How to Replace Co-60 Tracer when Faced with Unknown Variability of Initial Cobalt Content - 18059
- Electricite De France, Dismantling and Waste Management - EDF - DP2D, 154 Avenue Thiers 69458 LYON cedex 06 (France)
Electricite de France (EDF), radioactive waste producer, is responsible for managing waste from dismantling of its permanently shut-down nuclear power plants. The process has been opened for more than 10 years for some plants of the first generation and is under preparation for the first pressurized water reactor (PWR) plants to be dismantled. Nowadays it is generally admitted that waste disposal is the main constraint of dismantling. In France, waste producer is required by safety rules to obtain an agreement from French governmental agency (ANDRA) before any waste production and for each type of waste under project. Such an agreement which is a technical file, is the proof that the container, the way of waste conditioning, waste composition itself and especially the activity of each radionuclide (RN), comply with all the requirements of the disposal safety studies. We should also notice in French regulation that the declaration process of activities i.e. the way the radiological content of each container is computed and declared is a prerequisite to its disposal shipment. Taking into account that EDF has already prepared numerous files describing the means to fill the container itself, the main problem to cope with now is the declaration of each RN which is present in each container ready to be shipped to the disposal. The paper points out the general case of Difficult- To-Measure (DTM) radionuclide management and specially the high difference between waste from plants in operation and waste from dismantling plants. Starting from a '3D' neutron flux cartography computation at 100% power, a specific global strategy of DTM activation RN evaluation for each type of waste has been developed. As the only tracer is Co- 60, which is almost always the case in EDF dismantling, the way to compute the global scaling factors of mix of different waste initial composition is easy when the cobalt initial composition (before irradiation by neutrons) is known. But, in some cases, cobalt is not included in the steel composition required for conception purposes but only considered as an impurity which maximum quantity is known. The result is that, even for a given family of waste corresponding to the same object for dismantling, the tracer value variability is not any more correlated with the irradiation level of the activated waste, which is completely spoiling any of its tracer property. The more the cobalt level variability is high, the more the necessary conservative choice of minimum cobalt level to compute the activation scaling factor will lead to an important overestimation of DTM RN using these scaling factor with respect to Co-60. The paper describes a method using residual thermal power measurement and removing computed Co-60 residual thermal power with the help of gamma measurement to give a new tracer without any chaotic behavior. The possible application is studied on interim storage of irradiated graphite sleeves mixed with stainless steel wires. This method avoids overestimation of graphite inventories coming from activation by neutron flux and using scaling factors with respect to any failing gamma tracer. (authors)
- Research Organization:
- WM Symposia, Inc., PO Box 27646, 85285-7646 Tempe, AZ (United States)
- OSTI ID:
- 22975279
- Report Number(s):
- INIS-US-20-WM-18059; TRN: US21V0093015321
- Resource Relation:
- Conference: WM2018: 44. Annual Waste Management Conference, Phoenix, AZ (United States), 18-22 Mar 2018; Other Information: Country of input: France; 1 refs.; Available online at: https://www.xcdsystem.com/wmsym/2018/index.html
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COBALT 60
ELECTRICITE DE FRANCE
FRANCE
GRAPHITE
IRRADIATION
NEUTRON FLUX
NUCLEAR POWER PLANTS
OCCUPATIONAL SAFETY
OPERATION
PWR TYPE REACTORS
RADIOACTIVE WASTE DISPOSAL
RADIOACTIVE WASTE STORAGE
RADIOACTIVE WASTES
REGULATIONS
STAINLESS STEELS
WASTE TRANSPORTATION