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Nuclear power
Published in Peter N. Nemetz, Unsustainable World, 2022
Security risk: Nuclear reactors may be an enticing target for terrorist attack or as a source of radioactive material and there is no easy way of estimating the probability of this threat (New York Times April 4, 2016; Allison 2004). Bob Woodward, in his book Obama’s Wars (2011), has stated that one of the predominant concerns of the US government and military is the possibility that a terrorist group obtains a nuclear weapon and uses it against an American city. Terrorist groups might obtain such a weapon in several ways: by stealing it, purchasing a weapon or low-to-weapons-grade uranium or plutonium on the black market, or from a rogue or failed state. The International Panel on Fissile Materials (IPFM) (2021) estimated that the global stockpile of civilian plutonium was 316 shorttons in 2020. This is a particularly attractive target for terrorists since this element can be made into an atomic device without enrichment (see McPhee 1973; Willrich and Taylor 1974).
Chemical Processes in Fission Product Release and Transport
Published in J. T. Rogers, Fission Product Transport Processes in Reactor Accidents, 2020
Severe nuclear reactor accidents dominate the risk of the use of nuclear power. Nothing so distinguishes severe reactor accidents as the extensive release of radioactive materials from the reactor fuel and the potential escape of these radioactive materials into the environment. The release of radionuclides begins when the fuel is overheated and the cladding on the fuel ruptures. Release of radioactivity can continue as the fuel further degrades, melts, slumps from the core region, collapses into the lower plenum of the reactor coolant system and, perhaps, is expelled into the reactor containment. But, the mere release of radionuclides from fuel does not pose a direct public threat. Released radionuclides must migrate from the point of release to a point of escape from the plant before there can be public consequences.
Nuclear Energy
Published in Efstathios E. Michaelides, Energy, the Environment, and Sustainability, 2018
The amount of energy released in the fission of 92U235 and 94Pu239 solely depends on the products of the reaction and may be calculated from the mass defects of the particular reaction. The average energy of the fission of 92U235 has been calculated [1] to be approximately 200 MeV. Most of this energy is in the form of the kinetic energy of the fission fragments and is almost immediately dissipated into heat by atomic and molecular collisions. Additional energy (again in the form of heat) is continuously produced from the radioactive decay of the reaction products, the so-called “daughter isotopes.” This thermal energy must be continuously removed from the nuclear reactor by a circulating coolant, typically water or gas, which is called the “primary coolant.” During the normal operation of a nuclear power plant, the removal of heat from the reactor by the primary coolant provides the heat to a thermodynamic cycle, a Rankine or a Brayton cycle. The continuously produced heat is converted by the machinery of the cycle to electric energy. If for any reason the cycle stops and the primary coolant does not remove the produced heat, an emergency coolant must be injected in the reactor to ensure the removal of the heat produced. A failure of the cooling systems may result in the overheating of the nuclear reactor and, perhaps, a meltdown, which has catastrophic consequences.
Bifurcation Analysis of Xenon Oscillations in Large Pressurized Heavy Water Reactors with Spatial Control
Published in Nuclear Science and Engineering, 2022
Abhishek Chakraborty, Suneet Singh, M. P. S. Fernando
The safe operation of nuclear reactors is one of the most challenging aspects of the nuclear power industry. It involves a number of processes involving the generation of neutrons, their specific multiplications, their control, and the extraction of useful power out of the heat energy generated in the process. In most of the operating nuclear reactors, energy is produced by chain nuclear fission of 235U. In nuclear fission, a large nucleus like 235U is broken into multiple nuclei (fission products) with release of ~200 MeV of energy on absorption of a thermal/fast neutron(s). The heat which is produced in fission has to be removed by a coolant (generally H2O, D2O for thermal reactors and Na, Pb for fast reactors). This demands an efficient coupling between the neutronics and the thermal hydraulics to ensure a smooth, streamlined generation of power.
Characterising nuclear decommissioning projects: an investigation of the project characteristics that affect the project performance
Published in Construction Management and Economics, 2020
Diletta Colette Invernizzi, Giorgio Locatelli, Naomi J. Brookes
The above-mentioned concerns related to the uncertainties concerning the exact type and quantity of waste material on-site are strictly connected to the second most-emphasised NDP characteristic that affects the NDP performance, which refers to the clarity of the waste routes and the availability of storage and disposal facilities. During the lifetime of a nuclear facility, nuclear waste of very different nature is created. This waste can derive from the operations of a nuclear reactor and includes the spent fuel from the refuelling operations of a nuclear reactor (which is highly radioactive), or the gloves and suits used daily by operators in particular areas of a nuclear facility (which are considerably less radioactive). Moreover, it might derive from research experiments (and therefore most likely be in very small quantity but unique in its physical properties), or from the scrabbling of a layer of concrete from buildings wall to remove surface contamination (and therefore creating large volume of waste with similar physical characteristics), or other activities. All these different types of waste (and many others) need to be converted into a solid form that is resistant to leaching and is suitable for transportation, short-term storage and ultimately disposal (WNA 2019). Hence, each type of waste require a different “waste route”, and if these “waste routes” are not clear, the NDP performance is affected.
Methodology to optimize radiation protection in radioactive waste disposal after closure of a disposal facility based on probabilistic approach
Published in Journal of Nuclear Science and Technology, 2018
Ryo Nakabayashi, Daisuke Sugiyama
A cross-sectional view of the sub-surface disposal facility is shown in Figure 3 [13]. The waste has a relatively high radioactivity, such as parts of a nuclear reactor structure, used control rods, and channel boxes. The waste package layer is covered with engineered barriers and a natural barrier. In particular, the low-permeability and low-diffusivity layers of the engineered barriers and the host rock of the natural barrier are expected to prevent or delay the migration of radionuclides via the groundwater pathway from the disposal facility to the biosphere. Regarding the low-permeability and low-diffusivity layers, the thickness and type of material of each layer affect the performance. Regarding the host rock, the type of host rock (which will differ with the site) affects the performance. To ensure long-term safety in a disposal system design, a disposal system design with a high-performance site and facility design should be selected. However, the optimization of protection is not equivalent to minimization of the dose [14]. The thicker the engineered barrier layer in the design or the higher the performance of the material used, the lower the feasibility is considered to be (e.g. because of the increased cost). In the site selection, it is also necessary to consider the feasibility (e.g. public acceptability). In the optimization, we need to select the disposal system design by considering the balance between the exposure and the feasibility. Furthermore, as described in Section 2.1.2, not only the disposal system design but also the associated uncertainties of the scenario, model, data, and/or parameters have to be considered in the optimization.