ANS is committed to advancing, fostering, and promoting the development and application of nuclear sciences and technologies to benefit society.
Explore the many uses for nuclear science and its impact on energy, the environment, healthcare, food, and more.
Explore membership for yourself or for your organization.
Conference Spotlight
Nuclear Energy Conference & Expo (NECX)
September 8–11, 2025
Atlanta, GA|Atlanta Marriott Marquis
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!
Latest Magazine Issues
Aug 2025
Jan 2025
Latest Journal Issues
Nuclear Science and Engineering
September 2025
Nuclear Technology
August 2025
Fusion Science and Technology
Latest News
Ho Nieh nominated to the NRC
Nieh
President Trump recently nominated Ho Nieh for the role of commissioner in the Nuclear Regulatory Commission through the remainder of a term that will expire June 30, 2029.
Nieh has been the vice president of regulatory affairs at Southern Nuclear since 2021, though he is currently working as a loaned executive at the Institute of Nuclear Power Operations, where he has been for more than a year.
Nieh’s experience: Nieh started his career at the Knolls Atomic Power Laboratory, where he worked primarily as a nuclear plant engineer and contributed as a civilian instructor in the U.S. Navy’s Nuclear Power Program.
From there, he joined the NRC in 1997 as a project engineer. In more than 19 years of service at the organization, he served in a variety of key leadership roles, including division director of Reactor Projects, division director of Inspection and Regional Support, and director of the Office of Nuclear Reactor Regulation.
Akio Gofuku, Hidekazu Yoshikawa, Shunsuke Hayashi, Kenji Shimizu, Jiro Wakabayashi
Nuclear Technology | Volume 81 | Number 3 | June 1988 | Pages 313-332
Technical Paper | Fission Reactor | doi.org/10.13182/NT88-A16054
Articles are hosted by Taylor and Francis Online.
A real-time accident tracking calculation technique is investigated for in-depth diagnoses of internal state variables of a pressurized water reactor (PWR) plant in the case of a small-break loss-of-coolant accident (SBLOCA). The technique is composed of two parts: (a) a faster-than-real-time open-system simulator TOKRAC for calculating postaccident thermal-hydraulic behavior in the primary system of a PWR plant, and (b) several real-time state estimators for supplying the unobserved external input to TOKRAC. Observed and unobserved variables are defined as variables that are or are not directly measured by existing plant instrumentation. The external input to the open-system TOKRAC is assumed to be composed of several observed signals and several unobserved state variables: The former are the injection conditions of the emergency core cooling system and the operator actions, while the latter include the total heat transfer rate from the primary to the secondary side in the steam generator (SG) (SG heat transfer rate), the break size and approximate break location in the case of a primary pipe break, or the leak flow rate through an SG tube hole (SG leak rate) in the case of SG tube rupture. The SG heat transfer rate and SG leak rate are first estimated in real time using the observed signals of the SG secondary side. The Kalman filtering technique is applied to a simplified SG secondary model. Due to the estimation technique, the primary side of the PWR plant is separated from the secondary side with respect to heat and mass transfer; then the primary side thermal-hydraulic behavior is rapidly computed using TOKRAC. The unobserved external input, i.e., break size and approximate location of the pipe break in the primary side, is estimated within a short time after the pipe break using the estimated SG heat transfer rate and several observed signals of the primary side. Additional Kalman filters derived by a simplified primary system model are needed to ensure the whole accident tracking calculation. The validity of these estimation techniques is examined through computer experiments. The reference data are taken from the calculation results for several accidents of a Westinghouse-type PWR plant using RELAP4/MOD6 and the experimental data of loss-of-fluid test L9-3. The validity of the whole accident tracking calculation technique is also examined by a computer experiment of a 1.5% cold-leg SBLOCA of a Westinghouse-type PWR plant.
