The Neutronics of Heavy Ion Fusion Chambers Jeff

The Neutronics of Heavy Ion Fusion Chambers Jeff Latkowski and Susana Reyes 15 th Heavy Ion Inertial Fusion Symposium Princeton, NJ June 9, 2004 Work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405 -Eng-48.

Neutron transport affects a variety of components and raises a set of issues Hohlraum Capsule Liquid blanket First Structural Wall Blanket Radius JFL— 6/9/04 Final Focus Magnets

Neutron transport affects a variety of components and raises a set of issues Neutron energy multiplication Isochoric heating Neutron activation Radiation damage JFL— 6/9/04

Neutron transport affects a variety of components and raises a set of issues Neutron energy multiplication Isochoric heating Neutron activation Radiation damage JFL— 6/9/04 Output spectra Boosts power above fusion output (10 -20% typical)

Neutron transport affects a variety of components and raises a set of issues Neutron energy multiplication Isochoric heating Neutron activation Radiation damage JFL— 6/9/04 Affects liquid break-up & chamber clearing Imparts stresses to the first structural wall & other components

Neutron transport affects a variety of components and raises a set of issues Neutron energy multiplication Isochoric heating Neutron activation Tritium breeding Transmutation products Radiological safety Radiation damage JFL— 6/9/04 Waste management

Neutron transport affects a variety of components and raises a set of issues Neutron energy multiplication Isochoric heating Neutron activation Component performance Maintenance requirements Radiation damage JFL— 6/9/04 Component lifetime Waste management

In selection of a liquid, the tritium breeding ratio is a key issue q TBR of ~1. 1 is needed to cover uncertainties and losses: – – Decay Leakage 3 -D effects Nuclear data q Don’t want to be >>1. 1, but relatively easy to reduce the TBR JFL— 6/9/04

Liquid thicknesses are selected to provide adequate protection to the first structural wall q Lifetime limits (in displacements per atom) for structural materials of interest: – SS 304: 25 dpa (0. 83 dpa/y) – ODS-FS: 200 dpa (6. 7 dpa/y) q 304 -PCA might be a path to 100 dpa JFL— 6/9/04

Reweldability is desirable but probably not achievable for wall at reasonable thicknesses q Reweldability limit (issue is cracking) is 1 appm He q Welding to 10 appm He may be possible with stress modified welding technique JFL— 6/9/04

The waste disposal rating (WDR) is a measure of the level of activation within a component q WDR is calculated as the ratio of concentration to a concentration limit, summed over all radionuclides q WDR <1 indicates disposal via shallow land burial possible WDR for SS 304 first structural wall after 30 FPY JFL— 6/9/04

The waste disposal rating does not uniformly decrease with increasing liquid thickness 93 Nb(n, g) 94 Nb = 6. 5 98 Mo(n, g) 99 Mo 99 Tc = 95 191 Ir(n, g) 192 s. Ir = 15 JFL— 6/9/04

The neutron spectrum changes considerably in its magnitude but only a little in its shape JFL— 6/9/04

The waste disposal rating is a measure of the level of activation within a component q WDR peaks after ~10 years of irradiation q Beyond the peak, 98 Mo depletion occurs and WDR begins to fall q 93 Nb depletion occurs even earlier JFL— 6/9/04 WDR during irradiation for SS 304 wall behind 30 cm of flinabe

The waste disposal rating does not uniformly decrease with increasing liquid thickness Significant burn-up but high levels of activation JFL— 6/9/04 Liquid thick enough that burn-up drops Liquid thick enough that initial activation reduced

Radiation damage to and transmutation of the first structural wall q An important issue for fusion is the ratio of the He production rate to the displacements per atom (dpa) rate: – Fission-based neutron sources do not produce nearly as much helium as is produced in a fusion system (~0. 1 appm He/dpa) – For a dry wall fusion system ~10 appm He produced for each dpa – Leaves fission-based neutron sources as inappropriate tools for study of dry wall fusion neutron damage q The use of thick-liquids, however, significantly increases opportunities for the use of currently available fission-based neutron sources main advantage is not a change in the He/dpa ratio, but in the reduction of the dpa rate, which allows accelerated damage testing JFL— 6/9/04

An important issue is the ratio of He production rate to dpa rate HYLIFE-II w/ 60 cm Flibe: 5. 4 appm He/dpa JFL— 6/9/04 “Dry wall” HYLIFE-II: 7. 4 appm He/dpa

It is possible to alter He/dpa ratio in existing irradiation facilities q Greenwood & Graczyk report enhanced He production from 55 Fe in ferritic materials can isotopically enrich samples (expensive) q Longest et al. began use of Hf shields in HFIR to achieve 14 appm He/dpa gives desired ratio, but reduces overall damage & transmutation rates q Investigation of other dopants or other means to alter the He/dpa ratio is warranted JFL— 6/9/04

Summary q There a variety of neutronics issues that must be considered for heavy ion fusion systems: – – Neutron interactions in the target Neutron activation & transmutation reactions Isochoric heating Radiation damage q The various technical issues strongly affect important areas of power plant operation: – – – Chamber clearing Radiological safety Component reliability & performance Waste management Economics JFL— 6/9/04