Beginning of equilibrium cycle

The SPWR has no control rod and reactivity is controlled by the core inherent characteristics and chemical shim. Natural boron content in the primary coolant at the rated operating condition is 1,000 ppm in the BOEC (Beginning of Equilibrium Cycle) and 50 ppm in the EOEC (End of Equilibrium Cycle). 

Fig. 1. keff vs cask heavy-metal inventory of CRBR fuet. Beginning of equilibrium cycle isotopic mix. Pu -30.2% of ali heavy atoms. 

Fig. 13.4 shows the layout of the U-fiieled core. As shown in the figure, the core consists of two regions of fuel. Table 13.2 shows a summary of the core performance analysis results, obtained with the equilibrium cycle analysis. The beginning of equilibrium cycle (BOEC) to end of equilibrium cycle depletions were modeled with a bumup chain having descriptions for all of the U—plutonium (Pu)—MA isotopes. A zone reload without fuel shuffling was developed for the equilibrium cycle, wherein one-fourth of the inner core fuels and one-fifth of the outer core fuels were refueled at each outage. 

In the cobweb cycle, as drawn in Fig. X.2, the equilibrium is unstable. Any small perturbation will set up an ever-widening cycle. By the same token, if the farmers begin out of equilibrium, they will never come near it. If we draw the diagram differently, with the supply curve steeper than the demand curve, the opposite is true. After a while, the farmers converge to the equilibrium and return to it after any accidental perturbation. A preliminary conclusion might be that the realization of an equilibrium depends on details of the interaction. Some deviations from equilibrium correct themselves, while others get out of hand. 

Cyclic Steady State is the condition whereby die state at the end of each cycle is identical to that at its beginning. For a non-isotiiermal adsorption systan this may be represented by a mathematical model, comprising material, energy and momentum balances as well as adsorption equilibrium and kinetic models, the CSS can be repressed by ... 

It is critical to ensure that the length of time between the removal of a load from the preconditioning chamber and the beginning of its sterilization cycle is rigorously controlled It is all too easy, particularly in dry climates with very low humidities, for equilibrium to be rapidly lost. 

The core delayed neutron fraction () ) varies from 0.0065 at beginning of cycle in the Initial core to 0.005 at the end of an equilibrium cycle. This average delayed neutron fraction was obtained by weighting the P s of each of the three major core fission Isotopes, U-235, Pu-239, and U-233, by their relative contribution to the neutron production rate. For example, the relative production rate contribution from U-235 varies from 100% at the beginning of the initial cycle to 57% at the end of an equilibrium cycle. The relative production rates of these three nuclides are given In Table 4.2-13a. 

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