ARIES Studies Achieving High Availability in Tokamak Power
ARIES Studies Achieving High Availability in Tokamak Power Plants Lester M. Waganer The Boeing Company St. Louis, MO And the ARIES Team US/Japan Reactor Design Workshop At UCSD San Diego, CA 9-10 October 2003 Page 1 L.M. Waganer US/Japan Workshop 9-10 October 2003 ARIES Studies Cost Of Electricity Is the Critical Measure Of Commercial Feasibility Annualized Capital Cost + Yearly Operating Cost (Thermal Power x Recirculating Power) x Plant Availability Plant Availability is one of the strongest factors that determine the Cost of Electricity Existing Fossil and Fission Plants are maximizing their availability to stay competitive (e.g., 85%, 90%, 95%) New plants must produce competitive COE values Capital intensive plants (high Capital Cost) must compensate with other factors L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 2 ARIES Studies
Cost Of Electricity Is the Critical Measure Of Commercial Feasibility Annualized Capital Cost + Yearly Operating Cost (Thermal Power x Recirculating Power) x Plant Availability Capital Cost typically accounts for 80% of the annual cost to operate a fusion power plant L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 3 ARIES Studies COE Factors That Fusion Can Influence Annualized Capital Cost + Yearly Operating Cost (Thermal Power x Recirculating Power) x Plant Availability Factor Influence Capital Cost Fusion will probably higher capital costs than competitors Operating Cost Fuel very low cost; Maybe small operating staff; Power core maintenance may be high for wall, blanket, and divertor Thermal Power Thermal power level constrained by unit size, which is determined by utility size and transmission capability Thermal Efficiency
Fusion will have to push the limit with Brayton gas cycle to stay competitive with efficiencies around 60% (>1100C fluids) Recirculating Power Superconductors will help control recirculating power, but pumping liquid metals or helium increase recirculating power Availability Need long lived components (high MTBF) and short time to maintain (short MTTR) on all plant elements; need A > 90%?? L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 4 ARIES Studies What Establishes Plant Availability? Availability is defined as the time the plant is available for power production compared to the total calendar time. Availability = Operating Time Operating Time + Sum of Outage Times 1 = 1+ Mean Times To Repair (MTTR) Mean Times Between Failures (MTBF) + Preventative Maintenance Time Between Maintenance Periods Availability can be improved by:
Reducing time to repair and preventative maintenance actions Extending time between failures and maintenance periods L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 5 ARIES Studies Mean Time Between Failure Depends on Component Reliability and Wearout Power core components must be highly reliable Minimal unexpected failures are required to achieve maximum replacement during scheduled, concurrent, preventative maintenance periods Components must have long, predictable lifetimes Divertors, first walls, and blankets must operate in excess of 4 full power years (or be super fast to replace) All other components must be life of plant Shield, vacuum vessel, cryovessel, and structural components System design must incorporate redundant features to minimize operational shutdowns L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 6 ARIES Studies Mean Time To Repair (of Power Core) Is Established By Maintenance Philosophy Both planned maintenance and unexpected failures must be quick, easy, accurate, and reliable Modular replacements must be available upon demand Repair and/or maintenance of modules done offline to increase operational time and improve fidelity of repair
L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 7 ARIES Studies The Remainder of the Talk Will Concentrate on the Maintenance Aspects of Fusion Power Plants and How It Can Be Improved L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 8 ARIES Studies Operational Mean Time To Repair the Power Core Is Essential Include both scheduled and unscheduled outages Availability = Total Time/(Total Time + of Outages) Outage figure of merit is MTTR/MTBF (repair or replace) Plant must be designed for high maintainability Modular power core replacement Simple coolant and mechanical connections Highly automated maintenance operations Power core building designed for efficient remote maintenance Modules or sectors should be refurbished off-line Better inspection methods results in higher reliability L.M. Waganer US/Japan Workshop 9-10 October 2003
Page 9 ARIES Studies Criteria for Maintenance Approach List does not imply priority Apply to scheduled and unscheduled maintenance Reduce operational maintenance time Improve reliability of replacement modules or sectors Increase reliability of maintenance operations Failsafe approach Accurate and repeatable maintenance operations Reduce cost (size) of building and maintenance equipment Reduce the cost of spares Reduce the volume of irradiated waste and contamination from dust and debris Keep it simple L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 10 ARIES Studies ARIES Studies Show R&D Direction Starlite Demo Define demonstrations - Robotic maintenance - Reliability - Maintainability - Availability ARIES-ST Define vertical
maintenance scheme - Remove centerpost only - Remove total power core - Use demountable TF coils - Split TF return shell Elevation View Showing FPC Maintenance Paths ARIES-RS Integrate maintenance into power core - Design power core with removable sectors - Design high-temperature, removable structure for life-limited components - Arrange all RF components in a single sector - Define and assess maintenance options - Define power core and maintenance facility ARIES-AT Cutout View Showing Maintenance Approach Improve maintainability - Refine removable sector approach - Define contamination control during maintenance actions - Assess maintenance options - Define maintenance actions - Estimate scheduled maintenance times Page 11 L.M. Waganer US/Japan Workshop 9-10 October 2003 ARIES Studies Example of AT Sector Replacement
Basic Operational Configuration Core Plasma Plan View Showing the Removable Section Being Withdrawn Cross Section Showing Maintenance Approach Withdrawal of Power Core Sector with Limited Life Components L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 12 ARIES Studies Sector Removal Remote equipment is designed to remove shields and port doors, enter port enclosure, disconnect all coolant and mechanical connections, connect auxiliary cooling, and remove power core sector L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 13 ARIES Studies
ARIES-AT Maintenance Options Assessed In-situ maintenance All maintenance conducted inside power core Replacement in corridor, hot structure returned Life-limited components replaced in corridor, exo-core Replace with refurbished sector from hot cell (A) Bare sector transport (B) Wrapped sector transport (C) Sector moved in transporter (ala ITER) L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 14 ARIES Studies Compare Coolant System Maintenance for Corridor and Hot Cell Approaches Summary of Corridor Maintenance Connections Simple Connection Co-Axial Connection Blanket to Shield 4 4 Sector to Header 5 Total 4 9 Summary of Hot Cell Maintenance Connections Simple Connection Co-Axial Connection Blanket to Shield (4 in hot cell) (4 in hot cell)
Sector to Header 5 Total 5 Both approaches have same number of coolant plumbing connections, but the blanket to hot shield can be disconnected and reconnected off line for the hot cell approach. The hot cell approach would be faster and would assure a more reliable refurbished sector. L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 15 ARIES Studies Comparison of Maintenance Approaches In-Situ Advantages Smallest buildings Low maintenance and spares costs Corridor Advantages Low spares costs Reduced irradiated waste Scoring: 0 = Lowest, 4 = Highest Maintenance Approach Criteria (Importance) In-Situ Maintenance (Score) Corridor Maintenance (Score) Hot Cell Maintenance (Score)
Maintenance Time Slowest time as all operations have limited access. Arm or rail operations will be relatively slow and number of parallel operations will be limited. Moderately slow time as not only must the sector be removed, but also access to remove/replace blanket modules is limited. Has the highest number of connections to be accomplished. Fastest maintenance as number of on-line mechanical and coolant connections will be minimal and accessible. All refurbishment will be accomplished off-line. Replacement Sector Reliability Lowest reliability as all refurbishment and inspection must be in-situ with limited access. Limited time to complete. But it has lowest number of connections. Moderately low reliability, as access is limited. High number of connections. Limited time to complete. Highest reliability because of long time to complete and inspect refurbishment. High number of connections (same as Corridor Maintenance). Building Cost Probably the smallest building size,
even considering the volume for arm and rails. Might be the largest building size to provide space for refurbishment equipment in corridor. Slightly less building size than Corridor Maintenance to just accommodate removal and transport sectors. Maintenance Equipment Cost Not clear, but this approach probably has the lowest maintenance cost even with maintenance arm or rail. One or two simpler transporters are needed. Higher cost than Hot Cell approach as several portable refurbishment carts are needed to speed on-line maintenance. Also requires several transporters. Moderate cost for 4-8 transporters, but transporters are moderate cost compared to mobile refurbishment carts. Spare Equipment Cost Lowest spare equipment cost as all high temperature shielding structure modules are used to the fullest. Lowest spare equipment cost as all high temperature shielding structure modules are used to the fullest. Highest spare equipment as high
temperature shielding structure modules are extracted for refurbishment. Effect can be mitigated with fractional replacement. Waste Volume Lowest waste volume as all high temperature shielding structures are used to the fullest. Lowest waste volume as all high temperature shielding structures are used to the fullest. Highest waste volume as high temperature shielding structures are extracted for refurbishment. Effect can be mitigated with fractional replacement. Contamination Control Little contamination control as all cutting, disassembly, reconnecting, and reassembly is done within the torus. Better because all cutting, disassembly, reconnecting, and reassembly are done outside the torus. However the corridor can be contaminated during disassembly and reassembly. Minimal cutting and reassembly in torus or corridor. Contamination from segment probably controlled. Applicability to Scheduled and Unscheduled Maintenance
Lots of disassembly to reach most distant modules. Same approach on both. Some disassembly required to reach most distant modules. Same approach on both. Random access to all modules. Hot Cell Advantages Faster online replacement Higher sector reliability Better contamination control Applicable to both scheduled and unscheduled maintenance Totals L.M. Waganer US/Japan Workshop 9-10 October 2003 MAX. SCORE Page 16 ARIES Studies Sector Transport Approach Compare Transport Approaches Criteria stresses maintenance time and contamination control Minimal differences between
approaches Selected cask enclosed as baseline approach based on safety considerations Criteria (Importance) Bare Sector (Score) Shrink-Wrapped Sector (Score) Cask Enclosed Sector (Score) Time to Remove Cryoshield Door, Enclosure Port Door, and Vacuum Vessel Door Plus Transit to Hot Cell Transporter removes cryoshield door, enclosure port door, and vacuum vessel door. Bare sector is a fast transit with transporter. All serial operations. Removal of components and transit time should be as fast as bare sector. However time to accomplish shrink-wrap will increase the overall time. All serial operations. Cask must make a trip for vacuum door and also sector. Transit time should be twice the time as bare sector. Replacement Sector Reliability Building Cost Probably the smallest building size, Same as bare sector. with just enough corridor width to rotate transporter and sector.
Slightly larger corridor width to accommodate cask length and Width. Maintenance Equipment Cost Transporter multi-purpose removal of cryostat and vacuum vessel doors plus removal and transport of core sectors Same transporter as bare approach. Requires shrink wrap equipment to seal opening and cover sector which is an added cost. Requires transporter to remove sector. Requires mobile transporter cask to contain sector and transporter. Spare Equipment Cost Lowest spare equipment cost as only one type of maintenance equipment is required. Transporter spares plus the shrink Transporter spares + cask spares. wrap equipment spares. Waste Volume (Lowered impact as the volume is minor compared to core volume) Lowest waste volume, as all only Slightly higher waste than bare one type of maintenance equipment Approach. is required. Contamination Control
Little to no contamination control as there is no containment barrier after the sector is removed. Likely debris contamination and gamma irradiation during transit. Some control as there is a possible Best containment barrier to core. containment barrier after the Best debris and gamma irradiation sector is removed. Debris Protection. contamination should be controlled and gamma irradiation reduced during transit. Lots of disassembly to reach most distant modules. Same approach on both. Some disassembly requiredto reach most distant modules. (Importance increased) Applicability to Scheduled and Unscheduled Maintenance Waste would include the transporter plus the cask. Same approach on both. Random access to all modules. Totals MAXIMUM SCORE Nearly Equal Page 17 L.M. Waganer US/Japan Workshop 9-10 October 2003
ARIES Studies Compare Frequency of Power Core Maintenance Actions (Based on a power core lifetime of 4 FPY) Fraction of Core Replaced Frequency Assessment Recommendation 1/4 of core (4 sectors) 12 m/availability Yearly maintenance is feasible. Cooldown and start up durations will be detrimental to availability goals. Requires minimal number of hot maintenance spares. Too frequent. 1/3 of core (5 or 6 sectors) 16 m/availability Very similar to annual. Fixed tasks continue to be a major factor of outage time. Requires small number of high temperature structure spares. Maintain BOP every other cycle. #2 choice 1/2 of core (8 sectors) 24 m/availability Probably will match up well with BOP major
repair. Requires eight sets of spare hot structures. #1 choice Entire core (16 sectors) 48 m/availability This four-year frequency also might be well matched with the BOP major repairs. Requires a large number of spare hot structures and maintenance equipment. Probably would yield highest availability. #3 choice L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 18 ARIES Studies Decisions for High Availability Sector Replacement Is Preferred Over In-situ Replacement of Components Refurbished Sectors in Hot Cell Is Better Than Corridor Maintenance Bare Transport Is Equal To Cask Enclosed Transport to Hot Cell, but Cask Transport Provides Better Contamination Control Replacement of Half of Power Core Sectors Every 24 months Is a Good Match With BOP Major Refurbishment Periods L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 19 ARIES Studies
Impact of Power Core Maintenance on Building Configuration 2.6 m Bioshield (2.6-m-thick) is incorporated into building inner wall Building wall radius determined by transporter length + clear area access Extra space provided at airlock to assure that docked cask does not limit movement of other casks L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 20 ARIES Studies Power Core Removal Sequence Cask contains debris and dust Vacuum vessel door removed and transported to hot cell Core sector replaced with refurbished sector from hot cell Vacuum vessel door reinstalled Multiple casks and transporters can be used L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 21 ARIES Studies
Animation of Power Core Removal Sequence (1) Remove Shield (2) Move Shield to Storage Area (3) Remove Port Enclosure Door (4) Remove Vacuum Vessel Door (5) Move VV Door to Storage Area (6) Remove Core Sector (7) Transport Sector in Corridor (8) Exit Corridor Through Air Lock L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 22 ARIES Studies Fixed Maintenance Times for Power Core Shutdown Timeline Maintenance Action Duration of Serial Operations, h Shutdown and preparation for maintenance Cooldown of systems, afterheat decay De-energize coils, keep cryogenic Pressurize power core with inert gas Drain coolants, fill with inert gas Subtotal for shutdown and preparation Maintenance Action Assumes streamlined processes for core evacuation,
bake-out, and coolant fills Duration of Parallel Operations, h 24 2.0 2.0 Dominated by cool-down of systems and core 6.0 30 Startup Timeline Duration of Serial Operations, h Startup tasks Move transporters and casks to hot cell Evacuate core interior Initiate trace or helium heating Fill power core coolants Bake out (clean) power core chamber Checkout and power up systems Subtotal for startup Duration of Parallel Operations, h 0.8 10.0 10.0 8.0 12.0 4.0 34.0
12.0 L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 23 ARIES Studies Repetitive Maintenance Times for Replacement of a Single Power Core Sector Assumes a single cask and transporter Defines major maintenance activities Assumes all removal and replacement activities are remote and automated Repetitive actions require less than 1.5 days Maintenance Action Repetitive maintenance tasks Move cask to port and dock to port Open cask door and raise port isolation door Disengage vacuum vessel door Move transporter forward to engage vacuum door Remove weld around vacuum door Disconnect VS coil electrical and I&C connections Disconnect vacuum door water coolant connections Disengage door to prepare for removal Remove vacuum vessel door into cask Lower isolation and transporter doors and undock cask Move to hot cell, unload vacuum door, return, and dock Open cask door and raise port isolation door Disengage power core sector Move transporter forward to engage power core sector Disconnect I&C connections Disconnect five coax LiPb coolant connections Disengage mechanical supports
Disengage sector to prepare for removal Remove power core sector into cask Lower isolation and transporter doors and undock cask Move to hot cell, unload sector, load new sector, return, and dock Open cask door and raise port isolation door Move power core sector from cask into near-final core position Install power core sector Align sector and finalize position Engage mechanical supports Connect five coax LiPb coolant connections Connect I&C connections Disengage transporter and move back inside cask Lower isolation and transporter doors and undock cask Move to hot cell, load vacuum door, return, and dock Open cask door and raise port isolation door Move vacuum door from cask into near-final position Install vacuum door Align vacuum door and finalize position Prep, weld, and inspect door perimeter Connect door water coolant connections Connect VS coil and I&C connections Disengage transporter and move back inside cask Lower isolation and transporter doors and undock cask Subtotal for repetitive tasks Duration of Serial Operations, h Duration of Parallel Operations, h 1.0 0.2 3.6 0.2 2.0 0.2 1.0 0.2 1.0 0.2 2.5
0.2 3.2 0.2 0.2 2.0 0.6 0.2 1.0 0.2 3.0 0.2 1.0 7.7 1.0 1.0 5.0 0.5 0.2 0.2 2.5 0.2 1.0 5.7 1.0 3.0 1.0 0.5 0.2 0.2 34.8 L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 24 ARIES Studies Maintenance Times for Replacing Different Number of Sectors One cask and one transporter Number of Shutdown Time to Replace Sectors and Startup Sectors, h
Replaced Time, h 4 64 139.2 Optimum 5 64 174 Number 6 64 208.8 Of Sectors 8 64 278.4 16 64 556.8 30 h + 34 h Maintenance Action Duration, h 203.2 238 272.8 342.4 620.8 Maintenance Availability Actions Over for Scheduled Four FPYs, h Core Outages 812.8 0.9773 748.8 0.9791 Incl. in Above 684.8 0.9808 620.8 0.9826
Equivalent Days/Year 8.47 7.80 7.13 6.47 34.8 h x # Sectors The equivalent maintenance days per operating year (FPY) will be used to determine if this maintenance scheme can achieve the necessary plant availability. L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 25 ARIES Studies Multiple Sets of Casks and Transporters Can Improve Times Equivalent Annual Maintenance Times for Multiple Sets Number of Maintenance Casks and Transporters 1 8.47 7.80 7.13 6.47 2 5.57 4.90 4.23* 3.57 4 4.12 3.45 2.78 2.12 8
3.39 2.73 2.06 1.39 At least two sets should be used for redundancy (4.23 equivalent d/y) Availability improvements with more casks and transporters probably may not justify added cost (Retain as future option to enhance availability) Page 26 16 3.03 2.36 1.70 1.03 8.00 7.00 Maint Days/Year From prior slide Optimum Number Of Sectors No. of Sectors Replaced 4 5&6 8 16 6.00 5.00 4.00 3.00 2.00 1.00 0.00 0
1 2 3 4 5 6 Num ber of Casks and Transportors L.M. Waganer US/Japan Workshop 9-10 October 2003 ARIES Studies Need to Establish Availability Goals Consistent with Energy Community All reasonably new electricity-generating plants are now operating in the 85-90% class In 25-40 years, state-of-the-art will be 90+% For Availability goals, separate power plant into three parts: Balance of Plant (buildings, turbine-generators, electric plant, and miscellaneous equipment) Reactor Plant Equipment (main heat transport, auxiliary cooling, radioactive waste, and I&C) Power Core L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 27 ARIES Studies Allocate Availability Goals System Group
Avail Goal BOP (Balance of Plant) RPE (Reactor Plant Equip) Power Core Total Power Plant 0.975 0.975 0.947 0.900 Annual Days 9.37 9.37 20.56 ~ 39.3 The Annual Maintenance Days shown above represent both scheduled and unscheduled time. Assume equal times for both actions. Thus, the Power Core must have 20.56 days of annual maintenance to achieve a plant availability goal of 0.90 L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 28 ARIES Studies Power Plant Maintenance Times Allowable power core scheduled time is 10.28 d/FPY (1/2 of 20.56 d/FPY total power core goal) Two casks and two transporters can exchange 1/2 the core in 203.3 h (8.47 d) every other year Total power core replacement requires 16.93 d or 4.23 d/FPY (annual basis) This leaves an allowance of 10.28 d/FPY - 4.23 d/FPY and 6.05 d/FPY for other scheduled maintenance of other power core systems that are not maintained during the bi-annual replacement period.
L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 29 ARIES Studies The ARIES-AT Power Plant Should Be Able To Achieve 90% Availability L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 30 ARIES Studies Summary of Maintainability Approach and Availability Analysis Approach addresses the need to quickly accomplish remote maintenance in a safe and responsible manner Reasonable timelines are postulated for a highly automated maintenance system Power core availability goals should be attainable with a margin L.M. Waganer US/Japan Workshop 9-10 October 2003 Page 31
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