IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
Experiment to validate failed
fuel detection system
This experiment was
conducted with a special
subassembly having 19
perforated pins (with a total
exposure area of 112.8 cm 2 ) of
natural uranium loaded
successively at five different
locations. The main objectives
of the experiment were:
To calibrate Delayed
Neutron Detection (DND)
system at different power
levels, primary sodium flows
and sodium inlet
temperatures
To establish the feasibility
of localization of failed SA
using DND system
To check the response of
Clad Rupture Detection
(CRD) in argon system
To validate the failed fuel
localization setup.
The results were satisfactory
and validated the ability of the
DND system not only to detect
any clad breach, but also to
broadly identify the zone of
failure from the contrast ratios
of the east & west DND signals.
Failed fuel localisation system,
intended to determine the age
of the fuel performed well in
detecting the presence of Kr
and Xe in cover gas argon.
Residual life assessment of the
grid plate
Grid plate, which supports
entire core, is one of the
important components that limit
the life of the reactor. The life
limiting factors are residual
ductility and swelling.
Displacement per atom (DPA) is
one of the parameters that is
found to have good correlation
with the radiation damage to
the material. However, DPA
cannot be directly measured.
Fluxes above 0.1 MeV
contribute maximum to the
DPA. The fission reactions rates
in 237 Np have good correlation
with the DPA rate, as the crosssection
threshold is around 400
keV. Hence, Neptunium foils
were used to measure the grid
plate fluence. Standard
irradiation experimental
subassembly with a capsule was
used. The special capsule is
made of SS rod containing the
foils at the guide sleeve and
support plate of the grid plate
and core mid plane. As the
capsule is longer than the
standard irradiation capsules,
flow induced vibration test was
carried out with a dummy
subassembly at FRTG and the
vibration found to be
negligible. The subassembly
was loaded in 4th ring of the
core and the reactor operated
at 15.6 MWt for about 14 days.
The experimental carrier along
with the capsule was
discharged and sent to RML hot
cell for retrieving the foils from
the capsule and counting of
fission product activities.
Concurrently, test specimens of
SS 316 used in the reactor are
also being irradiated to
simulate the damage. They will
be retrieved at the end of the
14 th campaign after 70 days of
irradiation and measurements
of residual ductility and swelling
carried out. The results of both
these experiments will provide
the basis for the residual life
assessment of the grid plate.
Irradiation of PFBR test fuel pin
for initial gap closure
The peak Linear Heating Rate
(LHR) for PFBR fuel is 450
W/cm. From fabrication
considerations, the fuel
fabricator has asked for
relaxation of the tolerances on
the pellet diameter. This will
result in higher fuel-clad gap,
and the fresh fuel will hence
have to be operated at lower
LHR till the gap closes by
cracking and restructuring of
the fuel. The duration of
operation at low LHR has
implications on the economics
of power generation. To
determine the time required for
the gap to close, a single pin of
PFBR test fuel was irradiated in
FBTR for 14 days. Mixed Oxide
with 29% PuO 2 and rest UO 2
enriched with about 53.5% U 233
is used as fuel for this pin.
2 FAST BREEDER TEST REACTOR