Samarium Equilibrium

The valences of the rare-earth metals are calculated from their magnetic properties, as reported by Klemm and Bommer.14 It is from the fine work of these investigators that the lattice constants of the rare-earth metals have in the main been taken. The metals lutecium and ytterbium have only a very small paramagnetism, indicating a completed 4/ subshell and hence the valences 3 and 2, respectively (with not over 3% of trivalent ytterbium present in the metal). The observed paramagnetism of cerium at room temperature corresponds to about 20% Ce4+ and 80% Ce3+, that of praseodymium and that of neodymium to about 10% of the quadripositive ion in each case, and that of samarium to about 20% of the bipositive ion in equilibrium with the tripositive ion. 

The allenyl carboxylate 35 was obtained in an enantiomerically enriched form by the palladium-catalyzed reduction of the racemic phosphate 34 using a chiral proton source [53]. The two enantiomers of the (allenyl)samarium(III) intermediate are in rapid equilibrium and thus dynamic kinetic resolution was achieved for the asymmetric preparation of (i )-35 (Scheme 3.18). 

Noxon calculated the rate constant of O( D) quenching by 02 on the basis of unit quantum yield and of the equilibrium concentration of 0( >) atoms. His value of 6 x 10 11 cm3 molec"1 sec-1 agrees well with 7 x 10"11 cm3 molec"1 sec" 1 obtained independently (456), indicating that the assumption of unit quantum yield may be justified. Below 1332 A the production of O( S) is energetically possible. Filseth and Welge (348) have observed an emission at 5577 A due to the transition O( S)- O( D) in the flash photolysis of 02 below 1340 A. The intensity is so weak that Xe has to be added to induce the transition. No quantum yield of O(. S) production has been measured. Recently Stone et al. (937) have measured the llight time ofO atoms produced in the Hash photolysis of the molecular beam of 02 in the vacuum ultraviolet. The O atoms are detected by the chcmiionization reaction with samarium. The technique is similar to the one described in Section II 4.1. 

The neodymium oxide-vanadium(v) oxide and samarium oxide-vanadium(v) oxide systems have been investigated by thermal, i.r., and X-ray techniques. " Potassium neodymium double fluorides formed in the KF-Ndp3 system have been investigated by X-ray diffraction procedures. Formation of structures with statistical distributions of metal atoms at cationic positions was reported to be characteristic of the KF-Ndp3 system. The equilibrium diagram of the Al203-Nd203-Sr0... 

Sodium amalgam extraction can thus be used to remove the whole of the samarium, europium, or ytterbium from mixtures with the other lanthanons. If the initial concentration of any of these is large, the efficiency of the reaction may exceed 75%. Low efficiencies characterize the removal of traces of these elements. Efficiency is enhanced by keeping the acetate solution as nearly free from sodium ion as possible and withdrawing much of the sodium amalgam before it can react. The extraction is an equilibrium process. 

Alloy of samarium with cobalt (or with Co and Fe) are technologically the most important. Figure 3 shows the Co-rich portion of the Sm-Co equilibrium phase diagram, basically after den Broeder and Buschow (1972) and Perry (1977), but with a modification of the liquidus line (shown dashed) according to Ray (1986b), who... 

Samarlum-1 9 also contributes significantly to the fission product poisoning This Isotope Is stable and Is a product of the radioactive decay of promethium-l49 Sanarium poisoning reaches an equilibrium value at about 100 MMD/T eaqposure. The poisoning at equilibrium Is 0.65 k. After reactor shutdovn> the samarium poisoning will increase due to the decay of the precursor promethium-1 9 ... 

As decreases from large values in samarium (fig. 18(b)), a divalent trivalent transition is predicted for 4.0 a.u., which is only slightly greater than the equilibrium WS radius r s = 3.8 a.u. XPS evidence of a divalent component at the surface of Sm metal (Wertheim and Campagna 1977, Wertheim and Crecelius 1978, Wertheim 1979, Allen et al. 1978, 1980) as well as other theoretical work (Johansson... 

The excess measure of extra fuel lo needed to be critical in experiment insertions, f defect during operation, fission product poison, perpetual equilibrium be compared to the ten day samarium-149 is not cons the core s excess multip core fuel loading. 

Explain the dependence of equilibrium xenon and samarium on core neutron flux. 

Describe the equilibrium xenon and samarium balance in a reactor. 

List typical xenon and samarium time parameters including time to reach equilibrium and time to reach peak after shutdown. 

Both samarium and promethium would be expected to start at zero levels in the reactor and build up exponentially to equilibrium values. The 54.1 hour Pml49 half-life is the controlling time constant. After seven Pml49 half-lives or approximately 16 days, promethium and samarium will have reached equilibrium. The equilibrium values of samarium and promethium are obtained from equations (8.9) and (8.10). 

No, equilibrium samarium has a fixed value for any power level in a given reactor. It will vary with fuel loading since Zf contains fuel atom number density. 

If the reactor is started up following shutdown, promethium is depleted so samarium production from promethium decay is reduced. However, samarium burnout is maximum because of restoration of full flux at power and higher than equilibrium samarium concentrations. Samarium decreases rapidly until promethium formation by fission reestablishes samarium production to restore the equilibrium balance. Samarium burnout is illustrated in Figure 8.8, Once again, the time to reach equilibrium is about 16 days. 

Restoring flux causes samarium to burnout and eventually become restored to the equilibrium level. The rate at which burnout occurs depends upon power 1 eve 1. 

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