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Determination of Sr-89/Sr-90 in primary cooling water Steffen Happel • • • • • Nuclear Chemistry Department of Chemistry Philipps-University Marburg Method • Extraction of Strontium by solid phase extraction (SPE) using EiChroms Sr-spec® resin (prepacked column) • Determination of Sr-89/Sr-90 by liquid scintillation counting and Cerenkov counting • Sr recovery to be determined by AAS (Sr-carrier) • Sr-90: 0.5 MeV (Cerenkov-Detection efficiency < 0.5 %) • Sr-89: 1.5 MeV • Y-90: 2.3 MeV • Y needs to be separated from Sr Primary cooling water: • • • • Variety of different radionuclides B(OH)3 > 1000 ppm Np/Pu Cs B(OH)3 • No measureable retention on Sr-spec® column • precipitation during evaporation • Removal by cation-exchange • B(OH)3 is not retained on exchange resin • sample preconcentration Cs • Cs is retained on Sr-spec® column (up to 1 %) • can cause interference in liquid scintillation counting • need to remove when in large excess compared to Sr • removal: -precipitation by adding ammonium phosphomolybdate -use of second Sr-spec™ column -ion-exchange chromatography Horwitz et al. Cs removal by ion-exchange chromatography • 60 -70 % of the Cs-activity is removed by washing the ion-exchange resin with 10 mL 2.5 M HNO3 and 10 mL 0.1 M HNO3 • less than 10 % of the Sractivity is removed • to be optimized • disadvantage: loss of Sr Np/Pu • both retained strongly under high-acid conditions • would interfere in liquid scintillation counting • can be removed by the use of oxalic acid Horwitz et al. B(OH)3-removal Strontium extraction LSC- Option • • • • 5 mL Aliquot + 15 mL scintillation cocktail - total radioactive strontium 15 mL Cerenkov-counting - Sr-89 activity • Sr-90 activity calculated by subtracting Sr-89 activity from total Sr activity • take aliquot to determine Sr-recovery (AAS) Cerenkov-Option • 20 mL Cerenkov counting • - Sr-89 activity • take aliquot to determine Sr-recovery (AAS) • • • • • • wait for sufficient Y-90 ingrowth (2-8 days) add Y-carrier and evaporate to dryness add 5 mL 8 M HNO3 and load on to Sr-spec® column strip Y from column with 10 mL 8 M HNO3 submit collected eluents for Cerenkov counting take aliquot to determine Y-recovery (AAS) Comparison of Options • LSC-Option - results within 1 day - Sr-90 activity only few % of total Sr-activity - need good calibration - mixed waste (scintillation cocktail) • Cerenkov-Option - no mixed waste - single point calibration for Sr-89 and Y-90 - wait for Y-90 ingrowth - more accurate - less interference by other radionuclides • Because of Y-90 ingrowth samples should be counted within 3 hours • crown-ether bled from the column causes luminescence, therefore underground counting should be done with an appropriate blank sample Determination of Sr-89/90 using Sr-spec® • • • • • • • • Sr-spec®shows high selectivity for Sr Sr content should not exceed 5 mg per sample easy method need only few chemicals no HCl used results within 1 day (LSC-Option) no mixed waste (Cerenkov-Option) good Sr-recovery (about 50%) EiChrom, Inc. RWE AG KKW Biblis Dr. Ralf Sudowe