Determination of³⁶Cl in Nuclear Waste from Reactor Decommissioning

Abstract

An analytical method for the determination of 36Cl in nuclear waste such as graphite, heavy concrete, steel, aluminum, and lead was developed. Several methods were investigated for decomposing the samples. AgCl precipitation was used to separate 36Cl from the matrix elements, followed by ion-exchange chromatography to remove interfering radionuclides. The purified 36Cl was then measured by liquid scintillation counting. The chemical yield of chlorine, as measured by ICPMS, is above 70% and the decontamination factors for all interfering radionuclides are greater than 10(6). The detection limit of this analytical method for 36Cl is 14 mBq. The method has been used to determine 36Cl in heavy concrete, aluminum, and graphite from the Danish DR-2 research reactor.

Critical comparison of radiometric and mass spectrometric methods for the determination of radionuclides in environmental, biological and nuclear waste samples

“…The interest in the determination of 36 Cl in nuclear waste results from the long half life of 36 Cl and its high mobility in the environment, while the purpose of determination of 36 Cl in the environmental sample normally focus on the application of this radionuclide as a environmental tracer. 36 Cl is a pure beta particle emitter with a high energy (E max = 708.6 keV, 98.1%), it is therefore mainly measured by beta counting such as LSC [129,130,[136][137][138][139][140][141]. The reported detection limit of LSC for 36 C is 14 mBq using Quantulus TM low level LSC for 50 min counting time [136].…”

“…36 Cl is a pure beta particle emitter with a high energy (E max = 708.6 keV, 98.1%), it is therefore mainly measured by beta counting such as LSC [129,130,[136][137][138][139][140][141]. The reported detection limit of LSC for 36 C is 14 mBq using Quantulus TM low level LSC for 50 min counting time [136]. A complete separation of 36 Cl from the matrix and other radionuclides is required in this method.…”

“…A complete separation of 36 Cl from the matrix and other radionuclides is required in this method. Hou et al [136] reported a method for the separation of 36 Cl from different types of nuclear waste samples, such as graphite, concrete and metals. The 36 Cl was first released from the sample by acid digestion or alkaline fusion followed by acid leaching.…”

“…But the solubility of Ag 2 SO 4 is much higher than that of AgCl, and can therefore be separated by washing the precipitate with acidic solution [136].…”

“…For improvement of the detection limit, a post-irradiation separation of Cs can be carried out, the Cs on the irradiated cation exchange resin can be eluted by 5-8 mol/l HNO 3 , and the released Cs is then separated by AMP precipitation or cation exchange chromatography [219]. The separated Cs sample is measured by an HpGe detector; the content of 135 Cs can be calculated by counting the radioactivity of 136 Cs using its main gamma rays with energies of 818.5 keV (100%), and 1048.1 keV (80.3%). The detection limit of NAA for 135 Cs depends on the concentration of other Cs isotopes, especially 133 Cs and 137 Cs.…”