Transcript Passive Gamma Emission Tomography - a verification option of spent nuclear fuel prior to final disposal (pdf)

Passive gamma emission tomography
(PGET)
Tapani Honkamaa
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Contents
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Introduction
Description of the method
Motivation
Project history and timeline
Prototype Hardware
Prototype Software
Results from the test campaigns
Summary and future directions
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Introduction
• Research on Passive gamma emission tomogropgy (PGET) started
already in 1980’s
• R&D has been and is conducted specifically under R&D programmes
made for the IAEA nuclear material safeguards and financed my its
member states safeguards support programmes
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Hungary,
Sweden
USA,
Finland
EC
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Description of the method
rotation
fuel
assembly
scanning direction
scanned section
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And with more detectors arranged in 2 heads:
Head1
Head2
104 detectors
Tungsten
collimator
Housing
Heads consist of detectors and multislit tungsten alloy collimator
With sufficient number of detectors need for lateral movement is eliminated and
only rotational movement is needed
Detector spacing 4 mm, resulting in 2mm resolution.
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Geometry
Head1
Head2
104 detectors
CdTl
2x5x10mm
Main signal:
1274 keV
Fission product
Eu-154
Gamma-ray
-compton edge.
Tungsten
collimator
Housing
Requirement: imaging of Spent nuclear fuel assembly
PWR type 17x17 rods in rectangular lattice
Resulting to the need 2 heads, 104 detectors in each, detector
spacing 4 mm, resulting in 2mm overall resolution.
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Data production and imaging
Fuel
Assembly
Cross
sectional
image of
fuel
assembly
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Measurement
(scanning)
Image
calculation
Projections
at several
angles
Strength of PGET
• Method is accurate, it is capable of detecting a single missing pin
inside a fuel assembly – true partial defect method
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About nuclear material safeguards
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Goal of Nuclear Material Safeguards – Never again
Picture: Charles Levy, 9th of Aug 1945
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What it takes to build a nuclear weapon?
• Nuclear material (U or Pu)
– Difficult to get.
– Main effort in nuclear non-proliferation is put in here!
• Other components
– Rather easy to get
• Information and Expertise
– In general, this indormation is restricted by international agreements
– Adequate information is available publicly to build a primitive device
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…Why verification is conducted in nuclear material
safeguards?
• In order to prevent proliferation of nuclear weapons spent nuclear
fuel in under stringent control all over the world. The control is
exercised by international and national inspectorates
– International Atomic Energy Agency (IAEA) European Commission and
national regulators.
• Implementation of non-proliferation regime requires that
declarations and reports provided by nuclear operators can be
verified.
• Verification tools are needed
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Why Passive Gamma Emission Tomography?
• Current verification tools have quite limited sensitivity to so called
partial defects:
• Partial defect = part of the fuel diverted to nondeclared purposes
• IAEA Policy: a partial defect test with high detection probability on
all populations of easily dismountable spent fuel transitioning to
storages where re-verification is either difficult or even impossible.
– PGET strength is in its extraordinary sensitivity
– PGET would be an important component of the tool box of
complementary partial defect test devices.
• One interesting application: last verification before fuel assemblies
are moved into a geological repository for final storage.
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Final disposal of spent nuclear fuel
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Construction project of PGET prototype
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Project timeline
Loviisa
2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014
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Ollkiluoto
Ispra
Ringhals
Kick-off
Specifications
PO for arrays
Hardware construction
Delivery of arrays
System integration
Ringhals test
System repair&integration
Ispra tests
Olkiluoto
Loviisa
Reporting
Prototype, head open
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Software
• Two parts: Control Software and Data Processing Software
1. Control Software, attended
– Input: set up of the detectors and detector electronics and fuel
information
– Output: The unprocessed (raw) data
– Control software automatically invokes the data processing software.
2. Data Processing Software, automatic
– Input: Raw data
• Corrections are applied to the raw data, diagnostic modules, etc.
– Data analysis can be performed automatically
• Manual operation is possible for test/calibration.
– Output: information whether pins are missing as compared against a set
of operator declared information including fuel type – cross sectional
image.
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Prototype schema..
Notebook
with ports
….And in real life!
Driver +
PSU
AIR
WATER
Array 1
104 detectors
electronics
Array 2
104 detectors
electronics
MOTOR
with position
encoder
UNDERWATER HEAD
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Some technical issues in system integration
• Longest delay was in delivery of detectors. Procurement, 18 mo
delivery time, first acceptance test failed
• Some problems: detector arrays do not operate reliably, the read
out is working only in serial mode, and stepping motor generates
disturbances to the detector signals.
• Serial readout is a major issue.
– With present prototype measurement time is 1-3 h instead of 2-5
minutes
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Passive gamma emission tomographic
measurements, Ringhals
16-20 Nov 2009
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Ringhals tests
• Detector failure prevented the measurements
• Overheating of one ASIC (each head consists of 4 ASICs, each
controlling 26 detectors (4x26=104)
• Grounding issues: Stepping motor rotating 2x150 kg arrays takes a
lots of Amperes.
• Repair took a few months, then recalibrations, putting things
together, combating against grounding problems, etc.
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Ringhals 16-20 Nov 2009
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Ringhals 16-20 Nov 2009
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Ringhals 16-20 Nov 2009
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Ringhals 16-20 Nov 2009
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Passive gamma emission tomographic
measurements, Ispra
11-15 Jul 2012
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Ispra 11-15 Jul, 2012
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Ispra 11-15 Jul, 2012
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Ispra 11-15 Jul, 2012
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Measured objects, results
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The fuel items were simple 6, 8 and 12 rod objects
Long cooling time, low signal, long measuring times needed
Result: Imaging was successful
The data provided by another array was not satisfactory
– However, resolution provided by another array was sufficient
• The calibration was not perfect
– Did not prevent of having results
• The simple objects are not the real test for the usability of the
method.
– Self absorbtion is negligible.
• However, this was the first successful campaign for the prototype.
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Ispra conclusions
• The simples objects are not the real test for the usability of the
method. However, this was the first successful campaign for the
prototype.
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Passive gamma emission tomographic
measurements, Olkiluoto BWR
15-17 Mar 2013
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Measured objects, results
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The fuel items were 8x8 and 10x10 spent fuel assemblies
Cooling time varied from 3 to 32 y
Result: Imaging was successful, with some artifacts
Again: The data provided by another array was not satisfactory
– However, resolution provided by another array was sufficient
• The calibration was made better, but yet not at desired level
– Did not prevent of having results
• First successful campaign for the prototype with real NPP fuel.
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8x8-1 fuel
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10x10-9 fuel
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Passive gamma emission tomographic
measurements, Loviisa
15-17 Jan 2014
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Work prior the test
• Removing faulty detectors
• Recalibration
• Analysis software development for VVER fuel (BUTE)
– Modified for hexagonal fuel
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Setup
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Fuel
• VVER 440 type fuel is hexagonal
– Full assembly has 126 rods, center location is always empty
– Challenging geometry due to high self-absorption
• One assembly out of 6 had missing rods
• 5 assemblies measured, one twice
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Results
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Assembly with 3 missing rods
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Low-resolution image, noise reduced
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Loviisa Observations
• Measurement of one assembly took 2-3 hours, due to complex
design of the fuel 120 scans were needed (compared 48-60 for
BWR)
• The measurement of the fuel with missing pins was repeated due to
poor statictics
• The system was able to provide image immediately after
measurement
• In overall the system functioned well, two problems were observed:
– A few distorted profiles out of 120 was generated due to HW
malfunction: this is not critical for imaging VVER 440 assembly, they
were left out of analysis.
– Uniformity of measureing channels was not perfect, some corrections
were applied during the analysis
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Summary and future directions
• A Passive Gamma Emission Tomograph has been designed,
manufactured and successfully tested under IAEA support
Programme task JNT 1510.
• System is able to detect missing pin from BWR and VVER-440
assemblies.
• Successful tests with PWR fuel are not yet conducted, but
simulations predict that the result is most likely successful.
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Summary and future directions
• Readiness for deployment and availability for real verifications need
to be sustained
– New project established
• Improvement of the electronic readout is a prerequisite
– Shorten the measurement times
• Next important steps will be to provide unattended operation
• More in depth understanding about analysis is needed
– Quantitatively evaluate the cooling time and burnup for each fuel rod
– Effect of rods with burnable poisons
• Work continues now more intensively
– Goal is to have the functional, reliable and tested system available by
2023, when final disposal of spent nuclear fuel in Finland begins.
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