Determining Reactor Neutrino Flux

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Determining Reactor Neutrino Flux

• Jun Cao
• caoj_at_ihep.ac.cn
• Institute of High Energy Physics, CAS, Beijing

Neutrino 2010, Athens, Jun. 14-20, 2010
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Reactor Neutrino Experiments

• The first neutrino observation in 1956 by Reines
  and Cowan.
• Determination of the upper limit of mixing angle
  theta13 to sin22?13lt0.17 (Chooz, Palo Verde)
• The first observation of reactor anti-neutrino
  disappearance at KamLAND in 2003.

• Precision Experiments on theta13 (Daya Bay,
  Double Chooz, RENO)
• ?-electron or ?-nucleus scattering (TEXONO, MUNU,
  GEMMA, CvNS)
• Non-proliferation monitoring (France, US, Russia,
  Japan, Brazil, Italy)
• Possible 60-km baseline experiment

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Reactor Neutrino Flux at a Glance

• Using PWR (Pressurized Water Reactor) as examples
  in the following. (3-4) U-235 enrichment. gt
  95 is U-238.
• Neutrinos from subsequent ?-decays of fission
  fragments.

U-235 depletion
Neutrino spectra, ILL More neutrinos from a
U-235 fission than Pu-239
U-235, U-238 Pu-239, Pu-241
Pu-239 breeding
X
Isotope evolution, Palo Verde
0.1
Visible spectrum, multipled by inverse ?-decay
(IBD) Xsec.
Peak at 4 MeV
Neutrino rate, Palo Verde
Refueling outage Power trips Isotope evolvement
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Neutrino Flux Calculation
E? Neutrino energy fi Fission rate of isotope
i Si(E?) Neutrino energy spectra/f
Neutrino Flux
(fi /F) Fission fraction Wth Reactor thermal
power ei Energy release per fission
Thermal Power Wth
Heat balance test Online calibration
Core configuration Thermal power Operations Temper
ature pressure
Energy release/fission
Core Simulationfi/F
Flux
Spent fuel Non-equilibrium
Spectra of Isotopes Si(E)
Measurements Calculations
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Thermal Power

• KME, thermal power, Secondary Heat Balance
  Method.
• The most accurate measurement.
• Offline measurement, weekly or monthly
• Generally cited with (0.6-0.7) uncertainties in
  literature.
• KIT/KDO, thermal power. Good for analysis.
• Primary Heat Balance
• Online
• Weekly calibrated to KME power.
• RPN, nuclear power
• Ex-core neutron flux monitoring
• Online
• Safety and reactor operation control
• Daily calibrated to KIT/KDO power

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Core Simulation

• Qualified core simulation code is normally
  licensed, not available for scientific
  collaborations.
• Need a lot of information from the power plant as
  inputs, such as configurations, fuel composition,
  operations (control rods movement, Boron
  dilution, etc), inlet temperature, pressure, flow
  rate, etc.
• Fission fractions, as a function of burn-up,
  could be a by-product of the refueling
  calculation, provided by the power plant.

Burn-up is the amount of energy in Mega Watt Days
(MWD) released from unit initial mass (ton) of
Uranium (TU). For small power variation, fission
fraction can be gotten without redoing the
simulation.
Provided by CNPRI
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Spectra of Isotopes

• Lack of data of the ?-decays of the complex
  fission fragments, theoretical calculation on the
  neutrino spectra of isotopes carries large
  uncertainties.
• ILL measured the ? spectra of fissioning of
  U-235, Pu-239, and Pu-241 by thermal neutrons,
  and converted them to neutrino spectra.
  Normalization error 1.9, shape error from 1.34
  at 3 MeV to 9.2 at 8 MeV.
• U-238 relies on theoretical calculation, 10
  uncertainty (P. Vogel et al., PRC24, 1543
  (1981)). Normally U-238 contributes (7-10)
  fissions.

K. Schreckenbach et al. PLB118, 162 (1985) A.A.
Hahn et al. PLB160, 325 (1985)
Shape verified by Bugey-3 data Normalization
improved to 1.6
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Energy Release per Fission

• Slightly varied for different cores due to
  neutron capture. Uncertainties in (0.30-0.47).

Isotopes Energy (MeV)
U-235 201.70.6
U-238 205.00.9
Pu-239 210.00.9
Pu-241 212.41.0
M.F. James, J. Nucl. Energy 23, 517 (1969)
Kopeikin et al, Physics of Atomic Nuclei, Vol.
67, No. 10, 1892 (2004)
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U-238 (n,?) Reaction

• Besides fission products, U-238(n,?)U-239
  reaction contributes to neutrino yield. It is
  below inverse-? decay threshold (1.8 MeV) but it
  is important to low energy neutrino-electron
  scattering experiments (TEXONO, MUNU).

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Non-equilibrium Isotopes

• ILL spectra are derived after 1.5 days exposure
  time. Long-lived fission fragments have not
  reached equilibrium. Contribute only to low
  energy region.
• In Chooz paper it is estimated to be 0.3 and is
  ignored, comparing to other errors.
• Six chains have been identified, with half lives
  from 10h to 28y. (Kopeikin et al.)

Weighted by inverse-? decay Xsec.
Ratio to neutrinos in 2-4 MeV
Ratio to all neutrinos
X.C. Ruan et al. (CIAE)
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Spent Fuel

• Spent fuel stored temporarily adjacent to the
  core, could be up to 10 years.
• Similar to non-equilibrium contributions,
  long-lived fragments in spent fuel will emit
  neutrinos.

Weighted by IBD Xsec.
Contribution from one batch spent fuel It may
accumulate to several percent at 2-3 MeV.
Ratio to neutrinos in 2-4 MeV
Ratio to all neutrinos
top
Day 0 Day 1 Day 2 Day 3 Day 4 Day 5 Day 10 Day
20 Day 30
Energy Spectra
X.C. Ruan et al.
bottom
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Uncertainties from Past Experiments
CHOOZ, Eur. Phys. J. C27, 331 (2003)
Palo Verde, PRD62, 072002
R1.01?2.8(stat) ?2.7(syst)
Parameter Relative error
Neutrinos/fission 1.4
Power, target, distance 1.5
Combined 2.1
Parameter Relative error
Reaction cross section 1.9
Number of protons 0.8
Detection efficiency 1.5
Reactor power 0.7
Energy released per fission 0.6
Combined 2.7
Power contributes 0.7
KamLAND,PRL94081801, 2005.

• Neutrino spectra (1.9 ? 1.6 with Bugey data)
• Inverse ?-decay cross section (0.2)
• Fission fraction fk (5)
• Non-equilibrium fragments (0)

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Power Uncertainties

• Chooz 0.6, Palo Verde 0.7.
• Motivation of power uprates by the power plants ?
  Study the power uncertainties and improve the
  instrumentation.
• Uncertainties of secondary heat balance is
  dominated by the flow rate.
• Venturi flow meter. Most US reactors. Uncertainty
  is often 1.4. It can be as low as 0.7 if
  properly calibrated and maintained, but suffering
  from fouling effects, which could grow as high as
  3 in a few years.
• Orifice plate. France EDF reactors. Typically
  0.72. No fouling effects. Could be improved to
  0.4 with lab tests.
• Note Above flow meter uncertainties are at 95
  C.L. as defined in ISO 5167. Unless specified,
  the thermal power uncertainty given by the power
  plant is also at 95 C.L.
• Ultrasonic. Start to use in some US and Japan
  reactors. Type I TT 0.45, Type II TT 0.2
  (Djurcic et al.)

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An example

• EPRI document prepared by EDF, Improving
  Pressurized Water Reactor Performance Through
  Instrumentation (2006)
• For N4 reactor (Chooz type) with 4 steam
  generators

Empirical formula and uncertainty specified in
ISO 5167-1-2003. Correlated or Uncorrelated for
the 4 flow meters?
Orifice Plate

• If not assuming the discharge coefficients of the
  4 orifice plates are independent, the power
  uncertainty at 68.3 C.L. will be 0.37.

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Another Example

• Daya Bay and Ling Ao reactors (EDF, 2.9GWth) are
  all calibrated with SAPEC system, an EDF portable
  high precision secondary heat balance test system
  with its own sensors, databases, and data
  processing, of uncertainty 0.45. Ling Ao KME is
  predicted to have an uncertainty of 0.48 (95
  C.L.)
• 4 tests on Ling Ao KME show differences from
  0.031 to 0.065. Why?
• Used the same orifice plates but different
  pressure transmitters.
• It proves that the uncertainty is dominated by
  discharge coefficient.
• Ling Ao KME is in very good agreement with SAPEC.

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Uncertainties of fission fraction

• Depends on the simulation code. Only slightly on
  the inputs (has not been checked on other
  simulation code.)
• Compare measured and calculated concentration of
  fuel isotopes, sampled at different burn-up. Part
  of the qualification of the code.

One analysis of Apollo 2.5
Lester Miller thesis, ROCS
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Uncertainties of fission fraction

• Djurcic et al. collected 159 analyses for various
  codes and various reactors in US and Japan. In
  average, the simulated concentration of isotopes
  have uncertainties
• U235 4
• Pu-239 5
• U-238 0.1
• Pu-241 6

Djurcic et al. J. Phys. G Nucl. Part. Phys. 36
(2009) 045002

• Assuming the neutron flux in simulation isnt
  affected by the small variations, fission rate ?
  concentration.
• Due to the constraint of the total power, 5
  error on simulated isotope concentrations
  corresponds to 0.5 uncertainty on the detected
  ? rate via IBD reaction.

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IBD Event Rate Uncertainties

• Greatly simplified calculation of IBD rate
  uncertainties.
• Single reactor single detector

• ?W thermal power 0.4 (1 sigma),
• ?f average uncertainties due to 5 fission
  fraction uncertainty 0.5
• ?e average energy release per fission 0.4
• ?s spectra normalization 1.92. Assuming U-238
  contribute 8.
• ?c IBD cross section 0.2
• Single detector two reactors (equal distance)

• Near-far detectors multiple reactors. All
  correlated errors (common to all reactors) will
  cancel out. Uncorrelated errors will reduce
  depending on the configuration, e.g. to 0.05.

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Summary

• Before 80s, the reactor neutrino flux
  uncertainties 10.
• With a lot of efforts, especially by ILL, Bugey,
  Chooz, Palo Verde etc., it is improved to 2-3.
• More accurate thermal power, and more detailed
  study on errors.
• A global picture of uncertainties of fission rate
  from core simulation.
• Small corrections from spent fuel and
  non-equilibrium contributions.
• No new data for neutrino spectra of fuel
  isotopes, which is dominant for a single detector
  experiment. Thus for single detector experiments,
  it is still 2.
• Next theta13 experiments with near-far relative
  measurements will suffer little from reactor flux
  uncertainties (0.1), while complex correlation
  analysis should be done.

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• Thanks!

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Non-proliferation Monitoring

• Bowden, LLNL, 2008