Prompt jump

The solution may be described as consisting of a prompt jump followed by a transition region and terminating in a stable exponential behavior. The prompt jump is related to the most negative root p- of Equation (84). A formula valid for p- > A, which is always valid, is... 

The prompt jump is followed by a transition stage in which ratios of the Ci to N change from those of Equation (81) corresponding to stable operation at zero reactivity, to... 

The prompt jump approximation. The neutron Equation (77) may be written as... 

A consequence of the prompt jump approximation is the sudden change of N following a sudden change of p. If p changes from pi to p2, then N changes from Ni to N2 where... 

A related consequence is the prompt jump in the inverse period... 

In the numerical integrations of the one parameter Equations (77) and (78), numerical difficulties caused by the small value of Z can be avoided by the use of the prompt jump approximation which replaces the differential Equation (77) for N by the ordinary Equation (101). This reduction in the overall order of the system of equations must be accompanied by a changed set of initial conditions. Specifically, the initial conditions to be used are those which apply immediately following the prompt jump. Thus, in a problem where p changes suddenly, the calculation starts with the value of N following the prompt jump. If dpjdt changes suddenly, then the calculation... 

An exact calculation by Akcasu [14] of the reactor response to the sinusoidal reactivity input to a critical reactor shows that the amplitude of the SN/No vibration increases steadily with time instead of remaining constant as stated by the linearized result of Equation (120). A related result has been obtained by Potter [15] by considering departures from stable operation of the reactor at positive reactivities. He showed that the reactor is less stable for such departures than for departures from critical operation. These results are consequences of the fact that the reactor is more responsive with increasing reactivity, which may be seen to be the case from the prompt jump Equation (103). 

Some non-linear problems. Consider the problem of a sudden introduction of reactivity into a critical reactor with no source in which the feedback reactivity is proportional to the energy generated, as might be the case for a reactor with no cooling. Assuming that the reactivity is less than j8, the prompt jump approximation may be used, which in the one delay group approximation results in (compare Equation (106))... 

In a conventional point kinetics model, involving the concentration of xenon and the flux tending to bum it out, the problem is nonlinear. However, it seems reasonable to make the prompt jump approximation in which the neutron lifetime and the lifetime of the precursors are neglected in comparison with the periods of the iodine and xenon isotopes governing the problem. We can then regard the flux as a control variable that can be adjusted to different levels as required in an optimum program. 

Which ONE of the following describes the term prompt jump ... 

Which one of the following is correct concerning the prompt jump due to prompt neutron... 

A step insertion of positive reactivity to a critical reactor causes a rapid increase in the neutron population known as a prompt jump. This is caused by the ... 

An equal amount of a step change in positive reactivity is added to two identical critical reactors. Reactor A at a power level of 10 watts, and Reactor B at a power level of 1000 watts. Compared to Reactor A, the magnitude of the prompt jump in Reactor B will be ... 

The reactor director objects to this question and answer, in that it is defining prompt jump as the magnitude of the flux increase rather than the ratio of flux after and before the reactivity change. (The ratio is that used in analyses, and always appears as a ratio in the kinetic equations see Hetrick equation 2-47 or Keepin equations 8-9, 8-10). Answer b is equally valid. 

Solve problems for prompt and delayed critical reactors involving reactor period, power, positive and negative reactivity, prompt jump, and prompt drop,... 

When positive reactivity is added to experiences a sudden and rapid rise in powe almost immediate increase in the production This effect is called prompt jump and is il 4.5. For reactivity additions below prompt neutrons appear, the reactor slows its rate a stable positive period is established. S in power level occurs when negative reactiv to the core. The resultant sudden drop in population is illustrated in Figure 4.3. 

The magnitude of prompt jump and drop can be calculated from the following equation. 

Determine the prompt jump in reactor power as the result of... 

The first measurement was taken before the prompt jump had completely decayed away. 

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. 

Fig. 3.12. Flux variation following step change in reactivity, showing prompt jump by ratio...

The Room Temperature case corresponds to an isothermal unit cell at 296 K. For the Prompt Jump case, the temperature assumed for the Nordheim resonance treatment was increased to the assumed operating fuel temperature of 500 K. For the Temperature Defect case, the unit cell operating conditions were assumed. The fuel, clad, and moderator temperatures were assumed to be 500 K, 420 K, and 350 K, respectively. Radial expansion of the fuel and clad regions was modeled. The reduced moderator density was modeled and temperature dependent scattering kernels applied in the calculation. 

A positive reactivity of 0.1 is inserted stepwise as a reactivity perturbation. The feedwater flow rate and the turbine control valve opening are kept constant. The results are shown in Figs. 4.9 and 4.10. The power quickly increases to 111% of the initial value. It is consistent with the analytical solution of prompt jump. Then, the power decreases due to reactivity feedbacks from Doppler and coolant density. The main steam temperature changes by following the power. The main steam pressure and the core pressure increase due to increases in the temperature and hence the volume flow rate of the main steam. The fuel channel inlet flow rate changes with the core pressure due to the relation between the feedwater flow rate and the core pressure shown in Fig. 4.4. The plant almost reaches a new steady state in 40 s. 

A positive reactivity ( 0.1) is inserted stepwise by withdrawing the CRs. The feedwater pump speed and the turbine control valve stroke are kept constant. The results are shown in Fig. 7.68 [31]. The reactor power increases about 10% almost stepwise due to the prompt jump and then gradually decreases due to the reactivity feedbacks from the fuel temperature and coolant density. This behavior implies that the Super FR also has inherent self controllability of the reactor power despite the much smaller density reactivity coefficient compared to that of the Super LWR. The main steam temperature increases, which leads to an increase in the main steam and core pressures because the specific volume of the main steam increases. The increase in the core pressure leads to a decrease in the feedwater and core flow rates, which increases the main steam temperature further. As a result, the maximum increase in the main steam temperature is nearly 40°C while that in the Super LWR is only 9°C (see Fig. 4.10). 

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