NCSC-8

TO:

FROM:

SUBJECT: Reactor Period vs. Reactivity

The relation between excess reactivity and period (e-folding time) is

given by the inhour equation

period of the reactor, [gamma]f is the effective fraction of neutron delayed, qi is the

fraction of the delayed neutrons with period [tau]i (mean life).

The half-lives and yields for delayed neutrons in each group are

available.^{a1} Experiments at

that [gamma]f = 0.0086 and [tau]p = 135 x 10-6 seconds. Theoretically [tau]p = 1/V[sigma]a, thus,

considering only fissionable material we have the ratio of the

tor

We have, then, for the inhour equation

A plot of this is attached to the original report. With an excess

reactivity at 20°C of 0.0157, which is the calculated value for the

Reactor

be used in the design of the ceontraol amplifiers.

cc: Members of the Reactor Committee

Notes:

^{a1}