NUCLEAR PLANT WITH VK-300 BOILING WATER REACTORS FOR POWER AND DISTRICT HEATING GRIDS

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1 7th International Conference on Nuclear Engineering Tokyo, Japan, April 19-23, 1999 ICONE-7335 NUCLEAR PLANT WITH VK-300 BOILING WATER REACTORS FOR POWER AND DISTRICT HEATING GRIDS Yu.N. Kuznetsov*, F.D. Lisitsa, A.A.Romenkov, Yu.I. Tokarev Research and Development Institute of Power Engineering P.O. Box 788, RDIPE, Moscow, Russia Phone: , Fax: Specific requirements to nuclear power units for medium-size power and district heating grids are under consideration. Among the main requirements are the following: matching of units output with the grid stability, enchanced NPP reliability and safety, competitiveness of power generated. Design and main characteristics of two-units NPP with VK-300 reactors of SBWR-tipe being developed by RDIPE are described. NPP and rector safety problems including ones for underground NPP are consideration. Key words Water boiling reactor, District heating, Primary containment, Emergency cooldown, Underground plant location 1 POTENTIAL FOR MEDIUM SIZE NUCLEAR POWER PLANT The analysis of electric power and heat consumption in the Russian Far East and Siberia shows that these regions (especially those with small power systems) need the medium capacity power sources for heat and electric power generation that are capable of rivaling the organic fuel plants. Technical and economic estimates show that the required number of plants in the foreseeable future may be approximately as follows: 10 units of 100 MW electric power, 10 units of 300 MW and 2 units of 400 MW. There is information that nuclear plant (NP) of such power are in demand in Byelorussia. Medium power nuclear plant units should meet specific requirements. Their power governed by the demand should not exceed the limit ensuring stability of the power system at a sudden shutdown of the unit. Power limitation for autonomous power systems is unlikely to permit the use of units with the power of over MW in their mix. Larger capital investments due to power reduction should be compensated by simplified reactor and plant designs, less equipment and higher reliability, as well as smaller maintenance and repair costs with assurance of highest safety requirements. A major contributor to a higher efficiency of medium power nuclear plants is their dualpurpose application both for electric power and heat generation. At the same time, this circumstance demands that nuclear plants should be located closer to the consumer which 1

2 imposes stringent requirements to radiation safety assurance for population during normal operation and in emergencies. 2 CONCEPTUAL PROTOTYPE FOP KRASNOYARSK APPLICATION To a certain extent a prototype of a medium capacity district heating station is a nuclear cogeneration plant (NCGP) with VK-300 boiling water reactors that is being developed for Krasnoyarsk GKhK (Mine and Chemical Integral Works). The main peculiarities of this project are as follows: 1. The possibility of using the existing underground premises of the integrated works that will save construction costs and produce rather favorable conditions for protection of population of the nearby city of Zheleznogorsk against potential radioactive releases during accidents. 2. The use of the existing infrastructure of the integrated works ensuring operation of the decommissioned NCGP (that is in operation now) that considerably reduces the cost of building a new plant. The plant equipment is located in two parallel tunnels (Figs. 1, 2) (each reactor unit is located in its own tunnel) isolated from each other. Emergency cooldown tanks are located in the immediate vicinity of the reactor. The reactor department accommodates the cooling tanks and vaults for storage of reactor internals during refueling and preventive inspection of the reactor. Besides, the reactor units are located in leak-tight rooms designed for the pressure of 0.5 MPa. The plant rooms are connected with the day surface via an entrance gate with locks and water and air pipelines and electric cables are sealed. The rooms have a recirculation ventilation system. Hence, the plant rooms are permanently connected with the atmosphere only via small diameter tubes (50 mm) intended for rarefaction in controlled access rooms. Such an arrangement provides for practically full localization of radioactive releases that may appear in the rooms in case of accident. All basic plant equipment including turbine generators, boiler rooms, control rooms, electric equipment and chemical process equipment, are also located in the underground rooms. Refueling (Fig.3) is done by "dry" method through pulling the spent FA into a shield container that is carried to the cooling tank by a vehicle. Reactor internals are carried to the tanks and storage facilities in the same way. It is proposed that the plant should use an extraction turbine set. The design of the VK-300 boiling water reactor (Fig.4) is based on the technical decisions tested during operation of a VK-50 reactor that has been in service in Dimitrovgrad for more than three decades. First of all, they are in-vessel natural circulation circuit, coolant water chemistry, fuel composition and fuel element materials. The reactor project provides for the higher design margins of linear fuel rating and fuel temperature. The principal novelties to the project are in-vessel coolant separation and the primary containment that confines coolant leakage during primary circuit depressurization. Unlike most of BWRs, the control and safety system absorber drives are located on the reactor cover. It allows reducing the reactor vessel height approximately by the drive stroke through reducing a clearance between the vessel bottom and the core. Besides, it allows not 2

3 providing a special room for withdrawal and repair of the drives under the reactor which requires fewer amounts of mine workings.it is suggested that already manufactured and upgraded as low as possible WWER-1000 reactor vessels (new) should be used. The maximum value of the fast neutron fluence (E > 0.55 MeV) that is accumulated on the vessel during 60 years of operation, does not exceed /cm 2. Main plant data Number of reactor units 2 Thermal power, MW Heat generation capacity, Gcal/h Electric power, MW under district heating mode under condensation mode Steam parameters at the reactor outlet pressure, MPa 6.86 temperature C 285 moisture content % 0.1 Reactor steam output, t/h 1370 Number of hours of using installed power per year 7000 Number of hours of using nominal power for heat generation per year 5600 Uranium load, t Fuel enrichment, % 4 Fuel burnup, MW day/kg 42.4 Gross efficiency in district heating mode in condensation mode SAFETY SYSTEMS Underground plant location allows excluding the consideration of the stability of safety systems to failures during a whole range of accidents caused by external events. They are aircraft fall onto the nuclear plant, hurricanes, transport accident, explosions of commercial installations and facilities. Since fire may also be a source of safety system common-cause failures, the equipment of the systems' channels is located in different rooms. The safety system equipment is designed for operation during an ultimate design-basis earthquake. The project includes organizational and technical measures to avoid unauthorized access to the safety system rooms. The stability of safety systems to personnel errors is ensured by prohibition of operator interference with the accident management within 30 minutes after the accident starts (the interference is excluded by technical means). After this time expires, remote control or manual backup for actuation of safety system channels is permitted in the case of failures in their automatic actuation circuits or failure to actuate. 3

4 To avoid flooding of the process rooms, they will have a special sewage system with water gravity discharge. The main electrical components and devices are located such that no process service lines are run and no tanks with liquid media are present near them to flooding of the main electrical rooms. Hence, the sequence of physical barriers along the path of radioactive substances and ionizing radiation spreading for this plant may be presented as follows: Fuel pellet Fuel cladding Reactor vessel, primary circuit pipelines, gas mixture burning facility, residual heat removal pipelines and equipment Primary containment (PC), emergency cooldown tanks (ECTs) Reactor department's leak-tight rooms Underground plant rooms The designs and schematic arrangements of the emergency cooldown systems (Fig.5) provides for passive cooldown of the core without time limitation and without operator involvement during such accidents as loss of in-house power and primary circuit pipeline rupture. In emergencies, the isolation valves shut off the steam line and the feedwater pipeline on the primary containment boundary confining the radioactive coolant inside the primary contaiment (PC) and the coolant goes to the emergency cooldown tank: if a pipeline is ruptured inside the PC, the coolant goes by gravity to beneath the water layer in the tank, condenses there and goes back to the reactor via a release valve; if a primary circuit pipeline is ruptured outside the PC or if in-house power is lost, the coolant goes to the PC heat exchanger via the release valve and goes back to the reactor after it condensed. 4

5 Heat is further discharged from the emergensy cooldown tanks (ECT) via an additional water circuit between a water-to-water heat exchanger located in the ECT and a water-to-air heat exchanger located in the air channel. Hence, the radioactive coolant is confined in the PC-ECT system all emergency situations, except primary circuit pipeline rupture outside the PC. In the latter case, not more than 1.2 t of coolant with the radioactivity of 66 MBq by radioactive inert gases and 10.3 GBq by iodines enters the leak-tight reactor (or turbine) department due to fast actuation of the isolation valves. The simplicity of the reactor design and passive nature of safety systems actuation will allow ensuring a very low probability of a core damage during accidents (less than of events per reactor-year). Calculations show that due to the use of the existing underground premises and the existing infrastructure of the integrated works, the plant construction time will be reduced by 3-4 years and the capital investments will be cut by % as compared to the construction of a similar land-based plant. 4 CONCLUSION In accordance with the International scale of nuclear events, not more than a level 4 accident (an accident within the plant boundaries) is possible at the underground NCGP under design. 5

6 TURBINE ROOM REACTOR ROOM Reactor Core barrel Reactor cover Upcomer tubes Steam turbines Emergency tanks Fuel assembly Reactor Separator Sluice-gate camera Fig.1 Turbine and reactor room NPP. 6

7 TURBINE ROOM REACTOR ROOM Electricity equipment, centrol room Steam turbine Reactor Fuel assembly Warter purification system Primary conteinment vessel Core barrel Upcomer tubes Reactor cover Separator Fig.2 Turbine and reactor room NPP (longitudinal section). 7

8 Reactor room Charge fuel equipment Fuel container Rotation plate for taking aim at fuel assembly Fuel assembly storage room Reactor Separator, core barrel and upcomer tubes s Fuel assembly Reactor cover New fuels Spent fuels Fig.3 Fuel reloading schedule. 8

9 Fig.4 Reactor VK CPS drive; 2 - Reactor cover; 3 - Separators; 4 - Reactor vessel; 5 - Upcomer tubes; 6 - Core barrel; 7 - Fuel assembly; 8 - Iron-water shield; 9 - Core supportplate. 9

10 Condenser Air Heat exchangers Primary containment vessel Emergency tank Barboter Steam Feedwater Release valves Armoured concrete Rock Cut-off valves Reactor Fig.5 Primary containment vessel and emergency cooling systems of the reactor. 10