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HAMID
AIT
ABDERRAHIM
MYRRHA:
A
MULTIPURPOSE
HYBRID
RESEARCH
REACTOR
FOR
HIGH-TECH
APPLICATIONS
Background
Nuclear energy research aims
to
cope with
the
criti-
cal
topics
to
resolve
the
economical question
of
increasing
energy demand
and,
in
particular,
the
demands
for
public acceptability,
among
them:
a to
increase
the
absolute safety
of the
installations;
a
to
more
efficiently
manage
the
nuclear waste.
In
that respect,
the
development
of a new
type
of
nuclear
installation dealing with above constraints
of
technological
as
well
as
socio-economical
nature
may
be of
high
importance
for the
future
of
sustain-
able energy provision.
An
Accelerator Driven
System
or,
ADS,
- a
sub-critical core, operated
as a
nuclear amplifier
fed
with
primary neutrons
by a
spallation source
- has the
potential within
the
above
boundary
conditions
to
pave
the way to a
more
envi-
ronmentally safe
and
acceptable nuclear energy pro-
duction.
Indeed
a
sub-critical system driven
by an
accelerator
can be
turned
off
instantaneously
by
shut-
ting
down
the
feeding accelerator. Moreover,
it
will
give
the
chance
to
explore
the
potential
of
burning
waste minor actinides
(MA)
and
long-lived fission
products
(LLFP)
due to the
excess
of
neutrons
and
chain reactor control margins. Fundamental
and
applied
R&D are
crucial
in the
development
of
these
technologies
and
demand
the
availability
of
appro-
priate prototype installations.
The first
prototype
installations
have also
to
deal with these R&D-issues
related
to
accelerator driven system development.
The
continuation
of
nuclear
science
and
engineering
demands
the
availability
of
research
installations,
i.e.
research reactors
and
those
are
currently subject
to
constraints related
to
ageing, high operational
costs,
deep refurbishment
or
even replacement.
A
new,
inherently
safe,
and
economically viable system, that
could
be
used
in a
modular
way for
dedicated appli-
cations,
to
extend known
research
domains
and
explore
new
ones,
is
called for.
One of
SCK-CEN
core
competencies
is and has at all
times been
the
conception,
design
and
realisation
of
large nuclear
research
facilities such
as the
BR1,
BR2, BR3, VENUS reactors, LHMA hot-cells,
or the
HADES underground research laboratory (URL)
for
waste disposal.
SCK«CEN
has
operated
these
facili-
ties
successfully
thanks
to the
high
degree
of
qualifi-
cation
and
competency
of its
personnel
and by
insert-
ing
these
facilities
into international research
net-
works, contributing
hence
to the
development
of
cru-
cial aspects
of
nuclear energy.
One of the
main
SCK'CEN
research facility, namely
BR2,
is
nowa-
days arriving
at an age of 40
years just like
the
major
materials testing reactors (MTR)
in the
world
and in
Europe,
i.e.
ATR
(USA),
HFR
(EU-Petten), OSIRIS
(F-Saclay),
R2
(Sw-Studsvik).
The
MYRRHA
facil-
ity
(Multipurpose hYbrid Research Reactor
for
High-tech Applications) presently
in
pre-design
at
SCK-CEN,
has
been conceived
as
potentially replac-
ing BR2 as a
materials testing system
and to be a
fast
spectrum
facility
complementary
to the
thermal
spectrum
RJH
(Reacteur
Jules Horowitz)
facility,
in
planning
in
France.
This
situation
would
give Europe
a
full
research
capability
in
terms
of
nuclear R&D.
Furthermore,
the
disposal
of
radioactive wastes
resulting
from
industrial nuclear energy production
has
still
to
find
a
fully
satisfactory solution, especial-
ly in
terms
of
environmental
and
social acceptability.
As a
consequence, most countries with significant
nuclear power generating capacity
are
currently
investigating
various options
for the
disposal
of
their
nuclear
waste. Scientists
are
looking
for
ways
to
drastically
reduce
(by a
factor
of 100 or
more)
the
radio-toxicity
of the
High-Level
Waste (HLW)
to be
stored
in a
deep geological repository
and to
reduce
the
time needed
to
reach
the
radioactivity
level
of the
fuel
originally used
to
produce energy. This
can be
achieved
via the
development
of the
Partitioning
and
Transmutation
and
burning
MAs and to a
less extent
LLFPs
in
Accelerator
Driven Systems.
The
MYRRHA
project contribution
is
intended
to
con-
tribute
to the
demonstration
of the ADS
concept
at a
reasonable power level
and to the
demonstration
of
the
technological
feasibility
of MA and
LLFP
trans-
mutation
under real conditions.
Programme
From
the
very beginning
of the
MYRRHA project
in
early
1998,
the
MYRRHA team
is
developing
the
design based
on a
catalogue
of
applications that
are
considered
of a
primary importance
for an
experi-
mental
irradiation
facility.
The
project
is
intended
to
fit
into
the
European strategy towards
an ADS
Demo
facility
for
nuclear waste transmutation.
It is
also
intended
to be a
European, fast neutron spectrum,
irradiation
facility. This
was
dictating
the
design
parameters
as
summarised below:
a ADS
concept demonstration: coupling
of the
3
components
at
rather
reasonable
power level
(20 to 30
MWth)
to
allow operation thermal
and
reactivity
feed-back effects
and
their mitigation;
m
MAs
transmutation
studies: need
for
high
fast
flux
level
(<J>>o.75Mcv=
-1.1015
n/cm2.s);
Scientific staff
HAMID
Air
ABDERRAHIM,
THIERRY
AOUST,
BAUDOUIN
ARIEN,
PETER
BAETEN,
LEON
BAETSLE,
JEAN-LUC
BELLEFONTAINE,
PHILIPPE
BENOIT,
GILBERT BERGMANS,
SERGE BODART,
MlCHELE
COECK,
SIMON
COENEN,
DIDIER
DE
BRUYN,
MARC
DECRETON,
CHARLES
DE
RAEDT,
PIERRE
D'HONDT,
PHILIPPE
GOUAT,
SIMONE
HEUSDAINS,
ALEKSANDRA
IVANOSKA,
PATRICE
JACQUET,
PETER
KUPSCHUS,
DOMINIQUE
LAMY,
ENRICO LUCON,
EDOUARD
MALAMIJU,
NADIA
MESSAOUDI,
JAN
PAEPEN,
JOZEF
PEETERS,
PEDRO RODRIGUES
DE
ALMEIDA,
PAUL
SCHUURMANS,
VlTALI
SOBOLEV,
SVEN
VAN DEN
BERGHE,
ERWIN
VANDENBUSSCHE,
GERT
VAN DEN
EYNDE,
KLAAS
VAN DER
MEER,
STEVEN
VAN
DYCK,
RUDI
VAN
NIEUWENHOVE,
KATRIEN
VAN
TICHELEN,
FERNAND
VERMEERSCH,
HARM
WIENKE
Supporting
staff
ALEX
FRANSEN,
MARC LEHAEN,
MALCOM
PAGET,
JEF
VALENBERGHS,
STEFFI
VAN
GENECHTEN,
STAN
VAN
IERSCHOT,
TONY
VAN
NIEUWENHUYSEN,
ALFONS VERSTREPEN,
JOZEF
WAUTERAERTS
Reactor
Safety
137
s
LLFPs transmutation studies: need
for
high
thermal
flux
level
(<£>,,,=-1.1015
n/cm2.s);
83
radioisotopes
for
medical applications: need
for
high thermal
flux
level
(<E>lh=
-1.1015
n/cm2.s);
Si
material research: need large irradiation volumes
with
high constant fast
flux
level
(0>,McV=l~5.10'4n/cm2.s);
;!
fuel
research: need irradiation rigs with
adaptable
flux
spectrum
and
level
(Olot=1014
to
1015
n/cm2.s);
s
safety
studies
for
ADS:
to
allow beam trips miti-
gation,
sub-criticality
monitoring
and
control,
optimisation
of
restart procedures after short
or
long
stops, feedback
to
various reactivity injec-
tion;
s
initiation
of
medical
and new
technological
applications
such
as
proton therapy
and
proton
material
irradiation studies.
The
present MYRRHA concept
is
driven
by the
flex-
ibility
and the
versatility needed
to
serve
the
above
applications. Some choices
are
also conditioned
by
the
timing
of the
project. Indeed
as we
intended
to
achieve
the
operability
of
MYRRHA before 2010,
the
project team
has
favoured
the
mature technolo-
MYRRHA
Sub-critical
reactor
with
proton
beam
injection
from
the top
gies
or the
less demanding
in
terms
of
development,
for
example concerning
fuel
and
accelerator.
Nevertheless,
not for all
components
of
MYRRHA
do
of-the-shelf
solutions exist. Therefore,
a
thorough
R&D
support programme
for the risky
points
of the
project
has
been started.
Achievements
The
main achievements within
the
MYRRHA proj-
ect
are:
s
the
completion
of the
pre-design study
of the
MYRRHA device;
s
the
consolidation
of the R&D
support program
including
hydraulic
flow
design
of the
window-
less target,
the
vacuum
interface compatibility
for
the
windowless target,
the LM
corrosion,
the
material
research under irradiation conditions,
the
visualisation
under Pb-Bi;
K
the
development
of a
solid
R&D
network around
the
MYRRHA project
via
bilateral collaborations
and
the FP5
programme.
As
the
MYRRHA project
is in a
very progressive
stage,
the
sub-critical reactor design
is now
con-
ceived
as a
standing vessel
as
compared
to the
year
2000
design
of a
hanging vessel.
In
accordance with
the
above,
the
MYRRHA team
has
continued
to
develop
the
MYRRHA project based
on the
coupling
of
an
upgraded commercial proton cyclotron with
a
liquid
Pb-Bi windowless spallation target, surround-
ed
by a
Pb-Bi
cooled
sub-critical neutron multiplying
medium
in a
pool type configuration (see figure
below).
The
spallation target circuit
is
fully
immersed
in the
pool
and is
inter-linked with
the
core
but
its
liquid metal content
is
separated
from
the
core
coolant.
This comes
as a
consequence
of the
win-
dowless design presently favoured
in
order
to
utilise
low
energy protons
on a
highly
compact target
at
high
proton beam power density
in
order
not to
loose
out
on
core performance.
The
core pool contains
a
fast-spectrum sub-critical
core, cooled with
liquid
metal (LM) Pb-Bi eutectic
and
several islands housing thermal spectrum
regions located
in
In-Pile
Sections (IPS)
at the
periphery
of the
fast core
or in the
fast
core.
The
fast
core
is
fuelled
with typical fast reactor fuel pins with
an
active length
of 600 mm
arranged
in
hexagonal
assemblies.
The
central hexagonal position(s)
house(s)
the
spallation module.
The
core
is
made
of
hexagonal
fuel
assemblies composed
of 61 MOX
typical
fast reactor
fuel
pins
(Superphenix-like
fuel
rods) with
Pu
contents
of 30% and
20%.
The
hexa-
138
Reactor
Safety
gons
are
85-mm
flat-to-flat.
To
achieve
a
core con-
figuration
with
a Ks of
0.95,
one
needs
to
load
around
45 to 50
fuel
assemblies depending
on the
chosen
fuel
enrichment
and
burn-up. This represents
about
half
of the
available
fuel
assembly positions
in
the
core.
The
core structure will
be
mounted
on a
central sup-
port column corning down
from
the lid and
being sta-
bilised
by the
diaphragm,
the
separating septum
between
the
warm
and hot
LM
coolant, which
is
fixed
ultimately
to the rim of the
double-wall
vessel.
Since
access
from
the top is
very restricted
and
com-
ponents
introduced into
the
pool will
be
buoyant
due
to the
high gravity
of the LM, the
loading
and
unloading
of
fuel assemblies
is
foreseen
to be
carried
out
by
force-feedback controlled robots
in
remote
handling
from
the
bottom
in and out of the
core
structure.
The
pool will also contain
the
liquid
metal
main
pumps,
the
heat exchangers towards water
as
the
secondary cooling
and the
above robotic units
for
the
handling tasks under
liquid
metal.
The
Pb-Bi
coolant
is
maintained liquid
in all
circumstances
even
during
maintenance (~200 °C). During opera-
tion
the
inlet temperature
is
200°C
and the
outlet
temperature
is
400°C.
The
spallation circuit, inter-linking with
the
core,
connects directly
to the
beam line
and
therefore
ulti-
mately
to the
accelerator vacuum.
For
pumping
around
the LM and for
cooling,
it
contains
a
mechan-
ical impeller pump
and a
LM/LM
heat
exchanger
to
the
pool coolant (cold end).
For
regulation
of the
position
of the
free
surface
on
which
the
proton beam
impinges
(this defines
the
upper boundary
of the
spallation target
and is the
vacuum interface ulti-
mately
to the
cyclotron),
it
comprises
an
auxiliary
MHD
pump;
the
spallation loop
further
contains
services
for the
establishment
of
proper vacuum
as
well
as
corrosion limiting conditions.
The
device
is
shown
in the
figure above with
the
double-wall pool containment vessel, with
an
inner
diameter
of ca 4
m
and a
height
of
close
to 6
m,
sur-
rounded
by a
vessel providing
a
roughly
1.5 m
water
shielding that
is in
turn surrounded
by
concrete
to a
nominal thickness
of
1.5
m as the
ultimate biological
shield. This shield will
be
closed above
the lid by
forming
an
ce-compatible
hot
cell
and
handling area
for
all
services
to the
machine.
In
the
following paragraphs
we are
giving
the
achievements reached
in
2001
for the
various com-
ponents
of the
facility.
The
Accelerator
Having fixed
the
sub-criticality
level,
we
historically
started
the
design work with
a 250 MeV x 2
mA
cyclotron
as
advised
by the
Ad-hoc MYRRHA
Scientific Committee
and
that would have been
a
slight upgraded machine
from
the
cyclotron devel-
oped
by
IBA
(Ion Beam Applications)
for the
proton
therapy application. However, this beam power level
does
not
allow meeting
the
neutronic performances
demanded
from
the
core.
Therefore,
we
first
had to
increase
the
proton energy
to 350
MeV,
as the
gain
on
the
neutron intensity
due to the
energy increase
is
more than linear. Indeed,
the
neutron multiplicity
at
250 MeV is ~ 2.5 n/p
whereas
it is
-5-6
n/p at 350
MeV. Despite this energy increase
of the
incident
protons
we
also
had to
increase
the
proton current
to
5 mA to
arrive
at the
required source strength.
The
final
proton beam characteristics
of 350 MeV x 5 mA
then permitted
to
reach
a
fast neutron
flux
of
1.1015
n/s
(E>0.75
MeV)
at an
acceptable
MA
irradi-
ation
position under
the
geometrical
and
spatial
restrictions
of
sub-critical
core
and
spallation
source.
This upgrade
is
also regarded
as
being within
the
reach
of the
extrapolated cyclotron technology
of
IBA who
currently
propose
to
generate
the
above
proton specifications
by
accelerating
2.5 mA of
H2+
ions
to 700 MeV and to
split
the
latter into
protons
by
stripping
on a
foil.
Compared
to the
largest
continu-
ous
wave (CW) neutron source
-
SINQ
at
PSI
with
its
cyclotron generated proton beam
of 590 MeV and
1.8
mA - it is a
modest extrapolation
and
well with-
in
the
conceptual extrapolation
of the
SINQ
to the
"PSI Dream Machine" with
the
proton parameters
of
1
GeVx
10mA.
In
2001
IBA
focused
its
effort
on the
H,+
ions design
option
and on its
technical feasibility.
The
above con-
cept
needs
a
demanding vacuum design
of the
beam
path
to
avoid
gas
stripping
and a
stripper design with
high effective lifetime
and
coping
with high thermal
loads.
The
MYRRHA cyclotron would consist
of 4
magnet segments
of
about
45°
(cf. figure
on
next
page) with
2
acceleration cavities
at ca
20 MHz RF
frequency.
The
diameter
of the
active
field
is
about
10
metre.
The
diameters
of the
physical
magnets
of
about
16
metre with
a
total weight
exceeding
5000
tons.
The
handling
of
only part com-
ponents need
lifting
capabilities
of at
least
125
t, and
according
provisions
in the
building
need
to be
made.
The
magnets would
be
fabricated
by
assem-
bling
on
site
300-mm
thick plate
with
roughly
8-m
length.
The
achievable flatness during
the
fabrication
of
these plates
is for the
moment
a
concern.
Due to
Reactor
Safety
139
Schematic
view
of
the
MYRRHA
HPPA
(High
Power Proton
Accelerator)
Cyclotron
the
above mentioned dimensions
of the
machine that
are
approaching
the
upper
limit
of
this
technology,
IBA
is
considering
the
alternative
of a
supra-con-
ducting
cyclotron that
will
reduce drastically
the
dimensions
of the
machine.
The
Spallation
Source
The
following considerations dictated
the
choice
of a
windowless design:
9
because
of the
very high proton current density
(> 130
pA/cm2)
forced
by the
demand
for
high
core
performance
and the
therefore severe limita-
tion
of the
available diameter
of the
central hole
housing
the
spallation module
and the low
energy
proton beam
we
intend
to
use,
the
design
of a
window
for the
MYRRHA spallation looks near
to
impossible
for
reasons
of
unacceptable thermal
stress
and
severe embrittlement
in a
very
short
operational period;
B
a
windowless
design
avoids vulnerable parts
in
the
concept, increasing
its
reliability
and
avoiding
a
very
difficult
engineering task.
The
project team
has
focused
its
design
and R&D
support
effort
in
2001
on:
Feasibility
of the
windowless
design
The
design
of the
windowless target
is
very chal-
lenging:
a
stable
and
controllable free surface needs
to be
formed within
the
small space available
in the
fast
core
centre
(0omcr
120
mm).
The
concentrated
heat deposition
(-80%
of the
1.75
MW
total
proton
beam power)
is
dispersed over
a 13 cm
depth starting
from
the
surface
for a
proton energy
of 350
MeV
in
a
cylindrical volume with
an
inner diameter
of
72 mm.
This heat
needs
to be
removed
to
avoid
over-
heating
and
possible
evaporation
of the
liquid
metal.
After
a
successful experimental programme with
water
in
collaboration with
UCL (B) and FZR (D) at
scale
1/1 and a
first
confirmation
test-campaign
mak-
ing use of
Hg
as a
fluid
in
2000
at the
Institute
of
Physics
at the
University
of
Latvia
(IPUL)
at
Riga,
the
MYRRHA team conducted
two
supplementary
Hg
test campaigns
at
IPUL
in
2001.
New
injection
nozzles were fabricated
at
SCK«CEN
and
IPUL
on a
1/1
scale
of the
MYRRHA spallation module (see
figure
(a) on
next page showing
the
most promising
design).
The
results obtained during
the
second
cam-
paign increased
the
confidence
of the
MYRRHA
team
in the
feasibility
of a
controlled free surface
flow
with
a
heavy
LM
circulating
at
with
a
velocity
of
101/s,
as
illustrated
in the
figure
(b) on
next page.
The
ability
to
continuously
adjust
in
height
the
cen-
tral whirlpool
provides
the
pre-condition
for
comple-
mentary proton beam heating profile steering
to
avoid overheating
of
free
elements
of the
free sur-
face.
Cavitation
in
some
limited parts
of the
nozzle
and
some
spitting
of
droplets
from
the
free
surface
are
problems still
to be
solved
.
In
parallel with
the
experimental programme,
the
modelling
effort
using numerical simulations with
Computational Fluid Dynamics (CFD)
codes,
has
been continued
to
reproduce
the
existing experimen-
tal
results
and
giving input
for the
optimisation
of the
head geometry
in the
experiments.
We
will
use the
CFD
calculations
to
investigate
the flow
pattern
and
temperature profile
in the
presence
of the
proton
beam, which cannot
be
simulated experimentally
at
this
stage.
At
SCK-CEN
the CFD
modelling
is
per-
formed with
the
FLOW-3D
code
which
is
specialised
for
free surface
and low
Prandtl
number
flow.
This
effort
is
being backed
up at
Universite
Catholique
Louvain (UCL, Belgium) using
the
FLUENT
code
and at the
Nuclear Research
&
consultancy
140
Reactor Safety
(a)
-
60.000
The
MYRRHA
spallation
module scale
1:1
for the
IPUL
Hg
tests
(a)
Most promising
design,
—
(b)
Obtained
free
surface
Group
-
Petten (NRG,
The
Netherlands) using
the
STAR-CD code.
All the
three groups showed that
the
CFD
codes
are not yet
sufficiently
reliable
to
predict
the
shape
and the
fluid
velocity
at the
free
surface.
Therefore they
are not yet
adequate
for
heat transfer
calculations.
It was
also shown that
the
present
day
commercial
CFD
codes
are not
successful
in
model-
ing
of
droplet spitting.
A
development
effort
there-
fore
is
still needed
in
these fields
and is
already pur-
sued.
Compatibility
of the
windowless
free
surface
with
the
proton
beam
line
vacuum
As the
free surface
of the
liquid
metal spallation
source will
be in
contact with
the
vacuum
of the
pro-
ton
beam line,
SCK'CEN
is
concerned about
the
quantitative
assessment
of
emanations from
the
liq-
uid
metal
and
their
possible
interaction
with
the
pro-
ton
beam.
These
can
lead
to the
release
of
volatile
spallation products,
Pb and Bi
vapours
and of Po,
which
will
be
formed
by
activation
of Bi.
These
radioactive
and
heavy metal vapours
can
contami-
nate
the
proton beam line
and
finally
the
accelerator,
making
the
maintenance
of the
machine very
diffi-
cult
or at
least very demanding
in
terms
of
manpow-
er
exposure.
In
order
to
assess
the
feasibility
of the
coupling
between
the
liquid metal
of the
target
and the
vacu-
um
of the
beam line
and to
assess
the
types
and
quan-
tities
of
emanations,
SCK-CEN
has
build
the
VICE
experiment (Vacuum-Interface Compatibility Expe-
riment).
We
will
be
studying
the
coupling
of a
vacu-
um
stainless steel vessel containing
130 kg
Pb-Bi,
heated
up to
500°C,
with
a
vacuum tube
(104
~
1O6
Torr)
simulating
the
proton beam line.
A
mass spec-
trometer will measure
the
initial
and
final
out-
gassing
of
light
gasses
and the
metal vapour migra-
tion.
To
protect
the
vessel from liquid metal corro-
sion,
we
currently investigate
the
possibility
of
using
Mo and W
coating
or the
oxide layer formation
by
O2
controlled injection.
The
full
experimental device, including
the
vessel,
the
beam line simulation,
the
mass spectrometer
and
the
vacuum pumps,
has
been erected
at
SCK'CEN
and has
undergone high
vacuum
conditioning
at the
end of
2001.
The
Pb-Bi
will
be
undergoing pre-con-
ditioning (out-gassing,
O2
saturation,
and
oxide
cleaning
in a
separate
and
specially designed vessel
before being injected
in the
VICE vessel.
The
pre-
conditioning vessel
and its
associated tools
is to be
completed
at the end of
2001.
The
Sub-critical core
As
already mentioned above
due to the
objective
of
obtaining
a
fast
spectrum
core
and the
criterion that
no
revolutionary options were
to be
considered,
we
started
the
neutronic design
of the
sub-critical core
based
on MOX
fast reactor
fuel
technology.
As we
Reactor
Safety
141
wanted
to
limit
the
technological development
to the
choice
of
cladding material being compatible with
Pb-Bi,
the
initial
request
was to
limit
the Pu
enrich-
ment
to
maximum
30% in
weight
and the
maximum
linear power
to 500
W/cm. With
the low
proton ener-
gy
chosen (350
MeV),
leading
to a
spallation neutron
source
length
of ca
13
cm
(penetration depth
of
pro-
tons),
it was
also decided
to
limit
the
core
height
to
60 cm.
This height
is
compatible with
the
purpose
of
MYRRHA
to be an
irradiation
facility
for
technolog-
ical
developments.
The
fuel
assembly design
had to
be
adapted
to the
Pb-Bi coolant characteristics
espe-
cially
for its
higher density
as
compared
to Na. A
first
core
configuration with typical
SuperPhenix
hexago-
nal
fuel
assembly (122
mm
plate-to-plate with
127
fuel
pins
per
assembly) with
a
modified cell pitch
to
answer
the
requested performances
has
been con-
ceived. Nevertheless, this configuration
is
subject
to
the
large radial burn-up
and
mechanical deformation
stress
gradients that will make
fuel
assemblies
re-
shuffling
difficult
or
even impossible. Therefore,
we
also consider
now in
parallel
a
smaller
fuel
assembly,
85-mm
flat-to-flat, with
61
fuel
pins
per
assembly
allowing
a
larger
flexibility
in the
core
configuration
design.
The
active
core
height
is
kept
to 600 mm and
the
maximum
core
radius
is 100 cm
with
99
hexago-
nal
positions.
Not all the
positions
are
filled with
fuel
assemblies
but
could contain moderating material
(e.g.
ZrH2
pins
filling 6
hexagons around
a
hexago-
nal
position that becomes
a
thermal neutron
flux
trap
with
Olh
=
-1.1015
n/cm2.s).
There
are 19
core
posi-
tions
accessible through
the
reactor cover
and
princi-
pally
capable
of
housing thermal
flux
traps.
At
these
positions hexagons could also
be
housing
fast
neu-
tron
spectrum experimental rigs equipped with their
own
operating conditions control supplied
by
servic-
es
above
the
reactor
cover.
All the
other positions
can
be
housing either
fuel
assemblies
or
non-instrument-
ed
experimental rigs. About
1/2 of the
positions
should
be
filled
with
fuel
assemblies
to
achieve
a Ks
of
0.95.
It
is
worth mentioning here
one
particularity
of the
Pb-Bi
as a
coolant. Indeed,
due to its
high-density
(10.7
g/cm3),
the
fuel
assemblies will
be
floating
in
this
coolant. Therefore,
we
decided
not to
plug
the
fuel
assemblies form above into
a
supporting plate
in
the
traditional
way but to
implant them
from
beneath
into
the top
core plate that
is fixed to the
central sup-
port
column
and
diaphragm separating
the
cold zone
from
the hot
zone
of the
primary circuit
of the
reac-
tor.
The
fuel
assemblies
as
well
as any
non-instru-
mented experimental
rig or
moderating assembly
will
be
then manipulated from beneath
for its
posi-
tioning
in the
core.
By
doing
so one is
easing
the
access
to the
experimental position
from
the top of
the
reactor.
Two
interim
storages
for the
used
fuel
are
foreseen
inside
the
vessel
on the
side
of the
core
fixed to the
diaphragm.
They
are
dimensioned
for
housing
the
equivalent
of two
full
core loadings ensuring this
way
that
no
time consuming operations must take
place
in the
out-of-vessel
transfer
of
fuel
assemblies
nor
is
waiting required
for the
about
100
days
of
cool-down.
Calculations have shown
that
in
their
intended position
and
with
the
amount
of
foreseen
shielding they will
not
contribute
to the
criticality
of
the
sub-critical
core.
The
MYRRHA operation
cycle
will
be
determined
by
the Ks
drop
as a
function
of the
irradiation time
or
core burn-up. Taking into account
the
power density
distribution
in the
core,
we ran
evolution calculations
for
the
core
and we
observed
the
following:
an
initial
Ks
sharp drop
of
about
1800
pern
(Ks: 0.95
->
0.932)
after
5
days
of
irradiation time
due to the
fission
product
build-up.
After
reaching
a
sort
of
equilibrium
we
observe than
a
smooth decrease
of Ks
with
a
slope
of 5
pcm/day.
Thus
the first
operational procedure
has to
deal with
overcoming
the
initial
Ks
drop: either
by an
active
compensation
-
higher initial
Ks
that
can be
com-
pensated
by
partial coolant voiding
as the
voiding
coefficient
is
negative
- or by a
passive
one
-
condi-
tioning
the
fuel
assemblies thanks
to a
pre-irradiation
outside
the
core
for a
longer period than
5
days. Both
approaches
are
presently still under consideration.
The
targeted operating regime
is 3
months
of
opera-
tions
and 1
month
for
core
re-shuffling,
loading,
and
maintenance. This
will
lead
to Ks
drop
per
cycle
of
450 pcm at
maximum,
as
this value
is not
taking into
account
the
coupled
effect
of the
linear power drop
during
the
operation. This will correspond
to a
mul-
tiplication
factor drop
from
20 to
18.3 thus about
-9%.
Core
re-shuffling
with bringing
the
less burned
peripheral
fuel
assemblies towards
the
core centre
would
allow compensating partially this loss
of Ks.
The
intermediate cooling time between
2
irradiation
cycles does bring
an
extra accumulation
of
absorbing
materials
via
delayed radioactive decay.
The
objec-
tive
is to
maintain
the Ks
drop within
10%
range
by
using core reshuffling
and
partial reloading
of
fresh
fuel
with
a
total residence time
of the
fuel
in the
core
of
3
years i.e.
810
EFPD (equivalent
full
power day).
This objective looks
to be
achievable
but
needs
more
investigation.
142
Reactor Safety
Neutronlc
Parameters
1
g
••s
1-
;
J
;
i
i
s
«
Proton
beam
Eb
IP
neutron
source
n/p-yield
(V)
Intensity
Keff
Ks
Importance
Factor
MF
= 1 / ( 1 -
Ks)
fission
ratcs/p
from
fission
rates
from
formula
Av.
Power
density
Max
linear
Power
around
the
target
around
the
thermal
island
Max
Flux
>
1
MeV
Max
Flux
> O .75 MeV
Max
thermal
Flux
Number
of
fuel
pins
Units
MeV
mA
p/s
1017
n/s
MW
W/cm3
W/cm
<J"
c
"o
Large
asss.
Cora
small
assts.
Cora
Th.
Island
ZrH2+B4C
Th.
Island
ZrH2+HT9
Th.
Island
ZnH2+U
Th.
Island
Water
IPS
350
5
3.1207E+16
5.28
1.63-
0.94B
0.9592
1.29
24.51
SS.fi
232
475
0.83
1.14
2286
5.65
1.76
0.95
0.»556
1.13
22.52
40.01
88.®
40.
i
219
431
0.65
0.90
274S
|
5.5O
1.72
0.9S65
22.99
39.91
3S.7
39.9
141
380
287
0.34
4270
5.40
1.69
0.9411
16.97
28. OB
S7.S
ss.s
136
327
462
0.49
Sill
5.50
1.72
0.9510
20.42
36.24
ss.s
ss.s
199
363
382
0.7S
274S
5.53
1.73
0.9469
18.85
32.20
ss.s
SS.fS
156
3S7
591
0.55
0.73
1.10
3111
;(*)
DORT
calculations
have
been
normalized
to
1.24
10
n/s,
the
low-energy
neutron
source
recorded
over
a
partial
volume
of
the
spallation
thick
target
whereas
1.65
10
n/s
is
total
source
over
the
full
volume.
(**}
^
Ef
-
194
A/cV//.
Both present designs
of
MYRRHA
(large
fuel
assembly
and
small
fuel
assembly)
are
delivering
the
expected performances
in
terms
of
fast
and
thermal
fluxes,
linear
power
in the
core
and
total power.
The
table below
is
summarising
the
main parameters
of
both configurations
of
MYRRHA including various
thermal
islands
in the
small
fuel
assembly
configura-
tion.
Engineering
and
Safety Studies
for
MYRRHA
When considering
the
liquid metal cooled sub-criti-
cal
reactor
two
designs were possible:
the
loop
and
the
pool options.
The
loop option
has
been discarded
due to: the
very high vessel exposure
and
thus
the
radiation
damage
it
would undergo,
the
risk
of
LOCA (Loss
Of
Coolant Accident)
and
LOFA
(Loss
Of
Flow
Accident)
and the
difficulty
of the
inter-link-
ing of the
spallation target loop with
the
primary
reactor cooling loop. Finally
one
should mention
the
desired
flexibility in
loading
and
unloading experi-
mental devices.
The
pool design
has
been favoured because
it
avoids
the
penetration
from
beneath
of the
spallation target
circuit
into
the
main
vessel
and
thus enhances
the
safety
of the
design.
It
allow also having
an
internal
interim
storage easing
the
fuel
handling.
The
natural
circulation
(free
convection)
for the
extraction
of the
residual heat removal
in
case
of
loss-of-heat-sinks
(LOHS)
is
certainly easier
to
achieve, particularly
with
the
large thermal inertia that
is
also
an
argument
in
favour
of
this design. With
the
addition
of a
grav-
ity-fed
emergency heat exchanger
the free
convec-
tion
can be
ensured practically indefinitely, even
for
complete loss
of
power.
R&D
suOpport
network
around
MYRRHA
Beside
the
various
R&D
activities mentioned above
or
in
different
chapters
of the
SCK'CEN
scientific
report,
we
would like
to
mention particularly
a
dedi-
cated
R&D
support programme launched
in
2001
in
collaboration with
the
Ultrasonic Institute
of the
Kaunas University
of
Technology
(UI-KUT,
Lithuania).
In
this programme
we are
aiming
at
developing ultrasonic (US) visualisation system
making
use of
sensor able
to
operate under
LM
at
high
temperatures
(~400°C)
and
under high radioac-
tive environment. Such
a
development
is a
pre-requi-
site
for
increasing
the
operability
of a LM
based sub-
critical reactor.
The
programme consists
in the
first
Reactor
Safety
143
phase
to
develop
PZT and
LiNb03
US
sensors
at
UI-
KUT and
therefore
to
demonstrate
their
radiation
resistance
at
SCK«CEN.
For an
intended
second
phase
the
development
of
Quasi-image
forming
sys-
tems
using
the
above
elements
is
considered.
This
collaboration
is one
among
the
various
ones
making
part
of the
large
R&D
support
program
net-
work
that
has
been
erected
around
MYRRHA
either
via
bilateral
collaboration
with:
IBA,
NRG, UCL,
ENEA,
IPUL,
FZK,
FZR,
UI-KUT,
CEA,
PSI,
NRC,
IPPE,
OKBM,
BN,
ATL,
SDMS
or
other
institutions,
industries
and
research
centres
through
the
FP5
proj-
ects:
PDS-XADS,
SPIRE,
TECLA,
ASCHLIM,
MEGAPIE-TEST,
MUSE,
FUTURE,
ADOPT.
Perspectives
In
2002,
we
intend
to
subject
the
MYRRHA
pre-
design
to a
technical
assessment
by an
international
panel
of
experts
in the
field
of
research
facilities.
The
cyclotron
design
is to
undergo
a
similar
review.
The
outcome
of
this
evaluation
will
be
part
of the
input
information
to the
SCK-CEN
management
and
Board
in
order
to
take
decisions
for the
further
steps
of
the
development
of the
MYRRHA
project
namely
the
detailed
engineering
design
phase.
BELGONUCLEAIRE
(Dessel,
Belgium)
ATL
Archer
Technicoat
Limited (High
Wycombe, United Kingdom)
CEA
Commissariat
a
1'Energie
Atomique
(Cadarache
and
Saclay,
France)
ENEA Ente
Per
le
Nuove Tecnologie,
1'Energia
E
1'Ambiente
(Brasimone
and
Bologna,
Italy)
FZK
Forschungszentrum
Karlsruhe
(Karlsruhe, Germany)
FZR
Forschungszentrum Rossendorf
(Rossendorf, Germany)
IBA Ion
Beam Applications (Louvain-
la-Neuve,
Belgium)
IPPE
Institute
of
Physics
and
Power
Engineering (Obninsk, Russia)
IPUL
Institute
of
Physics
of
University
of
Latvia (Riga, Latvia)
NRC
Nuclear Research Centre (Soreq,
Israel)
NRG
OKBM
PSI
SDMS
UCL
UI-KUT
ULB
PDS-XADS
SPIRE
TECLA
ASCHLIM
MEGAPIE-TEST
MUSE
FUTURE
ADOPT
Nuclear Research
&
consultancy
Group (Petten,
The
Netherlands)
Experimental
Design Bureau
of
Machine Building (Nizhny
Novgorod, Russia)
Paul
Scherrer
Institute
(Villingen,
Switzerland)
SDMS
(Saint-Romans,
France)
Universite
Catholique
de
Louvain
(Louvain-la-Neuve,
Belgium)
Ultrasound Institute
of the
Kaunas
University
of
Technology
(Lithuania)
Universite
Libre
de
Bruxelles
(Brussels, Belgium)
Pre-Design
Studies
of
experimental
ADS
Irradiation
Effects
In
Martensitic
Steels Under Neutron
And
Proton
Mixed
Spectrum
Technologies, materials, thermal-
hydraulics
and
safety
for
Lead
Alloys.
Assessment
of
Computational
fluid
dynamics
codes
for
Heavy
Liquid
Metals
MEGAwatt
Pilot Experiment
-
TEST
Multiplication
of
external Source
Expiments
FUels
for
Transmutation
of
transURanium
Elements
ADvanced Options
for
Partitioning
and
Transmutation
Publications
H.
A'it
Abderrahim,
P.
Kupschus,
E.
Malambu,
Ph.
Benoit,
K. Van
Tichelen,
B.
Arien,
F.
Vermeersch,
P.
D'hondt,
Y.
Jongen,
S.
Ternier,
D.
Vandeplassche, "MYRRHA:
A
Multi-Purpose
Accelerator Driven System
for
Research
and
Development",
Nuclear Instruments
and
Methods
in
Physics Research,
Section
A, 463
(2001)
pp.
487-494.
144
Reactor
Safety
Presentations
V.
Sobolev,
S. Van
Dyck,
E.
Lucon,
P.
Kupschus,
H,
Aft
Abderrahim,
"Research programme
on
corrosion mitiga-
tion
in
MYRRHA multi-purpose
ADS for
R&D",
present-
ed at the II
International Workshop
on
Materials
for
Hybrid
Reactors
and
Related Technologies, ENEA, Brasimone,
Italy,
April
18-202001.
H.
Ait
Abderrahim, "MYRRHA:
A
Multi-Purpose
ADS for
R&D
contribution
to the
European XADS
Roadmap",
pre-
sented
at the II
International Workshop
on
Materials
for
Hybrid Reactors
and
Related Technologies, ENEA,
Brasimone, Italy, April 18-20 2001.
H.
Ait
Abderrahim,
"MYRRHA:
A
European Multi-
purpose
ADS for R&D
Contribution
to the
European
XADS Roadmap", presented
at
Svenska Symposium
on
Separation
och
Transmutation,
KTH,
Stockholm, Sweden,
April
19,2001.
H. Aft
Abderrahim, "The material challenges
in ADS
sys-
tems", presented
at the
Topical
Day on
materials
for new
reactor concepts,
Mol,
May 15,
.2001.
H.
Ait
Abderrahim, "MYRRHA:
A
Multi-Purpose
ADS for
R&D", presented
at
TUDelft
-
IRI
Colloquium,
the
Netherlands,
May
21,
2001.
P.
D'hondt,
H.
Ai't
Abderrahim,
P.
Kupschus,
E.
Malambu,
Ph.
Benoit,
K. Van
Tichelen,
B.
Arien,
F.
Vermeersch,
Y.
Jongen,
S.
Ternier,
D.
Vandeplassche,
"MYRRHA,
An
Accelerator Driven Sub-Critical Neutron Source
for
Medical
and
Industrial
Applications",
presented
at the 7*
International Conference
on
Applications
of
Nuclear
Techniques,
Crete,
Greece, June
17-23,
2001.
H.
Alt
Abderrahim,
P.
Kupschus,
E.
Malambu,
Ph.
Benoit,
K. Van
Tichelen,
B.
Arien,
F.
Vermeersch,
Y.
Jongen
and D.
Vandeplassche, "MYRRHA,
A
Multi-Purpose Accelerator
Driven System
for
R&D", presented
at the
International
conference
Power
Generation
and
Sustainable
Development, Luik, October
8 to 9,
2001.
G. Van den
Eynde,
"HEXNODYN,
a
time-dependent nodal
code application
to
MYRRHA",
presented
at the
Topical
Day on
Reactor Physics Computational Methods, Mol,
October
16,
2001.
E.
Malambu, "Application
of
DORT
and
MCNP-X
to
MYRRHA", presented
at the
Topical
Day on
Reactor
Physics Computational Methods, Mol, October
16,2001.
H. Art
Abderrahim,
P.
Kupschus,
Ph.
Benoit,
E.
Malambu,
K.
Van
Tichelen,
B.
Arien,
F.
Vermeersch,
Th.
Aoust,
Ch.
De
Raedt,
S.
Bodart,
P.
D'hondt,
Y.
Jongen,
S.
Ternier,
D.
Vandeplassche, "MYRRHA,
A
Multi-Purpose
ADS for
R&D. Pre-design phase completion", presented
at the
Workshop
on
Advanced Reactors
with
Innovative Fuels,
ARWIF
2001,
Chester,
UK,
October
22-24,
2001.
Ch. De
Raedt,
B.
Verboomen,
Th.
Aoust,
H.
Ait
Abderrahim,
E.
Malambu,
L.H.
Baetsle,
"Transmutation
and
Incineration
of MAs in
PWRs, MTRs
and
ADSs",
pre-
sented
at the
Workshop
on
Advanced Reactors With
Innovative
Fuels,
ARWIF-2001,
Chester,
UK,
October
22-
24,2001.
H.
A'it
Abderrahim,
P.
Kupschus,
Ph.
Benoit,
E.
Malambu,
K. Van
Tichelen,
B.
Arien,
F.
Vermeersch,
Th.
Aoust,
Ch.
De
Raedt,
S.
Bodart,
Y.
Jongen,
D.
Vandeplassche,
Ph. Van
Derkelen, "MYRRHA,
A
Multi-Purpose
ADS for
R&D.
Pre-design phase completion", presented
at the
Fourth
International Meeting
on
Accelerator Driven
Transmutation Technology
and
Applications,
AccApp'Ol/ADTTA'Ol,
Reno, Nevada, USA, November
11-15,2001.
Th.
Aoust,
Ch. De
Raedt,
E.
Malambu,
H.
Ai't
Abderrahim,
"Design Concept
of the
Thermal Flux
Island
in
MYRRHA
for
LLFP
Transmutation. Present status", presented
at the
Fourth
International Meeting
on
Accelerator Driven
Transmutation Technology
and
Applications,
AccApp'Ol/ADTTA'Ol,
Reno,
Nevada, USA, November
11-15,2001.
V.
Sobolev,
S. Van
Dyck,
P.
Kupschus,
H. Ait
Abderrahim,
"Researches
on
Corrosion Mitigation
in the
MYRRHA
Multi-Purpose
ADS for
R&D", presented
at the
Fourth
International Meeting
on
Accelerator
Driven
Transmutation
Technology
and
Applications,
AccApp'Ol/ADTTA'Ol,
Reno, Nevada, USA, November
11-15,2001.
K. Van
Tichelen,
P.
Kupschus,
B.
Arien,
H.
Alt
Abderrahim, "MYRRHA: Design
and
Verification
Experiments
for the
Windowless
Spallation
target
of the
ADS
Prototype
MYRRHA",
presented
at the
Fourth
International
Meeting
on
Accelerator Driven
Transmutation Technology
and
Applications,
AccApp'Ol/ADTTA'Ol,
Reno, Nevada, USA, November
11-15,2001.
J.U. Knebel, J.-C.
Klein,
D.
Gorse,
P.
Agostini,
F.
Groschel,
P.
Kupschus,
T.
Kirchner, J.-B. Vogt,
"MEGAPIE-TEST:
A
European Project
on
Spallation
Target Testing", presented
at the
Fourth International
Meeting
on
Accelerator Driven Transmutation
Technology
and
Applications,
AccApp'Ol/ADTTA'Ol,
Reno, Nevada,
USA, November 11-15, 2001.
K.
Van
Tichelen,
P.
Kupschus,
B.
Arien,
H. Ail
Abderrahim,
"CFD
simulations
of a
liquid
metal
free
sur-
face
flow
for
the
design
of the
windowless spallation
target
of
the
MYRRHA Accelerator Driven System", presented
at
ERCOFTAC,
KUL-Leuven,
December
7,
2001.
Reactor
Safety
145
Reports
H.
Ait
Abderrahim
and the
European Technical Working
Group
on
ADS,
"A
European roadmap
for
developing
acclerator driven systems (ADS)
for
nuclear waste inciner-
ation",
ENEA, ISBN
88-8286-008-6,
April
2001.
V.
Sobolev, "Preliminary design
of a
reference
fuel
sub-
assembly
for the
sub-critical core
of ADS
MYRRHA",
April
6,
2001.
RF&M/VS/rw
32.B043006.
85/MYRRHA-
Design/01-48,
p. 21.
V.
Sobolev, "Compatibility
of
structure
materials
of a
typi-
cal ADS
with
heavy liquid metal coolants: Brief review
of
experimental results".
SCK-CEN
report
R-3532,
May
2001.58
p.
P.
Govaerts,
P.
D'hondt,
H. Art
Abderrahim,
P.
Kupschus,
"MYRRHA,
A
Multipurpose Accelerator Driven System
(ADS)
for
Research
&
Development", SCK_CEN report
R-3523
for the
Meeting
of the
International Strategic
Guidance
Committee
on
MYRRHA, Ostend,
May
18-19,
2001.
P.
Govaerts,
P.
D'hondt,
H.
Ai't
Abderrahim,
P.
Kupschus,
"MYRRHA,
A
Multipurpose Accelerator Driven System
(ADS)
for
Research
&
Development", SCK_CEN report
5160/RvB
for the
Meeting
of the
Board
of
Directors,
Mol,
June
20,
2001.
V.
Sobolev, "Reference
fuel
pin
design
for the
sub-critical
core
of ADS
MYRRHA", Technical Note
NT-32-B043/01-
132
(RF&M/VS/rw
32.B043400
85/MYRRHA-
Design/01-132),
September
4,
2001.
1 p.
V.
Sobolev, "Reference
fuel
assembly design
for the
sub-
critical
core
of ADS
MYRRHA", Technical Note NT-32-
B043/01-133
(RF&M/VS/rw
32.B043400
85/MYRRHA-
Design/01-133),
September
17,
2001.
10 p.
A.
Ivanoska, "Reactivity changes assessment
of
MYRRHA", Training report, October
2001.
H. Ail
Abderrahim,
P.
Kupschus,
Ph.
Benoit, "MYRRHA
Project, Pre-design phase 1999/2001; General description
of the
primary systems
and
associated equipment",
(RF&M
/PhB/phb.32.B043300/S5/MYRRHA-Design/01
-
76-Rev.O),
November
2001.
E.
Malambu,
Th.
Aoust,
N.
Messaoudi,
G. Van den
Eynde,
Ch. De
Raedt, "Status
of
Neutronics Analysis
of the
MYRRHA
ADS -
Progress
Report", November
30,
2001.
Thesis
G.
Van den
Eynde,
"HEXNODYN
- A
Time-dependent
three-dimensional
hexagonal-Z
transport
code",
Faculty
of
Applied
Sciences, ULB, June
2001.
146
Reactor
Safety
