1. Oak Ridge National Laboratory Heavy Isotope Production Nuclear Data Needs
Susan Hogle, Julie G. Ezold
Nuclear Materials Processing Group Oak Ridge National Laboratory Oak Ridge, TN, USA
Workshop on Nuclear Data Needs and Capabilities for Applications Berkeley, California May-29

2. Heavy Isotope Production Programs
252Cf program, ongoing biennial campaigns
Super heavy element (SHE) target isotopes, as needed
249Bk, 251Cf, 242Pu, etc.
Potentially 254Es, 255Fm, 257Fm
Alpha-therapy medical isotopes, R&D phase
225Ac (via 229Th), 227Ac

3. Facilities – Irradiation and Processing
Various positions are available for irradiation at High Flux Isotope Reactor (HFIR) with different fluxes and volumes
Radiochemical Engineering Development Center (REDC) contains hot cells, glove boxes, radiologicial labs for fabrication and processing
HFIR Experimental Positions
REDC Facilities

4. 252Cf Production Program
Successive neutron captures in mixed Cm/Am (some Pu)
High fission losses, ~95% fissions in route to 252Cf
Composition, irradiation time, and flux spectrum dependent
Fission limits the total yield potential, as well as target design, and processing schedule flexibility

5. High uncertainties is many actinide cross sections
~5-10% uncertainty in absorption cross sections of most Cm-Cf isotopes
Uncertain resonance energies
High resonance and fast flux in HFIR, strong absorbers, many overlapping resonances
Developed target specific effective cross sections and experimentally calibrated paramaterizations
251Cf Absorption Cross Section
Red: ENDF/B-VII.1
Pink: ROSFOND
Black: JEFF-3.1

6. Optimization efforts aim to maximize 252Cf production per consumption of target material
Analyzed sensitivity of 252Cf production to neutron energy spectrum
Production is improved by inducing flux depressions in regions where fission fractions are greater

7. R&D ongoing for altering neutron flux spectrum
Variety of filter materials have been examined for potential to improve 252Cf production
Evaluation of each filter consists of iterative transport and depletion models, wrapped in an evolutionary algorithm to select filters based on performance
Full depletion must be simulated, due to constantly changing target composition and filter depletion
Performance of these models relies heavily on quality of resonance absorption data
Ongoing development of sensitivity analysis tools may allow examination of other reactor parameters

8. Experimental evaluation of filter effects
Initial algorithms pointed towards 103Rh as a potential filter material for 252Cf production
Multiple Cf precursor isotopes loaded into capsules, irradiated filtered and unfiltered
Significant improvement to both 244Cm and 245Cm – higher production and lower fission products
Designed (left) as built (top) and post irradiation (bottom) experimental capsules

9. Super heavy element target isotopes
Current focus is on 249Bk and 251Cf
249Bk produced as a byproduct of 252Cf program at ~10% mass yield
251Cf produced at ~2-5% mass yield
252Cf undesirable
Future needs may also involve 254Es and 255/257Fm
Low production from current program
Neutron filtering may have huge impacts on SHE target production
SHE target wheel and titanium foil target segment for 251Cf deposition at ~340 mg/cm2

10. 249Bk ideal for neutron flux filtering
Production from 248Cm largely unaffected by changes to thermal neutron flux
Depletion slowed when thermal flux depressed
Filter(s) should not overlap 248Cm resonances, and should be capable of lasting through irradiation
248Cm capture (blue)
249Bk total (green)
113Cd total (red)
Similar approach for 251Cf production to minimize 252Cf production
Filtered

11. 254Es via staged production with filtering
Staged irradiation-decay-irradiation of 252Cf to form 253Es
Thermally filtered irradiation to form 254Es
253Es capture (blue)
254Es total (green)
Need to avoid the 253Es resonance

12. 255Fm strategies not well developed
Multiple pathways to production, contributions are understood, but confidence in uncertainties is low
Absorption in 253Cf and 254Cf could be significant
254Es and 254mEs have high fission cross-sections

13. Alpha Therapy Isotopes
229Th produced via reactor irradiation of 226Ra to serve as a ongoing source of high demand 225Ac
228Ra builds up during target recycle, contributions from this branch are uncertain
Experimental 229Th yields have been below the theoretical values
229Th fission reduces yield and complicates recovery
Blue: ENDF/B-VII.1
Green: ROSFOND
229Th Fission Cross Section

14. Summary
Uncertainty in actinide absorption cross sections encumbers production capability
Resonance absorption is significant in many key actinides, but data may be poor, and analysis options are resource intensive
Optimization techniques require high fidelity data and analysis
Experimental efforts attempt to fill these gaps, but are problem specific

15. Acknowledgements
Research supported by the Isotope Program, Office of Nuclear Physics of the U.S. Department of Energy. ORNL is managed by UT-Battelle, LLC, for the U. S. Department of Energy under contract DE-AC05- 00OR22725.