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The ongoing effort to convert the world’s research reactors
The Ghana Research Reactor-1, located in Accra, Ghana, was converted from HEU fuel to LEU in 2017. Photo: Argonne National Laboratory
In late 2018, Nigeria’s sole operating nuclear research reactor, NIRR-1, switched to a safer uranium fuel. Coming just 18 months on the heels of a celebrated conversion in Ghana, the NIRR-1 reboot passed without much fanfare. However, the switch marked an important global milestone: NIRR-1 was the last of Africa’s 11 operating research reactors to run on high-enriched uranium fuel.
The 40-year effort to make research reactors safer and more secure by replacing HEU fuel with low-enriched uranium is marked by a succession of quiet but immeasurably significant milestones like these. Before Africa, a team of engineers from many organizations, including the U.S. Department of Energy’s Argonne National Laboratory, concluded its conversion work in South America and Australia. Worldwide, 71 reactors in nearly 40 countries have undergone conversions to LEU, defined as less than 20 percent uranium-235. Another 31 research reactors have been permanently shut down.
Mayank Goswami, Anupam Saxena, Prabhat Munshi
Nuclear Science and Engineering | Volume 176 | Number 2 | February 2014 | Pages 240-253
Technical Paper | dx.doi.org/10.13182/NSE12-26
Articles are hosted by Taylor and Francis Online.
Iterative algorithms for computerized tomography reconstruction employ a variety of grids, interpolation techniques, and solution procedures. A new projection-intersection (PI) grid is presented in this work. It comprises all the intersection points between the projection rays passing through the object. A few advantages include (a) a user-independent discretization process and (b) a reduction in reconstruction error caused by nonparticipating nodes. Computerized tomography reconstruction results by PI are compared with existing conventional grids. The multiplicative algebraic reconstruction technique (MART) and entropy maximization are used as solution techniques. We note that for simulated data, the PI grid gives better results when compared with the square-pixel grid. Two different sets of experimental data (obtained previously for a mercury-nitrogen flow loop and one with a known specimen with a static known profile) are processed with the above-mentioned options. A basic theoretical model (but experimentally correlated) is also used to verify the void reference level. Computerized tomography results for experimental projection data indicate a trend similar to the previous MART results, but a major difference is visible in the void-fraction distributions. This fact is important, as heat transfer coefficients are strongly dependent on the distribution of voids.