WWER designs

The original WWER design also does not provide for adequate condition monitoring of the mechanical equipment important to safety. This monitoring should be carried out with respect to vibration, displacement, position and condition as appropriate. 

Development and validation of natural circulation based systems for new WWER designs... 

Design improvements have been made in Ukrainian WWERs to meet safety requirements. Examples of design changes involve the emergency core cooling system, and improvement of the reactor control and protection system. Improved fuel management has resulted in reductions of fuel cycle costs in the range of 10 per cent. 

Designs of units with WWER under operation in Ukraine were developed in 70-s. The basic safety criterion laid into these designs was to provide for safety under all the design basis accidents/at that time, exclusively deterministic approach to safety level assessment was adopted as the basis. 

In 1992 -1993 almost at all WWER-1000 of Ukraine, Russia and then in Bulgaria incomplete RCCA insertion (i.e. RCCA stuck in intermediate position), RCCA drop time exceeds 4s (design time) have been revealed. The program of additional quarterly measurements of RCCA drop time was developed and implemented. In the case of RCCA operation violation (and when there was no chance to cease one) the unit had been transferred to the operational mode with three loops coolant circulation and with preliminary power reduction to 67% of... 

Within the context of these tasks, Russian design and scientific organisations are performing a complex of R D work on development of power units of new generation with advanced reactor plants of 1000 MW(e) power which meet new requirements for safety and economical efficiency of electric power production. Design decisions on Novovoronezh NPP-2 with WWER-lOOOA -392 reactor plant which assure significantly higher safety level and improve economical performance are briefly considered in the present paper. 

The advanced design of NVAES-2 has been developed on the basis of standard power unit with reactor plant V-320. These units are in operation for a long time at nuclear power stations in Russia, Ukraine and Bulgaria. Today 20 power units with WWER-1000 reactor operate, and total time of their work is 270 reactor-years. Power units of this type are also being constructed or planned in Czechia, Russia, Ukraine. In particular, unit 1 of Rostov NPP in Russia and unit 1 of Temelin NPP in Chechia are being commissioned this year. 

So, the WWER-1000/V-392 design is as a whole an evolutionary development of the operating standard unit WWER-lOOO/V-320. The design refers to a class of advanced light... 

Design of the WWER-lOOO/V-392 power unit makes maximum use of technical solutions proven by operation experience of existing WWER-1000 power units. Such consistency improves technical characteristics of the reactor plant including also operational availability and maintenance. At the same time, a number of new technical decisions on the unit systems and equipment are applied in V-392 design to take into account operating experience of WWER-1000 units and modem requirements to nuclear power plant competitiveness. Some examples of advancements aimed to improve the operational performance and plant economical efficiency, to decrease the costs of constmction, repair and maintenance of the systems and equipment are given below. 

Operation experience of standard fuel revealed certain drawbacks both concerning efficiency of fuel utilisation, and design of fuel assembly (highly absorbing material within the active part boron-based burnable absorber low design service life one-piece stmcture). Therefore designers and manufacturers of Russian fuel for WWER-1000 have developed the advanced FA with zirconium stmctural materials and this FA is being implemented at present. 

In WWER-lOOO/V-392 design it is supposed to use some passive systems intended for fulfilment of the main safety functions (reactor shutdown, decay heat removal, core cooling). These systems, in the first turn, are intended to improve considerably the plant safety. Alongside with this, passive systems, as a rule, are simpler in operation and maintenance, and therefore improve also the plant economical characteristics. 

Development of hardware for new MCS is performed according to complex programme of Minatom of Russia prescribing the development of software-hardware for MCS engineering for the nuclear power plants being reconstructed, under construction and under design, including advanced power unit WWER-lOOOA -392. 

In accordance with the national program of nuclear power development, a complex of R D work is being carried out by the Russian design and scientific organisations on development of advanced power units of new generation with reactor plant WWER-lOOO/V-392. These units meet up-to-date national and international requirements for safety and economic efficiency of electric power production. Permission of the Gosatomnadzor RF has been issued for the construction of the forerunner unit of this design at Novovoronezh NPP site. 

In the advanced WWER-lOOO/V-392 power unit design many new technical solutions are applied with a view to improve safety, to optimise economical indices and to minimise the expenses on maintenance of the station equipment and systems. 

The WWER RPVs have some significant features that are different from western designs. A sketch of typical WWER-440 and WWER-1000 pressure... 

The WWER RPVs (as well as all other components) must be transportable by land, i.e. by train and/or by road. This requirement has some very important consequences on vessel design, such as a smaller pressure vessel diameter, which results in a smaller water gap thickness and thus a higher neutron flux on the reactor vessel wall surrounding the core and, therefore, requirements for materials with high resistance... 

Irradiation Embrittiement of Reactor Pressure Vesseis (RPVs) Table 3.1 Comparison of main design parameters of WWER RPVs... 

Table 3.2 Design end-of-iife fiuence for WWERs, PWRs and BWR RPVs ...

Again, the thermal ageing sets contain 30 containers in five floors and are located in the upper part of the reactor in front of head flange ring. Such a design solves the problem of high lead factor (as in WWER-440), but results in several new ones, principally ... 

In the Czech Republic, modification of the surveillance programme for WWER-1000/V-320C RPVs was designed and realised. The main principles of this design include the following ... 

Thus, annealing of WWER RPVs can be limited only to a zone around a critical weld (in the lower part of the active core). However, old PWR RPVs with axial welds cannot be annealed by this method - heating of the whole vessel is preferred. Generally, two different designs for dry annealing have been applied up to now ... 

---