Mevex, Canada’s leading provider of accelerator design services and technical support, told NEI: “Of course we could build an accelerator to produce medical isotopes. It’s just a matter of who pays for it.”

Another, more speculative, possibility would be using an accelerator as a neutron source for a modified Maple core. In this case the core would be a subcritical assembly, used as a ‘neutron multiplier’.

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