OPAL CNS Moderator Performance Weijian Lu OPAL CNS Reliability from - PowerPoint PPT Presentation

OPAL CNS Moderator Performance Weijian Lu

OPAL CNS Reliability from Commissioning (Nov 2006) to Present 100 90 80 70 CNS Reliability (%) 60 50 40 30 20 10 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81 83 85 87 89 91 93 95 97 99 Reactor Cycle No. CNS Reliability (%) OPAL Reliability (%)

OPAL Reactor Facilities

What Happened to CNS Flux? • In early 2017, neutron users have noticed a significant drop in cold neutron flux ~ -20% • Possible causes – Neutron guides (fault discovered in 2011) – Source flux

Heat Load vs Reactor Power

CNS Heat Load vs Reactor Power 115% 110% 105% 100% 95% 90% 85% Nuclear Heat Load (normalised to 3.6 kW) OPAL Thermal Power (normalised to 20 MW)

Helium Temperature Sensor Drift Process Conditions Sensitivity Typical Operational Resultant CNS Flux (nominal) Variation by Variation Conservative Estimation Helium temp. sensor 15%/K ~ -1 K -15% drift • Sensors had recently been checked • Measured a stable bias of ~1 K subject to slow drift (years), but no evidence for cycle-to-cycle “oscillation”

CNS Heat Load (watts) 4400 4200 4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600 400 200 0 Heat Load (watts)

CNS Flux Sensitivity (1) Process Conditions Sensitivity Typical Operational Resultant CNS Flux (nominal) Variation by Variation Conservative Estimation D2O purity (99.5%) 6.66%/% ±0.5% ±3.33% D2O temp. (35 °C) -0.0228%/°C ±1 °C ±0.0228% D2O gap between -5.52%/mm negligible negligible CNS thimble and beam tube (1 mm) LD2 temp. (24.5 K) -4.38%/K ±0.5 K ±2.2% LD2 ortho/para ratio 0.288%/% Unknown but ±1% (order of magnitude (3:1) expected to be small estimation)

MCNP Calculation vs Measurement CNS Gain from 20.5 K to 19.6 K (4 Dec 2016) 1,10 1,09 1,08 1,07 1,06 1,05 1,04 1,03 Ratio 1,02 1,01 1,00 0,99 0,98 0,97 0,96 0,95 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Neutron Wavelength BILBY 5-Dec / 3-Dec MCNP Calc.

CNS Flux Sensitivity (2) Process Conditions Typical Resultant CNS Flux Sensitivity Operational (nominal) Variation Variation by Conservative Estimation Control rod 5.58% between Control rod N/A positions (critical actual movement pattern positions for the configuration and is repeated in that after 180° first core) every reactor cycle rotation Reactor core (first 4.56% between Fuel management To be assessed core and further the two cores strategy equilibrium core)

Fuel Management Programs • Cell code: CONDOR • Diffusion code: CITVAP – Flux and power density – Reactivity – Poison transients – Adjoint flux – Kinetic parameters

Core Power Density – Flux Tilt CG1-3 beam tube Reactor D 2 Core moderator D 2 O moderator CG4 beam tube

CNS Heat Load vs Reactor Power 115% 1,10 110% 1,05 105% 100% 1,00 95% 0,95 90% 85% 0,90 Nuclear Heat Load (normalised to 3.6 kW) OPAL Thermal Power (normalised to 20 MW) Flux Tile N-S biased to average

Conclusions • CNS heat load is an excellent indicator of source flux • Core configuration can have a significant impact on the CNS flux • Can be predicted by numerical calculations