Source Jerk Method
The source jerk method belongs to a group of source perturbation methods.But in principle, the source jerk method is essentially the same as the rod drop method, except that it is a subcritical measurement and the neutron source is removed instead of inserting a control rod. This method is based on the study of the transient response of the reactor to a rapid neutron source removal from a reactor.
In this case the subcriticality of the reactor (subcritical multiplication) can be determined from the measurement of the prompt drop. Also here the prompt drop can be measured because the delayed neutron precursor population will not change immediately. Following sudden source removal, the neutron population undergoes a sharp negative jump.
As was described in the Prompt Jump Approximation, the response of a neutron detector (n1 ➝ n2) immediately after a source removal from a subcritical reactor (ρ1 < 0) is related by:
where n0 is the neutron level with the source in place and n1 is the neutron level immediately after the source jerk. Since a source is much smaller and lighter than a control rod, it is much easier to quickly remove from the core. On the other hand, in commercial reactors, this method cannot be used, because in commercial reactors neutron sources (when used) cannot be simply removed from the core. Moreover commercial reactors contains high burnup fuel which is very important source of neutrons.
See also: Source Neutrons