Neutron capture fission product

Neurospora crassa calcium transport, 571 cation transport, 559 Neurosporin, 676 Neurotransmitters secretion calcium, 595 Neutral complexes electrical properties, 143 Neutron absorbers reprocessing irradiated nuclear fuel criticality, 926 Neutron activation analysis metal complexes biology, 550 Neutron capture fission product, 883 Nickel... 

Given the importance of the photon heating contribution in plutonium burning fast reactor cores, a comprehensive validation work is under way for ECCO/ERANOS. Within this framework, PSI has contributed with both an experimental and an analytical effort. On the experimental side, thermoluminescent detector (TLD) measurements were performed in some of the aforementioned CIRANO configurations. With regard to methods/calculational aspects, an important effort was necessary to produce consistent neutron kerma factors and photon spectra data (from photon production due to radiative neutron capture, fission, and both elastic and inelastic neutron scattering). 

The only large-scale use of deuterium in industry is as a moderator, in the form of D2O, for nuclear reactors. Because of its favorable slowing-down properties and its small capture cross section for neutrons, deuterium moderation permits the use of uranium containing the natural abundance of uranium-235, thus avoiding an isotope enrichment step in the preparation of reactor fuel. Heavy water-moderated thermal neutron reactors fueled with uranium-233 and surrounded with a natural thorium blanket offer the prospect of successful fuel breeding, ie, production of greater amounts of (by neutron capture in thorium) than are consumed by nuclear fission in the operation of the reactor. The advantages of heavy water-moderated reactors are difficult to assess. 

The basic requirements of a reactor are 1) fissionable material in a geometry that inhibits the escape of neutrons, 2) a high likelihood that neutron capture causes fission, 3) control of the neutron production to prevent a runaway reaction, and 4) removal of the heat generated in operation and after shutdown. The inability to completely turnoff the heat evolution when the chain reaction stops is a safety problem that distinguishes a nuclear reactor from a fossil-fuel burning power plant. 

In the early years of this century the periodic table ended with element 92 but, with J. Chadwick s discovery of the neutron in 1932 and the realization that neutron-capture by a heavy atom is frequently followed by j6 emission yielding the next higher element, the synthesis of new elements became an exciting possibility. E. Fermi and others were quick to attempt the synthesis of element 93 by neutron bombardment of but it gradually became evident that the main result of the process was not the production of element 93 but nuclear fission, which produces lighter elements. However, in 1940, E. M. McMillan and P. H. Abelson in Berkeley, California, were able to identify, along with the fission products, a short-lived isotope of... 

In a nuclear power plant, heat must be transferred from the core to the turbines without any transfer of matter. This is because fission and neutron capture generate lethal radioactive products that cannot be allowed to escape from the core. A heat-transfer fluid such as liquid sodium metal flows around the core, absorbing the heat produced by nuclear fission. This hot fluid then flows through a steam generator, where its heat energy is used to vaporize... 

Nuclear and magneto-hydrodynamic electric power generation systems have been produced on a scale which could lead to industrial production, but to-date technical problems, mainly connected with corrosion of the containing materials, has hampered full-scale development. In the case of nuclear power, the proposed fast reactor, which uses fast neutron fission in a small nuclear fuel element, by comparison with fuel rods in thermal neutron reactors, requires a more rapid heat removal than is possible by water cooling, and a liquid sodium-potassium alloy has been used in the development of a near-industrial generator. The fuel container is a vanadium sheath with a niobium outer cladding, since this has a low fast neutron capture cross-section and a low rate of corrosion by the liquid metal coolant. The liquid metal coolant is transported from the fuel to the turbine generating the electric power in stainless steel... 

Less is known about the fate of the fission and neutron capture products that could result in the precipitation of unique alteration phases depending on the availability of these species in the fuel matrix. Burns et al. (1997) theorized that many of the U(VI) alteration phases may be capable of incorporating the long-lived radiotoxic isotopes, including 237Np, 99Tc, and 239Pu. In this chapter, we will discuss the evidence for Np incorporation into U(VI) phases and the behaviour of Pu in corroded spent nuclear fuel (SNF). 

Table I. Concentration of fission and neutron capture products (in ppm I in a Ion- bunt-up spent nuclear fitel...

The concentration of fission and neutron capture products in a light water reactor (LWR) fuel (30 MWd/kg U) are listed in Table 1 and presented in graphical form in Figure 2 (adapted from Oversby 1994). 

Note that although only fission product species have been listed, comparable analytical data for numerous neutron capture isotopes show that these behave in a manner completely analogous to the fission products. 

Spent fuel from a reactor contains unused uranium as well as plutonium-239 which has been created by bombardment of neutrons during the fission process. Mixed with these useful materials are other highly radioactive and hazardous fission products, such as cesium-137 and strontium-90. Since reprocessed fuels contain plutonium, well suited for making nuclear weapons, concern has been expressed over the possible capture of some of this material by agents or terrorists operating on behalf of unfriendly governments that do not have a nuclear weapons capability. 

Studies of the effect of neutron irradiation are divided into three groups slow or thermal neutrons, fission products and reactor neutrons. The slow neutrons are obtained from a radioactive source or high energy neutrons that are produced by deuterium bombardment of a beryllium target in a cyclotron and slowed down passing thru a thick paraffin wax block. The fission products in one case are produced when a desired sample is mixed or coated with uranium oxide and subsequently irradiated with slow neutrons. The capture of neutrons by U23S leads... 

In thermonuclear weapons, neutrons are absorbed in a blanket of 238U, where they induce fission and thus increase the power of the explosion. Neutron capture in 238U also produces 239Pu, 240Pu and 241 Pu. About 15 PBq (400 kCi) of Pu isotopes were disseminated by atmospheric testing of thermonuclear weapons, with a peak period in 1961-2 (Hardy et al., 1973). Most of the activity was carried into the stratosphere by the heat of the explosion. At ground level, there was a seasonal variation in the air concentration, similar to the seasonal variation in bomb-derived fission products and tritium (Fig. 4.1), with peaks in early summer,... 

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