Reactor Neutrinos

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Reactor Neutrinos
n
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Lecture 1 Nuclear Reactors, Neutrino
Production and Detection Lecture 2 Results
from Neutrino Experiments and Future Experiments
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n?
The Mysterious Neutrino

• 1956 Reines and Cowan detect neutrinos coming
  from the core of a nuclear reactor
• 1962 multiple types
• Nothing more until neutrino oscillations
  confirmed in 1990s!

n!
4
g
_
511 keV
Eion
n
e
e
e-
Prompt
p
p
g
511 keV
n

g
n
2.2 MeV
p
200 ms
Delayed
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Energetics
mpc2 En mnc2 Ee Kn Ee En (DH
mec2) Dn Kn Ke En - 0.782 MeV 2mec2
Kn En 1.804 MeV (Kn is small)
DH 7289 keV Dn 8071 keV
Why?
annihilation energy
Eprompt Ke 2mec2
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A Mirror of the Neutrino Spectrum

• Eprompt En - 0.78 MeV Kn
• Prompt energy spectrum is close
• to being original neutrino spectrum
• convoluted with the cross section!

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Can actually see a neutrino oscillation in
reactor neutrino prompt energy spectrum
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This technique was first used by Reines and Cowan
still a great way to catch ns
big detector
Project Poltergeist
big people
Chooz Experiment
small people
small detector
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Current Experiments Using This Technique

• KamLAND (running)
• San Onofre (running)
• Double Chooz (under construction)
• Daya Bay (planned)
• RENO (planned)

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There are other techniques also
ne e- g ne e-
MUNU TEXONO
(magnetic moment experiments)
ne N g ne N
Chicago, LLNL, Taiwan,
(coherent scattering experiments)
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Why Reactor Neutrinos?

• Low Energy
• Large Cross Section of antineutrinos on
  protons
• High Flux
• Free!
• Lots of Sites

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Low Energy, Large Cross Section, High Flux
Rule of thumb 100 events /day/ton at 100
meters from typical power plant
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Free Antineutrino Sources of the World
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Why do reactors make antineutrinos?
235U n g X1 X2 2n 200 MeV
Fission fragments
40Zr94
58Ce140
Now 98 protons and 136 neutrons Before 92
protons And 142 neutrons
6 ns per fission
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These come from conversion of neutrons to protons
via beta decay of fission fragments and their
daughters, not from the fission directly.
ZXN g Z1YN-1 e- ne
Only about 25 of these antineutrinos are above
the 1.8 MeV threshold This spectrum can be time
dependent as the beta daughters come into
equilibrium
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Fortunately, the 1.8 MeV threshold ensures that
only large Q-value (and hence short half-life)
decays are observed. Typical time to
equilibrium is a few hours Spent fuel ponds
typically add lt0.1 due to long half life and low
Q But there are other time-dependent effects
(will discuss later)
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Types of Reactors

• Pressurized Light Water Reactor (PWR)
• Boiling Water Reactor (BWR)
• CANDU
• Naval
• Research
• Weapons Production
• New Technology

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Pressurized Light Water
(most common type)
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Advantages/Disadvantages

• Water in core does not boil. Keeps moderator
  density constant and avoids corrosion problems of
  fuel assemblies
• Fission products leaking into coolant are
  well-contained
• Negative temperature feedback
• Possibility of cold water incursion
• Efficiency of heat exchanger

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Inside the Core
Fuel assembly containing UO2 pellets enriched to
a few 235-U
Water Moderator Control Rods Fuel
Assemblies Periodic changeout
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Fission in a Standard PWR
235U nth g X1 X2 2nfast
but also 239Pu, 241Pu, and 238U others
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Plutonium Production
238U n g 239U g 9
239Np e n (23.45 m)
9 239Pu e n (2.36 d) 239Pu n g
240Pu g 240Pu n g 241Pu g
Note 238U and 240Pu have small cross
sections for fast fission. Thus, the content of
nuclear fuel changes with time as the reactor
core evolves.
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l burnup of 235U
j buildup of 239Pu
This will affect the neutrino rate and spectrum.
Important for most modern precision experiments.
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Burnup
evolving fuel composition changes
neutrino interaction rate downward due to in
growth of 239-Pu This may someday be useful
for analyzing fuel composition
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An aside
Pu-239 can be used to make nuclear
weapons. Easier to extract chemically than to try
and isotopically separate uranium. Pu-240 is
undesirable due to smaller fission cross section
and relatively large branching ratio to
spontaneous fission. Pu-240 content lt 7
weapons grade gt 20
reactor grade
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• To make lots of 239-Pu while reducing the
  content of 240-Pu one needs to have lots of 238-U
  fertile fuel and a short refueling cycle. Heavy
  water helps.
• Commercial PWR usually have enriched 235-U and
  strive for long refueling cycles
• PWR fuel a few 235-U. Weapons usually gt90
  enriched.
• Countries making nuclear weapons usually do so
  with a dedicated facility.

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Fast Breeder Reactors
Can be used to optimize conversion of 238-U to
249-Pu. 238-U blanket Fast fission
contribution is significant France, India,
Russia, Japan, (China)
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Other Reactor Types
Boiling Water
Naval
Similar neutrino spectrum as PWR BWR has slightly
different isotopic composition Naval has highly
enriched 235-U fuel
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Weapons
TRIGA
He added into fuel assemblies to make hot
neutrons. This makes them inherently incapable of
meltdown from removal of control rods. lt16 MW
Heavy Water, Non-Enriched Fuel, fast refueling
cycle. Typically lt1 GW. Neutrino experiments have
been done at such facilities!
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CANDU
Uses heavy water and non-enriched uranium
fuel No need for enrichment facilities continuo
us refueling without shutting down
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The Future Thorium?
Tons of 232-Th (USGS)

• 232-Th is also fertile
• produces 233-U
• 232-Th is loaded into an existing 235-U fueled
  reactor
• There is lots of 232-Th around as compared to
  235-U

• 360,000 INDIA
• 300,000 AUSTRALIA
• 170,000 NORWAY
• 160,000 USA
• 100,000 CANADA
• 35,000 S.AFRICA
• 16,000 BRAZIL
• 95,000 ALL OTHERS

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What is the spectrum of antineutrinos from a
reactor?

• Put very high purity isotopes into a nuclear
  reactor and cook to equilibrium
• Remove quickly and put into a beta spectrometer
• Measure combined beta spectrum off all the
  decaying fission products
• Convert beta spectra into neutrino spectra

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The beta spectrometer must have known absolute
acceptance as a function of energy Short-lived
(and hence High Q-value) isotopes will be
systematically shifted to lower abundance. This
implies increasing uncertainty at high energy.
Hahn, et al PLB (1985)
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Other problems

• Only about 75 of the observed total spectrum
  have been identified with known beta decay
  isotopes
• To fill out the spectrum, assume a constant
  Q-value/MeV density and use spectral shape of
  allowed decays.
• dY/dEe n(Q,Z)k(Q,Z)peEe(Q-Ee)2F(Ee,Z)
• Taking spectrometer and conversion errors into
  account, the neutrinos per fission spectrum for
  235-U, 239-Pu, and 241-Pu are known to 4.5 at
  low energy (2-5 MeV), increasing to as much as
  50 at 9 MeV (mostly from statistics)

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Resultant Spectra
Note 238-U has not been measured. Result shown
here is a calculation from Vogel (1981).
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Fortunately, 238-U contributes only 8 for a
typical PWR
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Conversion of Thermal Power to Neutrino Flux
Isotope Efission Eeff 235-U 202.79(6) 193.37
(33) 238-U 205.93(13) 194.60(81) 239-Pu 207.32(
8) 199.80(28) 241-Pu 211.04(12) 202.04(32)
Eeff Efission En Ebg (Kopeikin, et al
2004)
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Typical Nuclear Generating Station
Chooz-B PWR Type N-4 4.27 GW (Thermal)
How well is this known? h
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Thermal Power Measurement

• Nuclear Instruments (NIs) purpose is mainly for
  speed of response in safety context not
  typically used for accurate power measurement
• Main Coolant Loop Calorimetry (typically this is
  not the most accurate)
• Secondary Loop Calorimetry

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Secondary Loop
Main Steam Header
Rx TH
Reactor power MCP thermal input Pz heaters
thermal losses
SG
Rx TC
from condenser
SG blowdown
MFP
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Secondary Loop Calorimetry
mmshmsmbdhbd-mfwhfw PSG
mmsmbdmfw
h is specific enthalpy from steam tables e
p/r for a constant pressure process the
energy transferred is equal to the change in
enthalpy
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Typical Uncertainties

• Thermal Power can be known with a precision less
  than 1, and with some effort down to 0.5
• This is very important to maintain to plant
  within the safe operating envelope
• Also important for neutrino physicists!

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Cross Section
2p2 Enpn

• 9.52 (Enpv/1 MeV2) x 10-44
• cm2

s
tn fp.s. m5
j Why?
m electron mass f phase space
factor 1.7152 tn neutron
lifetime h/2p 1 c 1
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summary

• we have a worldwide network of intense
  antineutrino sources
• we understand the flux and spectrum to about 4
  (or 2 with empirical normalization from
  precision neutrino experiments)
• there is a large charged current cross section
  with a threshold of 1.8 MeV. We understand this
  to the level of 0.1
• detectors are not expensive, and the neutrinos
  are given away for free!