The Oak Ridge National Laboratory Gas-Cooled Reactor, Part 3: Plant Design Page: 7-12
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7.12
blower in the reactor inlet pipe in order that the temperature change caused
by a change in the positions of the by-pass valves will be sensed as quickly
as possible. Likewise, the temperature of the gas in one reactor outlet pipe
is used to regulate a number of the control rod actuators; this temperature
is measured as close to the reactor outlet as practical. Since there are four
outlet pipes each containing gas at the same temperature, the operator may
select manually any one duct for this control.
The response of the system to change is sluggish, primarily because of the
low ratio of power density to heat capacity in the system, as indicated in
Table 7.1. Further, the long system transit times, 100 sec for the water and
steam flowing through the steam generator and 10 sec for the helium circuit,
contribute to this sluggishness. Thus, it can readily be seen that this
reactor is not tightly coupled to its load.
Variations introduced by control actuators must be slow to prevent excessive
overshoots and undershoots in the parameters being controlled. In fact, the
full stroke of the by-pass valves should require on the order of 180 sec, and
the rate of reactivity change for the control rods regulating the helium outlet
temperature should be of the order of 5 x 10-6/sec which will require no more
than 4 rods. (See 7.3 below) In view of the sluggishness of the system, the
temperature of the steam from the steam generator is not to be regulated by
means of the control rods but rather will be controlled by the desuperheater.
The gas temperatures in the pipes will be measured by thermocouples which
are shielded from the radiant heat from the pipe inside surface. This
arrangement will virtually eliminate the effects of the pipe temperature, which
will lag behind the changes in gas temperature.
7.3 Control Rod Speeds
The control rod drive mechanism has already been described in Section 5.
The full rod stroke is 20 ft, the lower limit being the position where the
top of the neutron absorbing silver section is level with the top of the
core. All of the rods are to be at approximately equal heights at all times.
During start-up, all of the rods are manually withdrawn simultaneously by
means of a master switch. The operator can manually insert all of the rods
simultaneously at the normal insert speed at any time. The operator can also
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Oak Ridge National Laboratory. The Oak Ridge National Laboratory Gas-Cooled Reactor, Part 3: Plant Design, report, January 4, 1958; Oak Ridge, Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc100273/m1/80/: accessed March 29, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.