Control rods, black

The fuel is low-enrichment uranium dioxide (in the fuel loading strategy described here, the enrichment is 2.8%) the core includes 89 standard PWR fuel assemblies. The assemblies are Zircaloy-cladded with a rod array 17x17, including 264 fuel rods and 25 positions for zircaloy guide tubes for control rods (black, Ag-In-Cd grey, stainless steel) or for burnable poisons (borosilicates). The fuel rod pitch is 1.26 cm and the active length is 260 cm. 

It appears reasonable to apply the ordinary formulae for calculating p2 such as given in report (CP-104) by Christy and Monk. The only objection to this is that the cell is so great in the present case that the production of thermal neutrons is not uniform any more over the cell but shows a dip in the neighborhood of the rod. For this reason the formulae of (CP-104) give a too high thermal utilization p2 and hence tend to exaggerate the effect of the control rods. The equation (7rr is the area of a cell in which there is one control rod, (7ao = oo must be used in CP-104 since the rod is black)... 

Reacfivify can be controlled by black and gray absorbers arranged in groups or banks of three azimuthally symmetric absorber rods. These penetrate the vertical matrix of fuel channel tubes at an angle to the vertical. The reactivity can also be controlled by boron additions and by varying moderator temperature. 

Figure 11.2 shows the local flux distribution in the vicinity of a centrally located black control rod. The dimension b is the actual radius of the... 

Fig, 11.3 Extrapolation length for black cylindrical control rods. 

A similar computation to that given above may be carried out to determine the reactivity of a black control rod which leaves a hole in the reactor when withdrawn. For this case Eq. (11.10) is used in place of Eq. (11.5). 

In the treatment which follows we analyze the effectiveness of control rods in the form of hollow tubes of absorber (thermally black) material. 

Figure 1. Peak-to-peak amplitudes and retinal DNA concentrations related to retinal taurine concentration in 10 control and 38 taurine-deficient cats. Controls were considered to have 100% retinal taurine concentration, ERG amplitude, and retinal DNA concentration. Taurine-deficient cats were divided into six groups of 4 to 8 according to the amount of taurine in their retinas. For each group, average amplitudes (mean + SEM) for rod (black dots) and cone (circles) responses and average DNA values (squares) are presented. The coefficients of correlation for rod ERG amplitude and cone ERG amplitude to retinal taurine concentration were 0.90 and 0.84 respectively. (Reproduced with permission from Schmidt, Berson,...

S has several safety systems active, passive, and inherent (IAEA, 2003) (see Fig. 20.22). Active shutdown systems are (1) inserting reflectors by using gravitational force and (2) inserting black control rods. The passive safety system of 4S uses natural circulation in RVACS and Intermediate Reactor Auxiliary Cooling System (IRACS). In addition, inherent safety system uses Doppler effect via metallic fuel and large inventory of coolant. 

The interior surfaces of the skylight windows of the Technical Library in the Research Building are covered with 3M Scotchtint Solar Control Film, attached at the top and bottom by rods. This screening material is made of a flexible polyester film of 15/1000" total thickness and is aluminum vapor coated. The color selected was smoke (grey black) and,... 

As a very important topic in contamination buildup, the question is still open to what extent the data on corrosion product solubilities in the primary coolant are of importance for the behavior of trace amounts of cobalt. It seems to be still questionable whether cobalt ferrites as a well-defined compound with properties similar to the nickel ferrites can exist under PWR primary coolant conditions, whether cobalt atoms can be incorporated into a nickel ferrite lattice or whether traces of cobalt may be deposited onto the surfaces of the reactor core by adsorption on other, already deposited oxides. Such adsorption processes may occur even on the Zircaloy oxide films in the absence of any net deposition of corrosion products. Experimental investigations of the interaction of dissolved cobalt with heated Zircaloy surfaces (Lister et al., 1983) indicated that at low crud levels in the coolant cobalt deposition on surfaces is dominated by processes involving dissolved species, with adsorption/desorption processes being the responsible mechanisms. The extent of cobalt deposition is controlled by the type of oxide present on the Zircaloy surface thin black films of zirconium oxide will pick up less cobalt from the solution than thick white oxide films, even when the differences in the available surface areas of both types of oxides are taken into account. The deposition process seems to be little affected by the heat flux in the exposed metal. According to Thornton (1992), such adsorption-desorption exchange processes provide a pathway for radioactive species to be transported around the circuit even when the net movement of corrosion products is minimized this means that under such circumstances the processes of activity transport and of corrosion product transport may be decoupled. They may provide a pathway for target nuclides such as Co to be adsorbed onto fuel rod surfaces even in a core which is virtually free of deposited corrosion product particles. 

Figure 4.25. A layer of small silica particles, and a second layer of alumina, shown as short black rods, at A, increases the overall film thickness by / over the control, at B on surface of black glass G [Her (403)].

The solution for the intake, compression and exhaust strokes is very straightforward. The optimal piston velocity in each of these is constant, with a brief acceleration or deceleration at the maximum allowed rate at the juncture of each stroke with the next. The analysis was done both with no constraint on the maximum acceleration and deceleration, and with finite limits on the acceleration. The power stroke required numerical solution of the optimal control equations, in this case a set of non-linear fourth-order differential equations. Figure 14.3 shows the optimal cycle with limits on the acceleration and deceleration, both in terms of the velocity and position as functions of time. The smoother grey curves show the sinusoidal motion of a conventional engine with a piston linked by a simple connecting rod to the drive shaft that rotates at essentially constant speed. The black curves show the optimized pathway. 

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