# Presentation: 096025

## ISIS Second Target Station

**Project Summary**
**Target design, analysis and optimisation**

- Robbie Scott
- Mechanical Design / Project Engineer
- ISIS Facility

## Upgrade of ISIS – accelerator based, pulsed neutron source
Synchrotron accelerator shared between both target stations
Double the number of instruments

**Synchrotron accelerator shared between both target stations**
**Double the number of instruments**

- ISIS Second Target Station

## Designed for key future scientific needs:
Soft matter
Advanced materials
Bio-molecular science
Nano-technology

Scientific requirements imply need for specific flux characteristics:
Significantly enhanced cold neutron flux
Broad spectral range
High resolution
Moderators designed to provide excellent conditions for required flux characteristics:
Low frequency : 
10Hz  		
100ms frame	
Low power: 
48kW
60μA

- Soft matter
- Advanced materials
- Bio-molecular science
- Nano-technology
**Scientific requirements imply need for specific flux characteristics:**
- Significantly enhanced cold neutron flux
- Broad spectral range
- High resolution
**Moderators designed to provide excellent conditions for required flux characteristics:**
- Low frequency :
- 10Hz
- 100ms frame
- Low power:
- 48kW
- 60μA

- ISIS Second Target Station

## Slide 4

## Maximise use of ‘target’ materials
Design target geometry to match proton beam
Maximises target neutron yield, while minimising absorption
Optimise cross-sectional area 
Minimise volume of coolant channels
Maximises solid angle which moderators view

**Design target geometry to match proton beam**
- Maximises target neutron yield, while minimising absorption
**Optimise cross-sectional area **
**Minimise volume of coolant channels**
- Maximises solid angle which moderators view

- Neutronically efficient target design

## Baseline target design

- EPB

- D20 Out

- D20 in

- Stainless Steel Pressure Vessel

- D20

- Tantalum Cladding

- Flow Divider

- Tungsten Core

- Proton beam window

## Optimisation of baseline target design

**Reduction in pressure vessel wall by 70%**
**Reduction in coolant channel depth by 80%**
**Overall reduction in Target diameter of 28%**
- Allows moderators to move closer to neutron producing core
- Increases solid angle which moderators view
- Reduces probability of neutron absorption within target
**Resulted in significant increases in neutron flux (60%)**

## Back to the drawing board!

**Removal of proton beam window & introduction of new cooling channel concept**
- Proton beam no longer passes through Inconel window and D20
- Flow channel geometry altered – purely radial cooling
- Flux increase of approximately 5%
- Improved reliability

- Pressure distribution within target cooling channels

## Slide 9

## Materials

**Pressure vessel material choice**
- Replace stainless steel with Tantalum
- Further reductions in target diameter (now 63% of original size)
- Further 15% flux increase

## Consequences of design alterations

**Total predicted flux increase due to design alterations ****≈ 75 - 80%**
- Neutron flux 95% of pure Tungsten target
**However new cooling channel concept must be proven**
- Computational Fluid Dynamics (CFD) employed for analysis and optimisation of coolant channels
- CFD subsequently verified using flow tests

## CFD Analysis of initial design

**CFX used to Computational Fluid Dynamics analysis**
**CFD revealed problematic separation & pressure drop at inside of bend**
**Resulting recirculation would heat coolant excessively**

## Removal of recirculation

**A solution was required to remove the recirculation**
**The flow guide was modified into an aerofoil form**
- Prevents separation and subsequent recirculation

## Cavitation

**A fluid’s vapour pressure is proportional to temperature**
**If the pressure within a flow falls below the local vapour pressure, cavities (or bubbles) will form**
**As the cavities leave the low pressure region, they collapse,  damaging the vessel wall**

**2.4 bar**
**1**
**0**
**-0.7**

## Vapour Pressure H20

_**Vapour Pressure H20**_

## Cavitation Prevention

**High flow velocities within the target cause a pressure drop on the inside of the bend**
- If local vapour pressure is greater than local pressure, cavitation will occur
**Solution**
- Map vapour pressure onto flow model
- Increase inlet and outlet pressures                                   (maintaining differential) until pressure in all regions are above local vapour pressure
- Final inlet pressure 5 bar

## Modelling proton beam heat load within the target

- Modelling proton beam heat load within the target

**MCNPX used to calculate energy deposition by the proton beam within target**
**Curve fitting allowed the creation of functions which accurately describe the axial and radial variation of heat load **

## Thermally induced stress	

**Temperatures within target are calculated using CFD**
- Temperatures exported to an FEA package (ANSYS)
- Thermally induced expansions are then calculated
- Resultant stresses and are then calculated
**Differing coefficient of thermal expansion **
- Tungsten & Tantalum differ by 2μm/m/°C
- Small stresses

## Verifying CFD Results

**Prototype thermal test target, installed with a dense network of pressure tappings**
**5 cartridge heaters will supply 37kW of power, to test the cooling **
- Power varied axially along the target

## Manufacturing

**Majority of target simple to manufacture:**
- Tungsten core is encased in a 1mm sleeve of Tantalum
- Sleeve is e-beam welded, creating a hermetic seal
- Assembly is hot isostatically pressed (HIP)
- Ultrasonic NDT used to test HIP bond

## Tantalum pressure vessel complex to manufacture
Incorporates aerofoil structures on ID!
Former created on CNC mill 
Hot Isostatic Pressing is used to create the vessel from powder
Former leached away after 	              	        vessel created
Pressure vessel shrink fitted onto                            core, then assembly e-beam welded

- Incorporates aerofoil structures on ID!
- Former created on CNC mill
- Hot Isostatic Pressing is used to create the vessel from powder
- Former leached away after 	              	        vessel created
**Pressure vessel shrink fitted onto                            core, then assembly e-beam welded**

## Project Uncertainties

**Potential for erosion due to high coolant velocities**
**Pressure vessel manufacturing method yet to be proven**