IEA-R1 core modeled with 20 fuel elements yields 34% higher 177Lu specific activity

The preprint reports Monte Carlo modeling of multiple IEA-R1 core layouts using the KENO-VI module within the SCALE code system. The authors compared the current 29-element configuration against reduced-fuel arrangements and identified a near-cylindrical 20-element core that concentrates fissile material while preserving criticality margins. Central irradiation positions, particularly the EIBe beryllium element, recorded the largest flux gains, directly translating into higher radioisotope production rates. Power peaking factors remained within operational limits according to the reported tallies.

The 34% gain in 177Lu specific activity rests entirely on calculated thermal and epithermal flux spectra; no fresh experimental benchmark data for the proposed geometry are presented. Prior IEA-R1 flux measurements and 177Lu production campaigns at similar MTR-type reactors provide partial validation, yet the absolute flux increase predicted here exceeds values achieved in documented compact-core trials at other facilities. Safety margins for shutdown margin and reactivity coefficients are stated but not quantified against regulatory acceptance criteria.

If the modeled flux increase materializes, annual 177Lu output at IEA-R1 could rise without extending reactor operating days, easing supply pressure for prostate and neuroendocrine cancer therapies. Realization depends on successful fuel management changes and regulatory approval for the new loading pattern. The next required step is a series of low-power critical experiments followed by full-power flux mapping to confirm the calculated spectra before any production campaign.

Further gains would require either higher enrichment fuel or beryllium reflector optimization, options noted but not quantified in the study. Independent verification by another Monte Carlo code and a formal safety analysis report remain outstanding.