Measurement of 3H in soil cores from the Hyrax Event (U3bh) subsidence crater

Core samples were collected from two boreholes drilled in the subsidence crater of the Hyrax event (U3bh). The moisture in the core samples was extracted via freeze drying and tritiw-n was measured in the extracted moisture via `He accumulation mass spectrometry or liquid scintillation counting. Elevated tritium concentrations (IE4 - IE6 pCi/L extracted moisture as of the time of measurement) were observed in the extracted moisture from virtually all of the core samples with significant increases beginning at about 30 ft depth. No longer-lived fission products (144 Ce) or activation products (`OCo, `Eu, 114 En) were observed by gamma-ray spectroscopy in a subset of the core samples. This likely indicates that a catastrophic failure of containment (if it occurred) did not release significant radioactivities to this shallow depth (30 ft). The presence of `Cs at much greater depths (@210 ft, 64 m) may indicate that gaseous and/or vapor products were released shortly after the Hyrax event to a depth of about 210 ft. The relatively shallow depth where the elevated tritium is observed makes highly improbable any significant linkage between the elevated tritium concentrations and a Hyrax event containment failure. This may indicate that an additional source of enriched `H was introduced at this site