SIDEBAR 11.1

Research and Test Reactors

Research and test reactors are used primary as a source of neutrons for scientific and technical research and development applications and for the industrial production of isotopes. They are designed with high-power-density cores to produce a high thermal neutron flux (typically 1014–1015 neutrons per square centimeter per second) but have much lower thermal outputs (typically < 100 MW thermal) than reactors used to produce electricity (typically ≥ 3,000 MW thermal). These reactors have a wide range of designs, but typically comprise a cluster of fuel elements and control rods in a pool or tank of water with graphite, beryllium, or heavy-water reflectors. The cores and reflectors typically contain empty channels for irradiation of targets and test materials, and some reactors are designed with apertures in their pool or tank walls through which neutron beams can be accessed.

HEU is well suited as a fuel for these reactors because it provides a high density of U-235, which allows high neutron fluxes to be obtained in a compact core configuration. Maintaining this high performance can be a substantial technical challenge when converting these reactors to use LEU fuel because existing fuel designs result in U-235 densities that are too low. Conversion may require a redesign of the fuel elements and/or the development of LEU fuel material that has high U-235 densities. This fuel material must be stable under the irradiation conditions that exist in these high-performance cores. As discussed in the text, suitable replacement LEU fuels have not been developed for some very-high-power-density reactors; these reactors cannot be converted until such fuels are developed. The development of such fuels is a major current focus of the RERTR program.

for diagnostic and therapeutic procedures based on nuclear medicine techniques. More than 700 research reactors are known to have been commissioned worldwide, and 240 of these are currently in operation in 55 countries (Table 11.1); another 9 reactors are in various stages of construction and several more are planned.

Since 1975, significantly more research and test reactors have shut down each year than have started up. Of the 240 operating research reactors, 203 are or were fueled with HEU. Almost all of these reactors are supplied with HEU of U.S. or Russian origin with only a small number supplied with HEU produced in the People’s Republic of China (simply referred to as China in the following discussion).

The commerce in HEU for research reactors was recognized as a potential source of nuclear weapons-usable material beginning in the mid 1970s. Increasing concerns about the proliferation of HEU prompted the formation of the Reduced Enrichment for Research and Test Reactors (RERTR)



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