(738d) Real-Time Actinide Monitoring with Tensioned Metastable Fluid Detectors for Enhanced Safeguards and Security in Spent Nuclear Fuel Chemical Reprocessing Facilities

Introduction

It has previously been demonstrated that
tensioned metastable fluid detectors (TMFDs) offer a variety of unique
mechanisms for detecting alpha and neutron radiation while remaining
selectively insensitive to gamma photons and beta decay [1,2]. This paper will
discuss some of the capabilities of TMFD systems and how they can be utilized for
enhancing safeguards and security in spent nuclear fuel (SNF) chemical reprocessing
facilities. 

The TMFD technology is based on the
principle of radiation seeded cavity nucleation and growth to audible-visible
levels in tensioned metastable state liquids. 
When a nuclear particle interaction occurs in a sufficiently tensioned
liquid, rapid vaporization results in a visible bubble and an audible
mechanical shock [3]. The phenomenon is similar to bubble chambers and superheated
droplet detectors but in this case the metastability in the liquid is created
with tension (sub-vacuum pressures at room temperature) instead of thermal
superheat.

Two particular TMFD device
configurations have been developed for application to a variety at radiation
detection scenarios.  The first is the centrifugally
tensioned metastable fluid detector (CTMFD), which uses the centrifugal force
principle - created in a specialized rotating enclosure to create the tension
needed to detect nuclear particles.  By suitably
tailoring the liquid's metastable state, the as-desired sensitivity to energy
and signature of radiation particle can be controlled. The second device is the
acoustically tensioned metastable fluid detector (ATMFD), which uses resonance-mode
focused acoustic waves in the liquid (much like in a laser cavity) to induce oscillatory
compression-tension states.  Like for the
CTMFD, the ATMFD also offers the capability for energy and particle sensitivity
selection based by tailoring of the micro-second timed spatially-variant acoustic
wave fields [4].

Applications of
TMFD Technology to Spent Nuclear Fuel Chemical Reprocessing Plants

The
application of TMFDs for providing real-time monitoring of neutron and alpha
radiation emitting special nuclear materials (SNMs) like U, Pu, Np and Cm is discussed in sub-sections that follow:

SNM
alpha spectroscopy

The TMFD systems have been found capable
of radiation energy discrimination capabilities.  Unlike many traditional radiation detectors
which rely on electrical signal height or pulse shape discrimination, the TMFD
uses the inherently unique mechanics of its detection technique to offer
transformational spectroscopic capability. 
Various isotopes of SNMs such as Pu-239, Pu-238, Am-241, and Cm-242 emit
alpha radiation at distinct energies, the detection of which provides for the
tell-tale sign for their presence (or diversion). The detection mechanism in
the TMFD is threshold-based meaning under chosen conditions particles
depositing at or above the selected energy are detected while others are not ?
while also remaining unfettered by the presence of ?nuisance? radiation such as
beta-gamma emission.  Straightforwardly,
the amount of mechanical tension or negative pressure (Pneg)
that a liquid is placed will determine the specific energy of alpha radiation particles
it is sensitive to. 

Detection of alpha decay from actinides
and spectroscopy has been systematically demonstrated in the CTMFD by
dissolving known quantities of specific actinides into the detector fluid and
recording the detector response with Pneg.  Calibration has been done with several NIST
certified single isotope transuranic actinide solutions [5].  After doing these calibrations, it was not
only found that the difference in energy between the actinide elements was
easily detectable but also that the difference in energy between individual
isotopes of the same element could be detected.

Several applications of CTMFD based
alpha monitoring and spectroscopy in a UREX or PUREX SNF
chemical reprocessing facility are under study using a build-in protocol.  First, since Uranium exhibits the lowest
energy alphas of the actinides in the UREX process, it is easily ignored in
scenarios where there is no interest in the Uranium concentration.  Also, the ability to ignore uranium alphas
could allow for detection of unwanted transuranic extraction during the UREX
phase.

Since the Cm isotopes emit the highest
energy (~6MeV) alphas amongst the actinides of interest, they are the first to
detect.  By setting the CTMFD to be
sensitive to only Cm, the unwanted extraction of Cm prior to the TRUEX process
can be monitored in real-time.  Very
small quantities of actinides can be detected in the CTMFD.  The CTMFD has been shown to be sensitive to
quantities below 1 part per million for Uranium-238 and below 10 parts per
quadrillion for Pu-238.

Another key application of CTMFD based
alpha spectroscopy is for Pu isotopes monitoring.  Since the alpha energies of Pu are higher
than that of Np, the quantity of Pu in the NPEX
product stream can be determined.  Plutonium
would also be detectable in the UREX and CCD-PEG products if it were present
therein, unexpectedly.  Some
experimentation has also been done to measure the ratio of Pu-238 to
Pu-239.  Detection of mixtures of Pu-238:Pu-239 in ratios of 1:1, 2:1, and 3:1 have been
successfully conducted.

Active
Detection of Fissionable/Fissile Material

In many scenarios, it may be desirable
to monitor the location of fissionable/fissile materials in a reprocessing
facility without removing samples. 
Active interrogation offers non-destructive assay if the interrogating
radiation can be discriminated.  The
ATMFD's energy discrimination capabilities allow for lower energy particles
from an active interrogation source to be ignored while detecting higher energy
fission neutrons if fissionable material is present.  Simulations have been conducted using the
Monte Carlo nuclear particle transport code MCNP-PoliMi to predict the utility
of the ATMFD in active detection of fissionable material in a reprocessing
facility. 

The ATMFD has been modeled in
MCNP-PoliMi along with a representative 5cm diameter pipe filed with the UREX
feed liquid from a PWR with 3% enriched fuel with 33GW-day/MTU burnup [6]. The scenario was modeled as one of many example
applications of this technique.  Two
active interrogation sources were considered. 
The first was a 2.45 MeV D-D fusion neutron source and the other a 60
keV neutron source [7].  For active
interrogation to work, the ATMFD must be set to avoid detection of the source
particles.  This is accomplished by
lowering the acoustic drive power so that the detector is not sensitive to the
source neutrons. 

The simulations offer insight that using
a modest intensity interrogating neutron source of, ~ 10⁸ neutrons
per second, that fissionable material in a reprocessing facility should be
detectable [6].  For example, if the
interrogating neutron source is a D-D accelerator emitting 2.45 MeV neutrons,
the TMFD will be sensitive only to fission-induced neutrons above 2.45 MeV.  The same scenario utilizing a 60 keV source
would allow for detection of only fissile (vs
fissionable) material which could then be used to monitor the movement of
potential weapons grade SNMs with specificity, while ignoring many of the other
actinides which may not be of interest.        

Directional
Neutron Monitoring

Past research work by our group has
shown that the ATMFD is not only capable of detecting the presence of neutrons
while remaining completely insensitive to intense gamma fields (>10²³
g/cc/sec) [2] but also be capable of detecting directionality of incident neutrons
from SNMs [1].  Directional neutron
detectors offer vastly superior background suppression when compared to
traditional neutron detectors (e.g. He³, BF₃), and the
ability to image the neutron source directly. 
An ability which would be particularly advantageous in both passive
interrogation scenarios where one needs to discriminate neutrons originating
from a single targeted location and active interrogation scenarios where one
needs to discriminate interrogating neutrons (or photons) from neutrons
resulting from the fission of the targeted material.  Assessments have been conducted utilizing
MCNP-PoliMi to investigate the possibility of employing the direction-position
sensing capabilities of the ATMFD system to indicate the presence and location
of neutron emitting isotopes in various stages of SNF fuel chemical reprocessing
plant.

The
full paper and presentation will provide details of theoretical and
experimental assessments.

References

1. Archambault, B. A., J. A. Webster, J. R. Lapinskas, T. F. Grimes, R. P. Taleyarkhan and A. Eghlima, "Transformational Nuclear Sensors - Real-Time Monitoring of WMDs, Risk Assessment & Response," IEEE 978-1-4244-6056-5/10, pp.421-427, 2010.

2. Sansone, A., S. Zielinski, J. A. Webster, J. Lapinskas, R. P. Taleyarkhan and R. C. Block, "Gamma-Blind Nuclear Particle-Induced Bubble Formation in Tensioned Metastable Fluids," Transactions of the American Nuclear Society, Vol. 104, pp. 1033, Hollywood, Florida, June 26-30, 2011.

3. Taleyarkhan, R. P., C. D. West, and J. Cho, "Energetics of Nano-to-Macro Scale Triggered Metastable Fluids," Oak Ridge National Laboratory Report ORNL/TM-2022/233, 2022.

4. Lapinskas, J., et al., "Towards leap-ahead advances in radiation detection," Proceedings of the 16th International Conference on Nuclear Engineering (ICONE-16), Orlando, Florida, 2008.

5. Lapinskas, J., S. Zielinski, J. A. Webster, R. P. Taleyarkhan, S. McDeavitt, Y. Xu, "Tension metastable fluid detection systems for special nuclear material detection and monitoring," Nuclear Engineering and Design, 240, pp. 2866-2871, 2010.

6. Webster, J. A., R. P. Taleyarkhan, "Tensioned Metastable Fluid Detectors in Nuclear Security for Active Interrogation of Special Nuclear Materials - Part B," World Journal of Nuclear Science and Technology, Vol. I, pp. 66-76, 2011.

7. Hagmann, C. A., et al., "Active Detection of Shielded SNM With 60-keV Neutrons," IEEE Transactions on Nuclear Science. Vol. 56, pp. 1215-1217, 2009.