<p>Advanced liquid processing system (ALPS)-treated water was sampled from the K4-B tank group on March 24, 2022, in the presence of staff from the International Atomic Energy Agency (IAEA) and Tokyo Electric Power Company (TEPCO) Holdings, Inc. The Nuclear Safety Research Center (NSRC) of the Japan Atomic Energy Agency analyzed ten key radionuclides (³H, ¹⁴C, ⁶⁰Co, ⁹⁰Sr, ⁹⁹Tc, ¹⁰⁶Ru, ¹²⁵Sb, ¹²⁹I, ¹³⁴Cs, and ¹³⁷Cs) and three additional nuclides (³⁶Cl, ⁵⁵Fe, and ⁷⁹Se) in the ALPS-treated water as part of independent monitoring for the regulatory body. According to the obtained results, all radionuclide concentrations, except that for the ³H concentration, were ultralow and less than the standard values permitted for discharge. TEPCO’s analytical results were evaluated using the <i>En</i> number, which indicated satisfactory performance. In addition, reference values and ζ scores obtained via the IAEA’s interlaboratory comparisons were recalculated incorporating the NSRC’s results. All ζ scores for NSRC, IAEA, and TEPCO fell between − 2 and 2, demonstrating that the results are acceptable at a 95.4% confidence level.</p> Graphical abstract <p></p>