1. New nTOF target: Design Issues
Abstract: Following the radiation safety requirement that nTOF lead target shall not be in contact with the cooling water, an entirely new target assembly must be developed. The concept of a clad target is described.
Preliminary designs of target geometry and target integration in the existing cooling loop are shown, as well as structures for positioning and installation.

2. Outline Introduction Design issues Summary
Old Target versus New
Design issues
Radiation Safety  Target Cladding
Cooling  Geometry of Target Assembly
Integration  Supports & Installation
Summary
Estimated cost, manpower, time
Ans PARDONS
ABOC Days 22-24/01/2007

3. Introduction Satisfy the safety requirements of SC/RP
Clad lead target cooled by existing system
Guidelines for the new target design
Keep the neutron flux characteristics
Reduce radioactive waste (target mass)
Reduce overall activation
From ABMB meeting, 12 June 2006
Ans PARDONS
ABOC Days 22-24/01/2007

4. Remark This presentation shows:
First studies to identify design issues
First simulations (thermal, mechanical) give preliminary results to guide design
Estimations for cost, manpower & time
Work and results from:
SBM Ingénierie & AB/ATB & TS/MME
Ans PARDONS
ABOC Days 22-24/01/2007

5. ? Introduction Old Target
Lead blocks directly in contact with cooling water
Target mass > 4 tons
Support structure entirely stainless steel (water basin in aluminium  corrosion risk)
New Target ?
No direct contact between target lead & water circuit
Smaller target (~1 ton)
Optimised support structure (corrosion, activation, etc.)
Ans PARDONS
ABOC Days 22-24/01/2007

6. Design issues: Radiation Safety
Target Cladding
Metal(*) clad lead target with lead core
Consequences of cladding:
1. Thermal contact resistance between lead
and cladding. Need for good contact pressure between core and shell.
2. Core and shell will have different temperatures  different expansion  large forces on shell.
Proposal: Introduce initial core-shell gap, to have contact at nominal working temperature. Needs to be studied!
(*) Aluminium is used in the calculations. Material may have to change
for reasons of radioactive waste disposal (see talk Luisa ULRICI, today at 12:00)
Possible production method
Challenge
Lead:
Tensile Strength, Ultimate18 MPa
 Modulus of Elasticity14 GPa
Melting point ~320°C
Ans PARDONS
ABOC Days 22-24/01/2007

7. Cladding: Thermal equilibrium
Cylindrical target (R=26.5cm)
with 5mm aluminium cladding
deposited energy
3.4kW(*) to be evacuated
Assume adequate cooling
Results from thermal calculations:
Temperature rise from lead to aluminium ~ 75K
Estimated temperature rise of 130K between start-up and equilibrium  Target temperature reaches 150 °C which is acceptable (45% of lead melting temperature)
Cylindrical shape better cooled and generally easier for production
(*)Load case = 5 pulses/16.8s supercycle
Ans PARDONS
ABOC Days 22-24/01/2007

8. Design issues: Cooling
Cooling  Target Assembly Geometry
Maximum temperature:
Target: 150°C Water: 90°C
90°C!
Water Inlet Nozzles:
Flow=6l/s Velocity=0.01m/s
Natural convection
is dominant!
Water flow = 22 m3/h (6 l/s)
Pressure: pool is at atmospheric pressure
Inlet water temperature: 30°C
Water velocity at inlet: 0,01 m/s (10 inlet, Ø26mm)
Inlet water sections at each extremity of the pool
From water flow and dissipated power (~4KW):
average water temperature rise: ΔT~0,15K
Existing water flow not adapted to size of new target
Target is sufficiently cooled, but water temperature locally high
 Need to redirect / concentrate / guide the water flow around the target
Ans PARDONS
ABOC Days 22-24/01/2007

9. Optimized for cooling Challenge
Proposal: Filling part to help guide the water and increase local velocity
Water temperature:
Average: 22°C - Local:50°C
50°C
Water velocity around target:
Average: 0.02 m/s - Local: 0.1m/s
Filling parts
are efficient
Challenge
Filling parts: complex geometry, minimize mass
Support structure to be adapted
Impact on target integration to be evaluated
Ans PARDONS
ABOC Days 22-24/01/2007

10. Transient behaviour Dynamic effect
(*)Load case = 7ns burst, 1.2s pulse,
5 pulses/16.8s supercycle
Maximum target temperature vs. time  effect of each pulse and supercycle(*)
150°C
195°C
7 minutes
Temperature
Time
20°C
Dynamic effect
will cause shockwaves and cyclic stresses.
(time-scale = msec)
Fatigue?
Cracks?
Lifetime?
Lead melting temp = 320°C
Ans PARDONS
ABOC Days 22-24/01/2007

11. Transient elasto-plastic behaviour
12MPa
Time
Equivalent stress
0MPa
5MPa
1 millisecond
10MPa
Plasticity
First results:
Presence of plasticity
Fatigue driven failure of the material will occur in central region (number of cycles to be determined).
Next steps:
Get detailed material properties (literature / experiment)
Take into account the initial gap and the cladding material.
Fatigue analysis of both lead and cladding material.
Instantaneous hydrostatic elastic pressure EαΔT/(1-2υ) = 130MPa
Radial wave period (shown) ~250μs
Longitudinal wave period ~400μs
Lead:
Lead material properties [1,2]:
Young's modulus: 14 GPa
Yield stress: 12 MPa
Tangent modulus: 60 MPa
Poisson's ration: υ=0.44 (low volume change)
Thermal expansion coefficient: α=29,1.10-6/K
Melting point ~320°C
Radial wave period ~265μs
Lead
Challenge
Ans PARDONS
ABOC Days 22-24/01/2007

12. Design issues: Integration
Supports and guiding system
Need for precise positioning (access!)
Limited space available
Integrate “filling parts”
Installation vertical + horizontal
(moderator) T
First ideas: remotely actuated sliding table, tubes for moderator
To do:
Design
Prototypes
Production
Challenge
Ans PARDONS
ABOC Days 22-24/01/2007

13. Summary: Remaining design work
Cladding & gap
(define material, geometry, production method)
Optimise cooling circuit
(define geometry, link to target support)
Simulate dynamic behaviour
(perform material tests & calculations)
Integration of components
(define supports, guides)
Ans PARDONS
ABOC Days 22-24/01/2007

14. Estimated Cost, Manpower &Time
Cost target & supports:
240 kCHF
Manpower
AB/ATB: 1.5 FTE - SC/RP: 0.5 FTE - TS/MME: ?
Time for design (internal)
4 – 6 months
Time for target production (external)
6 – 9 months
Ans PARDONS
ABOC Days 22-24/01/2007