Neutron generation time

Relatively large neutron generation time (about 0.001 second) ... 

The ratio of the effective delayed neutron fraction (3eff) to the effective prompt-neutron generation time (f ) was measured for several unpoisoned configurations, employing both pulsed neutron and nOise analysis methods. The two methods were in satisfactory agreement, giving a best value of 4.76 x 10 sec". The correspon ng value for the beryllium-reflected reactor has been measured as 1.38 X lO sec". The much greater f for the water-reflected assembly is attributable to reflector delayed neutrons. 

The generation time of delayed neutrons is relatively long, t = 13 seconds, while that of prompt neutrons is exceedingly short, l = 1x10 seconds. The core neutron generation time, l, is the weighted average of the two. 

What is the difference between neutron generation time and neutron lifetime. 

Prompt neutron generation time, l, is nearly equal in value to neutron lifetime. The fission event included in... 

Delayed neutron generation time, r, is the weighted average of the mean generation times of the six delayed neutron precursors. Table 3.7 is a compilation of delayed neutron data for uranium 235 from Table 3.4. 

Delayed neutrons are a small fraction of all neutrons in the core, but they have a dominating effect on reactor time response. This is best illustrated by calculating a weighted neutron generation time,... 

Return to the example in section 3.3,6. Using the weighted neutron generation time, l j = o.l seconds, in one second, ten generations will occur, For a reactor starting at 3300 Mw with Keff= 1.001, in one second, reactor power would be 3300 (1.001) = 3333 Mw. Such a rate of power change is easily controlled. The final power of 3333 Mw can be contrasted with the value of 72,325,000 Mw calculated previously where the generation was caused by prompt neutrons alone. 

What are steady state, supercritical, and subcritical values of delayed neutron generation times. Why do these values vary ... 

Return to Chapter 3 and the weighted neutron generation time which includes both prompt and delayed neutrons. Since the denominator is unity, weighted generation time can be written ... 

A representative value of the delayed neutron decay constant, X, during positive reactivity additions is about 0.1. During a time of reactivity addition, the decay constant increases to an even higher value which means that the delayed neutron generation time, r, shortens, and reactor period shortens. 

There is a prompt jump caused by immediate effects of prompt neutrons. A stable period follows which is determined by the amount of reactivity inserted and the delayed neutron generation time. 

Solid lines are fitted for all data to the exact VTMR equation including all delayed neutron terms, and for all variables related with VTMRs -counting efficiency (counts/fission), reactivity, Pu-239 fission portion (assuming fissions are occured only by U-235 and Pu-239), neutron generation time and effective delayed neutron fraction. 

The point kinetic equations formulated by reactivity (p) and neutron generation time (A), are as following dn P - P... 

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