Prompt Generation Time

It is to be noted that Ci and C3 represent essentially the prompt and delayed reactivity effect, respectively, accumulated in one generation time, and are thus proportional to reactor power in this model. Equation (22) is, of course, a standard cubic equation which may be solved for a to give the natural oscillations of the system, and the system will be stable if the real part of [Pg.296]

The quantity k t) is the excess prompt reactivity and I is the prompt generation time. The small time variation of Z will be ignored throughout. The assumptions that all power is in the fundamental mode shape and that I is independent of time seem unlikely to lead to serious error, but do represent potential weaknesses in the argument. The equation for the time variation of power when a neutron source is present can be written ... 

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. 

Answer Since the prompt fission neutrons are released almost instantaneously, the generation time as far as these neutrons are concerned, is one-thousandth of a second. However, when the delayed neutron time of rou ly one per cent of the neutrons is averaged with the lifetime of the 99 per cent prompt neutrons, the effective generation time is changed from one-thousandth of a second to one-tenth of a second. 

Answer The reactor would be critical on prompt neutrons alone and would increase without waiting for any delayed neutron effect. The combination of keff 1.0075 and the l/lOOO second generation time would cause the chain reaction to increase at a tremendous rate. At the defined point of prompt critical," the reactor period would be of the order of one second. 

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. 

Define the six factors of K ff and typical values, the multiplication factor for an infinite reactor, criticality, subcriticality, supercriticality, reactivity, neutron lifetime with representative values, prompt generation time with representative values, and delayed generation time with representative values,... 

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

Using the values in Table 3,6 for water, the prompt generation time IS 2.47x10" seconds, Values ranging from 5x10 to 5x10" seconds are sometimes used, but a reasonable, representative value is = 1x10 seconds. Physically, this means that 10,000... 

What is a typical value of prompt generation time, 1 ... 

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. 

Generation time determines reactor period or startup rate. The shorter the generation time, the shorter the period and greater the startup rate for a positive reactivity addition. Prompt generation time, 1 x 1x10 sec. Delayed generation time,... 

Prompt neutron generation time, 1x10" seconds/generation,... 

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 ... 

As positive reactivity is added to the reactor, the effects, in terms of time response and generation time, of prompt neutrons are enhanced and the effects of delayed neutrons are diminished. 

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. 

Figure 5.1 describes the time behavior of the neutron population after a burst of neutrons is injected into the reactor. Region one is that of the initial buildup of the neutrons in the reactor as the source neutrons are slowed down. Region two, which is the main region of interest, is that of the exponential decay of the resultant neutron population. This decay is due to prompt neutrons hence the generation time to be considered is the prompt-neutron lifetime. In region three the neutron population has reached... 

Odelius and co-workers reported some time ago an important study involving a combined quantum chemistry and molecular dynamics (MD) simulation of the ZFS fluctuations in aqueous Ni(II) (128). The ab initio calculations for hexa-aquo Ni(II) complex were used to generate an expression for the ZFS as a function of the distortions of the idealized 7), symmetry of the complex along the normal modes of Eg and T2s symmetries. An MD simulation provided a 200 ps trajectory of motion of a system consisting of a Ni(II) ion and 255 water molecules, which was analyzed in terms of the structure and dynamics of the first solvation shell of the ion. The fluctuations of the structure could be converted in the time variation of the ZFS. The distribution of eigenvalues of ZFS tensor was found to be consistent with the rhombic, rather than axial, symmetry of the tensor, which prompted the development of the analytical theory mentioned above (89). The time-correlation... 

A rapid reaction kinetic technique (time scale = 10-1000 ps) that typically uses a Van de Graff accelerator or a microwave linear electron accelerator to promptly generate a pulse of electrons at sufficient power levels for excitation and ionization of target substances by electron impact. The technique is the direct radiation chemical analog of flash photolysis and the ensuing kinetic measurements are accomplished optically by IR/visible/UV adsorption spectroscopy or by fluorescence spectroscopy. 

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