Development of novel assays for ‘difficult-to-measure’ radionuclides in materials produced during nuclear decommissioning activities

THURSDAY 13 APRIL, 4 PM CET (HYBRID WEBINAR)

Inés Llopart Babot

AMGC-VUB

Development of novel assays for ‘difficult-to-measure’ radionuclides in materials produced during nuclear decommissioning activities

ASBTRACT :

When a nuclear reactor enters in a decommissioning phase, large amounts of materials are generated. Dismantled materials such as concrete or graphite have to be characterized for their radioactive content to prove conformity with regulations related to unconditional or conditional release and final disposal. Gamma emitters such as ⁶⁰Co or ¹³⁷Cs, easy to measure radionuclides (ETM), can be quantified by using gamma-ray spectrometry. However, in the case of pure beta- and alpha- particle emitters, called difficult to measure radionuclides (DTM), a radiochemical separation is needed to obtain the required selectivity of the analysis method. Moreover, the radiotoxicity, mobility and half-lives of the radionuclides are important factors to consider in the waste disposal repositories from the safety point of view. Scaling factors are commonly applied to estimate the activity of DTM radionuclides based on the measurement of ETM radionuclides, but the disadvantage of this method is the large uncertainty on the estimated results.  

This research focuses on analytical method development for several important DTM radionuclides, including ³⁶Cl, ¹²⁹I, ⁷⁹Se, ¹⁵¹Sm, ¹⁴⁷Pm and ⁴¹Ca. All these radionuclides are beta-particle emitting radionuclides and are considered in radiological safety assessments for waste management. ³⁶Cl and ⁴¹Ca are neutron activation products in graphite and concrete respectively, while ⁷⁹Se, ¹²⁹I, ¹⁵¹Sm and ¹⁴⁷Pm are fission products. 

The objectives of the project are: (1) development and optimization of sample decomposition techniques and (2) development of individual or sequential radiochemical separation and measurement methods and (3) application of automated radiochemical separation systems. Different type of samples such as graphite and concrete are considered in this project. For the sample decomposition, pyrolysis (RADDEC pyrolyser) and fusion (Katanax K3 automated fusion fluxer) techniques will be investigated. Liquid scintillation counting (LSC) will be used to determine the activity concentration levels of all the selected radionuclides (considering beta interferences) and triple-quadrupole inductively coupled plasma mass spectrometry (ICP-QQQ) will be used for quantifying the mass concentration of ³⁶Cl and ¹⁵¹Sm. 

The newly developed methodologies will reduce the uncertainties with respect to the inventory estimation for these DTM radionuclides, and thereby facilitate more accurate waste characterization and cost-effective waste management in nuclear decommissioning.