reactor neutrino monitor experiments in japan · withstand earthquakes and tsunami. ... detector...

Kyohei Nakajima (University of Fukui)Applied Antineutrino Physics 2018 in Livermore

Oct.10, 2018

Reactor Neutrino Monitor Experiments in Japan

Contents

• Purpose of reactor neutrino monitor• Status of nuclear power plants in Japan• PANDA experiment

- PANDA36 result (2012)- Background measurement (2017)

• Measurement plan• Summary

Purpose of Reactor Neutrino Monitor

• Engineering motivation- Real time monitoring of‣ reactor operation (ON / OFF)‣ fuel components (e.g. 235U, 239Pu)

• Physics motivation- Clarify the cause of 5 MeV bump‣ Study correlation between observed rate and fuel components

- Clarify the cause of “Reactor Anomaly”‣ ~6% deficit of the observed rate compared to the expectation

• Requirements of the measurement- High statistics→ Commercial reactor and the site close to reactor core

- Good S/N ratio→ Effective shield & veto system

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Status of Nuclear Power Plants in Japan• Mar. 2011: There were 54 nuclear reactors in operation before the

Fukushima Daichi nuclear disaster.- Supplying ~30% of the country’s electric power

• Jul. 2013: New stricter safety regulations were established to withstand earthquakes and tsunami.

• Now: 9 reactors in five plants met the new standards and 7 reactors are in operation now.- Supplying ~5% of the country’s electric power- 19 reactors will be decommissioned.- Monju (FBR; Fast breeder reactor) was decided to be

decommissioned in 2016.• Future: It is planned that nuclear energy will account for ~20% of

energy output by 2030.- Require ~30 reactor to be operating.




• Now: 9 reactors in five plants met the new standards and 7 reactors are in operation now.- Supplying ~3% of the country’s electric power- It was decided that 19 reactors will be decommissioned.- Monju (FBR; Fast breeder reactor) was decided to be

decommissioned.• Future: It is planned that nuclear energy will account for ~20% of

energy output by 2030.- Require ~30 reactor to be operating.




• Now: 9 reactors in five plants met the new standards and 7 reactors are in operation now.- Supplying ~3% of the country’s electric power- It was decided that 19 reactors will be decommissioned.- Monju (FBR; Fast breeder reactor) was decided to be

decommissioned.• Future: It is planned that nuclear energy will account for ~20% of

energy output by 2030.- Require ~30 reactors to be operating.

cited from https://www.nippon.com/en/features/h00238/

Nuclear Power Plants in Japan

Ohi

Tahakahama

Genkai

Sendai

IkataStatus in Jul.2018

All 9 reactors are PWR and based in western Japan.

BWR

BWR

Reactor Monitoring Community in Japan• We organized a reactor monitoring

community in Japan and shared research progress in a monthlymeeting.

• Members: 5 instituesUniv. of Fukui, Kitasato Univ., Tohoku Univ., Niigata Univ.,Nippon dental Univ.

- Plastic scintillator type‣ Kitasato Univ.: PANDA experiment‣ Niigata Univ.: Development of characteristic plastic scintillator

- Liquid scintillator type‣ Tohoku Univ., Univ. of Fukui: LS monitor (Gd-loaded LS with PSD)

• Considering the strict regulation in nuclear power plants, firstly we start to measure neutrinos by plastic scintillator in the ground.

• We will also continue the development of LS for the future measurement.

Meeting on Apr. 2016 (in Univ. of Fukui)

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7 Dec 2015 AAP2015 11

Observed: 21.8 ± 11.4 events/day

Expected: 17.3 ± 6.2 events/day

Efficiency Prompt Trigger 28.6% Etotal cut 44.2% E2nd cut 82.2% Fiducial cut 93.5% Prompt Total 9.7% Delayed Trigger 48.8% Etotal cut 79.1% E3rd cut 91.9% Delayed Total 35.5% Time window 91.2% TOTAL 3.15%

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Neutrino Monitor Measurement in 2012

• Measurement condition & result- Reactor power: 3.4 GWth, - Distance from core = 35.9 m- Period: ON 30days, OFF 34 days- ON-OFF = 21.8±11.4 events/day

• Measurement was performed in Ohi nuclear power plant with PANDA36 (36 modules) before the establishment of new safety regulation.

• Significance of neutrino signals was 2σ in PANDA36.• In PANDA100, the significance is expected to be near 4σ.→ It is important to know the background level in PANDA100.

Background Measurement in 2017• Background measurement was performed in the campus of

Kitasato Univ. to understand the background level in the ground.• Date: Aug.31~Sep.8, 2017 (1 week)

20 feet container

3m

1.8m0.5m

0.24m

Detector Location (Outside) Water Tank (24 cm thickness)

6m 200L foreach tank

• Result of water tank: γ-ray (accidentals) events below 3 MeV decreased by ~30%, but neutron (correlated) events increased by ~20% due to muon spallation in the water.

Result of Background Measurement• Event Selection in delayed coincidence method

- Prompt: 3 < Etotal < 8 MeV- Delayed: 4 < Etotal < 8 MeV, 1 < E1st & E2nd < 8 MeV, Nhit ≧ 3- Time difference: 50 < ΔT < 100 μsec (Neutron thermalization ~60 μs)

• Multi-neutrons induced by cosmic muons looks dominant.

3 4 5 6 7 8Energy [MeV]

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On-time (50-100 μsec)Off-time (1000-2000μsec)

• Events in on-time events: 0.083 Hz, Events in off-time: 0.012 Hz→ ~7000 events/day is expected in the ground level.

Plan of Next Measurement

Tohoku Univ.

Kitasato Univ.

Niigata Univ.Nippon Dental Univ.

Univ. of Fukui

Ohi

~120km(2 hours by car)

Fukui Prefecture

• We are asking to electric power company (KEPCO; Kansai Electric Power Company) about the measurement in Ohi nuclear power plant.- Same location of the PANDA 36 measurement in 2012

2018/10/08 13(11Google マップ

1 / 3 ページhttps://www.google.co.jp/maps/@35.5409744,135.6544251,555m/data=!3m1!1e3

Ohi Nuclear Power Plant

Unit 1

Unit 2

Unit 3

Unit 4

Unit Power Operation Status

1 3.4 GWth 1979~ Decomission decided2 3.4 GWth 1979~ Decomission decided

3 3.4 GWth 1991~ Restarting since Mar. 20184 3.4 GWth 1993~ Restarting since May. 2018

PANDA36

• Ohi nuclear power plant had supplied the second largest electrical output among nuclear power plants in Japan.

Google map

• We plan to perform measurement near Unit 3 or Unit 4 around 2019 spring in the ground level.

⑥ 竜巻に対する屋外SA設備の防護対策

概要

• （設計の考え方）屋外SA設備については、同じ機能を持つ設備が竜巻によって同時に損傷しないよう配置することで、必要な機能が損なわれない設計とする。具体的には以下の通り。

－（悪影響防止）固縛等の措置により、屋外SA設備が飛来物となりDB設備等に悪影響を及ぼさない対策。

－（位置的分散）同じ機能を持つDB設備を防護するとともに、DB設備や常設SA設備から離隔して配置。

・屋外SA設備が飛散し、DB設備等に悪影響を与えないよう固縛

・サスペンションによる耐震性（減衰効果）を阻害することがないよう、たるみを残して固縛

・可搬設備の機動性を考慮し、固縛の数は必要最小限に抑える。

屋外SA設備の竜巻防護対策の例（電源車）DB設備の竜巻防護対策の例（海水ポンプ）

・風速100m/sの竜巻を考慮

・上面はネットで飛来物の衝撃を吸収

・側面は鋼板で貫通を阻止

・竜巻が襲来しても損傷しない設計

参考資料5

Photo example of lashing

Requirement for Measurement Location• In the new safety regulation, if we leave cars or container, they

should be fixed using lashing apparatus which is against for tornado.

• Such system is almost occupied for emergency cars, and it is a hurdle to perform a measurement for a long time.

Measurement Plan in Ohi Plant

Detector PANDA36 PANDA100Target Mass [kg] 360 1,000 1,000

Distance from core [m] 36 ~45 ~100Efficiency [%] 3.2 9.2 9.2

Expected ν [/day] 19 98 20Expected BG [/day] ~3,000 ~7,000 ~7,000

• There are two criteria of measurement location where the lashing apparatus is available.- Distance from core: ~45 m or ~100m

• We try to measure for “1 month on-period” and “1 month off-period”, setting a detector in a container.

2018/10/08 13(28関西電力 (株)大飯原子力発電所 - Google マップ

1 / 2 ページhttps://www.google.co.jp/maps/place/関西電力+(株)大飯原子力発電所/@35.5…a93a48d:0x599cfcbabec4b2bd!8m2!3d35.5405648!4d135.6520164

画像 ©2018 Google、地図データ ©2018 ZENRIN 50 m

関西電力 (株)大飯原子力発電所

Unit 3

Unit 4

~100m

~45m

• Significance will be ~4σ at 45 m and ~1σ at 100m.

Background Measurement with LS in Ohi (2018)• We performed a environmental radiation measurement in the

nuclear power plant with a set of following detectors.- NaI (2 inches) for γ-rays- LS (BC501, ~3L) which has a PSD ability for fast neutrons- Plastic scintillators for cosmic muons

• Maybe this was the first measurement using LS in the nuclear power plant in the new safety standards.

φ20cm H9cm(~3L)

70×30×2cm

30×30×2cm

LS for fast neutrons Plastic scintillators for muons

• Measurement was performed in a 2 ton truck. (We should have continued to stay during the measurement.)

• Measurement condition- Date: 8 hours × 2 days in Feb., 2018- Location: 100 m from Unit 3 in Ohi

Measurement in Ohi A set of detectors

• We plan to perform a same measurement with a few tens litter of Gd-loaded LS in the next PANDA measurement.

Background Measurement with LS in Ohi (2018)

Summary

• Nuclear reactors are gradually restarting in Japan.- 9 reactors met a new safety standards and 7 reactors

in operation now.• Japanese members are working for reactor neutrino

monitor experiment in consortium.• We plan to perform a measurement in Ohi reactor

power plant with PANDA100 detector next spring.- Distance: 45 m or 100m from the core.- Significance: ~4σ at 45 m and ~1σ at 100 m

• We continue to develop the LS detector for the future measurement.

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