1. magnetic confinement - ENEA - Fusione

3. FUSION TECHNOLOGY 93
3.8 Liquid Metal Technology and
Hydrogen Effects on Materials
Fig. 3.31 - Area reduction
as a function of hydrogen
content at room and high
temperature.
Area reduction /Area red. virgin mat. (%)
120
100
80
60
40
20
EUROFER steel
T =20°C
T =100°C
T =200°C
0
0 1 2 3 4 5 6 7 8 9
cylindrical
specimens that had
been previously
electrochemically
charged with
hydrogen (contents
of up to 3 wppm) at
high temperature
(90°). The experimental
activities
were performed in
collaboration with
the University of
Pisa.
Hydrogen content (wppm)
As expected, the
hydrogen concentration necessary to have a marked decrease in the area reduction
coefficient was found to be quite high compared to that determined at room
temperature (fig. 3.31).
The experimental activity on hydrogen embrittlement will be completed during first
months of 2002.
3.8.5 Water detritiation systems (EU Task TTBA-D02)
The aim is to assess a design to simplify the WCLL blanket concept by eliminating
the TPBs on the double walled tubes of the primary cooling system and recovering a
significant part of the bred tritium directly through the water detritiation system
(WDS).
From previous studies, it was found that this approach to tritium management
strategy is feasible from a techno-economic point of view only if a steady-state
tritium concentration of several Ci/kg is allowed in the primary cooling loops. In
other words, the tritium specific activity in the primary cooling system must be a
good deal higher than that foreseen in the reference design (1Ci/kg).
A detailed safety analysis on the consequences of a relatively high tritium specific
activity in the primary coolant was, therefore, performed in collaboration with the
University of Bologna. The environmental tritium release was determined for an exvessel
loss of coolant accident (LOCA) in normal operation. The tritium specific
activity considered corresponded to the “economical optimum” for a water
detritiation system, based on electrolysis, distillation columns + vapour phase
catalytic exchange and combined electrolysis catalytic exchange (CECE), in all cases
with a tritium permeation rate (TPR) of 10 g/day from the breeder into the coolant.
Such a TPR corresponds to a PRF of 10 for the tritium permeation barriers. This value
is achievable, in principle, only by using double walled EUROFER97 tubes with
copper as brazing material. A water leak rate of 2 kg/h from the primary cooling
circuit was assumed, with 1.9 kg/h towards the steam generator vault and the
remaining 0.1 kg/h into the secondary circuit through the steam generators.
For an ex-vessel LOCA, even in the worst case, which corresponds to the highest
enthalpy content of the cooling water, the environmental tritium release was
determined to be much lower than the limit of 5 g of tritium in HTO form; this is the
maximum acceptable value according to the ITER Guidelines for Environmental
Tritium Release.