1.1.1 Location of Plant
The Ignalina NPP is located in the north-eastern part of Lithuania, near the borders of Latvia and Belarus. More details on the location of the Ignalina NPP are provided in Section 2.1.
1.1.2 Plant Panorama
The general Ignalina NPP panorama is shown in Fig. 1.1. The site of the nuclear power plant covers an area of about 0.75 km2. (In comparison: the Swedish Barsebeck nuclear power plant with two BWR reactors covers an area of about 0.24 km2). The buildings take up about 0.22 km2.
The Ignalina NPP possesses two similar units of RBMK-1500 reactors, as shown in Fig. 1.2. Each unit consists of five construction buildings; namely, buildings designated as A, B, V, G and D. There are also two separate reactor buildings A1 and A2 adjacent to a common building D1 and D2 with control rooms, electric instrumentation rooms and deaerator rooms. The last building is adjacent to a common turbine hall. The main buildings of the plant are situated about 400-500 m from the banks of lake Druksiai.
Both units have the following common facilities: low-activity waste storage, medium - and high-activity waste storage, liquid - waste storage, an open distributive system, nitrogen and oxygen manufacturing facility and other auxiliary systems. The building which houses the 12 diesel- generators (six diesel- generators per each unit) for emergency power supply is physically separated from other buildings. A separate water-pump service station is also built for each unit, serving the needs of uninterrupted supply of water.
A panorama of the auxiliary services for the Ignalina NPP is shown in Fig. 1.3. The general area of the Ignalina NPP, the city of Visaginas, the construction organisations and the auxiliary services encompass an area of about 26 km2.
Fig. 1.1 General panorama of the Ignalina NPP [2]
1,2 - service water pump stations, 3 - acetylene bottle depot, 4 - oil depot, 5 - oil system equipment room, 6 - transformers equipment tower, 7 - pump station for waste and liquid sewerage discharge, 8 - hydrogen- and oxygen-receiving facility, low-activity waste storage, 9 - low-level radwaste repository, 10 - medium- and high-activity waste storage, 11 - operational shower- water reservoir, 12 - drainage water tank, 13 - venting stack of the radwaste reprocessing building, 14 - bitumen storage, 15 - liquid waste storage, 16 - chemical water treatment building, 17 - primary grade water tanks, 18,19 - recreational facilities, 20,21 - gas purification systems, 22 - heat power station , 23,24 - building plant units 1 and 2, respectively, 25,26 - pressurised tank (accumulator) of the ECCS, 27,28 - purified deminiralized water tanks, 29 - car-washing facility, 30 -bitumen depot, 31 - special laundry, 32 - chemical reagent depot, 33 - equipment storehouse, 34 - noble-gas reservoir depot, 35 - reservoir facility with artificial evaporation, 36 - repair building, 37,38 - administrative buildings, 39 - cafeteria, 40 - diesel - generator building, 41 - compressor and refrigeration station, 42 - nitrogen and oxygen manufacture building, 43 - liquid nitrogen reservoir, 44 - 110/330 kV open distributive system.
Fig. 1.2 General units arrangements [2]
A1,A2 - reactor buildings, B1,B2 - demineralized water treatment facilities of the MCC, V1,V2 - reactor gas circuit and special venting system, G1,G2 - turbine generators with auxiliary systems, feed facilities and heat supply facilities, D1,D2 - control, electrical and deaerator rooms, D0 -heat pipe service and fire fighting facilities
Fig. 1.3 Panorama of auxiliary services [2]
1 - NPP site, 2 - open distributive system,
3 - construction base, 4 - purification constructions, 5 - artisan well site,
6 -supply base, 7 - motor transport department, 8 - car service station,
9 - industrial construction base, 10 - construction base, 11 - military base,
12 - health clinic, 13 - city of Visaginas, 14 - railway station,
15 - the city transformer, 16 -the NPP transformer,
17 - recreational area
1.1.3 Plant Layout
The structure and layout of the main buildings of the Ignalina NPP are subordinate to the peculiarity of the requirements of the RBMK-1500 reactor operation. Fig. 1.4 shows the top view of the buildings of unit 2, which indicates sections A-A and B-B through the building and are displayed in Figs. 1.5 and 1.6, respectively.
Building A contains an RBMK-1500 reactor with a Main Forced Circulation Circuit (MCC), and the following main auxiliary systems of the reactor: Emergency Core Cooling System (ECCS), Accident Confinement System (ACS) and Control and Protection System (CPS). The hall above the reactor is a large open workspace housing the refueling machine. The spent-fuel storage pond is situated in an adjacent hall, but separated from the reactor hall. The reactor compartment consists of a rectilinear structure, the horizontal cross-section of which is 90 m x 90 m and a height of about 53 m.
Building B contains demineralized water treatment facilities. The reactor gas circuit and the special venting system are located in building V. The building area for the special water treatment has dimensions of 66 m x 36 m, and the building for the reactor gas circuit measures 66 m x 25 m. Both of these buildings have a height of about 31 m.
Building D contains the main control room, the electrical instrumentation and deaerator rooms. The main control room, the batteries and the 6 kV switchyard are situated on the first floor and the deaerator room is situated on the second floor of this building. This common building for both units has an area of 600 m x 25.5 m and a height of about 44 m.
Building G houses the turbine generators with auxiliary systems, the feed and heat supply facilities. The turbines are positioned parallel to the reactor. The turbine hall is common to both units and consequently, houses the four 750 MW turbine generators on the second floor. The first floor of the turbine hall contains condensers, separator-reheaters, evaporators, condensate pumps and components for heat extraction to the district-heating system. The entire building measures 600 m x 51 m and is about 28 m high.
Fig. 1.4 Plan of the Ignalina NPP main buildings [2]
1 - reactor, 2 - pressure and suction headers, 3 - main circulation pumps, 4 - accident confinement system, 5 - spent fuel compartment, 6 - deaerators, 7 - turbine generators, 8 - condensate cleaning filters, 9 - first stage condensate pumps, 10 - separator - reheater
Fig. 1.5 Cross-section A-A of one unit of the Ignalina NPP [2]
1 - reactor, 2 - refueling machine, 3 - main circulation pump, 4 - separator drum, 5 - MCP pipelines
Fig. 1.6 Cross-section B-B of one unit of the Ignalina NPP [2]
1 - reactor, 2 - refueling machine, 3 - turbine, 4 - condenser, 5 - separator - reheater, 6 - evaporator, 7 - first stage of the condensate pump, 8- deaerator
1.1.4 Power Plant Parameters
The Ignalina NPP belongs the category of "boiling water" reactors, a simplified thermal diagram of which is provided in Fig. 1.7. As it passes through the reactor core the cooling water is brought to boiling and is partially evaporated. The steam - water mixture then continues to the large separator drums (3), the elevation of which is above the reactor. Here the water settles, while the steam proceeds to the turbines (4). The steam which remains uncondensed beyond the turbines is condensed in the condenser (6), and the condensate is returned via the deaerator (8) by the feed pump (9) to the water of the same separator drum (3). The coolant mixture is returned by the main circulation pumps (10) to the core, where part of it is again converted to steam.
This fundamental heat cycle is identical to the Boiling Water Reactor (BWR) cycle extensively used throughout the world, and is analogous to the cycle of thermal generating stations. However, compared to BWRs used in Western power plants, the Ignalina NPP and other plants with the RBMK-type reactors have a number of unique features. The most important features are discussed in the subsequent sections.
The Ignalina NPP uses an RBMK - type channelized reactor [3]. This means that each nuclear fuel assembly bank in this type of an RBMK - type reactor is located in a separately cooled fuel channel (pressure tube). There are a total of 1661 of such channels and the cooling water must be equally divided among that number of feeder pipes. Past the core, these pipes are brought together to feed the steam-water mixture to the above - mentioned separator drums.
The RBMK reactors belong to the thermal neutron reactor category. Due to the large number of metal piping in the core of this type of a reactor, the neutronic characteristics of the reactor are degraded. To improve the neutronic characteristics, the reactors of Ignalina NPP
Fig. 1.7 Heat cycle diagram
1 - reactor, 2 - fuel assembly, 3 - separator drum, 4 - turbine, 5 - generator, 6 - condenser, 7 - condensate pump, 8 - deaerator, 9 - feedwater pump, 10 - main circulating pump
use graphite to moderate (slow down) the fast fission neutrons. This requires a large amount of graphite, so that the graphite stack of the reactor becomes its dominant component, at least by volume.
The nuclear fuel assemblies of the Ignalina NPP are changed without shutting down the reactor. This is possible only for a channel type reactors. Since there are many channels, it is possible to disconnect one of them at a time from the reactor cooling system, change the fuel assembly, and then reconnect the channel.
Further similarities and differences in comparison with other types of generating stations are described in subsequent sections of this document. Table 1.2 presents several of the more important plant parameters [2].
Table 1.2 Fundamental parameters of the RBMK-1500 reactor [38,36,62]
|
Coolant |
water (steam-water mixture) |
|
Heat cycle configuration |
single circuit |
|
Power, MW: |
|
|
thermal (design) |
4800 |
|
thermal (actual) |
4200 |
|
electrical (design) |
1500 |
|
Core dimensions, m: |
|
|
height |
7 |
|
diameter |
11.8 |
|
Thickness of reactor's graphite reflector, m: |
|
|
end |
0.5 |
|
side |
0.88 |
|
Lattice pitch, m |
0.25 x 0.25 |
|
Number of channels: |
|
|
fuel |
1661 |
|
control and shutdown system |
235 |
|
reflector-cooling |
156 |
|
Fuel |
uranium dioxide |
|
Initial fuel enrichment for 235U, % |
2.0 * |
|
Nuclear fuel burnup, MWdays/kg |
21.6** |
|
Number of main circulation pumps |
8 |
|
Capacity of main circulation pumps, m3/s (m3/h) |
1.805 - 2.22 (6500 - 8000) |
|
Temperatures, oC: |
|
|
maximum acceptable temperature at center of fuel pellet |
2600 |
|
maximum acceptable graphite stack temperature |
760 |
|
maximum acceptable fuel cladding temperature |
700 |
|
maximum acceptable fuel channel temperature |
650 |
|
coolant temperature at fuel channel inlet *** |
260 - 266 |
|
feedwater temperature *** |
177 - 190 |
|
Pressures, MPa (kgf/cm2): |
|
|
at separator drum |
6.86 (70) |
|
at pressure header |
8.5 (86.6) |
|
Coolant flow rate through reactor, m3/s (m3/h)*** |
10.83 - 13.33 (39000 - 48000) |
|
Steam produced in reactor, kg/s (t/h)*** |
2056 - 2125 (7400 - 7650) |
|
Void fraction at reactor outlet, % |
23 - 29 |
|
Maximum fuel channel parameters: |
|
|
fuel channel power, kW |
4250 |
|
coolant flow rate through fuel channel, m3/s (m3/h) |
0.0111 (40) |
|
void fraction at fuel channel outlet, % |
36.1 |
* Now the fuel is being changed to 2.4 % enrichment fuel with erbium.
** At fuel enrichment for 235U 2%.
*** At 4200 MW (th).
When analysing emergency conditions and establishing safety measures, the RBMK-1500 design is based on the following safety criteria [4]: