Sodium-cooled fast neutron reactors are one of the most environmentally friendly reactor types and play an important role in the development of Russia’s nuclear power industry and the long-term supply of nuclear fuel for the industry. The long-term successful operation of the industrial-scale fast neutron reactor BN-600 and the commissioning of a new power unit with a more powerful BN-800 reactor have made Russia a world leader in the construction and operation of fast neutron reactors. This paper describes the stages of mastering the capacity of the sodium-cooled fast neutron power reactors BN-600 and BN-800 at the Beloyarsk NPP. Based on the experience of BN-600 and BN-800 operation, a power unit with a BN-1200M reactor is being created, which can be considered as the head in a series of power units with BN-1200M reactors. The creation of the series will significantly expand the fuel base of nuclear power by reusing spent nuclear fuel from other NPPs, and minimizing radioactive waste by burning the longest-lived isotopes from spent nuclear fuel from other reactors. The main task in creating the BN-1200M is to achieve economic characteristics that ensure its competitiveness with a serial thermal neutron reactor VVER of a similar power level. According to the General Scheme for the Placement of Electric Power Facilities approved by the Government of the Russian Federation until 2042, the lead power unit with the BN-1200 reactor will be built at the Beloyarsk NPP as power unit No. 5.

fast neutrons, nuclear fuel, radioactive waste, competitiveness, efficiency, sodium coolant, BN-600, BN-800

An important role in the evolution ofnuclear power in Russia and in providing the industry, in a long term, with nuclear fuel is assigned to fast neutron reactors (RBN) developed on the basis of the Beloyarsk NPP. The BN-600 reactor has been successfully operated for 45 years (08.04.1980), unit 4 with the BN-800 reactor saw its power startup on 10.12.2015, and a roadmap has been approved for the construction of unit 5 with the BN-1200 reactor facility.

It became possible to deploy RBN reactors and extend their role in the power industry evolution as a result of long-term phased investigations and accumulation of experience in using experimental, pilot and commercial test facilities and nuclear power plants (NPP) at Russia’s leading scientific centers, including IPPE, NIIAR, Kurchatov Institute, OKBM, OKB GIDROPRESS, NIKIET, and others (IAEA-TECDOC-1531 2006; ROSATOM 2009; Korol’kov et al. 2001; Antufiev et al. 1982; Vasiliev et al. 2003). Figure 1 illustrates the evolution stages of FNR technologies in the Russian Federation (IAEA-TECDOC-1531 2006).

Figure 1. 

Evolution of BN-type reactors.

Along with sodium coolant, a program is under implementation for building the BREST-OD-300 lead-cooled reactor facility at the site of the Siberian Chemical Combine (SCC) in Seversk, and an NPP design is in the process of development based on lead-bismuth coolant.

Unit 3 of the Beloyarsk NPP with the BN-600 fast neutron reactor is the world’s only NPP unit with a fast reactor of the commercial power level which is capable to operate reliably and safely for such a long time. Unit 3 was put into operation on 8 April 1980. In 2010, based on the expert appraisal results for non-replaceable equipment materials, as well as thanks to the replacement of the rest of the components and introduction of additional safety systems in parallel with large-scale modernization, a license was obtained from Rostekhnadzor to extend the unit’s design life for an extra period of up to 2020, followed further by a license for another life extension to 2025 with the possibility of further renewal. Work has been currently completed to extend the unit’s life to 2040.

The construction of the Beloyarsk NPP’s unit 4 with a BN-800 fast neutron reactor began in the mid-1980s, was suspended in the economic recession years in the 1990s, and was resumed in the 2000s. The BN-800 reactor reached initially the minimum controlled power level as part of its first criticality achieved on 27 June 2014. It was on 10 December 2015 that the unit was connected to the grid for the first time. The unit was put into commercial operation on 31 October 2016.

Apart from electricity generation, the BN-800 makes it possible to complete the components of the closed nuclear fuel cycle, which is required to achieve the strategic goal of Rosatom State Corporation, that is, to switch nuclear power to a new technology platform that forms the basis for a two-component nuclear energy system with joint operation of thermal and fast neutron reactors. To do this, the BN-800 reactor is operated with its core fully loaded with innovative uranium-plutonium MOX fuel.

Intrinsically, BN reactors feature a natural safety property: in the event of a deviation from a given operating mode, the nuclear reaction will stop by itself due to only physical properties, even without the need for automatics or operator intervention. BN reactors are also one of the most environmentally friendly reactor types.

Based on the experience of the BN-600 and BN-800 operation, a power unit with the BN-1200M reactor is under construction, which can be viewed as the prototype for a series of power units with BN-1200M reactors. When built, the series will extend greatly the fuel base for nuclear power by way of reusing spent nuclear fuel from other NPPs, involving the currently unused U-238 isotope from natural uranium enrichment in the useful production cycle, and minimizing the amount of radioactive waste by after burning the longest-lived isotopes from spent nuclear fuel of other reactors. The key objective in building the BN-1200M reactor is to achieve the economic performance to make it competitive to a serial VVER-type thermal neutron reactor of the same power level. The prototype unit with the BN-1200M reactor will be built at the Beloyarsk NPP as unit 5.

Long-term successful operation of the BN-600 fast neutron reactor of the commercial power level and active commissioning of the new power unit with a larger BN-800 reactor has made Russia the world’s leader in construction and operation of fast neutron reactors (Saraev et al. 1996, 2010; Ashurko et al. 2000; Oshkanov et al. 2004, 2005a, 2005b, 2008, 2010; Kostin and Vasil’ev 2007).

Due to the long period of the facility construction in 1994–2011, requirements were modified for the NPPs in the process of construction towards increased safety and reliability, the range of manufactured equipment changed greatly, and the design regulatory framework was modified. In 2011, in this connection, a resolution (No. BYeLAES-2-81R(4,6)2011) was adopted by Rosatom State Corporation to update the design.

In 2012–2014 the BN-800 detailed design was updated by Atomproekt JSC, the General Designer.

The updated detailed design of the BN-800 reactor was reviewed by FAU Glavgosexpertiza with the approval statement (No. 897-15/GGE-8909/02, dated 26.06.2015) obtained from the State Expert Examination Commission.

The unit’s final characteristics are presented in Tables 1, 2.

The following design solutions will be used to increase safety:

• integrallayout, a three-circuit cycle with pressure directed from the tertiary circuit to the primary circuit;
• compact core;
• negative reactivity coefficients;
• small initial reactivity margin;
• low pressure in the reactor vessel (close to atmospheric pressure);
• high heat capacity of sodium, no phase transitions;
• possibility of using U-Pu fuel in normal conditions;
• large sodium boiling margin (over 300 °C);
• developed natural circulation;
• an air system for emergency heat removal from the reactor based on passive principles of operation (natural circulation);
• two independent systems for removal of heat from the reactor based on different principles of operation with three channels in each (steam generators and the emergency reactor cooldown system with air heat exchangers);
• passive components have been added to the reactor emergency protection system (three independent reactor shutdown systems based on different principles of operation);
• fuel melt trap in case of beyond design basis accidents involving fuel melting.

The adopted engineering and design solutions exclude the need for evacuation of the public in the event of beyond design basis accidents.

Fig. 2 presents the schematic of the BN-800 reactor facility.

Figure 2. 

BN-800 reactor: 1 – reactor vessel; 2 – safeguard vessel; 3 – core; 4 – pressure chamber; 5 – fuel melt tray; 6 – reactor cavity; 7 –reactor coolant pump; 8 – upper fixed shielding; 9 – larger rotary plug; 10 – CPS column; 11 – protective cap; 12 – refueling mechanism; 13 – smaller rotary plug; 14 –intermediate heat exchanger (IHX).

The BN-800 power unit has a three-circuit thermal cycle (Fig. 3).

Figure 3. 

Schematic of the BN-800 unit thermal cycle: 1 – circulation loop equipment; 2 – primary circuit reactor coolant pump; 3 –intermediate heat exchanger; 4 – fuel assemblies; 5 – steam generator; 6 – buffer and discharge tanks; 7 –reactor coolant pump; 8 – emergency cooldown system (ECS) pump; 9 –ECS air heat exchanger; 10 – K-800-130/3000 turbine; 11 – generator; 12 – transformer; 13 – power out; 14 – low-pressure heaters; 15 – deaerator; 16 –electric feedwater pumps; 17 – high-pressure heaters; 18 – circulation pump; 19 – cooling pool; 20 – condenser; 21 – first stage condensate pumps; 22 – second stage condensate pumps.

Compared to the VVER design, a BN-type reactor has an intermediate sodium circuit which leads to its increased metal content, and a larger volume of installation and adjustment operations. However, the presence of the intermediate sodium circuit and the emergency cooldown system (ECS) allows first criticality to be achieved with no tertiary (steam-water) circuit systems being available, which increases the operating efficiency of the NPP at the commissioning stage.

The commissioning sequence for the Beloyarsk NPP’s unit 4 is shown in Fig. 4.

Figure 4. 

Commissioning stages of the Beloyarsk NPP’s unit 4.

Figure 5 shows the first criticality steps.

Figure 5. 

First criticality steps of the Beloyarsk NPP’s unit 4.

First criticality was achieved as specified in the phased commissioning program “First Criticality of the Reactor Facility. DN.P4.FP.001”. There were 21 programs developed for the activities at this stage.

On 26.06.2014, there were 400 core FAs, 90 side blanket (SB) FAs and 30 control and protection system (CPS) rods loaded into the reactor which corresponds to the state with the minimum critical weight.

The BN-800 MCPL with the minimum critical load was achieved on 27.06.2014. As the MCPL was achieved, a power level of ~ 0.1% N_nom was reached as confirmed by the neutron flux monitoring equipment (NFME) readings. At the same time, the position of the CPS members consisted of emergency protection (EP) members, passive emergency protection (PES) members, shim rods (SR) on the upper limit switches, and the control rod (CR) member: CR1 – 518 mm according to the position indicator (PI) readings, and CR2 – 531 mm according to the PI readings. The configuration of the core with the minimum critical power level is shown in Fig. 6.

Figure 6. 

MCPL core layout.

The initial stable power doubling period (chain reaction) was recorded at 10:10 am, and the MCPL was achieved at 11:58 am (local time). The diagram of the power change as the MCPL is achieved is presented in Fig. 7.

Figure 7. 

MCPL power change diagram.

It was obtained based on the analysis results that the NFME total calibration coefficient should be reduced by a factor of 6.6.

On 22.07.2014, there were 558 core FAs, 90 SB FAs and 30 CPS rods loaded into the reactor which corresponds to the startup reactor state.

The first criticality chronology is presented in Table 3.

In total, it took 544 days to achieve first criticality.

The duration of the activities as specified in the first criticality program, given the repeated activities after the FA upgrading, was 155 days.

1. The quantitative and qualitative criteria were confirmed for each individual test as required by testing programs and methodologies.
2. Experimental values of heat losses from the reactor and three secondary circuit loops were obtained.
3. The power density spatial distribution was measured by FA gamma scanning.
4. The sodium flow rate through FAs was measured.
5. Tests were conducted to determine the primary circuit hydrodynamic performance for the BN-800 reactor with the startup core.
6. Tests were conducted to determine the CPS rod efficiency in the startup critical state.
7. Tests were conducted to determine the CPS rod differential and integral efficiency, and the reactivity margin was determined.
8. Thermal elongation of the CPS rod actuator bars was measured.
9. Temperature, power and hydrodynamic reactivity effects were measured.
10. The flow meter readings in the process of testing in June-July 2015 (after the FA upgrading) coincide with the readings from July-August 2014 (prior to the FA upgrade) and the design performance in the permissible flow meter error limits.

Based on the results of the first criticality stage activities, no amendments to operating documentation are required.

The power startup was conducted in accordance with the Phased Program for Commissioning of the Beloyarsk NPP’s Unit 4.

Power startup goals and stages:

• confirmation of the reliable and safe operation of systems, equipment and the unit as a whole at the energy power levels;
• sequential stepped increase in the reactor power from 0% N_nom to 50% N_nom;
• testing and physical measurements at each stage as specified in the Power Startup Program;
• trial startup of the turbine at a power level of 15% N_nom;
• generator synchronization and first grid connection at the stage of the power rise to 35% N_nom;
• testing for the actual parameters and performance of systems and equipment to comply with the design in steady-state and transient modes of the power unit operation;
• 72-hour power unit testing at 50% N_nom;
• handover of the Beloyarsk NPP’s unit 4 for pilot operation.

The activities under the Program for the Trial Startup of the K-800-130/3000 Turbine were undertaken between 12:00 pm 24.11.2015 and 05:45 am 25.11.2015.

The following tests were conducted in the process of the program implementation:

• the mode with the high-pressure cylinder (HPC) warm up by outside steam was adjusted and tested;
• the turbine was initially started up and the no-load speed was achieved;
• operation of auxiliary systems was tested;
• the thermal-mechanical and vibration state of the turbine was tested in the process of the turbine rolling and idle operation;
• check valves (CV) and high-pressure control valves (HPCV) were leak tested.

At 21:21 pm 10.12.2015, following the activities under the generator testing program based on the short-circuit (SC) and no-load speed readings at a power level of 24.1% N_nom, the generator was synchronized and connected to the grid for the first time.

Results of the Beloyarsk NPP’s unit 4 BN-800 reactor power startup:

1. The activities at Stage C (Power Startup) were completed in full.
2. All deficiencies and deviations identified were resolved. The criteria for the Power Startup stage completion were achieved.
3. In the period between 07.02.2016 and 09.02.2016, the unit was operated for 72 hours in the base mode at a power level of at least 50% N_nom with design-basis operation of all auxiliary equipment and maintenance of the design technical and economic parameters.
4. There were no failures of normal operation devices and safety systems hampering reactor operation at 50% N_nom.

As decided by the working commission, the activities and tests scheduled under the Stage Program for Commissioning of the Beloyarsk NPP’s Unit 4 – Pilot Operation Program should be considered completed.

Based on the permit from Rosatom State Corporation, the Beloyarsk NPP’s unit No. 4 with the BN-800 reactor was put into commercial operation by Rosenergoatom Concern’s order dated 31 October 2016.

The BN-800, apart from electricity generation, allows the closed nuclear fuel cycle components to be finally refined, which is required to achieve Rosatom’s strategic goal of switching nuclear power to a new technology platform the two-component nuclear energy system is based on, that is, joint operation of thermal and fast neutron reactors. To this end, the BN-800 reactor has since 09.09.2022 operated with the reactor core fully loaded with innovative uranium-plutonium MOX fuel.

The 40-year experience of operating the Beloyarsk NPP’sunit with the BN-600 reactor has shown that BN-type reactors feature an inherent property of natural safety which ensures that the nuclear reaction will stop by itself in the event of a deviation from a given operating mode due to physical properties even without the need for automatics or operator intervention.

BN-type reactors are one of the most environmentally friendly reactor types.

Based on the experience of the BN-600 and BN-800 operation, a power unit with a BN-1200M reactor is under construction which can be viewed as the prototype for a series of units with BN-1200M reactors. When built, the series will extend greatly the fuel base for nuclear power by way of reusing spent nuclear fuel from other NPPs and minimizing the radioactive waste amounts by after burning the longest-lived isotopes contained in spent nuclear fuel from other reactors.

The major objective in building the BN-1200M reactor is to achieve such economic performance as will make it competitive toa serial VVER-type thermal neutron reactor of the same power level.

As defined in the 2042 Master Plan for the Deployment of Electricity Generating Facilities approved by the Russian Federation Government, the prototype power unit with the BN-1200 reactor will be built at the Beloyarsk NPP as unit 5.

Long-term successful operation of the BN-600 fast neutron reactor of the commercial power level and active commissioning of the new unit with a larger BN-800 reactor have made Russia the world’s leader in construction and operation of fast neutron reactors.