Status of Recent Detector Deployment(s) at SONGS

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• Status of Recent Detector Deployment(s) at SONGS
• December 14, 2007

Nathaniel Bowden Advanced Detectors
Group Lawrence Livermore National Laboratory
This work was performed under the auspices of the
U.S. Department of Energy by Lawrence Livermore
National Laboratory in part under Contract
W-7405-Eng-48 and in part under Contract
DE-AC52-07NA27344. Sandia is a multiprogram
laboratory operated by Sandia Corporation, a
Lockheed Martin Company,for the United States
Department of Energy under contract
DE-AC04-94AL85000
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Introduction

• Since 2003 a small detector based on Gd loaded
  liquid scintillator has been deployed at a
  commercial plant in the US (SONGS)
• This relatively simple and non-invasive design
  has demonstrated remote and unattended monitoring
  of
• reactor state (power level, trips)
• reactor fuel evolution (burnup)
• Recently, we have been investigating several
  paths to more deployable detectors
• Use of doped water Cerenkov detectors instead of
  scintillator
• Use of less flammable and combustible, more
  robust, plastic scintillator

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Reactors Produce Antineutrinos in Large Quantities

• 6 Antineutrinos are produced by each fission
• Antineutrinos interact so weakly that
• they cannot be shielded,
• but small detectors have useful interaction
  rates
• 0.64 ton detector, 24.5 m from 3.46 GW reactor
  core
• 3800 events/day for a 100 efficient detector
• Rate is sensitive to the isotopic composition of
  the core
• e.g. for a PLWR, antineutrino rate change of
  about 10 through a 500 day PLWR fuel cycle,
  caused by Pu ingrowth

Constant (Geometry, Detector Efficiency Detector
mass)
Fuel composition dependent Sum over fissioning
isotopes, Integral over energy dependent cross
section, energy spectrum, detector efficiency
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The Antineutrino Production Rate varies with
Fissioning Isotope PLWR Example
The energy spectrum and integral rate produced by
each fissioning isotope is different

• The fuel of a PLWR evolves under irradiation
  235U is consumed and
• 239Pu is produced

Energy (MeV)
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Prediction for a PLWR
Non-neutrino background
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LLNL/Sandia Antineutrino Detector SONGS1
(2004-2006)

• Detector system is
• 1 m3 Gd doped liquid scintillator readout by
  8x 8 PMT
• 6-sided water shield
• 5-sided active muon veto

see NIM A 572 (2007) 985
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SONGS Unit 2 Tendon Gallery

• Tendon gallery is ideal location
• Rarely accessed for plant operation
• As close to reactor as you can get while being
  outside containment
• Provides 20 mwe overburden
• 3.4 GWth gt 1021 n / s
• In tendon gallery 1017 n / s per m2
• Around 3800 interactions expected per day ( 10-2
  / s)

25 m
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Short Term monitoring Reactor Scram

• With a one hour integration time, sudden power
  changes can be seen
• In this case, a scram is detected via SPRT with
  99.9 confidence after 5 hours

Manuscript accepted by JAP
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Relative Power Monitoring Precision
Daily average 8 relative uncertaintyin
thermal power estimate (normalized to 30 day
avg.)
Weekly average 3 relative uncertaintyin
thermal power estimate (normalized to 30 day
avg.)
Manuscript accepted by JAP
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SONGS1 Fuel Burnup Measurement

• Removal of 250 kg 239Pu, replacement with 1.5
  tons of fresh 235U fuel

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SONGS1 was very successful, but.

• The liquid scintillator used is somewhat
  flammable, rather combustible, can spill
• LS must be transported as a hazardous material,
  and is transferred onsite into the detector
• With the SONGS1 run completed, we are leveraging
  the installed infrastructure to investigate
  several paths to more deployable detectors
• Use of doped water Cerenkov detectors instead of
  scintillator
• Use of less flammable and combustible, more
  robust, plastic scintillator

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Solid, non-flammable, less combustible, Plastic
detector

• Replace half of liquid scintillator with plastic
  scintillator (PS)
• Must retain neutron capture capability, ideally
  on Gd - commercial neutron capture PS not
  suitable/available (e.g. Boron loaded
  BC-454)
• Final design 2 cm slabs of BC-408 PS,
  interleaved with mylar sheets coated in Gd loaded
  paint

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Such a design is a trade off

• Reactor Operator/ Safeguards Agency
• Reduction in combustible inventory of 40
• No leakage or flammable vapour concerns
• No transportation of hazardous material required
• Preassembled

• Physics
• X Lower neutron capture efficiency on Gd
• (LS 80 / 20 Gd/H
• PS 60 / 40 Gd/H)
• X 10 fewer protons/cc
• X Dead material in main volume

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Design Optimization Gd loading/PS thickness

• Use a Geant4 simulation to explore the effect on
  neutron capture of varying
• Plastic slab thickness
• Gd loading
• Use 2 cm thickness, 20 mg/cm2 loading

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Design Optimization Optical Modeling

• Investigate several readout configurations to
  optimise position uniformity

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Construction
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Installation at SONGS
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Initial Plastic Data

• The plastic detector responds to neutrons in the
  expected fashion neutron captures on Gd are
  observed, as well as correlated (gamma,neutron)
  events from an AmBe neutron source

Response to AmBe neutron source
Correlated events
PRELIMINARY
Response to background at SONGS
Inter-event time
Energy
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Deployment Status
STOP PRESS!

• The plastic detector were successfully inserted
  into the SONGS Unit 2 Tendon Gallery during a two
  week campaign in August
• The removal of liquid scintillator reduced the
  combustible inventory in the gallery by almost
  40
• Neutron captures and correlated events are
  observed
• We use a scheduled reactor outage beginning Nov.
  27 to observe the detector antineutrino
  sensitivity

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Plastic detector outage data
PRELIMINARY
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Plastic detector outage data
PRELIMINARY
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Conclusion

• A robust antineutrino detector based on a large
  volume of commercial plastic scintillator has
  been designed, constructed and deployed
• This device has several important advantages over
  the liquid scintillator that it replaces in a
  commercial reactor environment
• Non-flammable, non-hazardous, and no possibility
  of liquid spillage
• Near complete preassembly is relatively simple
• The device clearly observes reactor
  antineutrinos, i.e. can monitor reactor state
• Forthcoming work will focus on detector stability
  and calibration, with a view to observing fuel
  burnup

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Test of compact steel shielding

• Low density shielding is the bulk of the detector
  volume
• Replace 60cm water shield with 10 cm steel and
  measure
• Change in gamma bkg - should be unchanged
• Change in correlated bkg (antineutrino like) due
  to
• Neutrons not attenuated by the steel
• Neutrons produced in the steel by cosmic ray
  muons

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Steel installation in Jan 07
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Steel results

• We compare detector halves near and far from
  steel wall

• As expected, gamma ray background is unchanged,
  but more neutrons get through, producing more
  correlated background

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Unscheduled SONGS Unit 2 outage

• Unit 2 went down for one week in late October for
  unscheduled maintenance
• Coincidently, wildfires came near the plant a few
  days later!

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Antineutrino Detection

• We use the same antineutrino detection technique
  used to first detect (anti)neutrinos
• ne p g e n
• inverse beta-decay produces a pair of correlated
  events in the detector very effective
  background suppression
• Gd loaded into liquid scintillator captures the
  resulting neutron after a relatively short time

• Positron
• Immediate
• 1- 8 MeV (incl 511 keV gs)
• Neutron
• Delayed (t 28 ms)
• 8 MeV gamma shower
• (200 ms and 2.2 MeV for H capture)

prompt signal n capture on Gd
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Acknowledgements and Project Team
Lawrence Livermore National Laboratory
Alex Misner Prof. Todd Palmer
Nathaniel Bowden (PI) Adam Bernstein Steven
Dazeley Bob Svoboda
David Reyna (PI) Lorraine Sadler Jim Lund
Many thanks to the San Onofre Nuclear Generating
Station