Transcript MoU-status march 2007

Direction-sensitive monitoring of nuclear power plants
R.J. de Meijer, F.D. Smit and R. Nchodu
EARTH Collaboration
Antineutrinos
• Postulated by Pauli to resolve the mystery
of continuous β-spectra around 1930.
• Realising the extreme small cross sections
for interactions (10-43) Pauli exclaimed: “I
have done something terrible by postulating
a particle that cannot be detected.
• Experimentally detected by Reines and
Cowan in the 1950’s.
Proposed initial experiment
Discovery
Experiments eventually carried out at Hanford, Washington
Nobel Price in Physics 1995 to Reines (Cowan had deceased)
IAEA-Oct 2008 Recommendations
• Consider antineutrino detection and monitoring
in the current IAEA programme;
• Consider antineutrino monitoring in Safeguards
by Design for power and fissile monitoring of
new and next generation reactors;
• IAEA work with experts to consider future reactor
designs, using existing simulation codes for
reactor evolution and detector response;
Pebble Bed Modular Reactor
• PBMR is a High
Temperature Reactor
(HTR) with a closedcycle, gas turbine
power conversion
system.
• A steel pressure vessel which holds about 450 000
fuel spheres containing enriched uranium dioxide
fuel encapsulated in triple-coated with silicon carbide
and pyrolitic carbon , moulded graphite spheres. The
system is cooled with helium and heat is converted
into electricity through a turbine.
PBMR
PBMR
• The vertical steel pressure
vessel is 6.2 m in diameter
and about 27 m high. It is
lined with a 1 m thick
layer of graphite bricks,
which serves as an outer
reflector and a passive
heat transfer medium. The
graphite brick lining is
drilled with vertical holes
to house the control
elements.
Application to PBMR
• Antineutrino measurements provide
information on elemental and isotopic
composition of an entire fissioning reactor
core, providing a type of bulk accountancy.
• So antineutrino detection provides a unique
alternative approach to maintaining
continuity of knowledge and near real-time
safeguards information about PBMRs.
Limitations
• Burn-up in the PBMR is not homogeneous.
• One single detector therefore provides
solid-angle integrated information.
• A modular set of detectors with a smaller
footprint would be preferred.
• Size reduction of antineutrino detectors
based on γ-rays not feasible.
• Simulation for
PBMR-400
loaded with
PuO2.
• Temperature
measurement is
no direct
indicator of
burn-up.
EARTH Programme
• Programme EARTH develops direction-sensitive
antineutrino detectors, which eventually put
together will form a network of about ten
telescopes looking into the Earth and map the
radiogenic heat sources.
• Each telescope contains ~ 4000 ton detection
material.
• Starts from proven, state of the art technology and
develops and incorporates new technologies.
Angle deviation
e+
νe
p
θ
n
10B+n
7Li+α
Positron position is a good approximation for reaction location.
Time difference e+ α
Am-Be source
T0 = 86 ± 9 ns
Recent developments…..
lead to new opportunities:
High-position resolution from
differences in arrival times
(Triangulation)
Detection principle GiZA
We are working at such a type of
detector. In the detector the
detection process generates light
flashes, to be detected by the four
photon detectors.
Depending on the location the
distance to the detectors differs
and so the arrival time of light
flashes at the detectors.
Detection of an antineutrino results
in two pulses shortly produced after
each other. From the position of the
two pulses the direction of the
incoming antineutrino is
reconstructed.
Background suppression

Delayed
coincidences
(~106);
Position
Pulse
requirements (~10);
shape (~101-2);
Constant
magnitude α-puls
(~101-2);
(Anti-)coincidences (~102-3);
Expected suppression factor: 1010-1014
Present development within Sensor
Universe
• Plausibility study liquid scintillation
materials, including construction of test
cells, construction design of GiZA and test
of cells in South Africa.
• Feasibility study by Polyvation, Groningen,
new detector materials based on light
emitting polymers.
Next steps within Sensor Universe
• Construct GiZA and test it at Koeberg
nuclear power plant (SA)
• “Copy” SONGS detector and demonstrate it
at Koeberg as preparation for implementing
it in Pebble Bed Modular Reactor (PBMR).
• Collaboration with IAEA, NRG, LLNL
(USA) and PBMR (?).
Direction sensitivity
• Capture reaction of antineutrinos on a
proton provides direction sensitivity in the
emission of the neutron.
• Direction sensitivity gets reduced by slow
down of neutrons by scattering.
• Early neutron capture by 10B or 6Li
preserves direction information and reduces
uncorrelated background.
Initial development EARTH detector
• For
direction sensitivity a modular detector concept
Conclusions:
is needed instead of monolithic.
• Addition of 10B reduces the number of neutron
scatters,ofandproblems
better preserves
the direction
• A number
of the monolithic
detectors
informationdisappear,
carried bynew
the challenges
neutron. (read-out
(background)
of
detectors)
comerequires
in return.
• many
Direction
sensitivity
detector units with a
high spatial resolution (1-2cm) for e+ and n.
• Design phase: Computer simulations, based on
• Leadskinematics,
to a detectortocomprising
of many
modules,
reaction
determine the
dimensions
of
containing
many
detector units.
This
requires
the each
detector
units and
to optimise
neutron
detection.
an advanced data-analysis en –handling system.
Principle
n
+
+
ne
e
e
PMT
p
p
PMT
n
ne
Direction sensitive detector modules
muon
shield
11
10
9
19
1
5
6
7
18
13
4
3
2
8
12
17
14
15
16
Development first phase POP
(successfully concluded)
• Use existing small (3.8 cm diameter; 2.5cm
long) detectors.
• Simulate double-pulse events with n-source.
• Determine time characteristics of coincidences
and pulse shape.
Double Pulses
Pulse shape (tail) is particle dependent. Important for
background suppression.
Delayed coincidences
Conclusions:
• Double pulse well detectable; there is a difference
in shape between n and γ. N (T )  N e
100
T / To
0
N0=116; T0=400ns
N(T)
10
• Addition
of 10B leads to a much shorter delay time
and hence reduces background (accidental
coincidences).
• Ready 1for the next steps with “real” antineutrinos.
0
400
800
1200
T (ns)
1600
2000
Development strategy EARTH
• Use existing, proven technologies and demonstrate
the Proof Of Principle (POP) of direction sensitive
antineutrino detection near a nuclear power plant
(strong source of antineutrinos).
• Develop in parallel new technologies for light
detection, detection materials, signal analysis and
processing, data storage. Only after sufficient
testing incorporate them in the detector set ups.
Development strategy EARTH
• Scale-up detector dimensions step by step.
(Started very small, next step is still small
but afterwards we intend to reach our goal
in one or two steps of development)
• Apply new technologies if appropriate.
• Look during development for applications
(financing).
Design Intermediate Detector GiZA
(Geoneutrinos in ZA)
Direction derived from positions of positron and “neutron” pulses
in delayed coincidence, determined by triangulation of the four
detector signals.
Muon-shield
γ + n shield
Expected properties
• Characterising antineutrinos with
appropriate background reduction;
• Position determination based on arrivaltime differences;
• Relatively easy to manoeuvre due to limited
volume and weight ~40l;
• Sufficient count rate for testing properties.
Optimisations
• Physical properties liquid scintillators;
• Designing and developing polymers with
high light output for α-particles and good
particle identification on pulse shape;
• Replacing PMTs by other light converters
not sensitive to magnetic disturbances.
• …….
Goals for the next phase
• Measure real antineutrino signature with Giza and
tubular detectors;
• Check possibilities triangulation;
• Investigate pulse characteristics and light
attenuation of gelled and polymer detectors;
• Investigate background reduction in the lab and in
an underground laboratory (Pyhäsalmi Finland);
• Design prototype detector for reactor monitoring.