ORNL-4191 - the Molten Salt Energy Technologies Web Site

3.1 MSRE OPERATING EXPE RI ENCE
C. E. Mathews J. L. Redford
R. W. Tucker
Instrumentation and control systems continued to
perform their intended functions. Component fail-
utes did not compromise safety nor cause excessive
inconvenience in the reactor operation. A moderate
amount of maintmance was required, as described
in the sections that follow.
Control System Components
3. Instruments and Controls
L C. Oakes
The 48-v dc relays continued to suffer damage
because of heat developed in the resistors built
into the operating coil circuits. Because of this
problem, redesigned relays had been procured and
some had been installed. After several months,
some of these also showed signs of detenoration
Therefore, following run 11, all 139 relays operat-
ing from the 48-v dc system were modified by re-
placing the bmlt-in resistors with externally
mounted resistors. This was done with the relays
in place, without disconnecting control circult
wiring, thus avoiding the possibility of wiring
mistakes inherent in relay replacement. No trouble
was experienced after the modificatlon.
Component failures were as follows. The coil in
a solenoid valve for the main blower 3 backflow
damper developed an open circuit. The fine-position
synchro on rod drive 2 developed an open circuit in
the stator winding and was replaced at the shutdown
in May. The fuel overflow tank level transmitter
was replaced after a ground developed in the feed-
back motor. The ground was subsequently found
'MSR Program Semiann. Progr. Rept. Feb. 28, 19G7,
ORNL-4119, p. 71.
47
and corrected. The span and zero settings of the
differential pressure transmitter (PdT-556) acmss
the main charcoal beds shifted drastically. Al-
though the pressure capability had never been ex-
ceeded, the diaphragm had apparently suffered
damage. Thus, when a new transmitter was in-
stalled in June, hand valves were installed in the
lines connecting to the off-gas system to be used
in protecting against unusual pressures during
system operations. The 1-kw 48-v-dc-to-120-v-ac
inverter, which supplics ac power to one of the
three safety channels, failed during switching of
the 48-v dc supply. It was repaired by replactrnent
of two power transistors. Only one thermocouple
(YE-FP-10B) failed due to an open circuit. (See p.
22 for discussion of thermocouple performance.)
Water was admitted to the steam dame on fuel drain
tank 1 on several occasions before the cause was
found to be an intermittent fault in a control module.
A freeze-flange temperature control module failed
because of excessive condenser leakage. At the
next shutdown, all similar condensers were checked,
and 33 were replaced because of leakage.
Nuclear Instruments
Four of the eight neutron chambers had to be
replaced. The fission chamber for wide-range
counting channel 1 was replaced because of a short
circuit from thc high-voltage lead to ground. The
fission chamber for wide-range counting channel 2
was replaced after moisture penetrated the protec-
tive cover on the cable. Moistute Leakage into the
cable to the BF, chamber required that the cable
and chamber be replaced. The output of the ion.
chamber in safety channel 2 decreased drastically
during a nonoperating period, and the chamber was
replaced prior to resumption of operatlons. The