Nuclide component materials

The type of approach described here is obviously more important for systems where the solution chemistry of the nuclide (charge, oxidation state and degree of complexation) is more complicated. Without supporting laboratory data, it is possible that significant retention values may be incorrectly interpreted as being due to radionuclide association with material in a particular size fraction. The components of the environmental sample might contribute to the separation process and retain species which on a size basis should readily pass through the filter membrane. 

Note that storage of helium in the core remains only one component of a noble gas model that can describe the range of noble gas observations. The core has only been evaluated as a possible storage of He. The incorporation in the core of other noble gases, and their relative fractionations, cannot be clearly evaluated without more data. Also, the distribution of radiogenic nuclides such as "" Ar, Xe, and Xe that are produced within the mantle must be explained with a model that fully describes the mantle reservoirs. While these issues may be tractable, a comprehensive model that incorporates a core reservoir remains to be formulated. It should be emphasized that the core does not completely explain the distribution of helium isotopes, since the issue of the " He-heat imbalance is not addressed at all by this model. It appears that even if high He/ He ratios are the signature of involvement of core material in the source of mantle plumes, several mantle reservoirs are still required. 

No general statement can be made about the elements that can be determined and the samples that can be analyzed, because these depend on the nuclear characteristics of the target nuclide (isotopic abundance), the nuclear reaction (cross-section and related parameters such as threshold energy and Coulomb barrier), and the radionuclide induced (half-life, radiation emitted, energy, and its intensity) for the analyte element, the possible interfering elements and the major components of the sample. CPAA can solve a number of important analytical problems in material science (e.g., determination of boron, carbon, nitrogen, and oxygen impurities in very pure materials such as copper or silicon) and environmental science (e.g., determination of the toxic elements cadmium, thallium, and lead in solid environmental samples). As these problems cannot be solved by NAA, CPAA and NAA are complementary to each other. 

The different reactivity control systems in a nuclear power plant allow keeping at any time the control of the nuclear fission reactions in the core power steering, safe reactor shutdown, wear compensation of the fuel. They are also part of the neutron protection of the out-of-core components. These systems can take various forms gas (such as helium 3 in some experimental reactors), liquid (soluble boron in pressurized water reactor (PWR) coolant to balance the reactivity evolution of the reactor), and most of the time solid (Table 15.1). In a reactor, they are most often combined [e.g., in PWR with Ag-In-Cd (AIC) plus boron carbide control rods and with boron present both as soluble boron and as boron carbide]. In all cases those materials incorporate neutron-absorbing nuclides, unlike the fuel which is a medium generally multiplier... 

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