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How Reactors Work
Published in Geoffrey F. Hewitt, John G. Collier, Introduction to Nuclear Power, 2018
Geoffrey F. Hewitt, John G. Collier
Because of the high rate of heat generated per unit mass of fuel (fuel rating), the response of a PWR to changes in operating conditions is much more rapid than that of an AGR It has been argued that this is a negative safety factor. Even when the reactor is shut down, the level of decay heat is such that the fuel must always be kept covered with water. We shall discuss these safety features in Chapters 5 and 6. Pressurized-water reactors have experienced problems with steam generators, which have failed due to corrosion on the secondary (steam-generating) side. Reactors are often more susceptible to problems outside the core than in it. Although it is now believed that design improvements can prevent these corrosion problems, most existing reactors are still prone to them. This is not a major safety issue, but it does limit their performance.
Reactor Thermal Cycles
Published in Robert E. Masterson, Nuclear Reactor Thermal Hydraulics, 2019
In practice, there are a couple of ways to create a superheated vapor. The first method is to increase the length of the tube nest so that the water–steam mixture completely vaporizes 80% or 90% of the way up the tube bank. The remaining 10% or 20% of this distance can then be used to heat the outgoing steam beyond the saturation temperature. The only drawback to this approach is that the steam generators must be made longer and heavier for a given operating pressure, and sometimes, this is not practical to do. The second way to achieve this goal is to reduce the pressure on the secondary side, while maintaining the same power and flow rate on the primary side. The third way to create some additional superheat is to reduce the mass flow rate for the same core power rating, but this also reduces the amount of steam that can be produced. In BWRs, the amount of superheat is constrained by the fact that the fuel rods cannot be allowed to dry out. In other words, there must always be a liquid film on the surface of the rods to keep the rods cool. This limits the temperature of the steam coming out of the core because the bulk temperature of the water–steam mixture can never exceed the superheat temperature. (Otherwise, the quality of the steam would be 100%.) In other words, the steam produced by a BWR is never really superheated. However, BWRs do not require steam generators, and they can deliver steam to the power turbines at a slightly higher pressure (about 1,000 PSI) than the steam generators in most PWRs do. So each type of reactor has a different strategy for optimizing the amount of energy that can be extracted from the coolant by the steam turbines. Thus, superheat is a proven way to dump as much energy into the steam as possible, and in the process, keeping it as dry as possible. In the thermal efficiency equation
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
Steam generator - A large complex system that transfers the heat of combustion of the fuel to the feedwater, converting it to steam that drives the turbine. The steam is usually superheated at subcritical or supercritical pressures (critical pressure =3208 psia or 221 bar). A modern steam generator is composed of economizer, boiler, superheater, reheater, and air preheater.
Theoretical and Experimental Investigation of Subcooled Flashing Flow through Simulated Steam Generator Tube Cracks
Published in Heat Transfer Engineering, 2019
Ram Anand Vadlamani, Shripad T. Revankar, Jovica R. Riznic
Damage to a steam generator tube impairs its ability to perform its required safety function in terms of both structural integrity and leakage integrity. Steam generator tubes as well as many other components of a CANDU and pressurized water reactors use Monel 400, Inconel 600 (Alloy 600), Alloy 690, and Alloy 800 which have experienced in-service corrosion and mechanical degradation of various forms [1]–[3]. There are many different degradation mechanisms that can occur related to steam generator tubes. They are susceptible to corrosion and mechanical damage, while at the same time must maintain more than 6.9 MPa (1000 psi) pressure differential between the inside and outside tube wall during normal operation. In the event of a main steam-line break in a pressurized water reactor where the secondary side drops to atmospheric pressure, the tube wall differential pressure, ΔP can be as high as 18 MPa (2560 psi). Traditionally, steam generators were designed with a sufficient safety margin against rupture. The design requirement of ASME code and the Nuclear Regulatory Commission for steam generator tubes is 1.4 • ΔP ≃ 25 MPa (3660 psi) [4]. These safety margins are based on the rupture or burst pressure of unflawed tubes. A typical unflawed Alloy 600 tube has an industry-expected burst pressure of ≃ 86 MPa (12500 psi) [5]. Steam generator operability requires the completion of steam generator tube inspections using non-destructive techniques, usually eddy current examination, in intervals ranging from 12 to 40 months.
Development of three-dimensional simulation method for two-phase flow in square-pitch tube bundle in secondary side of steam generators based on porous drift-flux model
Published in Journal of Nuclear Science and Technology, 2023
Yoshiteru Komuro, Atsushi Kodama, Naotaka Uchimichi, Yoshiyuki Kondo, Tomonori Mineno, Kengo Shimamura, Takashi Hibiki
A steam generator in a nuclear power plant is a shell-and-tube vertical U-shaped heat exchanger that generates steam using thermal energy from the reactor core. The heat of the primary fluid passing through the reactor core is transferred through the heat transfer tube wall to the secondary fluid in the steam generator. The primary fluid flows inside heat transfer tubes in a steam generator, and the secondary fluid flows outside tubes. The secondary fluid is single-phase sub-cooled water at the inlet of the steam generator. The flow is converted into a steam-water boiling two-phase mixture by receiving the heat from the primary fluid. The secondary fluid becomes almost single-phase steam at the outlet of the steam generator, and the steam rotates the turbine for power generation.
User-defined information sharing for team situation awareness and teamwork
Published in Ergonomics, 2019
Manrong She, Zhizhong Li, Liang Ma
Several studies considered information quality as the frequency of SA-relevant information sharing (e.g. Lin et al. 2016; Parush et al. 2011). Jehn and Shah (1997) used an expert rating through videotapes to evaluate the quality of shared information. In the present study, according to the hypothesis-testing strategy, the general diagnosis process could be divided into three stages: hypothesis generation, information acquisition, and hypothesis testing (Weber et al. 1993). The value of a piece of information can be evaluated through the number of irrelevant hypotheses that were eliminated by this piece of information. We set the basic value for each information element as one because the redundant information (the information that did not eliminate any candidate hypothesis, as defined by Duncan and Gray [1975]) might help verify the participant decision. If the information eliminated an irrelevant hypothesis, one was added to its value. The value of a piece of information was calculated using the number of eliminated hypotheses plus the basic value. During the experiment, six potential hypotheses were available (i.e. six possible leakage locations for participants to choose from). If the information ‘a triggered alarm for steam line radiation’ was shared, for example, the team-mate could deduce that a radioactive substance leaked into the secondary circuit. The failure might be a rupture in the U-shaped tube of the either steam generator. Then, the other four hypotheses were eliminated. Therefore, the value for this piece of information is five (i.e. four added with the basic value of one). Using this method, we calculated the value of each piece of information shared between team members. The shared information quality is equal to the average value of the shared information. The quality of the information received and pushed by the participants was also measured to study the individual sharing behaviour.