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Conference Spotlight
2025 ANS Winter Conference & Expo
November 9–12, 2025
Washington, DC|Washington Hilton
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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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Empowering the next generation: ANS’s newest book focuses on careers in nuclear energy
A new career guide for the nuclear energy industry is now available: The Nuclear Empowered Workforce by Earnestine Johnson. Drawing on more than 30 years of experience across 16 nuclear facilities, Johnson offers a practical, insightful look into some of the many career paths available in commercial nuclear power. To mark the release, Johnson sat down with Nuclear News for a wide-ranging conversation about her career, her motivation for writing the book, and her advice for the next generation of nuclear professionals.
When Johnson began her career at engineering services company Stone & Webster, she entered a field still reeling from the effects of the Three Mile Island incident in 1979, nearly 15 years earlier. Her hiring cohort was the first group of new engineering graduates the company had brought on since TMI, a reflection of the industry-wide pause in nuclear construction. Her first long-term assignment—at the Millstone site in Waterford, Conn., helping resolve design issues stemming from TMI—marked the beginning of a long and varied career that spanned positions across the country.
Kannan Umasankari, S. Ganesan
Nuclear Science and Engineering | Volume 167 | Number 2 | February 2011 | Pages 105-121
Technical Paper | doi.org/10.13182/NSE10-17
Articles are hosted by Taylor and Francis Online.
The design of an advanced heavy water reactor (AHWR) utilizing thorium is in an advanced stage. The AHWR is a boiling light water cooled, heavy water moderated pressure tube-type reactor, which derives most of its power from the thorium-uranium cycle with plutonium as the external fissile feed. The AHWR has several passive safety features, notably the negative coolant void coefficient of reactivity during both operational and transient conditions. It is of utmost importance to understand the mechanism of the coolant void reactivity (CVR), i.e., the effect of boiling on the neutron spectrum and hence the relative absorption in the different isotopes. We have performed a detailed reaction rate analysis for the isotopes in the AHWR lattice and estimated the individual components to the CVR. The AHWR fuel cluster is a heterogeneous one with both (Th,U) mixed oxide (MOX) and (Th,Pu) MOX fuel and also stainless steel as absorber in the central displacer region.The individual contributions of the different isotopes and reactions were calculated for three major energy domains - namely, fast, resonance, and thermal - as well as for an effective energy average (one-group). The general trend of the CVR with burnup is dictated by the relative absorptions. The major contributors to the CVR were hydrogen (in the coolant), 232Th, 233U, and 239Pu: 232Th and 233U exhibit a negative contribution, whereas 239Pu and H show a positive contribution to CVR. The net absorption reaction rate in 233U becomes less negative with burnup. Since it is close to the moderator, plutonium sees a more thermal spectrum and depletes faster. The positive contribution from 239Pu decreases with burnup. At higher burnups the relative absorption upon voiding in hydrogen increases, and this is a major contributor to the CVR becoming less negative.The results were compared for different nuclear data sets, ENDF/B-VI.8 (largely used for our design studies) and the newly available ENDF/B-VII.0. The CVR calculated with the ENDF/B-VII.0 showed significant differences at higher burnups. The ENDF/B-VII.0 data set gave lower negative value for the CVR at end of cycle. It was found that the difference in the capture cross section of the 232Th ENDF/B-VII.0 data set was largely responsible for the difference between the two data sets. All the simulations were done using the WIMSD code and the multigroup WIMS library using a 69-group structure.
