128
7 Fundamentals of Hydrogen Recycling
7.8 Simulation and Modeling
Numerical solution of diffusion equation using simulation codes as TMAP 7 [25]
has been often used for estimation of T permeation and retention in fusion reactor
materials. To simulate stoichiometry change or concentration changes of implanted
ions for higher fluences, ACAT-DIFFUSE Code is developed [26, 27]. In such codes,
damaging processes or modification of material properties like solubility and diffusivity given by energetic hydrogen injection are not considered. In other words,
in order to simulate or analyze interactions of energetic hydrogen with materials,
both process of energy transport and particle transport should be simultaneously
handled. In this respect particle simulations like molecular dynamic simulations
are encouraged, which are not described in this book. However, development of
adequate potential to handle atoms and molecules in excited state resulting from
injected energetic ions might not be enough. That means the situation is the same
with experimental investigation which requires consideration of energy dissipation
processes including the formation of excited atoms and molecules as discussed in this
book. Hartree–Fock molecular dynamics in which potential energy is recalculated
in every time step based on the Hartree–Fock molecular orbital theory seem suitable. Still, for discussion of dynamic motion of hydrogen, adiabatic approximation
or Born–Oppenheimer approximation is usually taken into account in Hartree–Fock
molecular orbital calculations may not be correct, because vibrational frequency of
hydrogen atoms, around 10
13 is too fast to be approximated being quiescent. For
understanding of interactions of hydrogen with fusion reactor materials, theoretical
modeling and adequate simulations enable to handle them are awaited.
7.9 Summary
Hydrogen (fuel) recycling (fueling, exhaust and wall retention) is the key to maintain burning plasma. Furthermore, radioactivity and poor resource of T fuel require
precise control of T flow and T inventory in a reactor. Under steady-state burning,
fuel throughput and exhaust should be mostly balanced. However small amount of
fuel is continuously lost in deposits on plasma shadowed and remote areas and in
PFM inside in the reactor vessel. Since the longtime integration of the loss, which
becomes T inventory in a reactor, could be easily over-regulated T level, reduction
of the T inventory both during and after the plasma operation are mandatory.
As described in Chap. 6, heating and modification (damaging) of PFM by power
load and hydrogen recycling synergistically occur, understanding and controlling
of hydrogen recycling is quite hard. In addition, no experimental apparatus which
gives similar power load given by energetic photons and hydrogen in a reactor are
available.
Hydrogen (H) behavior in metals has been long term research subjects for its
importance of hydrogen embrittlement. Nevertheless, it remains as unsolved subject.
7 Fundamentals of Hydrogen Recycling
7.8 Simulation and Modeling
Numerical solution of diffusion equation using simulation codes as TMAP 7 [25]
has been often used for estimation of T permeation and retention in fusion reactor
materials. To simulate stoichiometry change or concentration changes of implanted
ions for higher fluences, ACAT-DIFFUSE Code is developed [26, 27]. In such codes,
damaging processes or modification of material properties like solubility and diffusivity given by energetic hydrogen injection are not considered. In other words,
in order to simulate or analyze interactions of energetic hydrogen with materials,
both process of energy transport and particle transport should be simultaneously
handled. In this respect particle simulations like molecular dynamic simulations
are encouraged, which are not described in this book. However, development of
adequate potential to handle atoms and molecules in excited state resulting from
injected energetic ions might not be enough. That means the situation is the same
with experimental investigation which requires consideration of energy dissipation
processes including the formation of excited atoms and molecules as discussed in this
book. Hartree–Fock molecular dynamics in which potential energy is recalculated
in every time step based on the Hartree–Fock molecular orbital theory seem suitable. Still, for discussion of dynamic motion of hydrogen, adiabatic approximation
or Born–Oppenheimer approximation is usually taken into account in Hartree–Fock
molecular orbital calculations may not be correct, because vibrational frequency of
hydrogen atoms, around 10
13 is too fast to be approximated being quiescent. For
understanding of interactions of hydrogen with fusion reactor materials, theoretical
modeling and adequate simulations enable to handle them are awaited.
7.9 Summary
Hydrogen (fuel) recycling (fueling, exhaust and wall retention) is the key to maintain burning plasma. Furthermore, radioactivity and poor resource of T fuel require
precise control of T flow and T inventory in a reactor. Under steady-state burning,
fuel throughput and exhaust should be mostly balanced. However small amount of
fuel is continuously lost in deposits on plasma shadowed and remote areas and in
PFM inside in the reactor vessel. Since the longtime integration of the loss, which
becomes T inventory in a reactor, could be easily over-regulated T level, reduction
of the T inventory both during and after the plasma operation are mandatory.
As described in Chap. 6, heating and modification (damaging) of PFM by power
load and hydrogen recycling synergistically occur, understanding and controlling
of hydrogen recycling is quite hard. In addition, no experimental apparatus which
gives similar power load given by energetic photons and hydrogen in a reactor are
available.
Hydrogen (H) behavior in metals has been long term research subjects for its
importance of hydrogen embrittlement. Nevertheless, it remains as unsolved subject.