Water Radiolysis Issues T. Sekiguchi 2019. 10. 24 Contents 2 - PowerPoint PPT Presentation

Water Radiolysis Issues T. Sekiguchi 2019. 10. 24

Contents 2 • Water radiolysis • Hydrogen recombination system • Operation status • Issues • Summary October 24, 2019 11th Workshop on Neutrino Beam and Instrumentation (NBI2019)

conductor inner Pump up Drain tank outer conductor Horn Cooling Water System 3 • Water cooling of horn conductors • Water spray onto IC ⇒ collected in drain tank ⇒ pump up • Two independent pumps for water circulation • Water supply pump • Water suction pump @ 7~8 m above horns • Supply and suction flow rates are balanced manually Service Pit Machine Room He gas line He H 2 O He vessel Pump Suction Buffer tank pump Height He ~8m October 24, 2019 11th Workshop on Neutrino Beam and Instrumentation (NBI2019)

problem (2014.Oct) Corrosion (2012.Jun) Water drop problem (2012.Oct) Power supply problem (2011.Dec) Neutral grounding problem Neutral problem grounding problem (2016.Feb.&Apr.) 1.3x10 7 1.7x10 7 Hydrogen problem (2017.Oct) Water drop problem (2018.Mar) Capacitor (2017.Mar) (2010.Mar) Hydrogen 2nd-gen. horns Recovery from Big Earthquake Horn replacement Target He pipe replacement problem 0.1x10 7 0.2 1st-gen. horns 0.8x10 7 1.2x10 7 0.8x10 7 0.5x10 7 Horn Operation History 4 Cycle 3.52s 3.2s 2.48s 2.48s 2.48s 2.48s 2.56s 2.48s 2.48s → 3.04s 10 20 # horn pulse 0.2x10 7 0.5x10 7 October 24, 2019 11th Workshop on Neutrino Beam and Instrumentation (NBI2019)

Y. Katsumura, Radiation Chemistry, No.81, 2-7 (2006) Y. Katsumura, Isotope News, No.746, 48-49 (2016) Water Radiolysis 5 • Beam exposure to horn cooling water produces hydrogen gas • Water radiolysis • Ionization and excitation of H 2 O molecule by beam exposure • Primary products ： e aq- , OH, H, H 2 , H 2 O 2 ⇒ Final products : H 2 , O 2 , H 2 O 2 • Production ratio : H 2 , O 2 , H 2 O 2 = 1.3 : 0.1 : 0.99 ⇒ very small O 2 production • H 2 O 2 naturally decomposes, yielding O 2 • 2H 2 O 2 → 2H 2 O + O 2

Hydrogen Production and Recombination 6 • Measured production rate • ~ 260 L (4.7%) / 10 19 POT @ 485 kW • Hydrogen removal by recombination : 2H 2 + O 2 → 2H 2 O • Catalyst : Alumina pellet with 0.5% Pd • H 2 produced inside horns → Forced He (+H 2 ) circulation through catalyst • H 2 production rate greatly reduces to 5.8 L (0.1%) / 10 19 POT • However, H 2 still gradually increases → He flushing once per 1~2 weeks • H 2 concentration : 1% → 0.1% Service Pit � Machine Room � He gas line � Forced circulation � He � H 2 O � He vessel � Pump � Suction Buffer tank � pump Beam � Height H 2 � ~8m �

0.2 m 3 1.4 m 3 2.7 m 3 0.6 m 3 400 L/min Hydrogen Removal System 7 H 2 recombination catalyst Alumina pellet with 0.5% Pd

400 L/min Hydrogen Removal System 8 • He flushing to be performed once a week (or two weeks) • He flushing system • He bu ff er tank (~5.5m 3 ) in TS machine room • Pure He gas injected to water tank ⇒ Horns ⇒ He bu ff er tank • Old He gas stored for a week and exhausted to outside ⇒ short-lived nuclei to decay • One He flushing ⇒ 2/3 of entire He gas can be replaced with flesh He gas He+H 2 He bu ff er tank (~5.5m 3 ) He+H 2 He+H 2 He+H 2

400 L/min Hydrogen Removal System 9 • He flushing to be performed once a week (or two weeks) • He flushing system • He bu ff er tank (~5.5m 3 ) in TS machine room • Pure He gas injected to water tank ⇒ Horns ⇒ He bu ff er tank • Old He gas stored for a week and exhausted to outside ⇒ short-lived nuclei to decay • One He flushing ⇒ 2/3 of entire He gas can be replaced with flesh He gas Pure He gas He He+H 2 He bu ff er tank (~5.5m 3 ) He He He

400 L/min Hydrogen Removal System 10 • He flushing to be performed once a week (or two weeks) • He flushing system • He bu ff er tank (~5.5m 3 ) in TS machine room • Pure He gas injected to water tank ⇒ Horns ⇒ He bu ff er tank • Old He gas stored for a week and exhausted to outside ⇒ short-lived nuclei to decay • One He flushing ⇒ 2/3 of entire He gas can be replaced with flesh He gas Exhaust to outside He+H 2 He bu ff er tank (~5.5m 3 ) He+H 2 He+H 2 He+H 2

Prospect for 1.3 MW 11 • Operation criteria • Keep H 2 concentration below 3% • H 2 explosion limit in air = 4% • Prospect for 1.3 MW • H 2 concentration < 1% in 1 week operation @ 485 kW ⇒ < 3% @ 1.3 MW • Current production rate can be acceptable even with 1.3 MW beam • But there exists some problems that need to be solved for a safe operation

2017 Oct.~2018 May. Run6 Run9 2016 Oct.~2017 Apr. Run8 2016 Feb.~May Run7 2015 Feb.~May IE replacement Dual IE Single IE Ion Exchanger E ff ect on H 2 Concentration 12 Run period Run6 Run7 Run8 Run9-1 Run9-2 Run9-3 Single Single Single Dual Single Single Configuration (old) (new) (old) (new) (new) (new) Beam power ( kW ) 330 390 470 450 475 485 H 2 concentration (%) 0.4 2.5 1.5 4.0 1.0 2.4 Production rate 0.173 0.683 0.215 0.832 0.299 0.137 ( % / 10 19 POT) • H 2 production rate rapidly increased after Ion exchanger replacement • Moderate production rate for old IE, but water conductivity increased ⇒ IE’s lifetime • IE resins may be degraded due to oxidization by H 2 O 2

2018 Mar ~ May 4 April May 0 1 2 3 5 December 0 1 2 3 4 5 2017 Oct ~ Dec March November Single IE Single IE Dual IE Beam ON Beam ON October Water Conductivity Trend 13 • Water conductivity • A strange behavior during dual IE operation • Low conductivity during single IE operation • Conductivity got increased around middle of April • This indicates lifetime of IE ⇒ ~6.0 x 10 20 POT (or 2~3 months) October 24, 2019 11th Workshop on Neutrino Beam and Instrumentation (NBI2019)

E ff ect of H 2 O 2 14 • Hydrogen peroxide (H 2 O 2 ) • Production rate is close to that of H 2 (H 2 : H 2 O 2 = 1.3 : 1) • It corrodes IE resins ⇒ degradation of IE with presence of H 2 O 2 • Can be decomposed naturally : 2H 2 O 2 ⇒ 2H 2 O + O 2 • Catalyst can accelerate the decomposition • Resultant O 2 can work as a source O 2 for the recombination • Measurement of H 2 O 2 concentration • ~10 mg/L ⇔ estimated : ~500 mg/L @ 3.9x10 20 POT • This indicates that most of H 2 O 2 produced was decomposed • Even this small concentration of H 2 O 2 can a ff ect the IE resins Sensitive to 0.05-5mg/L Sensitive to 3-700mg/L 1/10 dilution No dilution No dilution October 24, 2019 11th Workshop on Neutrino Beam and Instrumentation (NBI2019)

Problems and Countermeasures 15 • Problems • Short lifetime of IE due to H 2 O 2 ⇒ IE replacement causes high H 2 production rate • H 2 gradually increases due to small O 2 concentration • Dissolved O 2 in cooling water (~1.9mg/L) • Can create superoxide O 2- (e aq- + O 2 → O 2- ), which can accelerate water radiolysis ⇒ dissolved O 2 should be removed • Countermeasures • Need ion exchanger resins which are tolerant to H 2 O 2 • O 2 degasifier to remove dissolved O 2 • Inject O 2 gas to solve the lack of O 2 for recombination ⇒ Safety control is an issue

Problems and Countermeasures 16 • Problems • Short lifetime of IE due to H 2 O 2 ⇒ IE replacement causes high H 2 production rate • H 2 gradually increases due to small O 2 concentration • Dissolved O 2 in cooling water (~1.9mg/L) • Can create superoxide O 2- (e aq- + O 2 → O 2- ), which can accelerate water radiolysis ⇒ dissolved O 2 should be removed • Countermeasures • Need ion exchanger resins which are tolerant to H 2 O 2 To be considered • O 2 degasifier to remove dissolved O 2 • Inject O 2 gas to solve the lack of O 2 for recombination ⇒ Safety control is an issue

H 2 O 2 Resistant Ion Exchanger 17 • H 2 O 2 is problematic for nuclear reactor business • H 2 O 2 resistant ion exchanger developed for nuclear reactor • Pd-doped ion exchanger can decompose H 2 O 2 and ⇒ Pd works as a catalyst • therefore can extend lifetime of ion exchanger T. Izumi et al (2018) October 24, 2019 11th Workshop on Neutrino Beam and Instrumentation (NBI2019)

Existing resin is overlaid New resin (~4L) Completed IE bottle Put new resins Remove existing resins (~46L) 50 L in total H 2 O 2 Resistant Ion Exchanger 18 • New resin • Resins produced by LANXESS and its performance proved by EBARA • I contacted the person in charge of the new resin and he was very interested in the application of this resin • As a trial, this resin was put into one IE bottle for a test • 4L of the old resins were replaced with new ones • To be tested during next beam time October 24, 2019 11th Workshop on Neutrino Beam and Instrumentation (NBI2019)

Tank Chiller (~2L) Evacuate O 2 DO F F (also H 2 O) H-Ex P P P O 2 Degasifier System 19 H 2 O (HTO) • Degasifier system installed • Concerns • H 2 O (HTO) also evacuated • Water in small tank gradually increased ⇒ Need drain • HTO should not be exhausted to the air October 24, 2019 11th Workshop on Neutrino Beam and Instrumentation (NBI2019)

Tank Drain tank P P P H-Ex Chiller F F DO Evacuate O 2 (also H 2 O) (~74L) (~2L) O 2 Degasifier System 20 H 2 O (HTO) • Degasifier system installed Overflow • Concerns • H 2 O (HTO) also evacuated • Water in small tank gradually increased ⇒ Drain tank added • HTO should not be exhausted to the air October 24, 2019 11th Workshop on Neutrino Beam and Instrumentation (NBI2019)