Challenges in the Development and Operation of the MW-class SNS - - PowerPoint PPT Presentation

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Challenges in the Development and Operation of the MW-class SNS - - PowerPoint PPT Presentation

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Challenges in the Development and Operation of the MW-class SNS Mercury Target Bernie Riemer SNS Upgrades Office J-PARC Symposium 2019 September 23-27, 2019 ORNL is managed by UT-Battelle, LLC for the US Department of Energy SNS mission is

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ORNL is managed by UT-Battelle, LLC for the US Department of Energy

Bernie Riemer SNS Upgrades Office J-PARC Symposium 2019

September 23-27, 2019

Challenges in the Development and Operation of the MW-class SNS Mercury Target

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2 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

SNS mission is focused on neutron scattering science

  • 1.4 MW accelerator

– 1 GeV protons – Linac & accumulator ring – 0.7 µs pulses at 60 Hz

  • Liquid mercury target
  • Groundbreaking in Dec. 1999
  • First protons on target in April 2006
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3 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

The SNS mercury target is a first of a kind target design: mega-watt class, liquid metal and short-pulse

Design basis beam power 1.4 MW Beam repetition rate 60 Hz Beam pulse length 0.7 µs Energy per pulse 23 kJ Proton energy 1 GeV Module material AISI 316L Module mass 1130 kg Length 2.1 m Mercury mass inside module 794 kg Mercury mass flow rate 19.4 t/min Radiation damage limit 12 dpa

The target is not safety credited Cost: ca. $1.5M

Inflatable metal seal to core vessel Water-cooled shroud Bulk mercury inlet (1 of 2) Bulk mercury return / spallation region

Mercury vessel

Center flow baffle

Replaceable target module consists of mercury vessel surrounded by a water-cooled shroud with leak sensors in interstitial space

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4 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

Early SNS target systems R&D was directed at foreseen challenges

  • Time-averaged heat removal from target

– One water and two mercury test loops for thermal-hydraulics

  • Isochoric energy deposition which initiates pressure waves

– Vessel beam pulse vessel cyclic stress needed estimation method – Mercury cavitation occurring under tensile pressure conditions

  • Target vessel material issues

– Compatibility with mercury – High-cycle fatigue strength (108 ~109 pulses) – Radiation damage limits

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5 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

SNS Target Development used 3 major facilities at ORNL as well as accelerator facilities in Los Alamos and Brookhaven

Water Thermal Hydraulic Loop

  • Flow visualization
  • Recirculation zone
  • Flow stability
  • CFD benchmark

Target Test Facility

SNS full-scale mercury test loop

  • Final CFD benchmark
  • Verify mercury process equipment
  • Operational experience

Mercury Thermal Hydraulic Loop

  • Mercury-to-steel wettability &

heat transfer

  • Design data for target window
  • Corrosion / erosion tests

Mercury target tests in proton beams

  • Vessel response

to beam pulse

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6 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

Water Thermal Hydraulic Loop (WTHL) flow visualization was used to develop and benchmark CFD simulations

Poor shear flow at wall ~stagnation

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7 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

The Mercury Thermal Hydraulic Test Loop (MTHL) became operational in 1999

EM Pump 27 L/min Test Section Hg-Water Heat Exchanger

Key heat transfer data for design of target beam window cooling passage

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8 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

Target Test Facility (TTF) – a SNS full-scale mercury test loop

  • Final CFD benchmark

– Ultrasonic Velocity Profilometry

  • Verified mercury full-scale process equipment
  • First use of EPICS control software for SNS
  • Now used for target gas injection R&D
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9 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

In-beam mercury target tests provided data to calibrate modeling of target vessel stress needed for fatigue life estimation

Energy Deposition Target Axisymmetric Target Large Effects Target Prototypical Shape Target

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10 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

Thermal shock R&D

  • Peak energy deposition in mercury for a single pulse = 13 MJ/m3 *

– Peak temperature rise is only ~ 7 K for a single pulse, but rate of rise is 107 K/s!

  • This is an isochoric (constant volume) process

– Beam deposition time (0.7 µs) << time required for

mercury to expand

– Beam size / sound speed ~ 30 ms

  • Local pressure rise is 38 MPa (380 atm

compared to static pressure of 3 atm!)*

  • Mercury expansion and wave reflection at

the vessel interface lead to tension and cavitation of the mercury

* SNS @ 2 MW

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11 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

Concerns about pulse cavitation erosion grew with findings by Kogawa et al. (J-PARC) in 2000

  • Studies on mercury wave speed employing an offline device with

prototypic pressure magnitude and rise time produced pitting damage with few impacts!

1 mm

  • SNS team conducted in-beam mercury

target tests using Los Alamos accelerator in 2001

– Pitting damaged confirmed – Projections to 108 ~109 pulses Only 200 beam pulses!

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12 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

22 SNS targets since operations began in 2006

  • Average power: 1 MW
  • Average energy: 2,180 MWh
  • 8 targets leaked

– First leak cause unconfirmed – Fatigue at welds: 4 – Cavitation damage: 2 – Latest issue is under assessment

Gas injection is key to reducing fatigue and cavitation damage

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13 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

The pressure wave / cavitation damage issue has been and remains an area of strong collaboration with J-PARC

  • Combined efforts

–

Material damage resistance studies

–

Gas injection techniques

–

Off-line and in-beam experimentation

–

Engagement with experts in academia and industry

–

Numerical studies

–

Post Irradiation and Examination and analysis

electro-Magnetic IMpact Test Machine (Offline mercury cavitation - JPARC) In-beam test of gas injection Flowing mercury test loop

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14 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

Post Irradiation Examination (PIE) of SNS targets is regularly conducted to understand damage after use

  • Samples are cut from beam entrance

window, cleaned, photographed, and erosion damage precisely measured

  • Target interiors are photographed
  • When leaks occur – samples extracted if

possible and analyzed

Target 9 (4,195 MWh)

Sample diameter: 60 mm

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15 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

SNS target gas injection started in 2017 - Cavitation damage is substantially reduced!

T18 – T20 targets used gas injection

Target 18 Qavg = 0.31 SLPM Pavg = 1121 kW Etotal = 1260 MWh Target 19 Qavg = 0.45 SLPM Pavg = 1187 kW Etotal = 1987 MWh

1.3 MW

Target 20 Qavg = 0.57 SLPM Pavg = 1287 hW Etotal = 2231 MWh

1.4 MW

Cavitation damage on center of inner wall

1.2 MW

Target 17 Qavg – no gas injection Pavg = 1127 kW Etotal = 1936 MWh

T17 – no gas injection

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16 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

Gas bubble injection also improves fatigue life by reducing pulse stress

Measurements show clear target vessel strain reductions with gas bubble injection in operating SNS targets

Gas off

Gas on strain (µε) time (ms)

  • First gas bubble injection: Nov. 2017
  • Improvements are repeatable
  • Improvements are independent of power levels
  • Improvements are proportional to gas injection level

40% strain reduction with gas

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17 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

2 MW operation of the SNS mercury target is coming with the Proton Power Upgrade (PPU) project

  • PPU doubles accelerator power to 2.8 MW to support a Second Target

Station and increase power to the First Target Station

  • The First Target Station was mostly designed for 2MW but at 1.0 GeV
  • Reliable target operation is required … with an acceptable replacement

frequency

  • Fatigue life and cavitation damage rate dependence on beam power are

both aggressively non-linear

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18 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

Reliable 2MW operation of the mercury target will be achieved with design changes and high-flow gas injection

  • Design changes that reduce pulse fatigue stress
  • Gas injection for cavitation damage and pulse stress reduction

– Swirl bubblers for small gas bubble generation (J-PARC technology) – Gas wall / bubbly curtain for localized cavitation protection – Gas rates up to ~1% of mercury flow (vs. current levels of ~0.05%)

  • Robust weld designs that ease inspections

1.4 MW Target Mercury vessel and Water-cooled shroud PPU 2MW mercury vessel preliminary design

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19 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

High power targets are challenging

  • Development and collaboration with J-PARC are helping SNS

achieve unprecedented power and reliability

  • The target design for 2MW operation incorporates lessons

learned from R&D and operating experience

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20 Riemer – SNS Challenges J-PARC Symposium 2019 September 23-27, 2019

We are very grateful for the open and fruitful collaboration with J-PARC Neutron Source Section over these years, and look forward to future years working together!