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 2015-May-29

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

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

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

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

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

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

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

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

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

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

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

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

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

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.