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Reactor On/Off Monitoring with a Prototype of Plastic Anti-neutrino Detector Array (PANDA)

Reactor On/Off Monitoring with a Prototype of Plastic Anti-neutrino Detector Array (PANDA). Yasuhiro Kuroda A , Yo Kato A , Nozomu Tomita A , Ryoko Nakata, Shugo Oguri , Chikara Ito B , Yoshizumi Inoue C , Makoto Minowa A,D

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Reactor On/Off Monitoring with a Prototype of Plastic Anti-neutrino Detector Array (PANDA)

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  1. Reactor On/Off Monitoring with a Prototype of Plastic Anti-neutrino Detector Array (PANDA) Yasuhiro KurodaA, YoKatoA, NozomuTomitaA, Ryoko Nakata, ShugoOguri, ChikaraItoB, YoshizumiInoueC, Makoto MinowaA,D Department of Physics, School of Science University of TokyoA Japan Atomic Energy AgencyB International Center of Elementary Particle Physics, University of TokyoCRSCEU, University of TokyoD

  2. Neutrino Reactor Monitoring • IAEA reactor safeguard regime • IAEA recommends investigation of near-field antineutrino monitoring capabilities • IAEA : Medium term goalCf ) IAEA Headquarters, Final Report: Focused Workshop on Antineutrino Detection for Safeguards Applications (2008) • Above ground deployment • Provide fully independent measurements of fissile content, through the use of spectral information • Reduced detector footprint • Our Efforts • Mobile above-ground detector • Segmented detector AAP2012 - the University of Hawaii, Manoa Campus

  3. PANDA • The proposed final detector consists of 10x10 modules • The target mass : about 1 ton • PANDA detector is designed to be loaded and operated on a van. Plastic Anti-Neutrino Detector Array AAP2012 - the University of Hawaii, Manoa Campus

  4. PANDA Module Aluminised Mylar light guide PMT Plastic scintillator Gd sheet • 10cm × 10cm × 100cm plastic scintillator • Easy to transport • Non flammable • Wrapped in gadolinium doped sheets (Gd:4.9mg/cm2) • Technique to create clear and colorless Gd doped plastic scintillator is less established AAP2012 - the University of Hawaii, Manoa Campus

  5. Detection Principle • Inverse beta decayνe + p → e+ + n • Prompt event • Energy deposit of e+ • e++e-→2γ • Delayed Event • An 8 MeV gamma-ray cascade following neutron capture on the gadolinium • Delayed coincidence method AAP2012 - the University of Hawaii, Manoa Campus

  6. First Prototype: Lesser PANDA • 2010 → 2011 • Background measurement at HamaokaNuclear Power Plant Unit3Nucl.Instrum.Meth.A690:41-47,2012 16 modules (4x4) AAP2012 - the University of Hawaii, Manoa Campus

  7. Second Prototype : PANDA36 • 2011 → 2012 • Our first reactor on/off measurement by neutrino is done by PANDA36 36 modules (6x6) AAP2012 - the University of Hawaii, Manoa Campus

  8. Data Acquisition 85% 5×16ch discriminator 72 × PMT 15% 72×PMT output data 3×32ch charge ADC 72ch PMT charge data Event timing information (time stamp) AAP2012 - the University of Hawaii, Manoa Campus

  9. Remote Monitoring for unmanned operation Univ.Tokyo Hongo Campus Simplified spectrum - Digest - Alert Mails Nuclear Power Plant Thermo-hygrometer Connected to LAN Router DoCoMo terminal with Global IP Temperature / humidity monitoring • Simple DAQ control (for emergency) • - Network connection • confirmation - Web server - Sending alert mails - Network connection confirmation Web Camera Monitoring Server Alert mails DAQ DAQ control Server data storage (HDD) Possible defects are checked through DoCoMo cellular phone network and the Internet AAP2012 - the University of Hawaii, Manoa Campus

  10. Typical cosmic muon event Position Energy deposit Stage 6 Stage 3 Stage 6 Stage 5 Stage 4 Stage 5 Stage 2 Stage 3 Stage 2 Stage 1 Stage 4 Stage 1 -60 60 -60 0 60 0 Position (cm) Position (cm) AAP2012 - the University of Hawaii, Manoa Campus

  11. Loading on a van • PANDA36 was loaded on a 2-ton van AAP2012 - the University of Hawaii, Manoa Campus

  12. Ohi Power Station Mihama Power Station Ohi Power Station Fukui • PANDA36 was moved to Ohi Power Station AAP2012 - the University of Hawaii, Manoa Campus

  13. Ohi Power Station : Unit2 PANDA36 35.9 m 3.4GWth AAP2012 - the University of Hawaii, Manoa Campus

  14. Backgrounds • Accidental Backgrounds • Natural radioactivity (gammas) • Thermal neutrons • Correlated Backgrounds • Fast neutrons (proton recoil)  extremely important • Double neutron capture • Long-lived cosmic-ray activation product We tried to reject these backgrounds by event selections. AAP2012 - the University of Hawaii, Manoa Campus

  15. Event Selection - 1 (neutrino) Time window: 8-150μsec E1st E2nd Etotal AAP2012 - the University of Hawaii, Manoa Campus

  16. Event Selection - 1 (neutrino) Time window: 8-150μsec AAP2012 - the University of Hawaii, Manoa Campus

  17. Event Selection - 1 (neutrino) Time window: 8-150μsec AAP2012 - the University of Hawaii, Manoa Campus

  18. Event Selection - 1 (neutrino) Detection efficiency: (3.15±0.93)% Predicted anti-neutrino rate: 18.1±6.5 events/day Time window: 8-150μsec Preliminary Observed event rate difference: 38.4 ± 8.4 events/day (large?) AAP2012 - the University of Hawaii, Manoa Campus

  19. Event Selection - 2 (neutron) Time window: 8-50μsec Selection intended to select fast neutron events E2nd condition is changed to reject the anti-neutrino events AAP2012 - the University of Hawaii, Manoa Campus

  20. Event Selection - 2 (neutron) Preliminary Time window: 8-50μsec Neutrino detection efficiency: (0.271±0.93) % ～ 0% Observed event rate change: 31.4 ± 8.5 events/day AAP2012 - the University of Hawaii, Manoa Campus

  21. Change of the fast neutron flux 2.5m Reactorbuilding Water tank 2.8m PANDA • Why did the fast neutron flux change? • It’s not so clear…But we speculated that it could be explained by changes in environment. • Three water tanks (used for scheduled inspection of the reactor) • Water could shield the fast neutrons AAP2012 - the University of Hawaii, Manoa Campus

  22. Change of the neutrino flux (selection-1) (selection-2) ≈0 : the contribution of the neutrino rate by selection-1 : the contribution of the fast-neutron rate difference by selection-1 : the ratio of the neutrino and neutron detection efficiencies (0.086±0.026 and 1.86±0.68 respectively). Preliminary (expected : 18.1±6.5 events/day) events/day Simultaneous equation to evaluate the change of the neutrino event rate AAP2012 - the University of Hawaii, Manoa Campus

  23. Next Step • Unexpectedly large change in fast-neutron flux • It could be subtracted using the second selection. But the subtraction increases the error.→ Water Shielding? (at the expense of small size and light weight) • 8x8=64 prototype • Designing new structure which includes shieldings • Estimating expected performance of next prototype AAP2012 - the University of Hawaii, Manoa Campus

  24. Summary 6x6 prototype of PANDA (PANDA36) was built It was loaded on a van and deployed above ground at Ohi Power Station Unit 2 (3.4GWth) Fully unmanned operation was demonstrated Detected neutrino event rate was 22.9±11.7 events/day (expected: 18.5±6.5 events/day) Next upgrade to 8x8 is on going. It may have neutron shielding AAP2012 - the University of Hawaii, Manoa Campus

  25. Backups

  26. Gadolinium doped sheet 50μm PET sheet Gd doped ink layer Gd density : 4.9mg/cm2 60% Of thermal neutrons are captured by one layer of the sheet (84% by two layer) AAP2012 - the University of Hawaii, Manoa Campus

  27. VME Modules AAP2012 - the University of Hawaii, Manoa Campus

  28. Cosmogenic Radioisotopes • 9Li, 8He • Decay time constant : • 9Li : 178 ms • 8He : 119ms • β-decay isotopes with a delayed neutron emission from the β decayed daughter • This background is negligible with a small detector. And it is strongly rejected by prompt event selection criteria E2nd≦520keV taking advantage of segmented design. AAP2012 - the University of Hawaii, Manoa Campus

  29. Double neutron capture Spectra of E2nd of the prompt events after selection-1 (neutrino selection) except for the prompt E2nd selection. • Double neutron capture • It is strongly rejected by prompt event selection criteria E2nd≦520keV taking advantage of segmented design AAP2012 - the University of Hawaii, Manoa Campus

  30. Selection : prompt - Etotal AAP2012 - the University of Hawaii, Manoa Campus

  31. Selection : prompt – fiducial cut AAP2012 - the University of Hawaii, Manoa Campus

  32. Selection : delayed - Etotal AAP2012 - the University of Hawaii, Manoa Campus

  33. Accidental Events Selection - 1 Selection - 2 Preliminary Preliminary • Observed accidental background rates using other time windows • Selection-1 : 8μs+1ms≦t≦150μs+1ms • Selection-2 : 8μs+1ms≦t≦50μs+1ms AAP2012 - the University of Hawaii, Manoa Campus

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