Inspection cell
The design of the inspection cell takes into consideration the following issues:
1. The position of the inspection cell
2. The flow of the containers in and out the inspection cell
3. The parameters which will need to be inspected
4. The methods and equipment used to inspect each of the parameters
5. The level of inspection
6. The rate of inspection
7. The accuracy of the inspection
8. The procedure of inspection of each container
9. Safety measurements
Parameters to be inspected
The inspection of a container will consist of two parts.
 Part 1: inspection for contamination and structural integrity of the package.
 Part 2: inspection of degradation and condition of waste stream.
For both parts of inspection individual data should be saved for each package. This
will give information about the behaviour and degradation of the package.
Inspection for contamination and structural integrity of the package will not include
measurement of any parameters since direct view of the package will be available.
Corrosion on drums can be easily checked by viewing susceptible for corrosion areas
(see corrosion section). Structural integrity can be checked in similar way.
The 2nd part of inspection requires measurement of various parameters. The
parameters than can be measured are:
 Radiation of the package
 Weight
 Dimensions
 Heat generation
 Density
The radiation of the package is an important issue since packages are allowed to
produce only a certain amount of radiation. That is 2mSvh-1 on its external surface. [2]
Furthermore, degradation of the material of the container is expected to occur
therefore a reduction in radiation will be a good sign. [3]. The expected radioactive
behaviour of different radioactive materials is shown in figure below.
Figure 1: The expected total activity against time for various radioactive materials. [3]
Weight of the package is also an important parameter. The loss of free water will
reduce the risk for corrosion and this could be detected by the change of the weight of
the package. [1]
Change in dimensions of the package will indicate corrosion on the package, gas
production due to corrosion and other reactions or phase changes of the waste. If large
deformations occur, plastic deformation of the package may result which will lead to
cracking of the package. Therefore, change in the dimensions will be an indicator to
the condition of the package in terms of the sorption, permeability and diffusivity. [1]
Finally, heat measurements will provide more information on the change of the waste
form since exothermic reactions will produce heat. [1]
Expected behaviour of the packages in terms of heat generation is shown in the figure
below.
Figure 2: Expected heat generation of various radioactive materials. [3]
As it can be seen from the above graph the general trend of the packages are to
produce less heat with time. However, some materials such uranium tend to
produce constant heat with some increase at the time of 10 000 years after their
storage.
For more specific information on the density and degradation of the package more
advanced method of testing should be provided. These tests should provide:
 Image of the waste stream
 Identification and quantification of the radio-nuclides within the waste stream.
 Check on the fissile content of the waste packages.
An image of the waste stream will provide information of the type of the waste
existing in the package along with its position. Although the type of waste in each
package will be known and recorded before storage there will be some waste which
will not be compliant. [4]
Inspection level
The inspection of the containers can be carried out in different levels. A possible
scheme would be the following:
First level of inspection:
The containers would be to visually check its integrity and condition. This would be
carried out along with the documentation validation. Since this level consists of very
basic inspection all the containers should go checked at this level.
Second level of inspection:
The containers would be inspected for radiation and contamination. Inspection for
radiation would consist of check of the radiation level of the package and comparison
to the standards and previous data obtained. Therefore, conclusions can be drawn
about the degradation of the material inside the package.
Inspection for contamination would be more directed to the condition of the container
itself than its content. Contamination check would consist inspection for salt and
chloride contamination i.e. corrosion on the drum. Corrosion can be either localised or
uniform. Checks can be carried out visually or with the use of camera.
All packages or at least a high proportion of packages should go through this level of
inspection
Third level of inspection:
Packages would be checked with more accurate methods and more information can be
obtained for the state of the content of the package at this level.
The weight and dimensions of the package can be measured using different methods
along with the heat generation of the package in order to indicate possible changes of
the waste stream of the container.
Furthermore, real time radiography could be used to identify the non compliant items
within the container and therefore describe the waste stream of the container.
High resolution segment gamma scanning could be used to accurately identify and
quantify the radio-nuclides presented in the waste streams. The accuracy of this
method is expected to be of the order ±20%.
Passive Neutron Multiplicity Counting can be also combined to provide mass and
isotopic composition information for plutonium, uranium and radionuclide within the
waste drum. However, the accuracy of this method is of order of ±50% and is limited
by the accuracy with which the location of specific sources can be determined.
This level of inspection should be carried out to a percentage of the waste containers,
probably to the more suspicious ones, containing graphite and high radioactivity
materials.
Fourth level of inspection:
This level of inspection is the more costly and would include a destructive test. This
level of inspection should not be used on a regular basis and should only be
performed if the previous levels of inspection do not provide the required information.
Rate of inspection
According to the design of the inspection cell, packages from the vault will be
inspected every 24 hours. However, new packages coming in the vaults can go
through a minor inspection, say Level 1. New packages with highly radioactive
content or graphite may go through a Level 1-3 inspection so that data is been
collected for future comparison issues.
Level 1 inspection might be the more time consuming since it will consist of visual
inspection. Documentation validation will just take seconds since RFID will be used
for documentation of the containers. Visual inspection can take up to 60 minutes.
Level 2