IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
Fig.2 Temperature dependence of
DND signals (SA at 00-00)
for signals without background.
Hence these values will prove
useful in deciphering the
location of an actual pin
failure.
The expected rise in signal
over background per cm 2 of
actual fuel failure is given in
Table 2. Considering the
counting statistics of the
detectors used for display on
the console, a measurability
criterion of 3 σ background
value implies a failure if the
background counts exceed by
6.7 % on the east and / or 4.8
% on the west under conditions
of sodium inlet temperature
prevailing more than 573K.
The analysis has brought out
that the system is capable of
detecting even fuel defects to
an extent of 0.5 to 1 cm 2 .
Using the measurability criteria
and the pattern of increase of
signal over background, it will
be possible to determine the
size of the clad opening and
localize the defect to the half
sector and the ring in which it is
located.
Fig.4 Response of the DND signal as
function of power (DND SA in 02/04
location)
85m 87 88 135 138 88
K r , K r , K r , X e , C s & R b .
This confirms that cover gas
activity will provide the first
confirmation of an actual pin
failure. General background
Fig.3 Response of the DND signal as
function of power (DND SA in 00/00
location)
The cover gas activity
monitors located in the CRD
circuit and common cover gas
reject circuit also responded
very well. Cover gas samples
collected at higher powers
41
showed the presence of A r ,
Fig.5 Response of the DND signal as
function of power (DND SA in 04/07
location)
Table 1 : Ratios of signals emanating from special SA at 10 MWt
Table 2 : Expected rise in signal (over background) per cm 2 of actual clad failure at 10 MWt
8 FAST BREEDER TEST REACTOR