Environmental Engineering Reference
In-Depth Information
Fuel assemblies are sometimes inspected while supported on the fuel han-
dling mast. More commonly, visual inspections are performed in fuel prepa-
ration machines located in fuel storage pools. The fuel preparation machines
are usually equipped with a rotating fi xture to enable inspections of all four
assembly faces without the use of the bridge crane and with a sensor to rec-
ord axial position.
Visual inspection equipment, typically consists of:
Television camera and spotlights.
In-pool support system for camera and lights.
Data acquisition, processing and storage equipment.
Linear variable differential transformers (LVDTs)
Poolside equipment equipped with linear variable differential transformers
(LVDTs) can be used to determine the dimensions of fuel assembly com-
ponents. As an example, LVDTs may be used to measure the dimensions of
the outer fl ow channel of BWR fuel assemblies. In this case the position of a
channel relative to a reference surface is measured. Each of the four channel
sides is measured by three transducers and consequently 12 axial traces are
obtained simultaneously over the circumference of the channel. From these
measurements, the bulge, bow, and twist may be calculated over the total
length of the channel. Bulge is an outward deformation of the channel faces
which results from the difference in pressure between the inside and the
outside of the fl ow channel and from the effects of fast neutrons on channel
creep. Twist is an angular deformation over the length of an assembly.
The length of the fuel channel is also of interest and can be measured
with in-pool devices that range from tape measures to caliper-like gauges
equipped with LVDTs or similar sensors. Length data are used to assess the
effects of differential growth in the axial direction on the fi t and remaining
growth margin of the channel relative to its fuel bundle. Length data can
also be used to estimate lateral bow in cases where time or equipment avail-
ability prevents more accurate, explicit measurements.
5.5.2 Hot cell examinations
Shielded containments are commonly referred to as hot cells, the word
'hot' being used as a synonym for radioactive. Hot cells are used in both the
nuclear power and the nuclear medicines industries. They are required to
protect individuals from radioactive isotopes by providing a safe contain-
ment box in which they can control and manipulate the equipment required.
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