The Multipurpose Applied Physics Lattice Experiment (MAPLE), later renamed MDS Medical Isotope Reactors (MMIR), was a dedicated isotope-production facility built by

AECL Atomic Energy of Canada Limited (AECL) is a Canadian federal Crown corporation and Canada's largest nuclear science and technology laboratory. AECL developed the CANDU reactor technology starting in the 1950s, and in October 2011 licensed this ...

and MDS Nordion. It was intended to include two identical reactors, as well as the isotope-processing facilities necessary to produce a large portion of the world's medical isotopes, especially

molybdenum-99 Molybdenum (42Mo) has 33 known isotopes, ranging in atomic mass from 83 to 115, as well as four metastable nuclear isomers. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. All unstable isotopes of molybdenum ...

, medical

cobalt-60 Cobalt-60 (60Co) is a synthetic radioactive isotope of cobalt with a half-life of 5.2713 years. It is produced artificially in nuclear reactors. Deliberate industrial production depends on neutron activation of bulk samples of the monoisot ...

xenon-133 Naturally occurring xenon (54Xe) consists of seven stable isotopes and two very long-lived isotopes. Double electron capture has been observed in 124Xe (half-life ) and double beta decay in 136Xe (half-life ), which are among the longest measured ...

iodine-131 Iodine-131 (131I, I-131) is an important radioisotope of iodine discovered by Glenn Seaborg and John Livingood in 1938 at the University of California, Berkeley. It has a radioactive decay half-life of about eight days. It is associated with nu ...

and

iodine-125 Iodine-125 (125I) is a radioisotope of iodine which has uses in biological assays, nuclear medicine imaging and in radiation therapy as brachytherapy to treat a number of conditions, including prostate cancer, uveal melanomas, and brain tumo ...

. An operational license for the MAPLE 1 reactor was granted in 1999, and the reactor went critical for the first time soon after. However, problems with the reactor, most notably a positive power co-efficient of reactivity, led to the cancellation of the project in 2008.

History

Background

With the completion of the

NRX NRX (National Research Experimental) was a heavy-water-moderated, light-water-cooled, nuclear research reactor at the Canadian Chalk River Laboratories, which came into operation in 1947 at a design power rating of 10 MW (thermal), increasing to ...

reactor in 1947,

Chalk River Laboratories Chalk River Laboratories (french: Laboratoires de Chalk River; also known as CRL, Chalk River Labs and formerly Chalk River Nuclear Laboratories, CRNL) is a Canadian nuclear research facility in Deep River, about north-west of Ottawa. CRL is a ...

possessed the world's most powerful research reactor. While the large neutron fluxes available in the reactor led to advances in such fields as

condensed matter physics Condensed matter physics is the field of physics that deals with the macroscopic and microscopic physical properties of matter, especially the solid and liquid phases which arise from electromagnetic forces between atoms. More generally, the s ...

and neutron spectroscopy, many experiments were carried out involving the production of new

isotopes Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...

. The field of

nuclear medicine Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is "radiology done inside out" because it records radiation emit ...

developed when it was realized that some of these artificially created isotopes could be used to diagnose and treat many diseases, especially cancers. Pioneering medical work done in the late 1940s and early 1950s established

as a useful isotope, as the relatively high-energy

gamma rays A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically sh ...

produced when it undergoes

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For e ...

are able to penetrate the skin of the patient, and deliver a greater portion of the dose directly to the tumor. The high neutron efficiency of the NRX's heavy water-moderated design, coupled with the high neutron flux of the reactor, made it relatively inexpensive for AECL to produce medical-grade cobalt-60. For example, the cost of the entire unit used to perform the first cobalt-60 treatment was about $50,000. By way of contrast, it would cost $50,000,000 just to produce enough

radium Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rathe ...

(which had been previously used as a therapy source) to perform the same procedure. With this promising start, AECL came to be a major world supplier of medical isotopes, using both the

reactor, and the NRU reactor, which came on-line in 1957. However, as these reactors began to age, it became clear that a new facility would be needed to continue the production of medical isotopes.

Beginnings

In the late 1980s, AECL began to acknowledge that continued isotope production would require the construction of a new reactor to replace capacity lost by the planned closing of the

in 1992, and the planned closing of the NRU early in the new millennium. Design work on a replacement, originally under the name "Maple-X10", began in the late 1980s. As part of a restructuring taking place around the same time, the medical isotopes side of AECL was reorganized as Nordion in 1988. Work on the X10 project essentially ended at this point. Nordion company was purchased by MDS in 1991, and an agreement was reached between AECL and MDS Nordion that a new facility dedicated to the production of medical isotopes would be needed. A formal agreement was signed to begin the project in August 1996. Following a year-long environmental assessment, construction began in December 1997. The design that resulted involved a facility with two identical reactors, each capable of supplying 100% of the world's medical isotope demand. The second reactor would function primarily as a back-up, to ensure that the supply of isotopes would not be interrupted by maintenance or unplanned shutdowns. This is made necessary by the nature of medical isotopes; many have short

half-lives Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

, and must be used within a few days of production. With treatments being constantly carried out around the globe, an uninterruptible supply was essential. There has been some local opposition to the use of highly enriched uranium ( HEU) in the reactor, as well as from activists in the United States who fear that the uranium could be stolen by terrorists and used to fabricate a bomb.

Current status

Originally planned to complete construction in 1999 and 2000, both reactors were instead completed in May 2000. An operational license was granted in August 1999 for the MAPLE I reactor, and extended to include the MAPLE II reactor in June 2000. Commissioning testing was begun immediately, with the MAPLE I achieving its first sustained reaction in February 2000, and MAPLE II following in October 2003. However, during testing, it was noted that some of the emergency shut-off rods in the MAPLE I reactor could fail to deploy in certain demanding situations. This failure was ascribed to workmanship and design issues, and related to fine metal particles accumulating in the control rods' housing and interfering with their free movement. In addition, later testing found that the reactors have a positive power co-efficient of reactivity (PCR), which was in disagreement with the prediction of the modelling, and was a significant barrier to commissioning. A positive power co-efficient means that the reactor becomes more reactive when it heats up; in the case of an unplanned power spike, such a design can "run away" and potentially cause a

meltdown Meltdown may refer to: Science and technology * Nuclear meltdown, a severe nuclear reactor accident * Meltdown (security vulnerability), affecting computer processors * Mutational meltdown, in population genetics Arts and entertainment Music * ...

. Consequently, significant efforts were made to resolve the outstanding issues, but progress towards commissioning the reactors was markedly slowed. During the subsequent eight-year-long delay in the start of commercial production, the project significantly overran its budgeted cost. The original budget was $140 million, but by 2005 it had already cost $300 million. Disputes over responsibility for the overruns between

and MDS Nordion added a further layer of complexity to the process. After considerable negotiation, AECL assumed full responsibility for the reactor in a settlement. The MAPLE facility was granted an extension on its operating license on 25 October 2007, which would permit operations until 31 October 2011. This (final) submission envisioned that the MAPLE 1 reactor would be operational in late 2008.October 2007 AECL submission to the CNSC, see Slide 8 on Page 4.
/ref> However, on 16 May 2008, AECL released a statement announcing that the MAPLE program had been terminated, as it had become "no longer feasible to complete the commissioning and start-up of the reactors". In this statement, AECL indicated that they would move to further extend the licence of the operating NRU reactor to continue the production of medical isotopes. The statement left unclear what long-term direction AECL would take for its medical isotope production business.

References

External links

Article on early cobalt therapy
* https://web.archive.org/web/20080618221319/http://www.aecl.ca/NewsRoom/News/Press-2008/080516.htm * {{Nuclear power in Canada Atomic Energy of Canada Limited Nuclear reactors