- Email: [email protected]
Status of ITER dimensional tolerance studies
Fusion Engineering and Design 88 (2013) 597–601
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Status of ITER dimensional tolerance studies F. Javier Fuentes a,∗ , Vincent Trouvé a , Emily Blessing b , Jean-Jacques Cordier a , Jens Reich a a b
ITER Organization, Route de Vinon sur Verdon, 13115 St Paul Lez Durance, France Dimensional Control Systems Inc., 580 Kirts Boulevard, Suite 309, Troy, MI 48084, USA
a r t i c l e
a b s t r a c t
i n f o
Article history: Received 14 September 2012 Received in revised form 20 December 2012 Accepted 18 January 2013 Available online 22 March 2013
The optimization of the manufacturing/assembly tolerances and processes in ITER Experimental Nuclear Fusion Device is one of the key tasks to optimize the fabrication cost, to prevent problems during assembly and to ensure that the critical homogeneity of the magnetic field and the positioning requirements of the plasma facing components can be achieved. This task is further complicated by the strong interplay among the various Tokamak systems, as for instance in the inner region of the machine where the clearances between Central Solenoid, Toroidal Field Coils, Thermal Shield, Vacuum Vessel and In-Vessel components have been minimized for their large influence on the magnetic flux and the overall machine cost. A 3D tolerance simulation analysis of ITER Tokamak machine has been developed based on 3DCS dedicated software. The dimensional variation model is representative of Tokamak functional tolerances and processes, predicting accurate values for the amount of variation on critical areas. In addition, dimensional simulations help to determine the key tolerances that contribute to a particular variation. This paper describes the current status of the Tokamak dimensional variation studies and its management plan, highlighting the status of compliance of allocated tolerances with input requirements. Management of risk issues and corrective actions are also described. © 2013 Elsevier B.V. All rights reserved.
Keywords: ITER Tokamak Dimensional analysis Dimensional management
2. Scope of dimensional studies
1. Introduction The cumulative down-up tolerance analysis for parts assembled together was verified in the past by root mean squared (RMS) of contributing tolerances on a two-dimensional plane, according to the following expression: Total variation =
Ti2
1/2
being Ti the tolerance of the ith dimension. This method makes the variation in three-dimensional space hard to analyze in complex structures like ITER systems. Full 3-D dimensional studies of the Tokamak basic machine and Tokamak building are being performed by the Design Integration Team within ITER Organization (IO), based on dedicated 3DCS Software from Dimensional Control Systems, Inc. Statistical variation analysis based on Monte Carlo simulations is currently used to assess the compliance status, identify risk issues and define mitigation strategies in early phases for performance/cost/schedule improvement.
∗ Corresponding author. Tel.: +33 442178051. E-mail address: [email protected] (F.J. Fuentes). 0920-3796/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fusengdes.2013.01.061
Dimensional studies will be used along ITER life-cycle to assess:
a. The risk mitigation strategies. b. The potential clashes in critical areas. c. The impact and feasibility of tolerance relaxation proposed by IO or Domestic Agencies (DA). d. The impact of Deviation Requests (DR) and Non-Conformities (NC) involving tolerances. e. The feasibility of assembly procedures. f. The reallocation and optimization of tolerances to as-built/asassembled.
The Tokamak dimensional variation analysis is a basic Configuration Management tool that provides: • Requirements and compensators performance at Tokamak and systems level. • The compliance status with functional/assembly requirements at room temperature (RT), operation, maintenance and other non-standard scenarios (combined with structural and thermal displacements from structural analysis and thermal scale mockups).
598
F.J. Fuentes et al. / Fusion Engineering and Design 88 (2013) 597–601
Model Inputs A s s e m b ly P r o c e du r e s
Based on CMMs
GD&T callouts, according ASME Y14.5M
Assembly of functional components, including references and allocated accuracies
Variation Analysis
3 D G e o me t r y
Pa r t Fu n c ti ona l To le r a n c e s
3DCS VariationModel
3DCS Model Construction Tokamak Tolerance Model based on CMMs, Part Tolerances and Asembly Moves
3 D CS Mode l Va ri a ti ons Statistical results from MonteCarlo runs to assess model compliance with the requirements
Requirements T o l e r a n c e R e q u i r e me nt s
R i s k I mp a c t
R i s k A s s e s s me n t
Top Level Functional and Assembly Requirements
Impact on performances, schedule and cost of Risk Issues identified from model measurements
Probability of NonCompliances with Top Requirements based on 3sigma or Worst Case
Risk Analysis
Model Established
M i ti ga ti o n St ra te g y
YES
M a i n C on tr i b u t o r s NO
Risk Mitigation
Should Risk Issues be Mitigated?
Update Requirements Optimize Part Tolerances Optimize Assembly Define Compensators
Part Tolerances Assembly Procedures Compensator Performance
Model Mature
O p t i mi z a t i o n S t u d i e s
Mode l Ma inte na n c e
I mpa c t St u d i e s
R e a l l o c a t i o n o f To le r a n c e s
Perform studies to improve Cost, Schedule and Performance Issues
Update the model to Current Baseline
Management of tolerance issues, including PCRs, DRs and NCs
According as-built and as-assembled data
Optimization/Maintenance
Model Mature as-built /as-assembled Fig. 1. Dimensional workflow diagram.
It is also a valuable tool to manage risk issues and mitigation strategies during the design, manufacturing and assembly phases, including: • Identification of risk issues based on non-compliant scenarios.
• Quantification of probability of occurrence of risk issues based on Monte Carlo runs. • Identification and assessment of mitigation strategies and customization logic, based on main contributors: part tolerances, assembly processes and compensator performance.
F.J. Fuentes et al. / Fusion Engineering and Design 88 (2013) 597–601
599
Fig. 2. Blanket tolerance requirements.
Finally, dimensional variation analysis is a cost-effective tool for managing tolerances and processes optimization during the construction phase 3. Dimensional management methodology Fig. 3. Toroidal Field Coils tolerance requirements.
Tokamak dimensional variation studies are based on parts geometry obtained from 3D Configuration Management Models (CMM) [1]. Manufacturing tolerances are applied per the Geometric Dimensioning and Tolerancing Standards (GD&T) [2], according to the allocated values. The assembly sequence and features used to locate parts in the final system are mathematically implemented in moves that the model performs after the tolerances have been applied. Geometric requirements for successful assembly and operation of the Tokamak are assessed for the probability of compliance from model runs (typically 5000) driven by a Monte Carlo Random Number Generator and the allocated probability distributions.
3.1.4. Optimization and maintenance Tolerance and processes should be updated as required during the construction phase. It should include: • • • •
Studies to improve cost, schedule and performances. Model update to current baseline. Impact studies on deviation requests and non-conformities. Reallocation of tolerances and processes according to as-built/asassembled data.
3.1. Workflow
Optimization could impact on mitigation strategies and model inputs. Model status in the output is mature (as-built/asassembled).
The dimensional workflow diagram throughout the machine life-cycle is represented in Fig. 1. Four different phases have been defined, according to the maturity level of tolerances and processes:
3.2. Statistical considerations
3.1.1. Identification of tolerance requirements Functional and assembly requirements are the main drivers to compliance studies and risk mitigation assessment. 18 functional requirements and 12 assembly requirements are currently identified at Tokamak and system levels (see Fig. 2 for Blanket requirements and Fig. 3 for Toroidal Field Coil requirements).
Compliance is currently based on 3 values, representing a probability of occurrence better than 99.7% Mitigation strategies are identified and assessed based on 3 non-compliant scenarios. Non-compliances having low/medium impact could be assessed at 2 (95% occurrence) or (68% occurrence) values. A mitigation contingency is also provided for worse noncompliant cases (very low probability of occurrence) having a high impact on performance, schedule or cost. Worst cases appear only 1 or 2 times within all runs, being statistically non-meaningful. The worst case scenario, based on all tolerances set at range limits, is performed only for critical non-compliance cases. Mitigation could have a high impact on cost/schedule in this case.
3.1.2. Variation analysis 3DCS Tokamak variation model is implemented during the design phase from 3D geometry, part functional tolerances and assembly processes. The status of compliance is derived from statistical results provided by Monte Carlo runs. Model status in the output is established (to-build).
4. Model status
3.1.3. Risk analysis Risk issues are identified from the probability of noncompliance with tolerance requirements during design and construction phases. Risk impact is assessed and mitigation strategies are defined based on main contributors provided by the model. Mitigation could impact on model inputs. Model status in the output is mature (to-build/as-built/as-assembled).
Current Tokamak variation model is representative of Tokamak basic machine, including Magnets, Vacuum Vessel, In-Vessel Coils, Blankets, Divertor, Remote Handling, Cryostat, Thermal Shield and Port Systems. The Tokamak Building B11 is partially included. The model is also representative of assembly processes. Model status is shown in Fig. 4. It should reach the established status (model implemented but risk issues not yet mitigated) at the end of 2012 and mature status (risk issues fully mitigated) at the
600
F.J. Fuentes et al. / Fusion Engineering and Design 88 (2013) 597–601
Functional/Assembly Requirements Toroidal Field Coils MAGNETS
Poloidal Field Coils Correction Coils Central Solenoid Magnet Feeders
VACUUM VESSEL
Risk Analysis
Model Optimization/Maintenance
3DCS Model under construction 3DCS Model under construction 3DCS Model Established. Risk Mitigation ongoing 3DCS Model under construction 3DCS Model Mature
TF Gravity Support Vacuum Vessel
Variation Analysis
3DCS Model Established. Risk Mitigation ongoing (Critical non-compliance issue)
3DCS Model Mature. Assembly should be reviewed/updated. Management of DRs from IO and DAs ongoing
Upper/EQ Ports
3DCS Model Established. Risk Mitigation ongoing
NB Ports
3DCS Model Established. Risk Mitigation ongoing
In-Vessel Coils
3DCS Model Mature. Assembly should be reviewed/updated
VV Gravity Support
3DCS Model Established. Risk Mitigation ongoing
Blankets
3DCS Model Established. Risk Mitigation ongoing
BLK
Blanket Manifolds Divertor
RH
Remote Handling
CRYOSTAT
DVT
Cryostat Support Cryostat Base Lower & Upper Cylinders Top Lid
3DCS Model Established. Risk Mitigation ongoing (Critical non-compliance issue) 3DCS Model Mature 3DCS Model construction delayed to 2013 3DCS Model should be updated 3DCS Model Mature 3DCS Model Established. Assembly should be reviewed. Risk Mitigation ongoing 3DCS Model Established. Assembly should be reviewed. Risk Mitigation ongoing
TS
VV Thermal Shield
3DCS Model Established. Risk Mitigation ongoing
BLG
Tokamak Building
3DCS Model Established. Risk Mitigation ongoing
Fig. 4. Tokamak variation model status.
end of 2013 (currently 55% of systems are at established level and 18% are at mature level). Other scenarios (including RH issues and assembly intermediate steps) will be implemented later. The status of Tokamak components is described hereafter. 4.1. Magnets The variation analysis for the Toroidal Field Coils (TFC), including 18 coil structures and gravity supports, is completed. Three different models for TFC assembly have been implemented to try to overcome the non-compatibility of tolerance requirements in Fig. 3. Probability of occurrence of non-compliance events is 55% for the radial positioning requirement, based on the best assembly scenario. The requirement on the gap between adjacent TFC at the level of Inner Leg Intercoil Structures (ILIS) (±0.5 mm variation with 2 mm nominal) is unfeasible with current tolerances/processes. Probability of occurrence of non-compliance events, based on clash between ILIS surfaces (gap < 0), is 46% for the same assembly scenario. Probability of occurrence of non-compliant events, based on both requirements, is 74%. Non-compliant scenarios could have a direct impact on the TFC assembly procedure. This is the main risk issue in the current analysis. Risk mitigation is ongoing, based on a detailed assessment of assembly procedures, assembly accuracies and allocated distributions. TFC deflection during vertical lifting should be also considered. Non-compatible requirements will be reviewed and updated. A conditional logic could be implemented to optimize TFC toroidal position according to the as-built ILIS gap. The potential impact on loop closure should be assessed. The variation analysis for the Poloidal Field Coils, Correction Coils and Magnet Feeders is ongoing. The variation analysis for the Central Solenoid is completed. Risk analysis is ongoing. 4.2. Vacuum Vessel Vacuum Vessel (VV) variation model has reached the mature status. VV assembly baseline (including the distributions allocated to assembly processes) should be reassessed and optimized (2013) based on detailed assembly tooling. Welding model and shrinkage
variation should be reassessed based on R&D studies to be performed during the Development Phase of the Welding Contract (scheduled for 2013). These issues could impact on marginal non-compliances in VV Splice Plates, VV Gravity Support assembly and lateral customization of Blanket Cartridges. 4.3. VV Ports and Port Systems The variation analysis for the VV Ports, including Equatorial (EQ), Upper and Neutral Beam Ports, is completed. EQ/Upper Port – Plug minimum clearances are compliant with the requirements (16 mm in Upper Ports, 9 mm in EQ Ports) in 99.5% of cases. Marginal noncompliances (worst case) should be mitigated, case-by-case, during the construction phase. Remote Handling (RH) transfer cask to building clearances has been also measured in the model. The variation analysis for Plug insertion is ongoing. 4.4. In-Vessel components The variation analysis for the Blankets, Blanket Manifolds, InVessel Coils for Edge Localized Mode control and plasma Vertical Stability (ELM and VS) and Divertor is completed. Divertor model has reached the mature status. A large effort has been made in the last months to implement a very detailed analysis of Blanket Cartridges customization. A conditional logic for Blankets repositioning has been implemented to mitigate the risk of cartridges over-customization above the 8.5 mm limit (see Fig. 2). That could represent up to 40% of non-compliant cartridges in VV Sectors in the absence of any compensator. This logic has a low-to-moderate impact in Blankets misalignment from nominal. (Less than 10% of Blankets are moved in 99% of cases. Displacements are less than 2 mm for 99.98% of cases) Model results are non-compliant (up to 22% of cases) with the minimum radial clearance requirements between VV-ELM (20 mm in Diagnostics cabling areas, 5 mm in other areas), ELM-Manifolds (5 mm) and Manifolds-Blankets (5 mm). This is a critical risk issue
F.J. Fuentes et al. / Fusion Engineering and Design 88 (2013) 597–601
that should be mitigated. Tolerance profile callouts and nominal gaps are being reviewed to improve this issue. 4.5. Cryostat The variation analysis for the Cryostat Base, Lower and Upper Cylinders and Top Lid is completed. Cryostat Base model has reached the mature status. The concrete ring support structure will be implemented later. Model measurements are non-compliant with the required alignment of Cryostat openings respect to the Tokamak Assembly Datum (TAD) reference system (±20 mm vertical, ±30 mm toroidal) in less than 5% of cases (except for toroidal position in the upper). Risk assessment is ongoing. Misalignment between VV Ports and Cryostat openings (up to ±40 mm vertical, ±60 mm toroidal in the Upper Ports) should be compensated at interface level. Compensator performances are under assessment. The detailed assembly procedure for the Cryostat Upper and Lower Cylinders should be reviewed/updated with India-DA 4.6. Thermal Shield The variation analysis for the VV Thermal Shield (VVTS) is completed. Measured variations of toroidal gap between adjacent VVTS 40◦ sectors (up to ±13 mm in the inboard, ±15 mm in the outboard) are not compliant with the allowable range of in-pit joints (6–26 mm, nominal 16). Risk mitigation is ongoing. The minimum clearance between VVTS and TFC in the inboard corresponds to the RT scenario (12.9 mm). This value is marginally non-compliant with the required 14 mm.
601
operation, VV baking, outgassing, In-Vessel maintenance, loss of power and Cryostat helium, water or air ingress. They should be used in conjunction with variation measurements and structural displacements to perform accurate gap studies on critical areas. 6. Conclusions The procedures for Tokamak dimensional management have been implemented in ITER, based on full 3-D variation analysis. Current studies include compliance assessment with tolerance requirements, risk assessment and risk mitigation. Dimensional studies are the required tool for the assessment of tolerance related Change Requests (PCR), Deviation Requests (DR) and Non-Conformities (NC) submitted by IO or any DA during the construction phase. Studies will also provide a valuable tool for efficient reallocation of tolerances and processes according to asbuilt/as-assembled data. Variation analysis is completed in 73% and ongoing in 23% of Tokamak systems. 18% of models have reached the mature status. The tolerance model covers 8 systems at Tokamak level 1 and 23 systems at level 2. It includes 600 single parts, 15000 points, 2200 part tolerances, 760 moves, 30 functional/assembly requirements and 6000 measurements to verify compliances and perform impact studies. Acknowledgments The key contribution of E. Blessing, from Dimensional Control Systems, is kindly acknowledged. The views and opinions expressed herein do not necessarily reflect those of ITER Organization. References
5. Tokamak thermal scale mock-up Thermal scale models have been developed in Catia based on approved CMMs for different thermal scenarios, including normal
[1] J.J. Cordier, Overview of the ITER design and integration status, in: SOFT, September 2012, Liege, Belgium, 2012. [2] Dimensioning and Tolerancing, ASME Y14.5M-1994, American Society of Mechanical Engineers.
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Status of ITER dimensional tolerance studies F. Javier Fuentes a,∗ , Vincent Trouvé a , Emily Blessing b , Jean-Jacques Cordier a , Jens Reich a a b
ITER Organization, Route de Vinon sur Verdon, 13115 St Paul Lez Durance, France Dimensional Control Systems Inc., 580 Kirts Boulevard, Suite 309, Troy, MI 48084, USA
a r t i c l e
a b s t r a c t
i n f o
Article history: Received 14 September 2012 Received in revised form 20 December 2012 Accepted 18 January 2013 Available online 22 March 2013
The optimization of the manufacturing/assembly tolerances and processes in ITER Experimental Nuclear Fusion Device is one of the key tasks to optimize the fabrication cost, to prevent problems during assembly and to ensure that the critical homogeneity of the magnetic field and the positioning requirements of the plasma facing components can be achieved. This task is further complicated by the strong interplay among the various Tokamak systems, as for instance in the inner region of the machine where the clearances between Central Solenoid, Toroidal Field Coils, Thermal Shield, Vacuum Vessel and In-Vessel components have been minimized for their large influence on the magnetic flux and the overall machine cost. A 3D tolerance simulation analysis of ITER Tokamak machine has been developed based on 3DCS dedicated software. The dimensional variation model is representative of Tokamak functional tolerances and processes, predicting accurate values for the amount of variation on critical areas. In addition, dimensional simulations help to determine the key tolerances that contribute to a particular variation. This paper describes the current status of the Tokamak dimensional variation studies and its management plan, highlighting the status of compliance of allocated tolerances with input requirements. Management of risk issues and corrective actions are also described. © 2013 Elsevier B.V. All rights reserved.
Keywords: ITER Tokamak Dimensional analysis Dimensional management
2. Scope of dimensional studies
1. Introduction The cumulative down-up tolerance analysis for parts assembled together was verified in the past by root mean squared (RMS) of contributing tolerances on a two-dimensional plane, according to the following expression: Total variation =
Ti2
1/2
being Ti the tolerance of the ith dimension. This method makes the variation in three-dimensional space hard to analyze in complex structures like ITER systems. Full 3-D dimensional studies of the Tokamak basic machine and Tokamak building are being performed by the Design Integration Team within ITER Organization (IO), based on dedicated 3DCS Software from Dimensional Control Systems, Inc. Statistical variation analysis based on Monte Carlo simulations is currently used to assess the compliance status, identify risk issues and define mitigation strategies in early phases for performance/cost/schedule improvement.
∗ Corresponding author. Tel.: +33 442178051. E-mail address: [email protected] (F.J. Fuentes). 0920-3796/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fusengdes.2013.01.061
Dimensional studies will be used along ITER life-cycle to assess:
a. The risk mitigation strategies. b. The potential clashes in critical areas. c. The impact and feasibility of tolerance relaxation proposed by IO or Domestic Agencies (DA). d. The impact of Deviation Requests (DR) and Non-Conformities (NC) involving tolerances. e. The feasibility of assembly procedures. f. The reallocation and optimization of tolerances to as-built/asassembled.
The Tokamak dimensional variation analysis is a basic Configuration Management tool that provides: • Requirements and compensators performance at Tokamak and systems level. • The compliance status with functional/assembly requirements at room temperature (RT), operation, maintenance and other non-standard scenarios (combined with structural and thermal displacements from structural analysis and thermal scale mockups).
598
F.J. Fuentes et al. / Fusion Engineering and Design 88 (2013) 597–601
Model Inputs A s s e m b ly P r o c e du r e s
Based on CMMs
GD&T callouts, according ASME Y14.5M
Assembly of functional components, including references and allocated accuracies
Variation Analysis
3 D G e o me t r y
Pa r t Fu n c ti ona l To le r a n c e s
3DCS VariationModel
3DCS Model Construction Tokamak Tolerance Model based on CMMs, Part Tolerances and Asembly Moves
3 D CS Mode l Va ri a ti ons Statistical results from MonteCarlo runs to assess model compliance with the requirements
Requirements T o l e r a n c e R e q u i r e me nt s
R i s k I mp a c t
R i s k A s s e s s me n t
Top Level Functional and Assembly Requirements
Impact on performances, schedule and cost of Risk Issues identified from model measurements
Probability of NonCompliances with Top Requirements based on 3sigma or Worst Case
Risk Analysis
Model Established
M i ti ga ti o n St ra te g y
YES
M a i n C on tr i b u t o r s NO
Risk Mitigation
Should Risk Issues be Mitigated?
Update Requirements Optimize Part Tolerances Optimize Assembly Define Compensators
Part Tolerances Assembly Procedures Compensator Performance
Model Mature
O p t i mi z a t i o n S t u d i e s
Mode l Ma inte na n c e
I mpa c t St u d i e s
R e a l l o c a t i o n o f To le r a n c e s
Perform studies to improve Cost, Schedule and Performance Issues
Update the model to Current Baseline
Management of tolerance issues, including PCRs, DRs and NCs
According as-built and as-assembled data
Optimization/Maintenance
Model Mature as-built /as-assembled Fig. 1. Dimensional workflow diagram.
It is also a valuable tool to manage risk issues and mitigation strategies during the design, manufacturing and assembly phases, including: • Identification of risk issues based on non-compliant scenarios.
• Quantification of probability of occurrence of risk issues based on Monte Carlo runs. • Identification and assessment of mitigation strategies and customization logic, based on main contributors: part tolerances, assembly processes and compensator performance.
F.J. Fuentes et al. / Fusion Engineering and Design 88 (2013) 597–601
599
Fig. 2. Blanket tolerance requirements.
Finally, dimensional variation analysis is a cost-effective tool for managing tolerances and processes optimization during the construction phase 3. Dimensional management methodology Fig. 3. Toroidal Field Coils tolerance requirements.
Tokamak dimensional variation studies are based on parts geometry obtained from 3D Configuration Management Models (CMM) [1]. Manufacturing tolerances are applied per the Geometric Dimensioning and Tolerancing Standards (GD&T) [2], according to the allocated values. The assembly sequence and features used to locate parts in the final system are mathematically implemented in moves that the model performs after the tolerances have been applied. Geometric requirements for successful assembly and operation of the Tokamak are assessed for the probability of compliance from model runs (typically 5000) driven by a Monte Carlo Random Number Generator and the allocated probability distributions.
3.1.4. Optimization and maintenance Tolerance and processes should be updated as required during the construction phase. It should include: • • • •
Studies to improve cost, schedule and performances. Model update to current baseline. Impact studies on deviation requests and non-conformities. Reallocation of tolerances and processes according to as-built/asassembled data.
3.1. Workflow
Optimization could impact on mitigation strategies and model inputs. Model status in the output is mature (as-built/asassembled).
The dimensional workflow diagram throughout the machine life-cycle is represented in Fig. 1. Four different phases have been defined, according to the maturity level of tolerances and processes:
3.2. Statistical considerations
3.1.1. Identification of tolerance requirements Functional and assembly requirements are the main drivers to compliance studies and risk mitigation assessment. 18 functional requirements and 12 assembly requirements are currently identified at Tokamak and system levels (see Fig. 2 for Blanket requirements and Fig. 3 for Toroidal Field Coil requirements).
Compliance is currently based on 3 values, representing a probability of occurrence better than 99.7% Mitigation strategies are identified and assessed based on 3 non-compliant scenarios. Non-compliances having low/medium impact could be assessed at 2 (95% occurrence) or (68% occurrence) values. A mitigation contingency is also provided for worse noncompliant cases (very low probability of occurrence) having a high impact on performance, schedule or cost. Worst cases appear only 1 or 2 times within all runs, being statistically non-meaningful. The worst case scenario, based on all tolerances set at range limits, is performed only for critical non-compliance cases. Mitigation could have a high impact on cost/schedule in this case.
3.1.2. Variation analysis 3DCS Tokamak variation model is implemented during the design phase from 3D geometry, part functional tolerances and assembly processes. The status of compliance is derived from statistical results provided by Monte Carlo runs. Model status in the output is established (to-build).
4. Model status
3.1.3. Risk analysis Risk issues are identified from the probability of noncompliance with tolerance requirements during design and construction phases. Risk impact is assessed and mitigation strategies are defined based on main contributors provided by the model. Mitigation could impact on model inputs. Model status in the output is mature (to-build/as-built/as-assembled).
Current Tokamak variation model is representative of Tokamak basic machine, including Magnets, Vacuum Vessel, In-Vessel Coils, Blankets, Divertor, Remote Handling, Cryostat, Thermal Shield and Port Systems. The Tokamak Building B11 is partially included. The model is also representative of assembly processes. Model status is shown in Fig. 4. It should reach the established status (model implemented but risk issues not yet mitigated) at the end of 2012 and mature status (risk issues fully mitigated) at the
600
F.J. Fuentes et al. / Fusion Engineering and Design 88 (2013) 597–601
Functional/Assembly Requirements Toroidal Field Coils MAGNETS
Poloidal Field Coils Correction Coils Central Solenoid Magnet Feeders
VACUUM VESSEL
Risk Analysis
Model Optimization/Maintenance
3DCS Model under construction 3DCS Model under construction 3DCS Model Established. Risk Mitigation ongoing 3DCS Model under construction 3DCS Model Mature
TF Gravity Support Vacuum Vessel
Variation Analysis
3DCS Model Established. Risk Mitigation ongoing (Critical non-compliance issue)
3DCS Model Mature. Assembly should be reviewed/updated. Management of DRs from IO and DAs ongoing
Upper/EQ Ports
3DCS Model Established. Risk Mitigation ongoing
NB Ports
3DCS Model Established. Risk Mitigation ongoing
In-Vessel Coils
3DCS Model Mature. Assembly should be reviewed/updated
VV Gravity Support
3DCS Model Established. Risk Mitigation ongoing
Blankets
3DCS Model Established. Risk Mitigation ongoing
BLK
Blanket Manifolds Divertor
RH
Remote Handling
CRYOSTAT
DVT
Cryostat Support Cryostat Base Lower & Upper Cylinders Top Lid
3DCS Model Established. Risk Mitigation ongoing (Critical non-compliance issue) 3DCS Model Mature 3DCS Model construction delayed to 2013 3DCS Model should be updated 3DCS Model Mature 3DCS Model Established. Assembly should be reviewed. Risk Mitigation ongoing 3DCS Model Established. Assembly should be reviewed. Risk Mitigation ongoing
TS
VV Thermal Shield
3DCS Model Established. Risk Mitigation ongoing
BLG
Tokamak Building
3DCS Model Established. Risk Mitigation ongoing
Fig. 4. Tokamak variation model status.
end of 2013 (currently 55% of systems are at established level and 18% are at mature level). Other scenarios (including RH issues and assembly intermediate steps) will be implemented later. The status of Tokamak components is described hereafter. 4.1. Magnets The variation analysis for the Toroidal Field Coils (TFC), including 18 coil structures and gravity supports, is completed. Three different models for TFC assembly have been implemented to try to overcome the non-compatibility of tolerance requirements in Fig. 3. Probability of occurrence of non-compliance events is 55% for the radial positioning requirement, based on the best assembly scenario. The requirement on the gap between adjacent TFC at the level of Inner Leg Intercoil Structures (ILIS) (±0.5 mm variation with 2 mm nominal) is unfeasible with current tolerances/processes. Probability of occurrence of non-compliance events, based on clash between ILIS surfaces (gap < 0), is 46% for the same assembly scenario. Probability of occurrence of non-compliant events, based on both requirements, is 74%. Non-compliant scenarios could have a direct impact on the TFC assembly procedure. This is the main risk issue in the current analysis. Risk mitigation is ongoing, based on a detailed assessment of assembly procedures, assembly accuracies and allocated distributions. TFC deflection during vertical lifting should be also considered. Non-compatible requirements will be reviewed and updated. A conditional logic could be implemented to optimize TFC toroidal position according to the as-built ILIS gap. The potential impact on loop closure should be assessed. The variation analysis for the Poloidal Field Coils, Correction Coils and Magnet Feeders is ongoing. The variation analysis for the Central Solenoid is completed. Risk analysis is ongoing. 4.2. Vacuum Vessel Vacuum Vessel (VV) variation model has reached the mature status. VV assembly baseline (including the distributions allocated to assembly processes) should be reassessed and optimized (2013) based on detailed assembly tooling. Welding model and shrinkage
variation should be reassessed based on R&D studies to be performed during the Development Phase of the Welding Contract (scheduled for 2013). These issues could impact on marginal non-compliances in VV Splice Plates, VV Gravity Support assembly and lateral customization of Blanket Cartridges. 4.3. VV Ports and Port Systems The variation analysis for the VV Ports, including Equatorial (EQ), Upper and Neutral Beam Ports, is completed. EQ/Upper Port – Plug minimum clearances are compliant with the requirements (16 mm in Upper Ports, 9 mm in EQ Ports) in 99.5% of cases. Marginal noncompliances (worst case) should be mitigated, case-by-case, during the construction phase. Remote Handling (RH) transfer cask to building clearances has been also measured in the model. The variation analysis for Plug insertion is ongoing. 4.4. In-Vessel components The variation analysis for the Blankets, Blanket Manifolds, InVessel Coils for Edge Localized Mode control and plasma Vertical Stability (ELM and VS) and Divertor is completed. Divertor model has reached the mature status. A large effort has been made in the last months to implement a very detailed analysis of Blanket Cartridges customization. A conditional logic for Blankets repositioning has been implemented to mitigate the risk of cartridges over-customization above the 8.5 mm limit (see Fig. 2). That could represent up to 40% of non-compliant cartridges in VV Sectors in the absence of any compensator. This logic has a low-to-moderate impact in Blankets misalignment from nominal. (Less than 10% of Blankets are moved in 99% of cases. Displacements are less than 2 mm for 99.98% of cases) Model results are non-compliant (up to 22% of cases) with the minimum radial clearance requirements between VV-ELM (20 mm in Diagnostics cabling areas, 5 mm in other areas), ELM-Manifolds (5 mm) and Manifolds-Blankets (5 mm). This is a critical risk issue
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that should be mitigated. Tolerance profile callouts and nominal gaps are being reviewed to improve this issue. 4.5. Cryostat The variation analysis for the Cryostat Base, Lower and Upper Cylinders and Top Lid is completed. Cryostat Base model has reached the mature status. The concrete ring support structure will be implemented later. Model measurements are non-compliant with the required alignment of Cryostat openings respect to the Tokamak Assembly Datum (TAD) reference system (±20 mm vertical, ±30 mm toroidal) in less than 5% of cases (except for toroidal position in the upper). Risk assessment is ongoing. Misalignment between VV Ports and Cryostat openings (up to ±40 mm vertical, ±60 mm toroidal in the Upper Ports) should be compensated at interface level. Compensator performances are under assessment. The detailed assembly procedure for the Cryostat Upper and Lower Cylinders should be reviewed/updated with India-DA 4.6. Thermal Shield The variation analysis for the VV Thermal Shield (VVTS) is completed. Measured variations of toroidal gap between adjacent VVTS 40◦ sectors (up to ±13 mm in the inboard, ±15 mm in the outboard) are not compliant with the allowable range of in-pit joints (6–26 mm, nominal 16). Risk mitigation is ongoing. The minimum clearance between VVTS and TFC in the inboard corresponds to the RT scenario (12.9 mm). This value is marginally non-compliant with the required 14 mm.
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operation, VV baking, outgassing, In-Vessel maintenance, loss of power and Cryostat helium, water or air ingress. They should be used in conjunction with variation measurements and structural displacements to perform accurate gap studies on critical areas. 6. Conclusions The procedures for Tokamak dimensional management have been implemented in ITER, based on full 3-D variation analysis. Current studies include compliance assessment with tolerance requirements, risk assessment and risk mitigation. Dimensional studies are the required tool for the assessment of tolerance related Change Requests (PCR), Deviation Requests (DR) and Non-Conformities (NC) submitted by IO or any DA during the construction phase. Studies will also provide a valuable tool for efficient reallocation of tolerances and processes according to asbuilt/as-assembled data. Variation analysis is completed in 73% and ongoing in 23% of Tokamak systems. 18% of models have reached the mature status. The tolerance model covers 8 systems at Tokamak level 1 and 23 systems at level 2. It includes 600 single parts, 15000 points, 2200 part tolerances, 760 moves, 30 functional/assembly requirements and 6000 measurements to verify compliances and perform impact studies. Acknowledgments The key contribution of E. Blessing, from Dimensional Control Systems, is kindly acknowledged. The views and opinions expressed herein do not necessarily reflect those of ITER Organization. References
5. Tokamak thermal scale mock-up Thermal scale models have been developed in Catia based on approved CMMs for different thermal scenarios, including normal
[1] J.J. Cordier, Overview of the ITER design and integration status, in: SOFT, September 2012, Liege, Belgium, 2012. [2] Dimensioning and Tolerancing, ASME Y14.5M-1994, American Society of Mechanical Engineers.