IGNALINA
NUCLEAR POWER PLANT
The
Ignalina nuclear power plant contains RBMK-1500 water-cooled graphite-moderated
channel-type power reactors. The RBMK-1500 reactor is the largest power reactor
in the world. The thermal power output of one units is 4800 MW, the electrical
power capacity is 1500 MW. The
Ignalina nuclear power plant, like all stations with RBMK reactors, has a direct
cycle configuration - saturated steam formed in the reactor proper by passing
the light water through the reactor core is fed to the turbine at a pressure of
6,5 MPa. The light water circulates over a closed circuit. The
first stage of the nuclear power project comprises two 750 MW turbines. Each
generating unit is provided with a fuel handling system and unit control room.
The turbine room, waste gas purification and water conditioning rooms are common
for all the units. |
REACTOR
DESIGN
The
main structural element of the reactor, a graphite stack with fuel channels,
absorberrods and surrounding metal structures, is housed in a concrete vault.
The vertical graphite stack columns contain fuel channels and control rod
channels. The graphite stack is carried by a welded steel structure resting on a
concrete foundation. On top the graphite stack is spanned over by an upper steel
structure resting on the annular water tank of the biological shield. A welded
shell enclosing the graphite stack, as well as the upper and bottom steel
structures form a sealed reactor space. To prevent graphite oxidation and to
improve heat transfer from graphite to fuel channels, the reactor space is
filled with a helium-nitrogen mixture. Provision
is made to replace the fuel channels and control rod channels on the shut-down
and cooled reactor. The
fuel channels are tubes whose lower and upper portions are fabricated from
corrosion-resistant steel, while the central part is made of Zircalloy. The
split graphite rings in the channels provide thermal contact with the graphite
bricks of the stack. Suspended
in the fuel channel is a fuel assembly bank. The
fuel assembly bank consists of two fuel assemblies. Each fuel assembly contains
18 fuel rods in the form of sealed Zircalloy tubes which are filled with uranium
dioxide pellets. Light
water coolant is fed into the lower end of the fuel channels. From the fuel
channel the coolant in the separators. To improve heat exchange, the upper fuel
assembly carries special intensifying grids. Removal
of irradiated fuel elements, their handling and charge of fresh elements are
performed on load by means of a refueling machine mounted in the central room. The
biological shield is made of carbon steel, serpentine crushed stone and gravel,
concrete, sand, water. |
TECHNICAL
DATA ON RBMK-1500 REACTOR
|
CIRCULATING
CIRCUIT
The
circulating circuit of the reactor is a system composed of fuel channels, steam/water
and water lines, steam separators, main circulation pumps, pressure, suction and
distribution headers with associated piping. The
circulating circuit consists of two loops. Each loop contains two horizontal
type steam separators interconnected on the water and steam sides. Each
separator houses inside a feedwater header. Feedwater flows from the header into
downcomers through perforated nozzles. The separated water, in mixing with the
conditioned, heated, and deaerated feedwater goes through the downcomers to the
suction header and the suction header and then is conveyed via suction pipes to
the four main circulating pumps one of which is kept in the stand-by duty. The
pumps are of a vertical, centrifugal, single-stage configuration. The rated pump
delivery is 8500 cu.m/h at a head of 200 mw.g., speed - 100 rpm, electric motor
output - 5500kW. The
delivery pipelines convey water from the main circulating pump is provided with
a stop gate, the delivery line (down the flow) mounts a check valve, a throttle
valve and a stop gate. The suction and pressure headers of each loop are
interconnected by six bypass lines, each provided with a stop gate and a check
valve. The bypass lines maintain natural circulation of coolant at emergency
shutdown of a main circulating pump. The
pressure header is connected through pipes with 20 distribution headers. On the
upstream end, each distribution header is provided with a stop gate, a check
valve and a mixer for water coming from the reactor emergency cooling system.
40-43 water supply lines are branched off each distribution header. Each
loop effects heat removal from half the reactor. The coolant flow distribution
among the fuel channels as a function of the core energy release is controlled
by shutoff control valves following the indications of flow meters mounted at
the inlet of water supply line to each fuel channel. |
STEAM
AND CONDENSATE FEED CIRCUIT
Steam
is conveyed from each separator to the turbines over two steam lines. The steam
piping is so arranged each steam separator is connected with two turbines. The
equipment and pipelines are protected against excessive pressure rise by a
system of steam dumping facilities which dump excess steam into the turbine
condensers or into the condensation pools of the accident isolation system. The
condensate of the steam spent in the turbines is conditioned in the
ion-exchangers, heated in the heat exchangers of the regenerative heating system,
deaerated and on passing through strainers is fed back by the electric feedwater
pumps over feed pipelines to the separators of the circulating circuit. |
TURBOGENERATOR
SETS
Each
unit contains two K-750-65/3000 turbines with 800 MW generators. The turbines
are double-flow tandem machines (one high-pressure cylinder and four
low-pressure cylinders) with reheat. The rotor speed is 3000 rpm. The
three-phase 50 Hz generators with hydrogen and water cooling are connected to
the outdoor substation. The turbines are controlled by computer-based control
system ASUT-750. |
FUEL
LOADING SYSTEM
Fuel
is charged and discharged by means of a refueling machine while the reactor is
on load. The
main element of the refueling machine is a casque with a biological shield
designed to take the working pressure within the fuel channels and equipped
within mechanisms serving the following functions:
The
refueling machine is provided with two systems of precise positioning over the
fuel channel-optical/television and contact. The
casque is mounted on a bogie moving along a bridge rail-bound in the central
room. The
refueling machine is controlled from the operator's room which is located behind
the wall of the central room. |
STATION
CONTROL AND MONITORING SYSTEMS
The
control and monitoring systems provide reliable and safe operation of the major
equipment and and maintain stable process parameters. Functionally
the monitoring and control systems comprise:
Most
of process parameters are monitored by a data logging system. Control
data are displayed on the unit control board using VDU, visual and recording
instruments, various announciation windows and indicators, mimic diagrams and
printers. The
station is controlled from the unit control board. General
control and coordination of the operators work are responsibilities of the shift
chief or his deputy. The
station incorporates provision for multiple protection of process equipment
initiates operation of various kinds of protective gear providing controlled
reduction of the reactor power at a rate of 2-4 per cent/s to the safe level. The
reactivity scramming which brings the reactor power down to zero, is applied in
rare cases. |
REACTOR
CONTROL AND PROTECTION SYSTEM
The
control and protection system is intended for reliable follow-up of the reactor
performance and its safe operation. The system provides start-up, automatic
maintenance of power at the set level, allows control of energy distribution
along the radius and heightwise of the core, compensates for fuel burn-up,
provides protection of the reactor under emergency conditions. The
control and protection system is built of fail-safe and redundant devices using
integrated circuits to receive and process signals from various sensors, as well
as to present the reactor status information to the operator. The
reactor power release and its distribution are controlled by 211 carbide boron
rods placed in the control channels and moved by individual servomotors mounted
on the top of the control channels. The control rods are cooled with water from
a special loop. Out
of the total numbers of rods, 40 ones are used for energy distribution control
through the height of the active zone of the reactor. 24
rods perform the function of prompt emergency safeguard introduced into the
active zone within 2.5 seconds under definite emergency situations. The
remaining rods are unified and serve the function of reactivity scramming,
automatic maintenance of the reactor power release at the set level, control of
energy distribution over the core radius. |
REACTOR
PROCESS MONITORING SYSTEM
The
reactor process monitoring system provides the operating personnel with
information and inputs data into the control and protection system. The
reactor process monitoring system consists of the following functional elements:
The
data logging system is configured in a three-level hierarchy using computers
SM-1M and SM-2M and interface facilities. The
energy release monitoring and control system includes energy release detectors
providing inertialess measurement of neutron flux density along the radius and
height of the core, and the equipment to process information and signals on the
control board. The
system monitoring tightness of the fuel assembly claddings includes
scintillation gamma-spectrometer sensors, equipment, to ensure operation and
movement of sensors in the intertube space of the steam lines, and facilities
for processing and output of data. The
system monitoring the coolant flow through the reactor channels consists of
tachometric transducer, and equipment affording frequency-to-analog signal
conversion. The
system monitoring the temperature of the reactor equipment contains mainly
heat-resistant cable heat-electric transducers. |
RADIATION SAFETY
The
RBMK-1500 reactor is provided with special elements and systems ensuring
radiation safety of the nuclear power plant and the environment both under
normal operating conditions and in the emergency cases.
The
system monitoring tightens of fuel rod cladding specially designed for the
RBMK-1500 reactors and applying modern techniques for detection of faulty fuel
rods and computer-based data logging provides the core radiation control. The
computerized radiation doze control system at the nuclear power plants with
reactors of the RBMK-1500 type is provided with facilities monitoring radiation
exposure of all components and systems of the station.All this helps to maintain
the radiation conditions at a safe level by implementing the purposeful actions
(removal of leaky fuel assemblies, decontamination, replacement and repair of
the equipment. To
reduce emissions of noble radioactive gases. A two-stage system is used for
cleaning gaseous and aerosol effluents discharged through a 150 m high stack
into hold-up chamber. When noble gases pass through it, their activity is
reduced due to natural decay. The second stage-activity suppression facility
purifies and reduces activity of noble radioactive gases by the method of
dynamic sorption using the radiochromatographis char columns. To
reduce radioactive aerosol emissions at the nuclear power plants with the
RBMK-1500 reactors provision is made for purification facilities absorbing
aerosols by special filters. The
nuclear power plants with the RBMK-1500 reactors use a closed-circuit water
supply system. Liquid radioactive effluents undergo special treatment. Radioactive
discharge into air and water is monitored continuously using instruments of the
computerized radiation dose control system. The
external radiation exposure surveillance service at the nuclear power plant with
the RBMK-1500 is equipped with instruments to analyze concentration of
radionuclides in the elements of the environment. The health physics laboratory
is provided with facilities and sampling methods, dozimetric, radiometric,
spectrometric instruments for objective assessment of the radiation conditions
in the environment. |
SPENT
FUEL STORAGE The
important province of NPP's safety-is spent fuel storage. Almost 99% of
radioactive elements, which were saved up during NPP exploitation, are there.
From the beginning of the exploitation the spent fuel is kept under the water at
special fuel pool storage, which are placed in the same buildings as reactor.
It's a temporary method so the international competition for the spent fuel
storage was announced. The Germany's company GNB won in the
competition.
The GNB made a contract with the INPP to supply 60 steel containers CASTOR. The
use of these expensive steel containers is the first stage of solution of spent
fuel storage. Safe spent fuel storage is guaranteed during 50 year. The new
tender for spent fuel storage was held. |