and a remote contact-making meter 
and multipoint recorder.* These de- 
tectors can be checked remotely by ex- 
posing a radioactive source on the 
actuation of a solenoid-operated shield- 
ing shutter. All channels are dupli- 
eated, and control action is initiated 
only upon a simultaneous — signal 
from both channels to minimize false 
“serams.’’ However, a signal from 
either channel is annunciated. 
For monitoring control areas for per- 
sonnel protection, more stable and 
accurate vibrating-condenser types of 
electrometers are used. 
Neutron-level transmitters are two 
Westinghouse fission chambers and two 
gamma-compensated ionization cham- 
bers designed by ORNL. They are 
conventional in design and use and will 
not be described here. 
Control Panels 
The main control board and console 
(Fig. 2) contain only those instruments 
necessary for the safe operation of the 
reactor. Switches and controls on the 
console itself are restricted to those nec- 
essary for nuclear startup, steady-state 
power operation, and emergency. All 
items are arranged in a ‘visual aid’’ 
form to reduce operational errors and 
to facilitate the training of operators. 
The graphic section is essentially a sim- 
plified schematic representation of the 
chemical process flow sheet, with in- 
struments, control switches, and valve- 
position indicators located in positions 
corresponding to their location or func- 
tion in the actual system. 
Annunciators are placed in the con- 
trol board directly above that instru- 
ment or that portion of the system on 
the graphic board with which their 
signal is associated. 
Key measurements are displayed on 
“full scale” recorders in the center sec- 
tion of the panel and include the fuel 
temperature, a multipoint temperature 
recorder, the multiarea radiation moni- 
toring recorder, the reactor power, the 
logarithmic neutron-level and count- 
rate-meter signals, and the blanket- 
temperature recorder. 
The patch panel on the extreme left 
is a “jumper board,” which is a sche- 
matic representation of the electrical 
control circuits. Provision is made for 
jumping certain individual contacts in 
the control circuit with a plug, and 
there are lights to indicate the position 
* Manufactured by the Victoreen Instru- 
ment Co., Cleveland, Ohio. 
—open or closed—of the contact in the 
system. The board is valuable for 
making control-circuits alterations nec- 
essary for experiments, as an aid in 
familiarizing operators with the elec- 
trical control circuitry, and, since the 
lights indicate contact position, as an 
operations aid during startup. The 
jumper board is placed on the main 
control board so that any jumper is in 
full view of the operator and cannot 
become a forgotten clip lead. Protec- 
tion for sustained power operation is 
also offered by the removal of startup 
circuits from control. 
Data-collection instruments and the 
transducers that drive the miniature 
pneumatic slave recorders on the 
graphic panel are located in an auxil- 
lary instrument gallery beneath the 
main control room, as are a 548-point 
thermocouple patch panel, a relay 
panel, the nuclear amplifiers, and the 
nuclear instrument power supplies. 
Other panels located near their re- 
spective equipment in the building in- 
clude the steam control station, the 
turbine control panel, two sampler con- 
trol panels, and a refrigeration-system 
control station. Standard 2-ft-wide 
modular cabinets and panels are used 
throughout to facilitate design changes. 
Special Components 
As HRT is similar to a fluid chem- 
ical process, the critical instrumenta- 
tion and control components are 
liquid-level transmitters, pressure and 
differential-pressure transmitters, and 
valves. However, the difficulties in- 
volved in replacing or performing main- 
tenance operations on process trans- 
mitters and valves requires that these 
components be extremely reliable. 
The design and improvement of these 
elements is an essential part of the de- 
velopment of homogeneous reactors. 
The pressurizer-level transmitter 
(Fig. 4), developed at ORNL, consists 
of a 5-in.-long  float-displacer sus- 
pended by two helical springs. An 
extension rod above the springs posi- 
tions a magnetic piston in the center of 
a differential transformer. Vibration 
of the float is damped by the action of 
the field from permanent magnets on a 
one-turn copper ring. 
In the transmitter the only non- 
welded closure is the 2,500-psi ring- 
joint flange, which makes the unit 
amenable to remote replacement. The 
transmitter is self-draining—a very de- 
sirable feature in systems containing 
radioactive fluids. Problems not com- 
pletely solved at present are zero shift 
due to modulus changes in the dis- 
placer supporting springs and a change 
in span with fluid density changes. 
However, both effects can be com- 
pensated at a constant operating tem- 
perature. ‘‘Constant’’-modulus spring 
alloys used to date are not flat over the 
temperature range from ambient to 
340° C and require a corrosion-resist- 
ant gold plating. 
A similar type of level transmitter is 
used on the fuel and blanket system 
storage tanks and has a design pressure 
of 500 psi. It differs in that it has a 
40-in.-long float and is damped by the 
interaction of two moving vanes at- 
tached to the float and a baffle attached 
to the housing. 
The letdown valve (Fig. 5) incorpo- 
7777 Pressure connection 
Weld seal 
Evacuoted 
reference---~— 
chomber 
é Sensing 
diophragm 
7 
Ronge spring—~ 
. 
r-— Magnetic piston 
with ss sheath 
lead port 
I 
. Motion-sensing coil 
FIG. 6. Absolute pressure transmitter capable of withstanding severe overranging 
29 
2 aN 
Electric--> 
