1. ISIS TS1 Project: Target Design and Analysis
Dan Wilcox
High Power Targets Group, Technology Department
3rd STFC FEA Workshop, Daresbury Laboratory, 19/05/2017

2. Overview Background Overview of TS1 Project target
Detailed design and optimisation
Cooling manifold design
Target plate optimisation
Pressure vessel design to PD5500
Beam window geometry optimisation
Fatigue simulation
Conclusions

3. Background – ISIS Facility
Target Station 1
Opened in 1984
Receives 4/5 beam pulses (160kW)
Proven reliability over many years
Target Station 2
Opened in 2007
Receives 1/5 beam pulses (32kW)
High neutronic efficiency
Synchrotron
800MeV proton energy
Up to 240uA beam current (192kW)
Pulsed at 50Hz

4. Background – ISIS Targets
Target absorbs the incoming proton beam and produces neutrons by spallation
Current TS1 target material is tungsten (good for neutron production), clad in tantalum for corrosion resistance
Split into plates and (heavy) water cooled to remove heat
A stainless steel vessel contains the target and coolant

5. General Target Challenges
High power density
Fatigue due to pulsed beam
Water leaks from target vessel
Meet physics requirements
Consider the neutronics performance of materials
Minimise volume of coolant and extra material around the core
Trade-off between physics performance and engineering reliability

6. TS1 Project – Aims and Objectives
Redesign TS1 target (and other components) to improve neutronic output, without compromising current reliability
Meet design limits on temperature and stress
Work closely with ISIS neutronics group to optimise physics output
Must be compatible with other TS1 components
Focus on increasing neutronic efficiency using modern software and analysis techniques, rather than increasing the beam power

7. Overview of TS1 Project Target
Tantalum-clad tungsten plates, same as current TS1
Heavy water cooling, stainless steel 316L pressure vessel
Still the best choice of materials and geometry, given the beam power
Mass of coolant, pressure vessel and manifold significantly reduced
Beam window
Target plates
Pressure vessel
Proton beam direction
Cross-flow channels
Heavy water
outlet manifold
Heavy water inlet manifold
Thermocouple well
Tantalum
Tungsten
Steel
Heavy water in/out

8. Overview of TS1 Project Target
Mass of material (kg)
Current TS1
TS1 Project
Reduction
Stainless Steel
73.8
8.1
89.0%
Tantalum
32.7
6.9
79.0%
Tungsten
47.3
46.0
2.8%
Total
153.8
61.0
60.3%

9. Cooling Manifold Design
Cooling manifold requirements:
Provide parallel flow to cylindrical plates
Even flow distribution between plates
Minimise pressure drop and water volume
Various options were prototyped in ANSYS CFX
Straight manifold without a divider gave the best flow distribution
Manifold cross section was also optimised
Full Taper
Straight With Divider
Straight No Divider
Half Taper

10. Cooling Manifold Design
Average heat transfer coefficients used as an input to thermal simulations
Average Heat Transfer Coefficient (W/m^2.K)
Plate Face
Plate Side
Small Channel
26700
23800
27000
Parameter
Current TS1
TS1 Project
Pressure Drop (bar)
0.72
0.43
Flowrate (kg/s)
8.6
8.0
Pressure drop and flowrate are within capacity of the existing pump

11. Plate Thickness Optimisation
Minimise number of target plates
Each plate increases the volume of tantalum and heavy water, and the number of manufacturing operations
Use the fewest possible plates without exceeding and thermal or mechanical design limits
The total length of tungsten + tantalum must be kept the same to ensure all protons are absorbed
Heat generation data from Monte Carlo simulation, e.g. FLUKA
Heat deposition in W/m^3

12. Plate Thickness Optimisation
Parametric model created in ANSYS:
Input a list of plate thicknesses
Geometry and mesh are generated automatically
The model is solved and results for each plate are returned
User has to interpret the results after each iteration, and set new inputs
Imported FLUKA data
Thermal and structural simulation
Solid Edge geometry with dimensions controlled from DesignModeller

13. Plate Thickness Optimisation
Optimisation result: 10 plates required at 200uA (reduced from 12)
Limiting factor was tantalum stress for the front 4 plates and surface temperature for the remaining 6
Tantalum stress limit based on current TS1 target as we know this is reliable
Parameter
Current TS1
TS1 Project
Design Limit
Reason for Limit
Core Temperature (°C)
184
196
N/A
Surface Temperature (°C) 35 88
100
Damage to adjacent components
Heat Flux (MW/m^2)
2.0
2.1
3.0
Burnout, plus safety factor
Tungsten Stress (MPa) 89 96
275
50% of tensile strength
Tantalum Stress (MPa)
116
112
Stress level in current TS1

14. Plate Thickness Optimisation
Max. Core Temperature = 196°C
Max. Surface Temperature = 88°C
Max. Tungsten Stress = 96MPa
Max. Tantalum Stress = 112MPa

15. Target Pressure Vessel
Vessel must withstand pressure from coolant (6.3bar worst case), but minimise volume of steel to improve neutronics
Rounded shape and internal support ribs reduce pressure-induced stress
Designed ‘in the spirit of’ British pressure vessel code PD5500
Steel support ribs
Tantalum
Tungsten
Steel
Proton beam

16. Target Pressure Vessel
PD5500 ‘Design by Analysis’ section gives guidance on using ANSYS results, but is not very specific and open to interpretation. In general:
Calculate design strength ‘f’ (minimum of 2/3 yield strength or 2/5 UTS)
Separate stress results into categories (primary membrane, primary bending, secondary)
ANSYS linearised stress results at locations of interest
Apply different limits depending on the location and type of stress:
Location Type
Stress Category
Membrane
Bending
Membrane + Bending
Total Including Thermal
General f
1.5f 3f
Discontinuity
Concentration
N/A
Note: Limits apply to stress intensity (Tresca criterion)

17. Target Pressure Vessel
Example: linearised stress intensity at location A (thin wall)
Stress Category
Membrane
Bending
Membrane + Bending
Total
Stress Intensity 19 97
113
112
Limit
149
224
447
Safety Factor
7.9
2.3
2.0
4.0

18. Target Pressure Vessel
Linearised stress intensity at all locations:
Summary of safety factors:
Path No.
Location
Type
Membrane
Bending
Membrane + Bending
Total 1
Thin Wall
General
7.9
2.3
2.0
4.0 2
Flange Root
Discontinuity
5.8
14.3
6.7
6.3 3
Through Rib
16.7
3.5
3.0
6.1 4
Window Centre
7.6
3.9
3.3
6.5 5
Window Edge
11.5
8.4
7.5
4.5 6
Channel Round
18.4
7.8
6.0
Vessel meets PD5500 requirements with a minimum safety factor of 2

19. Beam Window Optimisation
Beam window must withstand pressure from coolant (6.3bar worst case) and heating from proton beam
A thick window will have higher thermal stress
A thin window will have higher stress due to pressure
Curved window with flat centre provides the best tradeoff
Parametric model plus genetic algorithm in ANSYS DesignXplorer was used to optimise window geometry
Proton beam
Fluid
pressure
Parameter
Range
Tmin
1-4mm
Rflat
2-48mm
Rcurve
10-400mm
Rflat + Rcurve >= 51mm

20. Beam Window Optimisation
Mesh quality was checked for various combinations of the 3 inputs
Screening method was used first, to narrow down input domain
Initial attempts with ‘Adaptive Single Objective’ method minimised total stress, but increased primary stress in the process
Switched to ‘Adaptive Multi-Objective’ method with two objectives; minimise total and primary stress
Tmin = 1, Rflat = 40, Rcurve = 20
Tmin = 2, Rflat = 1, Rcurve = 50
Tmin = 4, Rflat = 10, Rcurve = 400
Tmin = 3, Rflat = 20, Rcurve = 40

21. Beam Window Optimisation
Pareto front plots show the best possible trade-off between the output variables
Parameter
Current TS1
TS1 Project
Peak Total Stress (MPa)
202
114
Peak Primary Stress (MPa) 44 59

22. Fatigue (Preliminary)
Work in progress, initial analysis has been completed:
Limited S-N curve data for all three materials
Beam pulse and beam trip cases simulated with ANSYS fatigue module; outputs Goodman equivalent stress amplitude
Number of pulse and trip cycles calculated assuming 5 year target life

23. Fatigue (Preliminary)
Compare new TS1 target operating conditions to S-N curve data:
No fatigue failure expected based on initial analysis
Look for very high cycle fatigue data for 316L or comparable steels
Beam Trips
Beam Pulses

24. Conclusions
Basic concept is similar to the current target; plates of tantalum-clad tungsten in a stainless steel vessel with heavy water cooling
Uses 60% less material, improving neutron output while reducing material cost and the volume of radioactive waste produced
Analysis work gives confidence that the target will be reliable
Meets all fluid, thermal and structural design criteria
Stress in cladding is less severe than current TS1 target
Pressure vessel meets PD5500 requirements with a safety factor of 2
Manufacturing of prototype parts is now underway