DESCRIPTION:

Dismantling a nuclear installation is often difficult due to the lack of knowledge about the position, identification and radiological characteristics of the contamination. The contamination is particularly difficult to define in a significant global background when the activities are relatively high. For example, identification and estimation of the activity becomes more complex in hot cells, where space is limited and human intervention is costly in terms of accumulated dose.

When embarking on a dismantling project, a number of elements must be specified as they relate to nuclear measurements:

• Definition of the needed investigations
• Detector choice
• Dose rate modeling
• Coupling dose rate measurement and model
• Coupling gamma spectrometry measurement model
• Coupling neutron measurement and model

These challenges often require application of nuclear measurement expertise in unique ways in order to accomplish the goals of the program. With careful methodology, it is possible to achieve not only measurement results, but also activities, and localization. Eventually it is possible to guaranty safety or process threshold corresponding to the needs of the site.

While the general methodology may be appropriate for similar dismantling efforts, in this example, we review the challenges of dismantling the facilities of a reprocessing plant: from dissolution to U, Pu and fission products (FP) extraction and storage in tanks. In such scenarios, a transversal project team may be assembled to support all dismantling sub-projects. Typically, the project team is charged with:

1. Definition of dismantling scenario
2. Design of waste packaging installation
3. Good waste categorization
4. Radioactive discharges optimization
5. Safety analysis (dose rate, criticality…)

The investigation may require many skills and means including:

• Video investigation capabilities
• Documentary research
• Laboratory analysis
• Nuclear measurements and modeling

This particular discussion will focus on nuclear measurements and modeling as they relate to the dismantling effort.