China
Africa
Explore chapters and articles related to this topic
Thermal Energy Production in Nuclear Power Plants
Published in Robert E. Masterson, Nuclear Reactor Thermal Hydraulics, 2019
Removing this decay heat from the core is one of the most important functions of the NSSS. It is also essential to do so even when a reactor accident cripples the rest of the plant. Otherwise, the core may melt and release unwanted radioactive materials into the environment. A large amount of decay heat can even be produced when a reactor is shut down normally. However, the rate at which this decay heat is produced will vary as a function of time, and the amount of energy that the decay heat can produce can be significant. The decay heat that is produced in a reactor core over time can be predicted by a famous equation called the Wigner–Way equation. The Wigner–Way equation is a semiempirical curve fit to the decay heat specifications provided in American Nuclear Society (ANS) Standard 5.1. The heat produced by the decay of the radioactive fission products in the core is given by
Loss of Cooling
Published in Geoffrey F. Hewitt, John G. Collier, Introduction to Nuclear Power, 2018
Geoffrey F. Hewitt, John G. Collier
The reactor must be designed to meet the above operating states. Certain faults—for example, those related to coolant circulation pumps or gas circulators-can give rise to an interruption in normal cooling. When such an interruption occurs, the reactor is shut down by its automatic safety systems. But as we saw earlier, heat generation continues after shutdown of the fission reaction due to the continuing decay of the fission products that have been generated: the decay beat. So all reactor systems are provided with alternative means of cooling in order to remove this decay heat in the event that the normal cooling system fails. The two most important safety systems are those associated with stopping (”tripping") the fission reaction within the reactor (the control rods) and those associated with providing an alternative cooling system, the so-called emergency core cooling system (ECCS). These engineered safety systems need to be brought into operation reliably when required.
Nuclear Fuels, Nuclear Structure, the Mass Defect, and Radioactive Decay
Published in Robert E. Masterson, Introduction to Nuclear Reactor Physics, 2017
Finally, the amount of decay heat Q that these radioactive materials produce is equal to the difference between the masses of the individual atoms or particles before they decay and the masses of the individual atoms or particles after they decay. From Einstein’s famous equation E = mc2, the decay heat produced iswhere c is the speed of light, and the summations in Equation 6.75 are to be performed over all the radioactive materials and their by-products. In the International System of Units, the speed of light is about 300,000,000 km/s. This implies that a very small amount of matter can be converted into a very large amount of heat. We will explore this process and its implications in more detail in Chapter 7. Decay heat must be taken very seriously when discussing nuclear power plants because it can continue to be produced by radioactive decay for days or even months after a reactor is shut down.
SCALE 6.2.4 Validation for Light Water Reactor Decay Heat Analysis
Published in Nuclear Technology, 2022
Energy release from the decay of radionuclides in nuclear fuel after its discharge from reactor, commonly termed “decay heat,” is a critical parameter for design, safety, and licensing analyses of used nuclear fuel storage, transportation, and repository systems. Well-validated computational tools and associated nuclear data are essential for calculation of the decay heat used in these analyses. This paper summarizes a study to validate the SCALE (Ref. 1) nuclear analysis code system version 6.2.4, used with evaluated nuclear data ENDF/B-VII.1, for decay heat analysis of light water reactor (LWR) used fuel assemblies. The current study is an extension of decay heat validation studies for previous SCALE releases 5.1 and 6.1, which used different nuclear data libraries, based on ENDF/B-V and ENDF/B-VII.0 evaluations.2–4 It also discusses the effect of using assembly-average versus axially varying modeling data in the decay heat calculation—which is of consequence to thermal analyses for used fuel transportation and storage systems—as well as the effect on the calculated decay heat of the nuclear data used in modeling the fuel transmutation and decay.
Application of continuous Markov-chain Monte-Carlo method to multi-unit risk evaluations considering interdependence of accident progression among multiple units
Published in Journal of Nuclear Science and Technology, 2021
Kento Sawada, Akio Yamamoto, Tomohiro Endo, Chikahiro Sato, Keisuke Maeda, Sunghyon Jang
[Heat balance and coolant injection models] The generated heat (i.e. decay heat) is used to increase coolant temperature or to generate steam when water exists. Enthalpy of the injected coolant at each time step is considered for the heat balance calculation. This calculation is carried out until the coolant level reaches the bottom of active fuel (BAF). It is noted that the fuel temperature is assumed to be constant until the coolant level reaches BAF, which is the assumption for simplification.When HPAC is available, the flow rate of coolant is controlled to keep the water level in RPV within the normal level.Once the coolant level reaches BAF, temperatures of fuel and core structures (fuel, cladding, channel box, control blade absorber, control blade structure), core support, and upper core internal structure start to increase. The fuel and core structures are heated until the melting point and then melted, i.e. the sensible and latent heats are considered. The core support and upper core internal structure are heated until the melting temperature, but their melt is not modeled in the heat balance calculation.
The Key Attributes, Functional Requirements, and Design Features of Resilient Nuclear Power Plants (rNPPs)
Published in Nuclear Technology, 2018
Unlike other forms of electric generating plants, NPPs cannot be completely turned off. Subsequent to shutdown, nuclear reactors continue to produce decay heat and therefore continue to require some form of cooling to maintain adequate heat removal. For example, nuclear fuel still produces ~1% of its original operating power 2 h after shutdown. The decay power level drops to ~0.4% 3 days after shutdown, ~0.3% 7 days after shutdown, and ~0.04% to 0.05% 6 months after shutdown. The time-dependent shutdown decay power produced depends on factors such as the original operating power level, time at power, reactor fuel composition, fuel burnup, etc.