# Presentation: 934036

## The Neutronics of

***Heavy Ion Fusion Chambers***

- Jeff Latkowski and Susana Reyes
- 15th 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.**

**Notes:**
Heavy Ion Inertial Fusion Symposium

## Neutron transport affects a varietyof components and raises a set of issues

***Capsule***

***Hohlraum***

***Liquid******blanket***

***Final******Focus******Magnets***

***Blanket***

***First Structural Wall***

***Radius***

## Neutron transport affects a varietyof components and raises a set of issues

***Neutron energy******multiplication***

***Isochoric heating***

***Neutron activation***

***Radiation damage***

**Notes:**
Total energy mult is ~1.1 to 1.2 (Sombrero was 1.08)

## Neutron transport affects a varietyof components and raises a set of issues

***Neutron energy******multiplication***

***Isochoric heating***

***Neutron activation***

***Radiation damage***

***Output spectra***

***Boosts power above******	******(10-20% fusion output******	****** typical)***

## Neutron transport affects a varietyof components and raises a set of issues

***Neutron energy******multiplication***

***Isochoric heating***

***Neutron activation***

***Radiation damage***

***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***

***Radiation damage***

***Tritium breeding***

***Transmutation products***

***Radiological safety***

***Waste management***

## Neutron transport affects a varietyof components and raises a set of issues

***Neutron energy******multiplication***

***Isochoric heating***

***Neutron activation***

***Radiation damage***

***Component performance***

***Component lifetime***

***Maintenance requirements***

***Waste management***

## In selection of a liquid, thetritium breeding ratio is a key issue

- TBR of ~1.1 is needed to cover uncertainties and losses:
- Decay
- Leakage
- 3-D effects
- Nuclear data
- Don’t want to be>>1.1, but relatively easy to reduce theTBR

## Liquid thicknesses are selected to provide adequate protection to the first structural wall

- Lifetime limits (in displacements per atom) for structural materials of interest:
- SS304: 25 dpa(0.83 dpa/y)
- ODS-FS: 200 dpa(6.7 dpa/y)
- 304-PCA might be a path to 100 dpa

**Notes:**
304 modified like Prime Candidate Alloy PCA (addition of carbides I think), is expected to reduce swelling and have life ~100 dpa or more. 

## Reweldability is desirable but probably not achievable for wall at reasonable thicknesses

- Reweldability limit (issue is cracking) is 1 appm He
- Welding to 10 appm He may be possible with stress modified welding technique

**Notes:**
I assume this is for first wall. I think HYLIFE-II added flibe between first wall and outer vacuum vessel so that VV did meet the limit.

## The waste disposal rating (WDR) is a measureof the level of activation within a component

- WDR is calculated as the ratio of concentration to a concentration limit, summed over all radionuclides
- WDR <1 indicates disposal via shallow land burial possible

***WDR for SS304 first structural wall after 30 FPY***

**Notes:**
Is this WDR for first wall? What material 304 or ODS?
How many years irradiation?
At 30 cm flibe, 304 lasts for < 1 year right? So these curves assume wall stays in longer than life at small thickness?

## The waste disposal rating does not uniformly decrease with increasing liquid thickness

**Notes:**
What are the numbers? = 6.5 = 95 are these half-lives?
Is this for 30 FPY?

## The neutron spectrum changes considerablyin its magnitude but only a little in its shape

## The waste disposal rating is a measureof the level of activation within a component

***WDR during irradiation for SS304 wall behind 30 cm of flinabe***

- WDR peaks after ~10 years of irradiation
- Beyond the peak, 98Mo depletion occurs and WDR begins to fall
- 93Nb depletion occurs even earlier

## The waste disposal rating does not uniformly decrease with increasing liquid thickness

## Radiation damage to and transmutationof the first structural wall

- 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
- 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

**Notes:**
Fission test reactors
...of the dpa rate allowing testing to total damage equivalent to years of operation????

## An important issue is the ratioof He production rate to dpa rate

**An important issue is the ratio****of He production rate to dpa rate**

## It is possible to alter He/dpa ratioin existing irradiation facilities

- Greenwood & Graczyk report enhanced He production from 55Fe in ferritic materials  can isotopically enrich samples (expensive)
- 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
- Investigation of other dopants or other means to alter the He/dpa ratio is warranted

## Summary

- There are 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
- The various technical issues strongly affect important areas of power plant operation:
- Chamber clearing
- Radiological safety
- Component reliability & performance
- Waste management
- Economics