Fourteen energy units of two types are in operation at 5 Ukrainian NPSs. 4 energy units more with VVER-type reactors are at different construction stages.
The operating of these energy units is taking place according to a temporary permission issued by the Ministry of Environmental Protection and Nuclear Safety of Ukraine. Permanent licenses will be granted after the submission of safety analysis reports for each energy unit.
Following special conditions must be met in order to obtain temporary permission to use energy units with VVER-type reactors:
Regular testing of control system and reactor protection system
Establishment of reasonable criteria for steam generator heat exchange tubes muffling and requirements for monitoring the system of collector tubes and bulkheads of steam generators integrity;
Designing and mounting ‘hot’ test bench for setting up and testing impulse safety device;
Maintenance of equipment past its useful life;
Special conditions for Chernobyl NPS energy unit No. 3 maintenance permission are as follows:
Security systems of turned off energy unit pipelines and primary loop pipelines’ welded connections related to ultrasound and radiographic monitoring;
Appreciation of technological channels re-equipment volumes according to gas gap exhausting;
Complex maintenance safety work has been done according to the special conditions for energy units with VVER-type reactors. It has been aimed at observance of control system regulation devices and reactor safety estimated time of failure
Total level of disturbances investigated during 1997-1998 was almost unchanged while it decreased in 1992-1998.
In general, an analysis of NPS maintenance conditions may lead to the following conclusions:
Ukrainian nuclear and radiation safety levels are acceptable, and Ukraine complies with the provisions of the Convention on Nuclear Safety. The national report of Ukraine was adopted by the Cabinet of Ministry and dispatched to the International Atomic Energy Agency in April 1998.
To maintain the reached level of safety, a series of technical and organizational measures were applied at NPSs during this year.
Conditions of further increase of NPS safety level are regular reappraisals of energy unit safety, preparation of ‘Safety Analysis Reports’, and quality systems for updating and implementation of full-scale simulators at NPSs.
Analysis of non-compliance at Ukrainian NPSs in 1998 shows the necessity of inspection and maintenance work at safety systems important for maintenance.
Problems of re-equipment and the basic technical equipment are still topical. Due to a shortage of spare parts repairs of equipment are carried out by arranging the parts of several operable elements or by repairing broken elements (by welding, fusing, etc.), which causes recurring equipment breakdowns.
The safety situation at the installation can be characterized by following facts.
Value abatement of neutron flux density and power of expositional dose of gamma radiation at monitoring places have been observed, but the quantity of measurements and technical condition of monitoring systems cannot guarantee measurement reliability.
4 cases of too high concentrations of alpha-active nuclides were observed and 1 case of radionuclide pollution of indoor air (max. excess four times as much) was also registered.
Too high levels of beta-active nuclides in the air or specific water activity were not registered.
Research of the radionuclide composition of water samples from the placements showed
that the main part of total activity was caused by strontium and cesium isotopes.
Maximum concentration of uranium isotopes in water was 0.095 g/l (far less than dangerous concentration). There is a danger that uranium will be accumulated in the form of high-activity sediments in places of water accumulation (at the lowest parts of the installation).
In cooperation with an international group of experts a complex plan of changing
‘Ukrittia’ to an ecologically safe system has been drawn up. This plan has been
officially approved and has been valid since June 1997.