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Nuclear Criticality Safety
NCSD provides communication among nuclear criticality safety professionals through the development of standards, the evolution of training methods and materials, the presentation of technical data and procedures, and the creation of specialty publications. In these ways, the division furthers the exchange of technical information on nuclear criticality safety with the ultimate goal of promoting the safe handling of fissionable materials outside reactors.
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2025 ANS Annual Conference
June 15–18, 2025
Chicago, IL|Chicago Marriott Downtown
Standards Program
The Standards Committee is responsible for the development and maintenance of voluntary consensus standards that address the design, analysis, and operation of components, systems, and facilities related to the application of nuclear science and technology. Find out What’s New, check out the Standards Store, or Get Involved today!
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Nuclear fuel cycle reimagined: Powering the next frontiers from nuclear waste
In the fall of 2023, a small Zeno Power team accomplished a major feat: they demonstrated the first strontium-90 heat source in decades—and the first-ever by a commercial company.
Zeno Power worked with Pacific Northwest National Laboratory to fabricate and validate this Z1 heat source design at the lab’s Radiochemical Processing Laboratory. The Z1 demonstration heralded renewed interest in developing radioisotope power system (RPS) technology. In early 2025, the heat source was disassembled, and the Sr-90 was returned to the U.S. Department of Energy for continued use.
Dr. Walter Loewenstein was the 35th president of the American Nuclear Society. He became a member of the Society in 1955, at that time joining the Mathematics & Computation and Nuclear Installations Safety Divisions. He remained with these Divisions until his death. In 1973, he became a Fellow of ANS. In 1985, he was elected to the Board of Directors, assigned to the Finance Committee.
Dr. Loewenstein was born in on December 23, 1926 in Gunsengen, Hesse, Germany. His family emigrated to the U.S. when he was a child in 1938, originally settling in Tacoma, Washington.
In 1945 at the age of 19, he was drafted to the U.S. Navy while he had been attending the College of Puget Sound. After bootcamp, he was sent to Chicago for electronics training and was stationed at Navy Pier. He was released from the Navy about one year after the end of the war and returned to college to pursue his education. He graduated in 1949 from University of Puget Sound with a degree in mathematics and physics. He earned his PhD from Ohio State in 1954 in chemical physics.
Fascinated with the growth in nuclear technology at Argonne National Laboratory (ANL), he became a part of their fast reactor physics team. He specifically was part of the Fast Critical Facility, a.k.a Zero Power Reactor III (ZPRIII). He traveled extensively in the 1950s between Chicago and Idaho working on the project.
In 1958, Loewenstein’s work at ANL switched from the general fast reactor to the core design for the small Experimental Breeder Reactor II (EBR-II). The team designed and produced a reactor without plans, but solely relied on their ingenuity and knowledge. Eventually he was moved to Scotland to assist with their reactors in 1959, but was brought back to ANL in the U.S. in 1961. He remained with ANL working on the EBR-II until his departure in 1973.
After leaving ANL, he began working with Electric Power Research Institute (EPRI). An opportunity had presented itself to Dr. Loewenstein, and he was appointed the director of Safety Technology Department with the Nuclear Power Division. He was promoted ten years later to the deputy director of the Nuclear Powers Division where he remained until his retirement.
Dr. Loewenstein served on the Board of Directors for several international cooperative research projects. He is the author of over 40 publications and holds three nuclear reactor patents. In 1978, Dr. Loewenstein was one of the participants in the “Risk Assessment Review Group Report” to the U.S. Nuclear Regulatory Commission.
Dr. Walter Loewenstein passed away on November 26, 2018.
Read Nuclear News from July 1989 for more on Walter.
