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Issues Facing New Nuclear Build
Published in William J. Nuttall, Nuclear Renaissance, 2022
If a water-cooled reactor loses effective primary cooling this can be a result of a loss of on-site power as at Fukushima or because of a break in the primary circuit pipework. Large scale pipe breaks are an example of a class of accident scenario known as loss of coolant accidents (LOCAs). In such a case, the reactor will shut down through the action of various safety systems and indeed because of a fundamental physics consideration—the reactor will have lost its neutron moderator. LOCAs are known to form a sizeable part of the discussion in Hewitt and Collier’s fascinating book Introduction to Nuclear Power. Readers seeking an introduction to the technical realities of reactor safety are recommended to consult that text [42]. Decay heat is an example of a reactor process occurring after the main fission chain reaction has stopped. Processes occurring as an immediate and direct part of the fission chain reaction described above are termed prompt processes and the neutrons immediately emitted in the fission process are termed prompt neutrons. In addition to the prompt neutrons, there are delayed neutrons typically emitted a few seconds after the prompt neutrons. In essence delayed neutrons arise from the beta decay of unstable fission product nuclei. Delayed neutrons are fundamental to the balance of criticality within a nuclear power plant. The fact that they respond more slowly than the prompt neutrons allows a nuclear power plant to be safely controlled by gradual adjustment of the control rods.
Thermal Energy Production in Nuclear Power Plants
Published in Robert E. Masterson, Nuclear Reactor Thermal Hydraulics, 2019
Heat is produced in nuclear power plants by the process of nuclear fission, which occurs in what is known as the reactor core (see Chapter 1) when the nucleus of a uranium or plutonium atom splits apart. This thermal energy is eventually distributed through the core by energetic fission products and by alpha, beta, and gamma rays that are produced in pairs when the atomic nucleus splits apart. Most of this heat is deposited in the fuel, but a few percent of it is deposited in the coolant and the cladding. Gamma rays also deposit some of this energy in the pressure vessel wall. Alpha particles are ionized helium nuclei with their electrons removed, beta rays are high-energy electrons or positrons, and gamma rays are high-energy photons. (Gamma ray energies are discussed in Section 5.7.) In addition to these particles, between two and four fission neutrons are produced when an atomic nucleus splits apart. Sometimes these fission neutrons are called prompt neutrons because they are produced immediately after the atomic nucleus fissions. The kinetic energy carried away by these neutrons is eventually converted into heat, and this increases the temperature of the core. Coolant is then pumped through the core to remove this heat, and the heated coolant is eventually sent to the nuclear steam supply system (NSSS) (see Chapter 8) to generate high-pressure steam. Practically speaking, trillions of fission reactions are required per second to generate meaningful amounts of electric power. In this chapter, we would like to explore the details of this process of energy production.
Fast reactors
Published in Kenneth Jay, Nuclear Power, 2019
The effect of the factors discussed in the last two paragraphs may be summarized as follows. A reactor may require all, or most, of the delayed neutrons to make it go critical (it is then said to be delayed critical); if this is so, the neutron generation time will be long and the power level can be made to change quite slowly by adding reactivity in sufficiently small amounts. If, however, the reactor will go critical on prompt neutrons only (prompt critical) the neutron generation time will be short and power will change rapidly for even a small addition of reactivity. Once the region of prompt criticality has been entered, the rate at which power rises depends on neutron lifetime. This, though only a thousandth of a second in a thermal reactor, is even shorter in a fast reactor, perhaps as little as a millionth of a second, so power would rise a thousand times as fast.
Radiation Protection at Petawatt Laser-Driven Accelerator Facilities: The ELI Beamlines Case
Published in Nuclear Science and Engineering, 2023
Anna Cimmino, Veronika Olšovcová, Roberto Versaci, Dávid Horváth, Benoit Lefebvre, Andrea Tsinganis, Vojtěch Stránský, Roman Truneček, Zuzana Trunečková
Detectors for early warning have been implemented in the low-occupancy areas (plant rooms) and in the close vicinity of the interaction chambers for work during the Clear mode (see Sec. IX), when production of ionizing radiation is not expected but can still occur in the extremely rare case of the failure of several layers of protection. To detect prompt gamma and electron radiation, inorganic scintillators with aluminum-garnet crystals (Y3Al5G12:Ce and Lu3Al5G12:Ce) were chosen, since these crystal materials have been proven to have excellent scintillating properties even in harsh radiation environments.67 Instead, prompt neutron radiation is detected by a proportional 3He counter inside a polyethylene sphere moderator (25-cm diameter). Possible activation in the experimental halls instead is monitored via Geiger-Müller counters68 positioned in areas where high activation levels are expected
Critical Assemblies: Dragon Burst Assembly and Solution Assemblies
Published in Nuclear Technology, 2021
Robert Kimpland, Travis Grove, Peter Jaegers, Richard Malenfant, William Myers
From a fission reaction, prompt neutrons are emitted within 10−12 s, and “delayed” neutrons are emitted by fission product decay a short time later. Reactors constructed early on during the Manhattan Project include CP1 (Ref. 1), the X-10 Reactor2 at Oak Ridge, Tennessee, and the water boilers3 at Los Alamos,aThe Manhattan Project name for the Los Alamos Laboratory was “Site-Y.” all operated in a state sustained by delayed neutrons. If the neutron multiplication factor was increased so much that prompt neutrons alone could support a divergent chain, the neutron population would grow exponentially, doubling in a small fraction of a second. A nuclear weapon would have to operate in this region.
Real-time subcriticality monitoring system based on a highly sensitive optical fiber detector in an accelerator-driven system at the Kyoto University Critical Assembly
Published in Journal of Nuclear Science and Technology, 2020
Kenichi Watanabe, Masao Yamanaka, Tomohiro Endo, Cheol Ho Pyeon
When an ADS experiment is conducted using a pulsed neutron source, the PNS method is considered to be suitable. In subcritical states, the neutron flux decreases just after the end of pulsed period of neutron injection. The subcriticality can be determined from the time evolution of the flux. When the reactor is operated, prompt and delayed neutrons are generated in the reactor core. The prompt neutrons decrease exponentially when the reactor is in a subcritical state. However, because the lifetime of the delayed neutrons is much longer than a pulse cycle, the generation and disappearance of delayed neutrons reach equilibrium. Then, the delayed neutrons appear to be constant in pulse operation. Consequently, the time evaluation of the neutron flux is given as