Environmental Engineering Reference
In-Depth Information
Hot cells are used to inspect spent nuclear fuel rods and to work with other
items, which are high-energy gamma ray emitters.
The methods utilized in a hot cell examination vary with the objec-
tive of the program, but usually begin with a visual inspection. Visual
inspections are used to characterize the external surfaces of a fuel rod,
including the crud and oxide layer, and to identify features of interest
for subsequent examinations. High resolution diametral profi lometry and
EC lift-off measurements are also used to characterize the thickness of
the crud and oxide layers relative to axial and azimuthal position, partic-
ularly if such measurements were not performed before transporting the
rod to the hot cell.
EC measurement with encircling, pancake or pencil coils can detect the
axial and tangential location of cracks and other damage that might not
be readily discernible in visual inspections; for example, small or incipient
cracks due to PCI.
Neutron radiography
- If a test reactor is adjacent to a hot cell, neutron
radiography can be performed on the fuel rod to non-destructively locate
regions with different hydrogen levels in the cladding. Depending on the
method used for capturing and displaying the neutrographic image, accu-
mulations of hydrogen are indicated by light or dark areas. Neutron radi-
ography can also reveal fuel washout in the case of degraded failed fuel. In
addition, neutron radiography provides geometrical information of the fuel
column for the selection of cutting positions of samples for ceramographic
examinations.
Destructive examinations
- The fuel and cladding can be examined by
means of a number of destructive methods including:
Fission gas collection and analysis.
Cladding oxide thickness (ID and OD) measurement.
Hydride concentration and morphology.
Second phase particle size and distribution.
Microstructure characterization.
Ceramographic characterization of fuel pellets.
Micro-gamma scanning across the diameter of fuel pellets.
Electron microprobe analysis of the fuel pellets and the pellet-cladding
interface.
The fi ssion gas that was released from the fuel to the free volume within a
rod is normally collected and analyzed as the fi rst step in the destructive
examinations of sound fuel rods. The collection process involves punctur-
ing the cladding and collecting the free gas in one or more containers of
known volume, pressure and temperature. This process not only captures
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