Energy deposition

Energy deposition modes

Mode 0: constant energy deposition per fission

This is the default energy deposition mode in which all energy is deposited locally at fission sites. The energy deposition per fission for nuclide $i$ is calculated as

$E_{{\textrm {fiss}},i}={\frac {Q_{i}}{Q_{235}}}H_{235}$,

where $Q_{i}$ is the fission Q-value for nuclide $i$, $Q_{235}$ the fission Q-value for U-235 and $H_{235}$ = 202.27 MeV is an estimate for the energy deposition per fission (including the additional energy released in capture reactions) in a typical light water reactor.

Mode 1: local energy deposition based on ENDF MT458 data

Similar to mode 0 all energy is deposited locally at the fission sites. The energy deposition per fission is calculated based on ENDF MF1 MT458 data which gives the components of energy release due to fission as a function of incident neutron energy (this dependency is not shown in the following equations). The energy deposition per fission for nuclide $i$ is given by

$E_{{\textrm {fiss}},i}=EFR_{i}+ENP_{i}+END_{i}+EGP_{i}+EGD_{i}+EB_{i}+E_{\textrm {capt}}$,

where $EFR_{i}$ is the kinetic energy of the fission products, $ENP_{i}$ the kinetic energy of the prompt neutrons, $END_{i}$ the kinetic energy of the delayed neutrons, $EGP_{i}$ the energy of the prompt gammas, $EGD_{i}$ the energy of the delayed gammas and $EB_{i}$ the energy of the delayed betas. These components are taken directly from the MT458 data and each component may depend on incident neutron energy. In addition, $E_{\textrm {capt}}$ is an user defined constant representing the additional energy release in capture reactions. The same constant is used for all nuclides and incident neutron energies.

Mode 2: local photon energy deposition

Instead of depositing all energy at the fission sites the neutrons deposit their energy along their histories in various reactions. The energy of the photons is deposited locally at the reaction sites. Energy deposition due to reactions other than fission is estimated using KERMA coefficients which are obtained by subtracting fission KERMA coefficients from total KERMA coefficients, both of which are produced with NJOY. Fission energy deposition is calculated separately and the energy deposition per fission for nuclide $i$ is given by

$E_{{\textrm {fiss}},i}=EFR_{i}+EGP_{i}+EGD_{i}+EB_{i}$.

Mode 3: coupled neutron-photon transport

This mode adds photon transport to mode 2 and photon heating is estimated using an analog photon heat deposition tally. Similar to mode 2 neutron heating due to reactions other than fission is calculated using KERMA coefficients and fission heating is estimated separately. The energy deposition per fission for nuclide $i$ is calculated as

$E_{{\textrm {fiss}},i}=EFR_{i}+EB_{i}$.