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Nuclei


Nuclear Waste

As of 2017, there is a world total of 451 nuclear reactors in operation (Figure 14-21). Disposal of the nuclear waste is governed by the "Joint Convention on the Safety of Spent Fuel Management and Safety of Radioactive Waste Management" which was signed by 42 countries in 1997. Figure 14-22 shows the composition of the spent fuel (SF) over a period of three years. It indicates that about 1% of it requires special treatment as
Nuclear Powers Spent Fuel Composition they are carcinogenic and have a long half life, while most the other hazardous wastes disappear during that time frame. Usually, the fuel rod would be removed from the reactor in 18 - 36 months. The more troublesome waste is those left behind from the cold war era before 1991. Figure 14-21 shows the 2017 inventory of nuclear warheads, the total of which is 10 times the number of reactors already. At the peak of cold war madness, there were about 125,000 warheads produced by the US and Soviet Union - enough to destroy the world many times over. Such waste has become a real problem for its disposal.

Figure 14-21 Nuclear Powers [view large image]

Figure 14-22 Spent Fuel Composition

See a list of the "US Weapons Production Sites" etc.

A good (or bad) example is the Hanford Site (Figure 14-23) where most of the bomb grade plutonium were made. Between 1944 and 1988, the United States built special breeder reactors on this site to make about 100 metric tons of plutonium for nuclear weapons (see Fuel Cycle, Figure 14-24). Highly radioactive plutonium were produced from the spent fuel rods which were removed from the reactor for further processing with strong acids to dissolve the plutonium from the fuel rods. This process left behind more than 100 million gallons of hazardous liquid waste. It is called
Hanford Site Fuel Cycle mixed waste because it contains both hazardous chemicals and radioactive materials. The cleanup effort is managed by the Department of Energy (DOE) with annual cost of 2 billion for another 20 years. As of 2017, the final goal of geological disposals has not been achieved. See "The Hanford Nuclear Site : A Legacy of Risk, Cost and Inefficiency"

Figure 14-23 Hanford Site [view large image]

Figure 14-24 Fuel Cycle, Tow Views
[view large image]


Classification IAEA Classification There are various schemes to separate contents of the nuclear waste into classes. In general, it is characterized by the waste's radioactivity, half-life, source, and method of disposal. Figure 14-25 shows one of those classification schemes. The International Atomic Energy Agency (IAEA) has provided a set of more comprehensive Safety Standards which are summarized in the followings (also see Figure 14-26 for a visual review).

Figure 14-25 Classification [view large image]

Figure 14-26 IAEA Classification
[view large image]

Nuclear Decay The decay mode of the radioactive isotope is closely related to the type of disposal of the waste. As shown in Figure 14-29 there is an optimal neutron to proton ratio for the existence of a stable nucleus. If a nucleus has too many neutron (high n/p ratio) the nucleus would undergo the beta decay process n p + e + e via the weak interaction to reduce to ratio. On the other hand, the e- capture process (the reverse beta process) p + e n + e would bump up the ratio when it is too low. For heavy nucleus with Z > 82, the alpha decay through quantum tunnelling is the preferable mode to optimize the attractive strong interaction and the Coulomb repulsion. Gamma decay is the emission of high energy photons (see Table 14-05 below for more information about these decay modes). Table 14-06 is a list of radioactive isotopes from which the type of waste can be determined by the half life and decay mode.

Figure 14-29 Nuclear Decay [view large image]


Decay Modes Radioactive Levels

Table 14-05 Types of Decay Mode [view large image]

Figure 14-30 Dosage Scale



Radioactive Isotopes

Table 14-06 List of Radioactive Isotopes (from ScienceStruck) [view large image]

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