WWER

X-ray diffraction studies on hydrated triorganotin compounds H2O SnRsX have provided several examples of water engaged in /wwer-sphere coordination to tin in five-coordinate molecules. For iwwer-sphere coordination, the complexes tend to pack in arrangements in which the number of hydrogen bonding interactions involving the coordinated water molecule is maximized. For example, o-phenanthroline monohydrate, which chelates to a plethora of transition metals, forms with triphenyltin chloride an outer-sphere coordination complex in which the coordinated water molecule [O Sn = 2.42 A]... 

The project of BRUS-150 integral type reactor of 500 MW thermal power and 150 MW electric power has been developed. The core, steam generators, pumps and all lead-bismuth loops are located in the reactor vessel, so that leak-proof vessel contains total amount of lead-bismuth. BRUS-150 reactor can be also used for transmutation of minor actinides accumulated in WWER type reactors and for utilization of weapon grade plutonium (for the main characteristics -see Table 2.2)... 

Annual loading of actinides from spent fuel of WWER kg 100 48... 

IAEA TECDOC-1492, Improvements of Radioactive Waste Management at WWER Nuclear Power Plants, IAEA Publications, Vienna, Austria, 2006. 

A broad spectrum of approaches and results for various types of reactors operated in the European region (WWER, RBMK, CANDU, Westinghouse PWR, BWR) were covered in the presentations. 

In the framework of the reconstruction programmes for Units 5 and 6 with WWER-1000 type reactors and for Units 1 to 4 with WWER-440 type reactors, Kozloduy NPP included the task of performing Level 1 PSA analyses for these units during shutdown conditions. 

In 1995, a meeting of an expert group from the Moscow Centre of WANO was held at Dukovany NPP on problems concerning the loss of natural circulation for WWER-440 reactors. The events concerning the loss of the natural circulation were discussed and reviewed in detail, the causes were analysed and the remedies were proposed to prevent the reoccurrence of similar events. 

In addition, the exchange of operational event information will continue. This exchange of information is carried out for WWER-440 NPPs operators and also within the framework of WANO NPPs operators. 

Traditionally, a PSA for NPPs with WWER and RBMK reactors is only performed for full power operation. 

Russia has a certified computer code Rainbow which can be applied to analyses of some transient and accident development processes for shutdown modes of WWER. In the future, the Rainbow code may be evaluated by applying it to the WWER shutdown modes. There is also a need for a similar work in evaluating computer codes for analysing RBMK shutdown modes. 

During normal power operation, the water level in WWER-440 reactors is not monitored. In cold shutdown, a standard reactor level measurement is used based on water differential pressure in the U-tube, with the scale between 180 and 250 cm of narrow-range level. The positive reference leg of the U-tube is connected to a tube used for continual monitoring of boron concentration in reactor coolant. This standard reactor level measurement is activated prior to the depressurization of the main reactor seal flange plane and removal of the head. 

For WWER reactors, a methodology for analysis of LPS has been developed as presented in the report IAEA-EBP-WWER-09. 

Systematic analysis of events during LPS conditions should be included into a standard format and context of safety analysis reports subject to approval by regulatory authorities. The effort should cover a list of initiating events and set of acceptance criteria typical for LPS conditions. The IAEA report IAEA-EBP-WWER-09, after its extension to cover all LPS plant operational states, provides a good basis for such work. Unfortunately, an equivalent report has not been developed for other reactor types used in the region, i.e., in particular for RBMK types. It has to be emphasized that list of initiating events may differ considerably for PWR, RBMK, and CANDU type reactors. 

Degradation of natural circulation during shutdown conditions, mainly in WWER reactors, should be accounted for adequately when estimating the shutdown risk in PSA studies. Detailed computer analyses of thermal and hydraulic processes should be carried out to show whether and at what time these processes could lead to core damage. 

WWER water moderated, water cooled energy reactor... 

AR153 Analysis of differences in fuel safety criteria for WWER and Western PWR nuclear power plants. No. 1381, 22 December 2003. 

ARl 70 Benchmark study for the seismic analysis and testing of WWER-type NPPs, No. 1176,... 

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. 

Within FP-5 project RETROSPEC work will be done to improve the evaluation of the neutron doses induced in reactor structural materials in those cases where no or unreliable data from surveillance specimens are available (for example the older generation of WWER-440 type reactors). The objectives of this project are to develop procedures and guidelines for retrospective dosimetry which are independent of the type of steel and of the time elapsed after removing the material from the reactor. 

Note that also WWER operational safety issues such as embrittlement and accident assessment and management are mentioned. 

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. 

During operation of units with WWER, also, as the new norms and rules were developed and enacted, the attempts were made as to put them into compliance with these regulatory requirements. However, these measures were of local nature and in many cases unfeasible from both technical and economical reasons. 

Under development of the Program on Safety Improvement of NPP with Rector Facilities WWER-1000, WWER-440 as the methodological basis the IAEA classification was adopted as to extent of impact from considered deviations from upon the in-depth-protection (lAEA-EBP-WWER-05). Subdivision of deviations into four categories according to their safety-significance allowed to identify the main directions of work and list of the immediate measures of significant impact upon safety which could be undertaken in the visible terms, namely, by 1998. 

The Ukrainian RA had developed the procedure on licensing of the technical decisions connected with upgrading of NPP units. As an example of this procedure implementation the measure on development of the system to remove hydrogen from SLA under emergency modes can be named under development at Rivne NPP in compliance with the Program on Immediate Work on Improvement of NPP with WWER-1000, 440 Safety". 

According to the program on improvement of units 1 and 2 (RF WWER-440A -213) safety at Rivne NPP, the decision was made to develop the measures on removal of hydrogen from leaktight premises. 

Since 1995, to reduce bending of FA and provide for safe operation of units at NPP with reactors of WWER-1000 type in Ukraine the following measures undertaking started during planned outages ... 

In Ukraine there are fourteen water-cooled power reactors in operation (II WWER-1000, 2 WWER-440 and 1 RBMK-1000) with a total installed capacity of 12880 MW(e). It makes 25% of the total installed capacity of the electric power stations. Four WWER-1000 units are under construction. In 1999 NPPs produced 72,072 x 10 kW.h of electricity (42,1% of the country electricity). The share of electricity produced by NPPs constantly increases because of the economic crisis and the fact, that electric power production by the NPPs is much cheaper than that of the thermal power plant station (Fig.l). It is most probable that the WWER-1000 reactors in Ukraine will have been generated up to 93-96 per cent of all NPPs electric power and about 40-50 per cent of the total electricity produced during 2000-2010. 

Basing on the data of Ukrainian WWER-1000 FA operation we can state, that the probability of FA leaking detection after first, second, third and fourth year of operation will be distributed as follows ... 

Detection of leaky spent fuel is put into practice under requirements of "Instmction for detection of the fuel rods tightness of WWER-1000 reactors (0401.00.00.000 DNG). Instmction was issued by Russian competent institutes, 0KB Gidropress and Russian Research Center "Kurchatov Institute" respectively. 

Summarizing the presented data we can state that the increase of Ukrainian WWER-1000 fuel burnup has not worsened fuel reliability. 

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