Xenon oscillations

The coDibination of a large core (in comparison to the neutron migration distance) and the relatively hif power density in N Reactor resiats in a coogplication in the dynamic behavior of the reactor which is associated with the formation and destruction of xenon. 

Xenon instability can persist only above a threshold flux whiLch depends both on the size of the reactor and the flux distribution in the reactor. The over-all temperature coefficient also influences the oscillatory tendency a negative over-all coefficient raises the threshold flux whereas a positive coefficient has the opposite effect - thus acting as an additional driving agent for the oscillation. 

The parameter listed in the table is a measure of the severity of the disturbance. It is the ratio of the peak local power obtained in a free oscillation to the minimum local power. Amplitude ratios of the magnitudes indicated have never been obtained in any of the Hanford reactors chiefly because the cycling periods are long (on the order of 2 -30 hours) thereby allowing adequate time to either damp out the oscillation by proper control action or to shut down the reactor if control action is not successful. 

The chief factors then contributing to N Reactor s better stability against xenon osclUatlonare as follows  

1) The ratio of equilibrium flux to threshold flux Is low compared to the K Reactors. 

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Optimum Spatial Flux Control Project Phase II - Xenon Oscillation Studies for the Pickering Reactor , CEND-3932-2, Combustion Engineering, Windsor, Contract AT (30-1) - 3932 (1969)... 

The active core height has been chosen to allow a maximum power rating while assuring axial power shape stability to xenon oscillations over a normal burnup cycle. 

Figure 4.2-12 represents the current evaluation of axial xenon oscillation stability to the hypothetical xenon redistribution. The relative power in axial element 4 (in top half) and element 10 (at bottom of core) were used to illustrate the power stability to the h)rpothetical xenon redistribution. The power factors in these two element locations prior to the transient were 1.42 for element 4 and 0.67 for element 10. As noted from the results given in Figure 4,2-12, the power perturbation is damped and the relative power in these two locations returns to values that are close to their original values after about 75 hours. 

Xenon peaking Xenon oscillation transient Xenon equilibrium Xenon d... 

The staff found that in 1968 a study was done by SRL to determine xenon oscillation dependence on various reactor parameters (Reference 16). This study indicated that xenon oscillation depends primarily on the neutron flux level, spectrum, and shape the neutron migration area reactor dimenstons saturation xenon worth and the temperature coefficient of reactivity. Of these parameters, only the neutron flux level and shape and the temperature coefficient were found to represent viable design variables. 

The staff also reviewed RTR-2595 and DPSOL-105-1158, "Xenon Oscillation Control" (Reference 19), and found instructions for suppressing power oscillations should they occur during normal operation. Any power oscillation can be suppressed by inserting the safety rods and shutting the reactor down. 

WSRV, DPST-68-372, "Xenon Oscillation Dependence On Reactor Parameters."... 

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