Poisoning ratio

The Poisson ratio, like the bulk, tensile, and shear creep compliance, is an increasing function of time because the lateral contraction cannot develop instantaneously in uniaxial tension but takes an infinite time to reach its ultimate value. In response to a sinusoidal uniaxial stretch, the complete Poison ratio is obtained ... 

In reactor control problems and in reactor neutron balances, the quantity of interest is the poisoning ratio r, which is the ratio of neutrons absorbed by the poison to neutrons absorbed in fission. Assuming for simplicity that the neutron flux is constant throughout the reactor, the xenon poisoning ratio at steady state is... 

If the xenon processing is to have any appreciable effect on the steady-state poisoning ratio, then the processing rate /x must be sufficiently large to increase the value of the group ( xe + 0< xe+/xe) E<1- (2.119). For example, for a flux of 3.5X10 /(cm -s), the... 

The transient poisoning ratio, which is the ratio of the neutron absorption in Xe to fission absorption if the reactor is to be started up again after shutdown time t, is obtained from Eq. (2.122) ... 

Figure 2.16 shows the growth of xenon to its steady-state value during reactor operation and its subsequent decay after the reactor is shut down. The quantity plotted is the xenon poison ratio, which is the ratio of the rate of absorption of neutrons by xenon to the rate of absorption of neutrons in fission of NxtOxJNfOf. Curves are given for fluxes of... 

X 10, 1 X 10, and 3X 10 n/(cm s). Note that the steady-state poison ratio is higher the higher the flux. Note also that the poison ratio increases after the reactor is shut down and that the increase becomes very large for fluxes of 10 n/(cm s). 

Figure 2.16 Xenon poison ratio during reactor operation at constant flux and after shutdown.

Table 2.15 gives direct fission yields y [B3], effective thermal-neutron absorption cross sections a and half-lives (cf. App. C) for radioactive decay that are used below to evaluate the poisoning ratio for this chain. Effective cross sections were calculated from cross sections for 2200 m/s neutrons and for neutrons of higher energy from cross-section data given by Bennett [B3], applied to the neutron spectrum of a typical pressurized-water reactor. 

Figure 2.18 shows the contribution of individual nuclides to the poisoning ratio as a function of time, starting with fresh, unirradiated fuel at time zero. The poisoning ratio of Sm builds up very quickly to 0.0113, the fission yield at mass 149, and then increases more gradually because of additional Sm production by neutron capture in nuclides of mass 147 and 148. Other nuclides of this chain that make appreciable contributions to the poisoning ratio include Pm, Pm, Sm, " Sm, and Sm. The overall poisoning ratio, the sum of the contributions of individual nuclides, is shown in Fig. 2.19. 

Figure 2.18 Individual nuclide contribution to total poisoning ratio of Sm decay chain.

Figure 2.19 Buildup of poisoning ratio of Sm chain in fresh pressurized-water reactor fuel containing 3.2 w/o U.

Figure 2.20 shows how the poisoning ratio of this chain varies if the reactor is shut down after initial operation for 7300 h for various periods of time T and then operated at a flux of 3.496 X 10 w/(cm s) for additional time T. The behavior shown in this figure is considered representative of this reactor after it has been refueled several times with one-third of the oldest fuel replaced by fresh fuel. 

In the operating reactor, it is assumed that the total poisoning ratio for all hi -cross-section fission products from U and the U caused to undergo fission by fast neutrons from U, q u, has the same value as in the reference design ... 

In addition, fission products come from other fissile species such as Pu and Pu, each of which has its own total poisoning ratio q for high-cross-section fission products formed from that species and from caused to undergo fission by fast neutrons from it ... 

Nuclide Subscript Absorption cross section, Ufl, b Neutrons produced Ratio of capture to fission cross section, a Poisoning ratio of high-cross section fission products, Q... 

The mechanical properties used in the definition of polypropylene were the averages of the results obtained in tensile tests carried out on the samples subjected to artificial aging and the initial polypropylene samples. The material of the semi-sphere was defined as a linear steel with a Yoimg modulus E = 210GPa, density y = 7850 kg/ m and Poison ratio u = 0.3. 

The results of tensile tests recorded allow for obtaining the mechanical properties of the materials studied. The Young s modulus of both materials was calculated from oi (stress at a strain of 0.0005) and 02 (stress at a strain of 0.0025) according to the standard UNE-EN ISO 527-1. Tables 2 and 3 shown the Young s modulus and the tensile strength obtained of the tensile tests. The other mechanical properties used were density y = 7850 kg/rrP and Poison ratio u = 0.3. 

These relations enable one to relate the shear viscoelastic functions to their tensile counterparts. At high compliance levels, rubbers are highly incompressible, and the proportional relation between the tensile and shear moduli and compliances holds. However, at lower compliances approaching Jg, the Poison ratio fi (which in an elongational deformation is -(Mw/dM, where w is the specimen s width and / is its length) is less than Eqs. (28) and (29) are then no longer exact. For a glass ju T. When G(t) = K(t), E t) = 2.25 Gif). 

If the density of a material remained constant while it was stretched elastically, what would the Poison ratio have to be What would the bulk modulus have to be Is it realistic to assume that the density remains constant while a material is deformed elastically ... 

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