Update on the Next Generation Safeguards Initiative’s Spent Fuel Project with Emphasis
on Differential Die-Away Research
T. Martinik1, 2, S.J. Tobin1,2, 3, S. Grape1, A. Håkansson1, P. Jansson1, S. Jacobsson-Svärd1
1Uppsala University, 2Los Alamos National Laboratory, 3Representing the Research of 7 U.S. National Laboratories, 11
Universities and 3 Spent Fuel Assembly Measurement Collaborators
Purpose/Goals of this NGSI Spent Fuel Project?
General purpose: strengthening the technical toolkit of safeguard inspectors
Technical goals have evolved:
1. Determine heat emitted from assembly
2. Improve the capability to detect diversion or replacement of pins
3. Estimate initial enrichment, burn-up and cooling time
4. Estimate Pu mass in spent fuel
Time-line of NGSI Spent Fuel Project
Phase I: Primarily Simulations
• Libraries of spent fuel assemblies
• Monte-Carlo (MCNP) simulation of response from 14 NDA technique with wide range of spent fuel libraries
Phase II: Prioritization for Development
• Down-select for promising, near-term (5 yrs) deployable systems
Phase III: Measurements
• Integrate complementary techniques into a few systems
• Deploy a few proof-of-principle/prototype instruments
Before entering a reactor:
• Only three isotopes of note: 235U, 238U and 16O
In the reactor, in a very high neutron flux:
• Many reactions take place creating many isotopes in a relatively short period of time: • Induced fission creating many fission products (gamma sources
and neutron absorbers)
• Neutron capture and beta decay create many actinides (strong neutron sources and neutron absorbers)
After reactor, complex “isotopic soup” decays, each isotope with its own characteristic time dependence and isotopic chains
High level description of commercial fuel assembles
Theme: the isotopic composition is complex but it is driven by a few parameters: IE, BU and CT
General thoughts on the utility of NDA signal integration, Swedish context
Passive Gamma (primarily from the outer two rows)
• 137Cs, f(BU, CT) but not of IE, indicative of heat, t1/2= 30. y
• 154Eu, f(BU, IE, CT), t1/2= 8.6 y
Total Neutron (somewhat uniform sensitivity to each pin)
• For most spent fuel of interest to safeguards, 244Cm (t1/2= 18. y) dominant origin of neutrons, but recall M ~2 for SFA
• Very strong function of BU, (BU3 or 4)
These signals used by Fork, Enhanced Fork and SMOPY detectors … with useful, but limited utility
General thoughts on the utility of NDA signal integration, Swedish context
Differential Die-Away Self-Interrogation (DDSI)
• Signal of interest is the time-correlated neutrons relative to every detected neutron (as much as 1 G byte/s of data)
• Spatial sensitivity is rather uniform, signal is propagated through neutron chain reactions
• The time behavior of correlated neutrons depend on all the factors that impact multiplication (fissile material, neutron absorbers, moderation, geometry, etc.). Hence the DDSI signal is sensitive to the cumulative effect of a range of isotopes in the fuel.
Differential Die-Away (DDA)
• Tomas Martinik of Uppsala University will explain in more detail • Introduction: rich data obtained by measuring how a burst of
neutrons changes in time and space in the assembly
Conceptual depiction of how we are performing integration
• To verify parameters of SFA: Initial enrichment (IE), Burn-up (BU), Cooling time (CT), fissile content , total Plutonium mass;
• External neutron pulse -> induce fission in SFA -> fission neutrons detected in 3He Differential Die-Away (DDA):
• Based on difference between 2 main groups of neutrons: BURST: 14.1 MeV external source, detected with die away time = 45us; FISSION: induced by thermalized burst neutrons, die away time = 100-200 us;
By V. Henzl
DDA method + instrument
H2O
Stainless steal
Tungsten
Neutron generator
Lead
Cd lined polyethylene with 3He tubes
By P. Blanc
Front Detectors
Back Detectors
15 GWd/tU
30 GWd/tU
45 GWd/tU
60 GWd/tU
2% 3% 4% 5% Cooling time
• 1 year • 5 years • 20 years • 80 years
By V. Henzl
Initial Enrichment, Burn-up and Cooling time measurement
possibility
Recent goals of investigation: • To see if asymmetric BU effects
detector count rate when measured for different orientation of SFA => effect on IE, BU,CT, total Pu,… ?
• Crucial question: Do we need to measure from all 4 sides ?
Various different SFA:
• # SFA: 34 assemblies • IE: 2,3,4 [%] • BU: 15,30,45 [GWd/tU] • CT: 1,5,20,80 [y]
Various types of asymmetry : • ”STANDARD” • ” EXTREME”
Asymmetric Burn-up
Signal change for different fuel assembly orientation
• Front detectors: Signal dependent on orientation (higher/lower burn-up), neutrons penetrate mostly through the corner of SFA: Different multiplication -> thus signal changes +/- 4 %
• Back Detectors: No significant changes –> independent on orientation • Total Signal: Sum of Front and Back; within the range of +/- 1.5 %
• Investigate in detail how the signal change effects IE, BU, CT, fissile content, total
Plutonium determination • Instrument Simplification: effect of removing heavy parts: Lead, Stainless steel;
using Cd liner, different detectors(fission chambers),… • Design this Instrument to be applicable for testing measurement campaigns in
CLAB and in future inside the encapsulation facility
By N. Lundkvist
H2O
Stainless steal
Tungsten
Neutron generator
Lead
Cd lined polyethylene with fission chamber tubes
Cd lined polyethylene with 3He tubes
Nearest Future plans:
Questions? Comments?
Detected Passive Active
Neutron Total Neutron 252Cf Interrogation with Prompt Neutron
Passive Neutron Albedo Reactivity Differential Die-Away
Self-integration Neutron Resonance Densitometry
Delayed Neutrons
Differential Die-Away Self-Interrogation Lead Slowing Down Spectrometer
Neutron Coincidence Neutron Resonance Transmission Analysis
Gamma Passive Gamma Delayed Gamma
Nuclear Resonance Fluorescence
X-Ray X-Ray Fluorescence
The response of 14 NDA Techniques Were Simulated for 64 Assemblies
What is the State-of-the-Practice in Spent Fuel NDA?
– Cerenkov Viewing Device (ICVD, DCVD) – Detects Cerenkov glow from water around assembly
– Spent Fuel Attribute Tester (SFAT)
– 137Cs is present
– FORK
– Fission chambers → total neutron (driven by 244Cm)
– Ion chambers and CdTe → fission fragment gammas
FORK Detector
PWR Assembly
Channel System LLC
SFAT IAEA
DCVD Cerenkov Image
The ease of use of these instruments was an important feature in their selection by inspectorates. Yet,
