Multipurpose Applied Physics Lattice Experiment
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- For other meanings of, see Maple (disambiguation)
The MAPLE (Multipurpose Applied Physics Lattice Experiment) dedicated isotope-production facility is a current project jointly undertaken by AECL and MDS Nordion. When completed the facility will include two identical reactors, as well as the necessary isotope-processing facilities. When operational, MAPLE will be capable of producing a large portion of the world's medical isotopes, especially Molybdenum-99, medical Cobalt-60, Xenon-133, Iodine-131 and Iodine-125
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[edit] History
[edit] Background
With the completion of the NRX reactor in 1947, AECL's Chalk River Laboratories 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 and neutron spectroscopy, many experiments were carried out involving the production of new isotopes. The field of nuclear medicine 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 40's and early 50's established Cobalt-60 as a useful isotope, as the relatively high-energy gamma rays produced when it undergoes beta decay 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 (which had been previously used as a therapy source) to perform the same procedure. 1
With this promising start, AECL came to be a major world supplier of medical isotopes, using both the NRX 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.
[edit] Beginnings
In the late 80's, AECL began to acknowledge that continued isotope production would require the construction of a new reactor to replace capacity lost by the closing of the NRX in 1992, and the planned closing of the NRU early in the new millennium. As a result, it was decided to build a new facility dedicated to the production of medical isotopes on-site at Chalk River Laboratories. As the result of an understanding between AECL and it's daughter company, MDS Nordion, that such a facility was required when Nordion was spun-off in 1991, design work for the reactor was undertaken during the first half of the decade.
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, and must be used within a few days of production. With treatments being constantly carried out around the globe, an uninterruptible supply was essential.
A formal agreement was signed to begin the project in August, 1996. Following a year-long environmental assessment, construction began in December, 1997. 2
There has been some local opposition to the use of highly-enriched uranium (HEU) in the reactor, 3, as well as from agencies in the United States who fear that the uranium could be stolen by terrorists and used to fabricate a bomb. 4
[edit] Current status
Construction of the two reactors was completed by 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 rod's housing and interfering with their free movement. As a result, the entire project has been on hold since July, 2000, while the control-rod system has been redesigned to have a greater operating tolerance, and the new system installed and re-tested. In addition to the now four-year-long delay in the start of commercial production, the project has significantly overrun it's original cost. AECL and MDS Nordion are currently in mediation over the future of the project, especially the sharing of the increased costs.
