Fast-nonleakage probability

Note that g denotes the fast nonleakage probability and p the resonance-escape probability in the usual way [see Eqs. (4.260)]. Clearly, the probability that a neutron will not be absorbed in traversing the lethargy interval (0,w) is the product of the probability that it will not be absorbed in the interval (0,w ) and the probability that it will not be absorbed in (u, w) thus for u < u,... 

Equation (6.103) applies since the resonance-escape probability for any particular interval is independent of the past history of the neutron. The fast nonleakage probabilities are also independent, and it follows that... 

The fast nonleakage probability based on these data may be computed from Eq. (6.79) it is found to be th = 0.7364. 

We demonstrate the calculation of a temperature coefficient by considering the initial startup condition of the CP-5 and show how this coefficient may be used to predict the excess reacftivity (or multiplication) of the reactor at room temperature. Specifically, we compute the temperature coefficient of the hot clean reactor from the temperature derivatives of its thermal utilization, fast nonleakage probability, thermal nonleakage probability, and resonance-escape probability. The change in fc for a given change ST in temperature is then easily computed from the relation (6.142). 

The temperature coefficient of the fast nonleakage probability is obtained from (6.169), which requires an estimate of ath- Now... 

If the resonance-escape probability has been obtained by some other means, then a knowledge of Xjoo yields g. It is interesting to note that, for very large specimens, the value of g obtained in this way should agree well with the Fermi age expression for the fast nonleakage probability, that is,... 

The quantities pth and g h in (9.84) denote the resonance-escape and fast nonleakage probabilities to thermal in the usual way [(4.260) and (6.79)). Penally, note that since the reactor described by (9.84) is not critical the multiplication constant will be different from unity and may be obtained from the relation... 

B. Density Coefficient A decrease in density decreases the macroscopic cross sections, which results in an increase of the mean free paths for absorption and scattering. The result is that the thermal diffusion length (L) and neutron age (t) increase. Because of the increase in L and T, the thermal and fast nonleakage probabilities are reduced. From Eq. (1) note that the reduced nonleakage probabilities decrease kg , which means that the reactivity effect is negative. A partial compensation for the effect of an increased L and t on the nonleakage if the core volume exp[Pg.193]

The new quantities are (fast nonleakage probability), (capture to fission ratio above fast fission threshold), e (fast-fission factor), and 6, which is defined by the equation... 

---