After the solution sample is atomized and ionized in the high-temperature plasma, the first quadrupole (Q1) selects ions with a mass-to-charge ratio (m/z) of 79, allowing both ⁷⁹Se⁺ and ⁷⁹Br⁺ to enter the collision/reaction cell. Upon the introduction of NH₃ gas, Br⁺ is neutralized through a charge transfer reaction and subsequently removed from the ion path. In contrast, ⁷⁹Se⁺ remains unreacted and is selectively transmitted through the second quadrupole (Q2) to the detector.

 

^＊1 "Other matrix" refers to elements and radionuclides constituting the concrete matrix (e.g., Na, Al, ¹³⁷Cs, ⁹⁰Sr)

Rapid and reliable radionuclide inventory assessment is essential for the disposal of the large volume of radioactive waste generated by the TEPCO’s Fukushima Daiichi Nuclear Power Station (FDNPS) accident. However, rapid assessment of ⁷⁹Se, a critical nuclide for environmental impact, has been challenging. Conventional radiation method requires not only extended counting times due to its long half-life but also laborious chemical separation to remove interfering co-existing nuclides.

At the Okuma Analysis and Research Center, we have established practical, nuclide-specific analytical methods^＊2 for difficult-to-measure radionuclides^＊3. These methods combine hydrochloric acid (HCl)-free solid phase extraction with inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) to simplify and accelerate analysis while reducing the burden on analytical facilities associated with corrosion. In this study, we applied the same concept to ⁷⁹Se and developed a practical analytical procedure.

⁷⁹Se was separated and purified from the concrete matrix via stepwise chemical separation using anion exchange resin and activated alumina. Measurements were performed using ICP-MS/MS using ammonia (NH₃) as the reaction gas. Interferences, including the ⁷⁹Br isobar and argon-based polyatomic ions, were effectively reduced (Fig. 1). Consequently, the combination of chemical separation and ICP-MS/MS measurement suppressed the ⁷⁹Br interference signal to approximately one ten-millionth of its original intensity.

The method limit of detection (MLOD)^＊4 of this method was 0.1 Bq g⁻¹. In addition to being sensitive enough to be well below the proposed regulatory limit^＊5 of 23 Bq g⁻¹ for trench disposal, the analysis can be completed within a few days, and a substantial reduction in analysis time is expected compared to conventional methods. Based on these results, the effectiveness of this method for FDNPS waste analysis was confirmed.

 

^＊2 i.e., Routine methods for waste inventory assessment

^＊3 e.g., ⁹³Zr, ⁹³Mo, and ¹²⁶Sn

^＊4 MLOD when using an approximately 1 g test portion (concrete sample)

^＊5 Japan Nuclear Safety Commission, Radioactivity Concentration Upper Limit for the Disposal of Low-Level Radioactive Solid Waste, 2007, Reference Materials 3, Table 13, p.3–21 (in Japanese).

  Nuclear Regulation Authority (NRA) Digital Archive: https://www.da.nra.go.jp/detail/NRA093215158

This study includes some results obtained from Agency for Natural Resources and Energy (ANRE), Ministry of Economy, Trade and Industry of Japan (METI) as part of the subsidy program "Project of Decommissioning, Contaminated Water and Treated Water Management (Research and Development of Processing and Disposal of Solid Waste (Investigation on Standard Analytical Methods Using Simplified and Accelerated Analytical Technology))" starting FY2022.

Paper URL: https://doi.org/10.1007/s10967-025-10143-w

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