1. magnetic confinement - ENEA - Fusione

3. FUSION TECHNOLOGY 75
3.4 Magnets
3.4.8 Feasibility study on eddy current testing of ITER coil case
welds (ITER Task TW1-TMS/MMTFRD)
The feasibility study carried out through experimental tests was successfully
concluded. All the tests were performed in laboratory conditions on a series of
samples containing artificial and natural faults. Eddy current techniques were
successfully used to inspect tungsten inert gas (TIG) and submerged arc multipass
welding (SAW) on thick austenitic 316 LN. The VR-11 probe developed by ENEA
showed very high sensitivity compared to other commercial probes. Probe angle
configurations of 45° and 90° for lateral and central defects, respectively, were
assessed. Working frequencies of 15, 30 and 60 KHz were identified to better
distinguish between superficial and sub-superficial defects. Defects such as voids
and collages with only a few mm of extension can be detected with a good
probability.
With these results it was possible to specify the requirements for operating in field
conditions: probe frequency and data processing (fig. 3.10). Hence, the requirement
now is to validate passing from a prototype
system to an industrial testing system.
C2C30
30 kHz
In conclusion, the ITER coil case multipass
welding can now be inspected with the
eddy current technique proposed and
developed by ENEA. This technique is
easier, faster, less expensive and more
reliable than any other nondestructive
testing techniques. Moreover, at the
moment, it seems to be the only applicable
technique for thick-cast stainless-steel
multipass welds.
B/E-C frontal image
Fig. 3.10 - Reference block: central line (lateral passes
overlapping) inspection by VR-11 probe at 90°, lift-off 4 mm.
The most important target (the feasibility)
has been reach-ed, and the final goal (ITER
coil case real test) can be reached, too,
through subsequent engineering efforts.
[3.28] H. Iida, V.
Khripunov, L. Petrizzi,
Nuclear Analysis Report,
Nuclear Analysis Group,
ITER Garching JWS,
ITER report G73 DDD 01-
06-06 (2001)
[3.29] H. Iida et al.
“Nuclear Analysis of
ITER-FEAT” in preparation
[3.30] MCNP 4B, Monte
Carlo N-Particle Transport
System, Los Alamos
National Laboratory Ed.
by J. Briesmeister, LA-
12625-M, (1993)
3.5.1 3-D nuclear analysis for ITER-FEAT design
3.5 Neutronics
ENEA was strongly involved in the neutronics analysis for the ITER-FEAT (500-MW
fusion power) through support to the Nuclear Analysis Group (NAG) of the Joint
Central Team (JCT) in the nuclear analysis itself and in editing the NAG final report
[3.28, 3.29]. A fairly sophisticated nuclear analysis was performed by means of the
best-assessed nuclear data and codes and the most detailed models. A new 3-D basic
model for MCNP [3.30] was constructed according to a shared effort between the JCT
and the Home Teams (HT) of the ITER-EDA. The basic model is a 20° toroidal sector
with proper boundary conditions at both sides (fig. 3.11). The model includes
analysis of a) global and local nuclear heating for the design of each component; b)
global and local shielding optimisation for hands-on maintenance; c) radiation
conditions in materials sensitive to irradiation; d) activation of materials including
the cooling water.
Among the above nuclear responses, nuclear heating in the toroidal field coil (TFC)
inboard legs required very high accuracy, even at a very early stage of design