Passive gamma emission tomography PGET Tapani Honkamaa SÄTEILYTURVAKESKUS

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Passive gamma emission tomography (PGET) Tapani Honkamaa SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Contents • • Introduction Description of the method Motivation Project history and timeline Prototype Hardware Prototype Software Results from the test campaigns Summary and future directions SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

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 – – – Hungary, Sweden USA, Finland EC SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Description of the method rotation fuel assembly scanned section scanning direction SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

And with more detectors arranged in 2 heads: Head 1 Head 2 104 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 2 mm resolution. SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Geometry Head 1 Head 2 104 detectors Cd. Tl 2 x 5 x 10 mm Main signal: 1274 ke. V Fission product Eu-154 Gamma-ray -compton edge. Tungsten collimator Housing Requirement: imaging of Spent nuclear fuel assembly PWR type 17 x 17 rods in rectangular lattice Resulting to the need 2 heads, 104 detectors in each, detector spacing 4 mm, resulting in 2 mm overall resolution. SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Data production and imaging Fuel Assembly Cross sectional image of fuel assembly SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY 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 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

About nuclear material safeguards SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Goal of Nuclear Material Safeguards – Never again Picture: Charles Levy, 9 th of Aug 1945 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

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 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

…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 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

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. SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Final disposal of spent nuclear fuel SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Construction project of PGET prototype SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Project timeline 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Loviisa 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 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

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. SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

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 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

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 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Passive gamma emission tomographic measurements, Ringhals 16 -20 Nov 2009 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Ringhals tests • Detector failure prevented the measurements • Overheating of one ASIC (each head consists of 4 ASICs, each controlling 26 detectors (4 x 26=104) • Grounding issues: Stepping motor rotating 2 x 150 kg arrays takes a lots of Amperes. • Repair took a few months, then recalibrations, putting things together, combating against grounding problems, etc. SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Ringhals 16 -20 Nov 2009 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Passive gamma emission tomographic measurements, Ispra 11 -15 Jul 2012 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Ispra 11 -15 Jul, 2012 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Measured objects, results • • 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. SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

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. SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Passive gamma emission tomographic measurements, Olkiluoto BWR 15 -17 Mar 2013 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Measured objects, results • • The fuel items were 8 x 8 and 10 x 10 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. SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

8 x 8 -1 fuel SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

10 x 10 -9 fuel SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Passive gamma emission tomographic measurements, Loviisa 15 -17 Jan 2014 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Work prior the test • Removing faulty detectors • Recalibration • Analysis software development for VVER fuel (BUTE) – Modified for hexagonal fuel SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Setup SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

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 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Results SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Assembly with 3 missing rods SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

Low-resolution image, noise reduced SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

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 SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

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. SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

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. SÄTEILYTURVAKESKUS • STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY