4.3. Delayed-Neutron Precursors

The net rate of change of the delayed-neutron precursor population is given by

(4.3-1)\[ {\dot{C}}_{\text{i}}\left( t \right) = \frac{\beta_{\text{i}}\phi\left( t \right)}{\Lambda} - \lambda_{\text{i}}C_{\text{i}}\left( t \right)\]

where \(\beta_{\text{i}}\) is the effective delayed-neutron fraction for precursor \(i\), and the initial, normalized steady precursor population is given by

(4.3-2)\[ C_{\text{i}}\left( 0 \right) = \frac{\beta_{\text{i}}}{\lambda_{\text{i}}\Lambda}\]

In terms of the individual precursor delayed-neutron fractions, the total effective delayed-neutron fraction is given as

(4.3-3)\[ \beta = \sum_{\text{i}}\beta_{\text{i}}\]

The number of delayed neutron precursors is entered in input variable NDELAY, the effective delayed neutron fractions are entered in input array BETADN, and the delayed neutron precursor decay constants are entered in input array DECCON. The prompt neutron lifetime is entered in input variable GENTIM.