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Thermal Power with Neutrinos
Motivation - Principle Absolute and relative accuracy Mini-detectors, running exp and projects. David Lhuillier, CEA-Saclay CEA - Saclay
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Motivations Standard power measurements:
n counters: very large dynamic, high sensitivity to relative changes. But flux distortions lead to complex translation into Pth number. Heat evacuated by coolant: depends on flow profile and turbulences. Pth/Pth? Getting an argued answer turns out to be a challenge (or maybe Michel didn’t try hard enough, he contacted only 12 potential speakers)... Neutrino approach: very complementary, mostly independent syst errors. Interest for absolute measurement and low frequency remote monitoring using simple and low cost detectors. Prototype of ~1m3 mini-detector to establish achievable precision. David Lhuillier, CEA-Saclay CEA - Saclay
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Leading Order Approach
Fission of 235U 235U Z=N Z N 36 56 Fission products evolve toward stability via decay chains Rb 37 92 38 Sr e (no threshold) David Lhuillier, CEA-Saclay CEA - Saclay
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Leading Order Approach
ocsillate: P(ee) = P(E,L) But no significant flux distortion with E= few MeV and L = few 10m Kamland, PRL 90 (2003) Sensitive to weak interaction only, almost no int. with matter≤10-17 barn Reactor core spectrum flux = direct image of Pth David Lhuillier, CEA-Saclay CEA - Saclay
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Eprompt = E-Mn-Mp+me
e Detection e + p e+ + n inverse process: Prompt e+ signal Eprompt = E-Mn-Mp+me & Threshold: Mn -Mp + Me = 1.8 MeV Delayed n capture after thermalization David Lhuillier, CEA-Saclay CEA - Saclay
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e Detection Huge flux compensate tiny cross section.
int. rate 1.8 MeV threshold Huge flux compensate tiny cross section. Miniature detector very close to reactor core can reach pretty high counting rate: ( det = 50%) 1t 25m of 1GWe reactor 1% stat on total flux within 5.5 days David Lhuillier, CEA-Saclay CEA - Saclay
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Going to NLO Fuel burn-up: David Lhuillier, CEA-Saclay CEA - Saclay
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Fissile Isotopes spectra
Fission fragments from 239Pu heavier in the light hump 235U 239Pu A corresponding energy spectra are different David Lhuillier, CEA-Saclay CEA - Saclay
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Fissile Isotopes spectra
All curves normalized to same number of fissions 235U 239Pu E / fission 201.7 MeV 210.0 MeV < E> (E>1.8 MeV) 2.94 MeV 2.84 MeV / fission (E>1.8 MeV) 1.92 1.45 < int > ≈ cm2 ≈ cm2 For a constant Pth, the of neutrino flux from pure 235U would be 1.6 times larger than the one from pure 239Pu ! David Lhuillier, CEA-Saclay CEA - Saclay
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Fractional # of fission
e flux vs Time Fractional # of fission Time 235U 238U 239Pu 241Pu 70% 6% 20% 4% 1 year 49% 40% 5% 1 year cycle of a PWR Pe = 0.9 GW 1/3 fresh fuel, 1/3 one year old, 1/3 two years old Pth = cst ! 10% (only) decrease over 1 year Depends on fuel history, detection thresholds & resol. k(t) independent of Pth for a given reactor (?) Normalized to T=1day 35% constant E resolution David Lhuillier, CEA-Saclay CEA - Saclay
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e spectrum shape vs Time
Set clever cuts and weights to reduce (Pth) or enhance (non-prolif) sensitivity to burn-up? Margin reduced by stat loss at high E and background at low E. Get isotopic composition and then Pth from energy shape only? Does current knowledge of e energy spectra allow to get rid of fuel history? David Lhuillier, CEA-Saclay CEA - Saclay
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Integral Measurements @ ILL
K. Schreckenbach et al. Phys. Lett. B160 (1985) 325. e- High resolution spectrometer Reference for previous reactor experiments +3% norm. error e- Target foil (235U, 239Pu, 241Pu) in thermal n flux Stotal = S235U + S239PU + S241PU + …S238U Spectra assumed to be at equilibrium after 1 day of irradiation Possible check of deviation from equilibrium and improvement of e- conversion procedure using detailed simulation. (see M. Fallot’s talk) ILL research reactor (Grenoble, France) David Lhuillier, CEA-Saclay CEA - Saclay
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Stand Alone Measurement
Fuel composition assumed constant during data taking and extracted only from shape of total spectrum. Almost perfect detector. P. Huber & T. Schwetz, Phys .Rev. D70, (2004). <N/fission ~ 3% Left with det. uncert. det,mtarget, … (optimistic here, let’s make it 2%) Infinite statistic asymptotes: Absolute norm. of spectra: 50 kg of Pu! 1 error # of e events David Lhuillier, CEA-Saclay CEA - Saclay
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Stand Alone Measurement
Best absolute accuracy currently achievable ~3% Already useful to electricity companies? (let me know…) Is Nevt>105 mandatory? No! : input of fuel composition, even with few % accuracy, improves a lot the above stat convergence. Same power accuracy asymptote can then be reached within few days. David Lhuillier, CEA-Saclay CEA - Saclay
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Improve Absolute Accuracy (?)
Dominant error ~3% Controlled at <% level <N>/fission + det x mtg x effects <Ereleased>/fission ∫N ∫Nfission Pth Measure ∫ Nxdet x mtg over full 50 days cycle(s), with virtually pure 235U spectrum. Chemical analysis or spectroscopy of removed fuel could provide Nfissions at 2% level? Would shunt all complex stuff about n flux evolution and fission. Non negligible experimental effort but 1% improvement on Pth could be a big deal… Calibration measurement at research reactor, e.g. ILL-Grenoble: David Lhuillier, CEA-Saclay CEA - Saclay
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Monitoring All correlated errors cancel out
Dominated by “effective” statistical convergence after cuts and background subtraction Looks promising: 1% stat should be achievable within few 25m from Pth>1GW reactor. Comparable or higher accuracy already provided by other methods but provide a remote non-intrusive monitoring with limited knowledge of fuel evolution. “Portable” mini-detector could cross-calibrate different reactors, possibly of different types. Ultimately limited by control of background and detector stability. New! David Lhuillier, CEA-Saclay CEA - Saclay
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Miniature Detectors David Lhuillier, CEA-Saclay CEA - Saclay
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PWR Rovno reactor (Russia) ~1m3 of mineral oil + 0.5 g/l Gd
Kurchatov’s Pioneers (see V. Sinev’s talk) PWR Rovno reactor (Russia) 1.3 GWth 15 cm steel chamber Liquid scintillator active shielding 1986 50 cm Boron Polyethylene chambers Plastic scintillator active shielding WIND ROSS H2O 3He ~1m3 of mineral oil g/l Gd d= 0.78 g/cm3 84 PMT, det – ~50% David Lhuillier, CEA-Saclay CEA - Saclay
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Proportionality to Pth after burn-up correction
Kurchatov’s Pioneers Proportionality to Pth after burn-up correction Clear signal Pth and burn-up monitoring Rate per 105 sec Experimental burn-up curve n/(1+k) = gWth =0.733 ± evt./MWth Detector rate per 105 s Reactor power in % of 1375 MW Days David Lhuillier, CEA-Saclay CEA - Saclay
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SONGS detector deployed at the San Onofre Nuclear Generating Station
Sandia/ LLNL (see N. Bowden’s talk) SONGS detector deployed at the San Onofre Nuclear Generating Station 3.4 GWth ~1021 /s 3800 int. expected per day in 1m3 liq. scint. target Low cost and robust detector Automated, non intrusive measurement David Lhuillier, CEA-Saclay CEA - Saclay
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Sandia/ LLNL Remarkable monitoring of reactor operation.
Removal of 250 kg 239Pu, replacement with 1.5 tons of fresh 235U fuel Remarkable monitoring of reactor operation. ~450 evts/day after cuts Reactor Power (%) 20 mwe overburden: large induced correlated background. Spoiling stat. convergence David Lhuillier, CEA-Saclay CEA - Saclay
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Double Chooz Inspired Detector
(T. Lasserre’s proposal) CEA-DSM-DAPNIA David Lhuillier, CEA-Saclay CEA - Saclay
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Geometry 2.4 m 1.6 m GEANT4 Simulation based on the
GLG4Sim & DCGLG4Sim packages Chimney : 12 mm Acrylics vessel Chimney scint. volume (8 liters) 2.4 m 1.6 m Buffer liquid (1.5 m3 min. oil, L~50m) 17 PMTs (8’’) Steel/Lead Shielding (100 mm) Buffer Vessel (Stainless steel + surface) Monolithic Target Volume (1.86 m3 Gd_scint, L~5m) Target Vessel: 12 mm Acrylics vessel David Lhuillier, CEA-Saclay CEA - Saclay
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Optical Model Target liquid Full detector from above
Visible photon (2 eV) single track Target liquid 20% PXE+80%dodecane 0.1% Gd-doped Scintillator Fluors: 6 g/l PPO, 25 mg/l Bis-MSB d=0.8, 7000 photons/MeV, L~5 m PMTs 2 rings of 12 and 5 8’’ modules Full PMT optical Model implemented R(,λ), A(,λ), T(,λ) Acrylics: 8 mm (L~5 m, cutoff <400 nm) Visible photon (2 eV) single track 17 PMTs, Top view 17 PMTs, side view David Lhuillier, CEA-Saclay CEA - Saclay
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automated source deployements along Z axis
Spatial Response Calibration pipe for automated source deployements along Z axis very good light collection due to Tyveck Acylics vessel Tyveck coating 511 KeV escape 99% of the light collected within 300 ns 800 p.e./MeV Light collection + escape 35% variation Vessel bottom Vessel Top 2.4 m Could be largely improved by PMT read out at both ends of detector. chimney 1.6 m David Lhuillier, CEA-Saclay CEA - Saclay
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Detector Efficiency induced positrons induced Gd capture
8 MeV Gd peak (Only) Capture efficiency Gd ~ 88% Quenching from Birk’s law d(E quenched) = dE / (1 + kB dE/dx) Time cut coincidence time of 100 s t ~ 97% Global efficiency tot ~ e x Gd x n x t ~ 0.57 No position reconstruction because highly reflective Buffer surface Energy response Ee+> 2.5 MeV p.e.> 1000 e~ 85 % En > 4 MeV p.e. > 1800 n~ 79 % David Lhuillier, CEA-Saclay CEA - Saclay
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Burn-up ~5 days measurements plotted every 50 days
2 fixed fuel compositions (in fraction of fission per isotope) 235U= Pu= U= Pu=0.02 235U= Pu= U= Pu=0.08 Kolmogorov-Smirnov statistical test. Nul Hypothesis: the two ‘burn-up’ induce identical p.e. spectra ~28500 events ~5 days of data taking (including efficiencies) Photoelectron Hits spectrum KS prob (shape ony) <10-8 (rate+shape) David Lhuillier, CEA-Saclay CEA - Saclay
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Cd cylindrical covers (1 mm thick)
Toward a Real Thing Still looking for funding of prototype construction Design study to be completed in the next few months (geometry, shielding, safety, robustness, automatization…). Determine sensitivity to fuel composition Investigating possible other detection techniques Cd cylindrical covers (1 mm thick) 16X16 matrix of 3He proportional counters 920 mm sensitive length Distilled water Fiducial volume (Np = ×1028 ± 0.5%) n + 3He p + 3H 3He counters: Very efficient and stable detectors Could be combined with e+ signal in scintillator for better background rejection Wind detector type, V. Sinev David Lhuillier, CEA-Saclay CEA - Saclay
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Relies on singles… N2 gain big enough to fight surface background?
Coherent Scattering (see J. Collar & H. Wong’s talks) Gain of a factor ~N2 in cross section No kinematical threshold More compact detector Weak neutral current on Xe Weak charged current on p int. rate Flux Relies on singles… N2 gain big enough to fight surface background? David Lhuillier, CEA-Saclay CEA - Saclay
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Conclusion Absolute precision:
3% achievable. More accurate calibration might be possible at research reactors. Systematic errors very complementary to standard procedures. Monitoring: Remote and automated measurements at 1% precision achievable at few days frequency at GWsth reactors. Unique opportunity of cross calibration of different cores. Mini-detectors: Shielding/veto is a critical issue for “surface” sites. Looking for funding of a miniature detector in France. More talks to come about running experiments… David Lhuillier, CEA-Saclay CEA - Saclay
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David Lhuillier, CEA-Saclay
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Calibration Goal: monitor detector response along z axis
Case 1: no spatial reconstruction Only a relative calibration over the detector live time Case 2 : use some time information to do “some” reconstruction + correction Gamma radioactive sources Allow to follow the positron response variation with z Automatization of the calibration Fully automatized system Relative detector response along the z axis normalised to e+ response at the center of the Target Acylics vessel Top Calibration pipe for source deployements Along z axis David Lhuillier, CEA-Saclay CEA - Saclay
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Positron Signal Energy deposited Photoelectron spectrum
Low E tail due to 511 keV escape Quenching from Birk’s law d(E quenched) = dE / (1 + kB dE/dx) Efficiencies 1 MeV 98.2 % 2.5 MeV 71.8 % 3 MeV 50.4 % Photoelectron spectrum Account for detector response looks like reactor induced e+ ! David Lhuillier, CEA-Saclay CEA - Saclay
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Induced Gd Capture Energy deposited Photoelectron spectrum
8 MeV Gd peak (Only) Low E tail due to from n-capture on Gd Quenching from Birk’s law Gd capture Gd ~ 88% Efficiencies of Energy cut: 4 MeV 68 % & 6 MeV 25.6 % Photoelectron spectrum Account for detector response Spread of the n-Gd capture peak David Lhuillier, CEA-Saclay CEA - Saclay
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3He Integral detector based on He-3 counters
Experimental site Bugey 5 reactor 25 mwe 15 meters from the core 30 /m2/s Integral detector based on He-3 counters 10 cm of lead to stop gamma’s 25 cm of Water & 4 mm of B4C to slow down and capture fast neutrons 10 cm of Scintillator (liquid) to tag the muons (172 Bq) stainless steel tank of 130x130x120 cm3 filled with distilled water 256 He-3 counters to detect neutron production from inverse beta decay + bkg. Neutron detection principle n + 3He p + 3H measure the 765 keV energy released from the products p & 3H Interest of using F-ADC to get multiple neutron signals David Lhuillier, CEA-Saclay CEA - Saclay
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Simul - Data e- 235U e- 239Pu David Lhuillier, CEA-Saclay
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