Outsized waste

Disposal of large waste items

Two examples of outsized waste
ANDRA has opted to dispose of certain objects subject to low-level radioactive at its industrial repositories in the Aube department. It is easier and less polluting to dispose of such objects without cutting them up into pieces. The figure shows two examples of large objects that have been disposed of directly by ANDRA: Baskets used to store spent fuel at the Penly nuclear power plant; vessel heads, which are the upper section of the metal chamber that contains the core of a PWR reactor.

Most of the low-level and very low-level waste packages held by ANDRA at its industrial repositories in the Aube department (CSA) are medium-sized; the largest are metal boxes with a volume of 10 cubic metres. However, there are a few cases for which such capacities are inadequate. Waste producers such as EDF expressed a wish to dispose of large waste components directly, for technical and economic reasons, and because not cutting them up decreases operators' exposure to radioactivity.

Disposal solutions were therefore needed for such outsized waste items. Accordingly, in 2000 the safety authorities authorised the disposal of baskets previously used to store spent reactor fuel, as well as 55 PWR reactor vessel heads.

Looking ahead, the planned dismantling of nuclear installations will be a major source of large waste items. The experience already acquired and the flexibility with which the CSA repository coped with the first such outsized objects augur well for the response to future dismantling waste requirements.

Container for a spent fuel basket
Baskets previously used to store spent fuel assemblies ipools adjacent to reactors are placed in a 40 m3 container, which when full weighs around 30 tonnes. This operation is performed at the power plant in preparation for transport. Furthermore, the basket's structure is strengthened for the transport operation, enabling it to withstand the additional pressure when the container is filled with cement, in a final pouring operation performed in the disposal cell.
Containers of spent fuel baskets at the CSA repository
These large containers filled with baskets previously used to store spent fuel have been placed in a disposal cell upon arrival at the Low- and intermediate-level, short-lived waste disposal centre in Soulaines, in the Aube department, where they will be filled with cement in a grouting operation, permanently immobilising the baskets.
Spent fuel storage baskets

It was necessary to dispose of baskets previously used to store spent fuel assemblies in a pool adjacent to reactors. Such baskets are contaminated by contact with fuel assembly cladding and end caps, and, in the event of a cladding breach, by spent fuel pellets. In principle, they are not very radioactive.

The baskets were placed inside 40 cubic metre containers for transport and disposal. These containers were too heavy to be passed over the walls of a disposal cell. A breach had to be made in the wall, to allow the truck to enter. Once inside the disposal cell, the containers were filled with cement and the baskets sealed. At the end of this five-day grouting operation, the breach in the wall was filled in and other waste packages were placed in the cell, which was then filled in with cement slurry, completely sealing it.

PWR reactor vessel heads

A vessel head is the upper section of the chamber that contains the core of a PWR reactor. It is designed to withstand the very high pressure (155 bars) of the water flowing between the fuel elements. The control rods and other control mechanisms as well as a number of safety devices are mounted on the vessel head.

Reactor vessel head convoy
This photo shows a reactor vessel head being transported by truck from the power plant to the CSA repository in the Aube department. A specially designed container is used for such transport operations. A total of 55 such reactor vessels are scheduled for replacement, beginning in 2004.

Reactor vessel heads are replaced during a reactor shutdown, after a number of years in operation. This mechanical shell becomes slightly radioactive as a result of prolonged contact with reactor contact and the related neutron flux.
Due to their weight (91 and 120 tonnes, respectively, for 900 and 1300 MW reactors), it was not possible to dispose of vessel heads in normal disposal cells. As a result, special-purpose disposal cells had to be built, equipped with a 160-tonne crane and opening roof.

At the reactor site, the vessel head is placed inside a container, which is in turn placed inside another container for the transfer by road to CSA. Upon arrival, the vessel head and its container are unloaded from the transport container and placed in a bay in the disposal cell. A machine is then set up to inject cement slurry around and inside the vessel. The interior of the vessel is filled with cement through the control rod conduits on the vessel head.

The first in a series of 55 vessel heads was disposed of at the CSA repository in 2004. The procedure was subsequently repeated at a rate of 6 to 8 vessel heads per year.

ANDRA video on solutions for outsized waste packages: View video

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