Belene moves forward

The results of a 2008 a public opinion poll on the construction of Belene nuclear power plant in Bulgaria showed that 72% of Bulgarian citizens and 97% of the local residents support the construction of the plant. Surprisingly, despite the project difficulties, these results are similar to a poll conducted in 2004, showing ongoing support for the project.

The go-ahead for the Belene nuclear plant was originally given in 1981 and construction of the first two units began in 1987. In 1990, the Bulgarian government decided to suspend the project due to financial difficulties.

The project kicked back into life in the early 2000s, when Bulgaria’s Natsionalna Elektricheska Kompania (NEK), with architect-engineer for the project Parsons E&C Bulgaria, and the financial consultant for the project Deloitte, began to reassess plans for the plant. They had a new motivation: the loss of 880MW of Bulgarian electricity from 2007. As a condition of the country’s accession to the European Union, Bulgaria had to shut down two (units 3 & 4) of the four remaining units of its only nuclear power plant at Kozloduy by the end of 2006.

NEK named Atomstroyexport as the main contractor for Belene unit 1 and 2 construction in November 2006. After beating an offer led by the Czech Skoda Alliance, Atomstroyexport will supply two of its VVER-1000 PWRs. The units, the new variant AES-92 or V-466 type, are third generation reactors offering secondary containment, four-train safety channels and passive safety elements.

In February 2007, NEK announced a tender to raise debt financing of EUR250 million to be used to finance the design, procurement of equipment and civil works for Belene during the first year of its implementation. The credit facility was to act as bridging money until the financial closure of the development. The French bank BNP Paribas won the first tender for Belene NPP financing in May 2007, and the company singed a contract with NEK on 4 June 2008.

In January 2008 an EPC contract for design, construction and commissioning of units 1 & 2 of Belene was signed by NEK and Atomstroyexport. The value of the contract is almost EUR4 billion. But funding for the project has not yet been secured, which could lead to delays. The Bulgarian government is under pressure to secure funding and has been offered a EUR3.8 billion Russian loan to finance the project.

Cranes erect structural steel at the Belene site in early 2009.

In October 2008, after beating Electrabel of Belgium to become a strategic partner in the plant, RWE Power of Germany signed an agreement with NEK that formally established their partnership for construction of the new two-unit nuclear power plant. The companies agreed to form a joint project company, Belene Power Company (BPC), to carry out project development, including a financing concept, followed by construction and management of the plant. BPC will be 51% owned by NEK, with RWE holding the remaining 49%.

In late November 2008, reactor supplier Atomstroyexport signed a deal with the European consortium CARSIB, consisting of Areva and Siemens. CARSIB is to carry out design of the instrumentation and control systems (I&Cs) for normal operations systems and the unit’s safety systems. It is to supply the heating, ventilation and air conditioning systems, and the electric systems. Supply of refrigerating machines and additional safety equipment, such as the hydrogen recombiner, is also within the scope of the CARSIB consortium’s obligations. Atomstroyexport and Areva previously worked together during a project to modernisation of Kozloduy.

Reactor design legacy

The V-466 is the latest version of the VVER-1000 and builds on the experience gained with the mass-produced V-320 version of the VVER-1000, developed by Russian PWR design organisation Gidropress.

There are now about 25 VVER-1000 V-320 type units operating in Russia, Ukraine, Bulgaria (at Kozloduy) and the Czech Republic, which according to Atomstroyexport underlines the validity of the original engineering parameters and the reliability and operational safety of both systems and components. Thus far, type V-320 reactors have recorded more than 400 reactor-years of operation.

That design dates from 1977, when Atomenergoproekt of St Petersburg, Gidropress in Podolsk and Finnish utility IVO (now Fortum) began development of a new nuclear power plant design based on the VVER-1000 V-320.

Fourteen years later, the organisations put forward a plant of this particular design in the bidding to build Finland’s fifth nuclear reactor, at Loviisa that was later abandoned in the wake of a decision by the Finnish government.

Improvements to the V-320 resulted in creation of the V-428 version of the VVER-1000. A power plant with two units of this type has been constructed in China, at Tianwan. According to Atomstroyexport, the V-428 version incorporates ‘evolutionary’ measures to enhance safety, but preserves to the maximum extent possible the basic V-320 layout and equipment configuration.

The V-466 is the next stage in the evolution of the VVER-1000, and is essentially an advanced version of the V-428. The V-466 includes the International Atomic Energy Agency recommendations, along with the latest Russian and international standards, taken into account. Additional passive safety systems were introduced into the new design, which was updated by Atomenergoproekt. It was this latest version of the VVER-1000 that was entered in the bidding for Bulgaria’s Belene project.

V-466 features

The V-466 provides an installed capacity of 1060MWe and is designed for both baseload and load following. The reactor is designed to operate for 7900 hours per year at nominal capacity, with refuelling once per year. The primary circuit comprises the reactor, the pressure compensation system and four circulation loops, each including a horizontal type steam generator, a reactor coolant pump and a main circulation pipeline of 850mm diameter. The main reactor data is given in Table 1.

The steam generators transfer heat to water flowing in the secondary circuit, which consists of the steam-generating part of the steam generators, main steam pipelines, turbine plant, auxiliary and service systems, deaeration equipment, and feedwater heating and supply to steam generators and blowdown systems.

The turbine plant consists of a steam turbine and a generator mounted on the same foundation. The turbine is equipped with condenser, recuperative water heating plant, and separators/ steam superheaters. It also has unregulated steam extraction for the heaters of the recuperation system and for power plant in-house needs.

Computer image of the fully-built Belene plant, in elevation view

The main task of nuclear plant safety assurance is the protection of operating personnel, the public and the environment from unacceptable radiation exposure under all operating conditions, including design-basis and beyond-design-basis accidents.

In the V-466 this is achieved through the implementation of multiple safety systems:

• A double containment with an intermediate shell

• A passive leakage filtration system

• A system of hydrogen removal based on passive recombiners

• A sprinkler system to lower the containment pressure during accidents

• A device for core melt (corium) localisation

According to Atomstroyexport, these measures, for all practical purposes, eliminate the possibility of exceeding the maximum emergency release for beyond-design-basis accidents, including severe accidents with complete nuclear fuel melting. High reliability of safety functions is ensured by implementation of mutually-redundant passive and active safety systems, and also through the use of diversity.

Passive safety systems incorporated in the V-466 include a passive system for heat removal from the steam generators, a system of prompt boron injection into the primary circuit, hydraulic accumulators incorporated in the reactor emergency cooling §system, intermediate shell filtration system, and the corium localisation device.

The corium localisation device is designed to perform several functions in the event of a severe accident with fuel melting.

• Retention of solid and liquid fragments of the damaged core and also parts of the reactor pressure vessel

• Assurance of cooling water supply to corium as well as steam removal

• Transfer of heat to cooling water

• Retention of the reactor pressure vessel bottom should it become detached

• Minimisation of release of radioactive substances and hydrogen into the containment inner space

The corium localisation device is designed to perform these functions with minimum control effort required of the plant operating staff. The corium can be localised and cooled indefinitely.

After an accident, and under complete plant blackout conditions, there is sufficient reserve of water available in the containment sump to assure cooling of the corium for 24 hours. The core can be reliably retained for longer periods once replenishment of the water reserve from external sources has been established.

Atomstroyexport has stated that the reactor is protected against external hazards by the outer shell of the double containment. The inner part of the containment is made of prestressed reinforced concrete with stainless steel cladding on the inside. The outer shell, which does not use prestressing, is able to withstand stresses including a seismic load with maximum horizontal acceleration of 0.2g, wind load, and aeroplane crashes, according to the company.

Fuel

Russia’s TVEL has offered to supply TVSA (alternative type of fuel assemblies) nuclear fuel for Belene. According to TVEL, the fuel has an average reload batch of 42 fuel assemblies in 4-year cycle. The fuel has a 320-effective-day lifetime, compared with 295 for Kozloduy plant. Average enrichment of the uranium oxide fuel is 4.3% (by weight).

Due to the fuel pellet dimensions (7.6×1.2mm) it will have an increased uranium charge. The UO2 grain size will have a minimum of 25mm.

The average burnup will be around 55MWdays/kgU, with maximum burnup of up to 60 MWdays/kgU.

TVEL has stated that TVSA has several important design features such as vibration-resistance spacers, arch-shaped grids, and an anti-debris filter.

According to the supplier, it also possible to implement the fuel assembly design with an increased fuel stack length. This design feature provides a lower linear heat generation rate and enhances fuel operation safety.

TVEL’s fuel assembly design with increased fuel stack length is approved as a principal fuel design for all VVER-1000s.

TVEL can supply follow-up options such as training and education for Bulgarian specialists in fuel-handling and using computer codes. It can also supply fuel assembly inspection and repair rigs, and other specialised equipment and training.