Measurement and characterisation of radioactive materials

Management of nuclear materials contained in waste

In order to improve the management of nuclear materials contained in waste, the IRSN/IRSN wanted to accurately know what technical facilities the operator was using to qualify and to quantify the nuclear material contained in the waste.

In this respect, the operators completed a questionnaire sent to them by the IRSN/IRSN on this subject. The production of waste is simply made up of their waste activities. Each installation performs a sort according to its own criteria. The criteria used for this categorization are the nature of the waste (solid or liquid), the measuring devices, the type of packaging.

Therefore, earth and demolition rubbish is found, (plaster, breeze blocks, metals, dismantled machinery), metallic waste (small part tooling, shells and end pieces, electrical cables, fuse bases), technological waste from installation operations (plastics, cloth, papers, glass and metals), liquid waste (liquid effluent, silts and used solvents), as well as resins and incineration ashes.

Quantification of the mass of nuclear materials requires varied methods and facilities given the diversity of the waste.

However, it is possible to mention that:

• Quantification of the plutonium and uranium in the solid technological waste calls, in general, for the use of gamma spectrometry and passive neutron counting (notably for the plutonium). These measuring facilities whether used separately or not, have been used to quantify the nuclear material contents in 87% of items containing materials put out for waste annually.
• Quantification of plutonium and uranium in the solid metallic waste (solid parts) requires the use of active neutron interrogation. In fact, if the metal objects are relatively voluminous they reduce the emission of the gamma photons.
• Quantification of the plutonium and uranium in liquid waste often requires optical emission spectrometry for the uranium and spectrometry α for the plutonium.
• For large volume containers, the dose flows are measured, the measurement results of which are not related to the mass of nuclear material. Weight measurements are also used to quantify the material contained in the bags. The detection limits for the measuring facilities are very varied according