Pacific Northwest National Laboratory recently commissioned a new shallow underground laboratory, located at a depth of approximately 30 meters-water-equivalent. This new addition to the small class of radiation measurement laboratories located at modest underground depths houses the latest generation of custom-made, high-efficiency, low-background gamma-ray spectrometers and gas proportional counters. This paper describes the unique capabilities present in the shallow underground laboratory; these include large-scale ultra-pure materials production and a suite of radiation detection systems. Reported data characterize the degree of background reduction achieved through a combination of underground location, graded shielding, and rejection of cosmic-ray events. We conclude by presenting measurement targets and future opportunities.

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Executive SummaryThe Direct Feed Low-Activity Waste flowsheet provides for the early production of immobilized lowactivity waste (LAW) by feeding waste directly from Hanford tank farms to the Hanford Tank Waste Treatment and Immobilization Plant (WTP) for vitrification. Prior to the transfer of feed to the WTP LAW Vitrification Facility, tank waste supernatant will be pretreated by the Tank Side Cesium Removal (TSCR) system to meet the WTP LAW waste acceptance criteria (<3.18E-5 Ci 137 Cs/mole of Na). This pretreatment will remove cesium from the waste stream using ion exchange (IX). The selected media for IX is crystalline silicotitanate (CST), product number UOP-IONSIV-R9140-B, manufactured by Honeywell UOP LLC (Des Plaines, IL).Testing was requested by Washington River Protection Solutions to better define IX processing using Low-Activity Waste Pretreatment System (LAWPS) prototypic IX unit operation process steps at full height and medium height. The information is intended to significantly contribute towards establishing accurate process flowsheets for the individual feed campaigns planned for the LAWPS.Column testing at both the medium (12% of the full bed height) and full height scales was conducted to evaluate process variables and scale up performance of Cs exchange onto the CST, Lot 8056202-999. Nominal process conditions used 5.6 M Na simulant processed at 1.8 bed volumes per hour (BV/h) at 20 °C. Process variables included 1) increased process temperature to 35 °C, 2) increased Na concentration to 6.0 M, 3) added organics to the 5.6 M Na simulant, and 4) flowrate changes. The medium scale tests used single columns containing 44 mL of <25 mesh CST in a 1.44 cm diameter column, 27 cm tall CST bed. The full height columns used lead/lag columns containing 1.15 L unsieved (as-received) CST in 2.54-cm-diameter columns, 226 cm tall CST beds. Two process flowrates were tested at the full height: 1.30 and 1.82 BV/h. IX testing with simulant solutions was conducted using TSCR prototypic IX unit operations: feed processing, feed displacement with 0.1 M NaOH, water rinse, and solution expulsion with compressed air. Figure ES.1 shows the effect of variable process parameters on the Cs load profile from the medium height column testing. Increased residence time was shown to improve Cs load performance. The Cs loading was sensitive to increased temperature; a 15 °C rise in temperature reduced the effective Cs load capacity at the equilibrium Cs feed condition 31% and dropped the BVs processed to contract limit 30%. Added organics had a marginal effect on the Cs load profile up to the 450 BVs tested with a 15% reduction in BVs processed to the contract limit. Increasing Na concentration to 6.0 M had a marginal adverse effect on the Cs load profile where the percentage of BVs processed to the contract limit was reduced by 15%. Figure ES.2 shows the load profiles for the full height column tests; processing at slower flowrate showed slightly improved exchange performance. Figure ES.3 compares the medium to full height ...

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PNNL has developed two low-background gamma-ray spectrometers in a new shallow underground laboratory, thereby significantly improving its ability to detect low levels of gamma-ray emitting fission or activation products in airborne particulate in samples from the IMS (International Monitoring System). The combination of cosmic veto panels, dry nitrogen gas to reduce radon and low background shielding results in a reduction of the background count rate by about a factor of 100 compared to detectors operating above ground at our laboratory.