Divertor System Final Design and Key Issues

ARIES Electronic Project Meeting
December 4, 1998

Material Issues

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Design Summary

DBTT and Fracture Toughness

The unirradiated ductile-to-brittle transition temperature for W is quite high -- around 800°C. Our strategy is to:

  1. stay well below the ultimate strength,
  2. ensure we maintain a "cold-worked" microstructure, and
  3. perform some simple fracture mechanics analysis.
Analysis

The peak stress is 393 MPa (see analysis), compared with an allowable of 675 MPa at 1000 °C.

After 5 dpa at 800°C the fracture toughness is 30 MPa-m1/2
The critical crack size for 400 MPa load is 1.8 mm:
a = (KI/s)2 / p

Cycling could be a problem.

Fabrication and bonding

Reference technique is powder metallurgy (HIP) forming of pipes and web plates

Bonding to steel substructure is done with T~1200°C braze material.

New porous metal concept

ULTRAMET foam