1. 1 Draft Discussion Materials for Session 10: Device Availability Factor and Plasma Duty Factor in FNF Discussion on: 1.What availability goals are required for FNF? What are the corresponding MTBF and MTTR for various components and for base blanket? 2.What are the requirements on periods of continuous operations (test campaigns)? What are the requirements on the plasma duty cycle during these test campaigns? 3.What is the minimum achievable plasma dwell time? Maximum burn time during a pulse? Maximum plasma duty cycle? 4.What is needed to realize the above goals for the device availability factor and plasma duty factor? Discussion Facilitator: Burgess Summary Preparer: Ying

2. 2 Some RAM terminology Availability (Due to Unscheduled Events)= A U MTBF = mean time between failures = 1/failure rate MTTR = mean time to repair AUAU = represents a component (Outage Risk) = (failure rate) (mean time to repair) = Device Duty Factor= A S x A U Plasma Duty Factor = Fluence (integrated neutron wall load) = Neutron wall load x Calendar years x (Device Duty Factor x Plasma Duty Factor ) (Plasma duty factor = 1 for steady state operation) Availability (Due to Scheduled Outage) = A S

3. 3 Lower Diverter Test Module Upper Breeding Blanket Lower Breeding Blanket Shielding Blanket Test Section Upper Diverter TFC Center Leg Plasma R 0 =1.2 A=1.5 к=3.2 δ=0.4 I p = 12 TFC Return Leg / Vacuum Vessel Support Platform Inboard FW (10cm) Outboard FW (3cm) Access Hatch (VV/TFC Return) Diverter/SOL Shaping Coil Sliding Joint Inlet Piping Outlet Piping Vacuum Seals Neutral Beam Duct Poloidal Field Coils ST Component Test Facility (CTF)  Provides fusion nuclear technology test environment in support of Demo development  ITER-Era  Wall load: ~ 1 MW/m2  Fluence,~ 3 MW- yr/m2, (6 MW-yr/m2 later phase)  High Plasma Duty Factor Goal (30%),steady state, no dwell  User Facility maximizing test ports  Builds on ITER RH approach and technology

4. 4 Disconnect upper piping Remove sliding electrical joint Remove top hatch Remove upper PF coil Remove upper diverter Remove lower diverter Remove lower PF coil Extract NBI liner Extract test modules Remove upper blanket assembly Remove lower blanket assembly Remove centerstack assembly Remove shield assembly Upper Piping Electrical Joint Top Hatch Upper PF coil Upper Diverter Lower Diverter Lower PF coil Upper Blanket Assy Lower Blanket Assy Centerstack Assembly Shield Assembly NBI Liner Test Modules Similar to fission power plants, large vertical top access with large component modules with simple vertical motion expedites remote handling, minimizes MTTR and maintenance outages All welds are external to shield boundary are hands-on accessible Parallel mid-plane/vertical RH operation ST CTF has High Maintainability, Low MTTR, Using Large Integrated In-Vessel Modules

5. 5 ST CTF Preliminary Component RH Time Estimates

6. 6 ST CTF Very Preliminary RH Class 1 Annual Maintenance Time Estimate = ~ 1/4 Year A typical annual RH Class 1 remote maintenance campaign might replace: – 2 divertor modules (6 weeks*) – 6 midplane port assemblies (3 weeks ea.*) – NBI ion sources (1 week ea.*) * Two 8 hr shifts per day, 6 work days per week during shutdown Each uses a different RH system, parallel operations are possible, and the midplane port changeouts are limiting provided at least 2 are being changed (6 weeks serial time) Assuming 3 midplane port RH casks are available for parallel operations, it is estimated to take ~ 8 weeks to complete the above tasks provided spare units are available. Add shutdown and machine pump down / conditioning time of 1 month, and the total outage from plasma burn to plasma burn is ~3 month or 0.25 of the year One unplanned port assembly failure (TBM, RF heating or diagnostics) that shuts the machine down, and that can't be delayed until the scheduled maintenance time, will consume ~ 6 weeks of maintenance time and 1 month of shutdown / startup time, or ~ 0.25 of the remaining year. Every shutdown requiring opening and venting of the vessel will require in excess of a month to recover, hence in-vessel maintenance should be planned and grouped together If components are operated to failure, 1 divertor + 1 midplane port failure not occurring at the same time frame could consume ~ 5 to 6 months of the year.

7. 7 Current Baseline Requirements for In-vessel/ex-vessel RH Interventions The ITER remote handling equipment design and procurement is based on a maintenance requirement plan. COMPONENTS MAINTENANCE REQUIREMENTS PLAN

8. 8 Initial comments on burn and dwell time (B. Nelson, W. T. Reiersen, L. Cadwallader) The 400 seconds burn time in ITER is an inductive limit, i.e. they don't assume they can get much current drive. On ITER (with S/C coils), the operable limit seems to be the cryogenic system due to an economic limitation, not a technical limit. S/C coils can also be limiting if the helium transit time is long relative to the burn time - this could reduce the temperature headroom because the helium entering the high field region keeps getting hotter over time because equilibrium is not yet reached. The NBI system could be the limiting factor for CTF, since the cryo- pumps will not pump indefinitely and they don't seem to be able to have two sets working alternately for NB systems.

9. 9 Reliability/Availability/Maintainability Critical Development Issues for DEMO and Fusion Power Availability is determined by: a) reliability of components (unscheduled maintenance) b) life time of components (scheduled maintenance) c) time required for replacement (down time) High availability is essential if fusion is to be economically competitive

10. 10

11. 11 DIII-D Tokamak Systems System Failure Rate (/hr) Preliminary system failure rate goal for a fusion power plant Preliminary system failure rate goal for ITER λ > 1E-01 10 -1 10 -2 10 -5 10 -3 10 -4 Lee Cadwallader Fusion Safety Program ARIES-Pathways Project Meeting, GIT, Atlanta, GA, December 12-13, 2007 Fusion experiments track “mission availability” which is actual operating hours compared to funded operating hours in the calendar year. Tokamaks are 60-80% mission available over 8 or 10 hour days of perhaps ~20 weeks/year. This is ~11% calendar availability. Such availabilities are early in a technology development path.

12. 12 Example MTBF and MTTR of various major components of a Demo

13. 13 Example MTBF and MTTR from Existing Tokamak Systems to Apply to an FNF Total Facility A U (with 4 weeks pre and post conditioning) = 0.5984 *(48/52)= 0.552

14. 14 What FNF availability needed to achieve 3 MW- y/m 2 in 10 years for 1 MW/m 2 neutron wall load

15. 15 Example MTBF and MTTR from Existing Tokamak Systems to Apply to an FNF (ST- CTF)

16. 16 Example MTBF and MTTR from Existing Tokamak Systems to Apply to an FNF (ST- CTF)

17. 17 Draft Discussion Materials for Session 10: Device Availability Factor and Plasma Duty Factor in FNF Discussion on: 1.What availability goals are required for FNF? What are the corresponding MTBF and MTTR for various components and for base blanket? 2.What are the requirements on periods of continuous operations (test campaigns)? What are the requirements on the plasma duty cycle during these test campaigns? 3.What is the minimum achievable plasma dwell time? Maximum burn time during a pulse? Maximum plasma duty cycle? 4.What is needed to realize the above goals for the device availability factor and plasma duty factor? Discussion Facilitator: Burgess Summary Preparer: Ying

18. 18 Back up slides

19. 19 Session 10 Summary (to be revised during the discussion) Fusion system has many major components located inside the vacuum vessel. –Failures such as coolant leaks require shutdown (and redundancy in the PFC/blanket is not feasible) –Repair/replacement takes long time The reliability requirements on Divertor/FW/Blanket are challenging due to a large surface area, long MTTR, and harsh environment, and must be seriously addressed in FNF/CTF. –Predicting achievable MTBF requires real data from integrated tests in the fusion environment. One of the missions of FNF/CTF is to learn how to achieve a high device availability under DEMO prototypical conditions, which include high heat load and surface heat flux, and moderate neutron fluence (i.e. 6 MW-y/m2.) This mission fills the RAM Gap that was identified in the FESAC Greenward Panel. A PRA-like approach that defines a RAM goal for each major fusion component can guide fusion energy development in a cost effective manner.

20. 20 Example MTBFs & MTTRs from Existing Tokamak Systems with in-vessel RH MTTRs to Apply to an FNF

21. 21 Example MTBF and MTTR from Existing Tokamak Systems to Apply to an FNF

22. 22 For Blanket Component Availability resulting from unscheduled maintenance requirements is more demanding than lifetime requirements MTTR = mean time to replace n = number of blanket segments = 80 (assuming 16 coils/sectors, 5 inboard + outboard blanket segments per sector) = failure rate per blanket segment MTBF = 1/ (Mean Time Between Failure) Note: a blanket segment has a full poloidal length in height and 1/48th toroidal circumference in width)

23. 23 Reliability Growth Testing is Key to Ensuring High FNT Component Reliability A key objective of reliability growth testing in CTF will be to reduce the failure rate to an acceptable level Beginning of life (BOL) failure mechanisms are easiest to address, because the failure rate is higher. Improvements during the constant failure rate regime are sometimes elusive because the failure rate may be very small. These failures will be difficult to see in reasonable test times. A Reliability growth testing program involves an iterative design/test/fix sequence aimed at improving component reliability. Without such a program in a simulated nuclear fusion nuclear environment, FNT components intended for the first fusion facilities will represent new design applications without engineering precedence and will suffer from a lack of confidence in their estimated reliability. Component failures are generally described by a “bathtub” curve.

24. 24 Reliability Analysis Method for Component Testing Reliability Growth Model A model allows the designer to estimate the amount of development effort needed to ensure that a reliability target is reached Failure Models, Effect and Criticality Analysis An analysis process enables the test planner to identify the most critical constituents which must be addressed at the early stages of testing Statistical methods are available to estimate: 1.Cumulative test time required for MTBF demonstration tests at some confidence level 2.the required sample size and the test time per test article for achieving goal MTBF Bayesian Approach An approach taking into account the data (if available) from similar technology experiences which would result in test time saving NAVAIR reliability growth improvement model An aggressive program of reliability development implies a higher growth rate and lesser testing times required for achieving the target MTBF

25. 25 An Example CTF Device Duty Factor Scenario A detailed assessment should be done during the CTF design exploration study 1. Group CTF into three major component categories 2. Perform best estimate of scheduled/unscheduled availability for each major component category Engineering Components (coils, heating, current drive, tritium system, vacuum vessel) Divertor (and Breeding Blanket Modules for tritium breeding) - Database from fission reactor testing - Reliability oriented (low T & p) Test Modules for Demo Blankets and Divertors Reliability growth Availability Time 10% 30% Duty cycle increases; while approaching steady state operation Insertion of test modules for Demo blankets and divertors 2035 Initial availability with which has a low plasma duty factor? Insert test modules as the plasma duty factor grows to 80%? Availability drops to 9% as a result of test module insertion 3. Availability grows as reliability growth proceeds

26. 26WG1 Presentation at JET 24/09/07 Ensuring the reliability of ITER systems - engineering practices, configuration control, and QA to support the procurements The achievement of the specified reliability and availability by ITER is challenging and requires careful attention to the Design, Quality Assurance, Testing, Maintenance and control of operation at every stage in the construction and operation of the facility. The appointment of a RAM officer and setting up of contracts with the EU and US to provide support are important initial steps, but more manpower must be found to avoid delay to the procurement. Better definition of the design and approval processes is required. Significant delays and design changes must be anticipated to arise from the detailed RAM analysis.

27. 27 Major components of an ST-CTF

28. 28 Example Port Assembly Replacement Tasks and Time Estimates (from ITER and FIRE) Conditions and Assumptions Midplane port assembly is removed as an integrated assembly that is lip-seal welded to port, structurally attached at end of port (bolts and/or wedges) and is removed or installed in a single cask docking. Port assembly is transferred to hot cell and is replaced with a new or spare unit. If the removed assembly is to be reinstalled, the hot cell processing time must be added. If a port assembly is removed for other than a short period of time, the open port may be shielded to allow personnel access in the ex-vessel region of the machine. The time to install a shielded enclosure at the port is not included in the following estimate and would add days to the estimate. Operations are conducted in two 8-hour shifts per day (16 hrs total), 6 days per week. Time to leak check welded lip-seals and pipes not included. Could add a few days to campaign. Time to detritiate and vent the vessel after shutdown, and pump down and clean the vessel after maintenance are not included. Could add ~ 1 month to shutdown period.

29. 29 Example Port Assembly Replacement Tasks and Time Estimates (cont’d) Task and Time Summary (assuming 16-hr days, 6 work days per week) 1) Hands-on prepare port for cask docking and 60 hrs3.75 days port assembly removal 2) Remotely remove port assembly and transfer to hot cell (remote) 28 hrs1.75 days 3) Remotely exchange port assembly at hot cell and return to port20 hrs1.25 days 4) Remotely replace port assembly in port25 hrs1.5 days 5) Hands-on port assembly recovery tasks56 hrs3.5 days 189 hrs11.8 days Subtotal = 11.8 days + 2 days for leak tests, misc items = 13.8 days = 2.3 weeks (6 work days/week) With 27.5% contingency = 17.6 days = ~ 3 weeks (6 work days/week, 16 hrs per day) Assuming 24/7 continuous work weeks = [189 hrs + (2 x 16 hrs)] 1.275 = 282 hrs = 12 days or ~ 2 weeks