IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
IV.C.3. Application of Zircaloy-4 for Highly Corrosive
Nitric Acid Environments in Reprocessing Plants
Reprocessing of spent nuclear
fuel used in FBRs involves use
of nitric acid of high
concentrations
and
temperatures for dissolvers and
evaporators which are highly
corrosive. The materials chosen
for the fabrication of such
reprocessing plant equipment
should possess excellent
corrosion resistance, ease of
fabricability and reliability.
Conventional austenitic
stainless steels are not
preferable in such highly
oxidizing conditions as they
undergo severe intergranular
corrosion. Studies carried out
earlier indicated good
corrosion resistance of
Commercially Pure Titanium
(CP-Ti) and Ti-5%Ta as
compared to AISI type 304L SS
in highly oxidizing nitric acid.
Thus, titanium was chosen for
fabricating electrolytic dissolver
of CORAL plant, with a
dissimilar joint by explosive
joining process for linking to
type 304L SS equipment in the
plant, for reprocessing of spent
fuel from FBTR. For future
reprocessing plants, based on
research and international
experience, developmental
efforts have been made for the
fabrication of dissolvers by
using Ti-5%Ta-1.8%Nb alloy.
The excellent corrosion
resistance of zirconium in nitric
acid has been known for over
50 years. Zirconium is highly
resistant to nitric acid
environments and is considered
as candidate material for
various applications in spent
nuclear fuel reprocessing plants
involving highly concentrated
nitric acid medium. Zirconium
and its alloys are thus
considered as candidate
materials for various
applications in spent nuclear
fuel reprocessing plants
involving nitric acid of high
concentrations at high
temperatures. Also, unlike
titanium and its alloys,
zirconium is unaffected by
vapour and condensate of
boiling nitric acid.
An attempt was made to study
the corrosion behaviour of
Zircaloy-4 (Zr-with Sn-1.4%,
Fig.1 (a) Corrosion rate of materials in three phase corrosion test, (b) Potentiodynamic polarisation curves of
wrought and welded samples, in 11.5M HNO 3 medium.
FUEL CYCLE 107