Address radiological activity of all types
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Dan Peng steps onto a narrow steel frame just above a 6-meter-deep pool, which holds a nuclear reactor about to go critical. Clad in a lab coat with a pocket radiation dosimeter, sweating in the stifling reactor hall here on the outskirts of Ghana's capital, the young nuclear physicist edges out to a tube jutting above the water's surface. He grabs a cord leading out of the tube and reels it up, hand over hand, until a cigar-shaped capsule emerges—a packet of neutron-absorbing cadmium. It's the last of three that were immersed in the pool as a safety measure, to ensure that the reactor's new low-enriched uranium (LEU) core did not achieve a self-sustaining fission reaction—criticality—before the team was ready.
At the edge of the pool, several other physicists and engineers, colleagues of Peng's at the China Institute of Atomic Energy (CIAE) in Beijing, huddle behind a bank of instruments. On one digital display, numbers change in a blur as the neutron count shoots up, then levels off. Now, the only bulwark against criticality is a single control rod piercing the heart of the reactor.
"We're ready," says a smiling Li Yiguo, a CIAE nuclear physicist and leader of a landmark effort in nuclear nonproliferation at the Ghana Research Reactor (GHARR-1). Li asks a colleague to summon dignitaries to mark the culmination of a 10-year odyssey to remove GHARR-1's highly enriched uranium (HEU) fuel—weapons-grade material—and replace it with LEU, which cannot be used for a nuclear bomb without further enrichment.
The operation, which took place in July at the Ghana Atomic Energy Commission in Accra, is a milestone in a dogged effort since the end of the Cold War to remove enriched uranium and plutonium from countries that do not have nuclear weapons. Spearheaded by the United States and the International Atomic Energy Agency (IAEA) in Vienna, the initiative took on added urgency after the 9/11 attacks, out of fear of al-Qaida or another terrorist group laying hands on nuclear materials. Small, HEU-fueled research reactors, including GHARR-1 and four other Chinese-made miniature neutron source reactors (MNSRs) operating in the Middle East and Africa, were a high priority. But reengineering an MNSR's core—a cylindrical array of 350 fuel and dummy pins that is a little larger than a gallon paint can—to run on safer fuel posed unique challenges
http://www.sciencemag.org/news/2017/08/ ... out-africa
" man fears time, but time fears the pyramids "