|The TRIGA Mark-II reactor was
installed by General Atomic (San Diego, California, U.S.A.) in the years
1959 through 1962, and went critical for the first time on march 7, 1962.
Operation of the reactor since that time has averaged 220 days per year,
without any long outages. The TRIGA-reactor is purely a research reactor
of the swimming-pool type that is used for training, research and isotope
production (Training, Research, Isotope Production, General Atomic = TRIGA).
Throughout the world there are more than 50 TRIGA-reactors in operation,
Europe alone accounting for 10 of them.
The TRIGA-reactor Vienna has a maximum continuous power output of 250 kW (thermal). The heat produced is released into a channel of the river Danube via a primary coolant circuit (deionized, distilled water at emperatures between 20 and 40 *C) and a secondary coolant circuit (ground water at temperatures between 12 and 18 *C), the two circuits being separated by a heat exchanger.
The reactor core consists of some 80 fuel elements (3.75 cm in diameter and 72.24 cm in length), which are arranged in an annular lattice (Figs. 1 to 3). Two fuel elements have thermocouples implemented (Fig. 4) in the fuel meat which allow to measure the fuel temperature during reactor operation. At nominal power (250 kW), the center fuel temperature is about 200 *C. Because of the low reactor power level, the burn-up of the fuel is very small and most of the fuel elements loaded into the core in 1962 are still there. Should these fuel elements ever become unserviceable, they will be sent back to the United States.
Inside the fuel element cladding (aluminum or steel), the fuel is in the form of a uniform mixture of 8 wt% uranium, 1 wt% hydrogen and 91 wt% zirconium, the zirconium-hydride, being the main moderator. Since the moderator has the special property of moderating less efficiently at high temperatures, the TRIGA-reactor Vienna can also be operated in a pulsed mode (with a rapid power rise to 250 MW for roughly 40 milliseconds). The power rise is accompanied by an increase in the maximum neutron flux density from 1x1013 cm-2s-1 (at 250 kW) to 1x1016 cm-1 (at 250 MW). This negative temperature coefficient of reactivity, as it is called, brings the power level back to approximately 250 kW after the excursion, the maximal pulse rate is 12 per hour, since the temperature of the fuel elements rises to about 360 *C during the pulse and, therefore, the fuel is subjected to strong thermal stress.
The reactor is controlled by three control rods which contain boron carbide as absorber material. When these rods are fully inserted into the reactor core, the neutrons continuously emitted from a start-up source (Sb-Be photoneutron source) are absorbed by the rods and the reactor remains sub-critical. If the absorber rods are withdrawn from the core (two of them by an electric motor and one pneumatically, Figs. 5 and 6), the number of fissions in the core and the power level increases. The start-up process takes roughly one minute for the reactor to reach a power level of 250 kW from the sub-critical state. The reactor can be shut-down either manually or automatically by the safety system. It takes about 1/10 of a second for the control rods to fall into the core.
The reactor is controlled by four nuclear channels (Fig.7), their signals are displayed both at a colour graphic- monitor and at bar graph indicators (Figs.8a and b).
a) The auto-ranging wide-range
channel NM-1000 controls the reactor power from the source level (around
b) Two independent linear channels,
NMP-Ch and NMP-Ph control the reactor power from the source level up to
c) For the control of reactor
pulse operation an uncompensated ionisation chamber is used. This chamber
In accordance with its purpose
as a research reactor, the TRIGA Mark-II is equipped with a number of irradiation
devices (Figs. 9 and 10):
The neutron radiography facility is used to investigate components by neutron irradiation similar to X-ray radiography. However, neutrons show especially hydrogen or neutron absorber material in solid matter.
MAIN TECHNICAL DATA OF THE TRIGA MARK-II REACTOR VIENNA
|1. REACTOR CORE|
|fuel-moderator material||8 wt% uranium
91 wt% zirconium
1 wt% hydrogen
|uranium enrichment||20% uranium-235|
|fuel element dimensions||3.75 cm in diameter
72.24 cm in length
|cladding||0.76 mm aluminum or 0.51 mm steel|
|active core volume||max. 49.5 cm diameter, 35.56 cm high|
|core loading||3 kg of uranium-235|
|material||graphite with aluminum cladding|
|radial thickness||30.5 cm|
|top and bottom thickness||10.2 cm|
|reactor shielding construction||heavy and standard concrete
6.55 m high, 6.19 m wide, 8.76 m long
|reactor tank||1.98 m in diameter
6.40 m in depth
|radial:||30.5 cm of graphite;
45.7 cm of water and at least
206 cm of heavy concrete
|vertical:||above the core 4.90 m of water
10.2 cm graphite;
underneath the core 61.0 cm water,
10.2 cm graphite and at least
91 cm standard concrete
| 5. IRRADIATION DEVICES
(1) four beam holes 15.2 cm in diameter
|6. CONTROL SYSTEM
|7. CHARACTERISTICS IN CONTINUOUS OPERATION|
|Thermal power output:||250 kW|
|Fuel element cooling:||natural convection of the tank
below 100 kW, pump circulation cooling above 100 kW
|tank water cooling:||heat exchanger|
|thermal flux:||1x1013 cm-2s-1
in the central irradiation tube
1.7x1012 cm-2s-1 in the irradiation tubes
|prompt temperature coefficient:||-1.2x10-4 dk/k°C|
|mean prompt neutron lifetime:||6.0x10-5 s.|
|8. CHARACTERISTICS IN TRANSIENT OPERATION|
|peak power||250 MW|
|prompt pulse energy yield||10 MW s|
|prompt pulse lifetime||40 ms|
|total energy yield||16 MW s|
|minimal period||10 ms|
|maximum reactivity insertion||1.4% dk/k = 2$|
|maximum repetition frequency||12/h|
|number of fissions during a pulse||3x1017|
|maximum fuel temperature:||during the pulse
9 seconds after the pulse 360 °C