Nuclear
Engineering
and
Design
280
(2014)
144–149
Contents
lists
available
at
ScienceDirect
Nuclear
Engineering
and
Design
jou
rn
al
hom
epage
:
www.elsevier.com/locate/nucengdes
Automatic
X-ray
inspection
for
the
HTR-PM
spherical
fuel
elements
DU
Yi
a
,
WANG
Xiangang
a,∗
,
XIANG
Xincheng
b
,
LIU
Bing
b
a
Institute
of
Nuclear
and
New
Energy
Technology
(INET),
Tsinghua
University,
Energy
Science
Building
A309,
Haidian
District,
Beijing
100084,
China
b
Institute
of
Nuclear
and
New
Energy
Technology
(INET),
Tsinghua
University,
Energy
Science
Building,
Haidian
District,
Beijing
100084,
China
h
i
g
h
l
i
g
h
t
s
•
An
automatic
X-ray
inspection
method
is
established
to
characterize
HTR
pebbles.
•
The
method
provides
physical
characterization
and
the
inner
structure
of
pebbles.
•
The
method
can
be
conducted
non-destructively,
quickly
and
automatically.
•
Sample
pebbles
were
measured
with
this
AXI
method
for
validation.
•
The
method
shows
the
potential
to
be
applied
in
situ.
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
12
July
2014
Received
in
revised
form
19
September
2014
Accepted
23
September
2014
a
b
s
t
r
a
c
t
Inefficient
quality
assessment
and
control
(QA&C)
of
spherical
fuel
elements
for
high
temperature
reactor-
pebblebed
modules
(HTR-PM)
has
been
a
long-term
problem,
since
conventional
methods
are
labor
intensive
and
cannot
reveal
the
inside
information
nondestructively.
Herein,
we
proposed
a
nondestruc-
tive,
automated
X-ray
inspection
(AXI)
method
to
characterize
spherical
fuel
elements
including
their
inner
structures
based
on
X-ray
digital
radiography
(DR).
Briefly,
DR
images
at
different
angles
are
first
obtained
and
then
the
chosen
important
parameters
such
as
spherical
diameters,
geometric
and
mass
centers,
can
be
automatically
extracted
and
calculated
via
image
processing
techniques.
Via
evaluating
sample
spherical
fuel
elements,
we
proved
that
this
AXI
method
can
be
conducted
non-destructively,
quickly
and
automatically.
This
method
not
only
provides
accurate
physical
characterization
of
spherical
fuel
elements
but
also
reveals
their
inner
structure
with
good
resolution,
showing
great
potentials
to
facilitate
fast
QA&C
in
HTM-PM
spherical
fuel
element
development
and
production.
©
2014
Elsevier
B.V.
All
rights
reserved.
1.
Introduction
Research
and
development
of
Chinese
high
temperature
gas-
cooled
reactor-pebblebed
modules
(HTR-PM)
have
been
carried
out
by
the
Institute
of
Nuclear
and
New
Energy
Technology,
Tsinghua
University,
and
a
2×
250
MW
th
HTR-PM
demonstration
plant
is
under
construction.
HTR-PM
uses
the
all-ceramic
spherical
fuel
ele-
ments,
with
approximate
420,000
fuel
elements
inside
each
reactor
core
(Zhang
et
al.,
2009).
The
spherical
fuel
element
is
designed
to
be
60
mm
in
diameter,
comprising
an
inner
fuel
zone
and
an
outer
blank
shell.
Approximate
12,000
TRISO
coated
particles
of
1
mm
in
diameter
are
to
be
uniformly
dispersed
in
the
fuel
zone
and
pressed
into
the
graphite
matrix
(Zhang
et
al.,
2009).
The
fabrication
∗
Corresponding
author.
Tel.:
+86
10
62798840/10
62797809;
mobile:
+86
13911711812.
E-mail
addresses:
duyi11@mails.tsinghua.edu.cn
(D.
Yi),
wangxiangang@tsinghua.edu.cn
(W.
Xiangang),
inetxxc@tsinghua.edu.cn
(X.
Xincheng),
bingliu@tsinghua.edu.cn
(L.
Bing).
procedure
is
very
complicated
[2.3.4]
and
errors
can
occur
occasionally,
such
as
mass
center
shifts,
and
inhomogeneous
distribution
of
the
particles.
All
these
errors
will
introduce
poten-
tial
risks
to
HTR-PM
operation
safety.
Therefore,
spherical
fuel
element
inspection
has
long
been
valued
as
a
critical
step
in
quality
assessment
and
control
(QA&C)
for
both
fuel
element
development
improvement
and
production
monitoring.
Shape
and
size
characterization
of
spherical
fuel
elements
can
be
done
by
direct
measurement,
but
inside
knowledge
of
these
fuel
elements
required
destructive
methods
which
would
produce
radioactive
wastes
meanwhile.
Considering
tremendous
amounts
of
spheri-
cal
fuel
elements
produced
for
use,
these
conventional
inspection
methods
are
very
time
consuming
and
labor
intensive,
and
are
not
ideal
to
manage
this
QA&C
task.
Hence,
fast,
robust
and
automatic
inspection
methods
are
needed
(Fig.
1).
X-ray
digital
radiography
(DR),
as
an
important
and
widely
used
non-destructive
testing
technique,
has
shown
potential
to
be
used
for
spherical
fuel
element
QA&C
[2.4.5.6].
In
DR
images
of
spher-
ical
fuel
elements,
various
information
can
be
contained,
such
as
http://dx.doi.org/10.1016/j.nucengdes.2014.09.016
0029-5493/©
2014
Elsevier
B.V.
All
rights
reserved.