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.
Division Spotlight
Decommissioning & Environmental Sciences
The mission of the Decommissioning and Environmental Sciences (DES) Division is to promote the development and use of those skills and technologies associated with the use of nuclear energy and the optimal management and stewardship of the environment, sustainable development, decommissioning, remediation, reutilization, and long-term surveillance and maintenance of nuclear-related installations, and sites. The target audience for this effort is the membership of the Division, the Society, and the public at large.
Meeting Spotlight
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!
Latest Magazine Issues
May 2025
Jan 2025
Latest Journal Issues
Nuclear Science and Engineering
July 2025
Nuclear Technology
June 2025
Fusion Science and Technology
Latest News
High-temperature plumbing and advanced reactors
The use of nuclear fission power and its role in impacting climate change is hotly debated. Fission advocates argue that short-term solutions would involve the rapid deployment of Gen III+ nuclear reactors, like Vogtle-3 and -4, while long-term climate change impact would rely on the creation and implementation of Gen IV reactors, “inherently safe” reactors that use passive laws of physics and chemistry rather than active controls such as valves and pumps to operate safely. While Gen IV reactors vary in many ways, one thing unites nearly all of them: the use of exotic, high-temperature coolants. These fluids, like molten salts and liquid metals, can enable reactor engineers to design much safer nuclear reactors—ultimately because the boiling point of each fluid is extremely high. Fluids that remain liquid over large temperature ranges can provide good heat transfer through many demanding conditions, all with minimal pressurization. Although the most apparent use for these fluids is advanced fission power, they have the potential to be applied to other power generation sources such as fusion, thermal storage, solar, or high-temperature process heat.1–3
Fei-Jan Tsai, Min Lee
Nuclear Technology | Volume 205 | Number 4 | April 2019 | Pages 524-541
Technical Paper | doi.org/10.1080/00295450.2018.1500831
Articles are hosted by Taylor and Francis Online.
This study assessed the effectiveness of in-vessel retention (IVR) in terminating the progression of an accident sequence initiated by a station blackout and large loss-of-coolant accident in a pressurized water reactor with thermal power of approximately 5000 MW. In the IVR design, external reactor vessel cooling is established by flooding of the reactor cavity. A water channel is introduced into the outer wall of the reactor vessel, and an insulated layered structure is added around the vessel. The amount of heat removed from the corium pool in the vessel lower plenum is limited by the critical heat flux (CHF) at the outer surface of the vessel wall. An integrated assessment was conducted in three steps. First, the responses of the reactor coolant system and containment were simulated using MELCOR. The predicted transient heat load at the vessel wall was then fed into RELAP5-3D, where the flow of natural, buoyancy-driven convection within the IVR water channel was simulated. Finally, the main thermal-hydraulic parameters in the IVR channel were substituted into the ULPU, SULTAN, SBLB, and MELCOR CHF correlations, and the effectiveness of IVR was assessed. The MELCOR simulation demonstrated that the heat load at the vessel wall of the lower plenum is dependent on the configuration of the debris. The heat flux to the vessel wall reached a maximum at 483 min, at an inclination angle of approximately 68 deg. The peak heat flux moved from a small inclination angle to a larger angle as the accident progressed. Both MELCOR and RELAP5-3D calculations predicted a gradual buildup of natural convection flow within the IVR channel following the application of a heat load to the vessel wall. The MELCOR code significantly overpredicts the mass flow of natural convection flow. Both codes predicted that the flow would experience large-amplitude fluctuations as the water in the IVR flow channel reached saturation. These fluctuations were attributed to instability induced by two-phase flow.
If the inlet temperature can be kept sufficiently low to obviate boiling in the IVR channel, RELAP5-3D predicts that the channel flow will approach an approximately steady state. The selected CHF correlations predicted significantly different CHFs. The MELCOR correlation, which is a correlation based on pool boiling, produced the most conservative predictions, and the CHFs predicted by SBLB had the highest value. The minimum margin was found between 55 and 75 deg in all correlations. With the exception of the MELCOR correlation, the CHF ratio predicted by the other three correlations is greater than 1.2.