[en] In 2001 a modernization of the Accident Localization System (ALS) on unit 4 was accomplished. The outage duration was longer then usually and special dose budget was elaborated. All ALS work was performed by external organization. An ALARA implementation was recognized priority. The really accumulated collective doses were analyzed and conclusions drawn. A short film on CD was prepared. Two conclusions are drawn: 1. Good work management and a first attempt of effective empowerment of the workers gave satisfactory results; 2. Although the work was not typical, and performed for a first time, the ALARA implementation reduced the projected collective dose with 19%

[en] The authors present a general analysis of the mass and energy balance in the WWER-440/V230 confinement structure in case of a 200 mm LOCA, based on results from CONTAIN calculations. The character of the heat transfer to the confinement building structures is analyzed and its influence on the confinement parameters is evaluated. The results show that the building structures heat consumption is comparable to that of the Spray System heat exchanger. (author)

[en] The paper present the behavior of the accident localization system in case of pipeline rupture in the primary circuit of the units 3 and 4 after the implementation of the modernization program. The program includes installation of a jet-vortex condenser. The cases with double rapture of a pipeline D_y200 mm and D_y500 mm are described. In the result of the program implementation the radiation consequences are significantly limited due to the condenser playing the role of a filter during the first second of the accident as well as due to the low values of the pressure during the whole accident. Thus the modernization program fulfills its purpose to assure non-exceeding of the radiation limits in case of double rupture of a main circulation pipeline

[en] The modernization of the units 5 and 6 of the Kozloduy NPP is discussed. The Program for modernization of the units has been implemented in order to bring them into accordance with international safety standards. The main aspects of the modernization are: implementation of digital technologies, improvement of the operators interface, improvement of the concept for in-depth protection, installation of diagnostic systems, improvement of the secondary circuit operation, improvement of the power supply systems reliability etc

[en] The Steam Generator Water Level Control System is one of the most important for the normal operation systems, related to the safety and reliability of the units. The main upgrading objective for the SG level and SGWLC System modernization is to assure an automatic maintaining of the SG level within acceptable limits (below protections and interlocks) from 0% to 100% of the power in normal operation conditions and in case of transients followed by disturbances in the SG controlled parameters - level, steam flow, feedwater flow and/or pressure/temperature. To achieve this objective, the computerized controllers of new SG water level control system follows current computer control technology and is implemented together with replacement of the feedwater control valves and the needed I and C equipment. (author)

[en] The authors present a set of models of operator actions for avoiding the risk of deep vacuum in the Confinement in case of a 200 mm LOCA on WWER-440/V230. The models are based on the plant operating experience. The actions performance and efficiency are analysed with representative CONTAIN calculations. The results form the basis for development and validation of Emergency Operating Procedures for LB LOCA accidents at units 3 and 4 of NPP Kozloduy. (author)

[en] The history of operation of the Kozloduy NPP, several modernization programs of the units 3 and 4 and the consequences from the shutdown are presented

[en] The task indicated in the title is part of a comprehensive upgrading program for Units 3 and 4 of the Kozloduy plant executed in a Consortium between Framatome ANP (a Framatome and Siemens company) and the Russian company Atomstroyexport. It comprises an evaluation of the residual service life of components/systems/plants subject to acceptance by international experts, identifying the need for further investigations/calculations in certain cases, and finding solutions for improvements that achieve a consensus of safety and economy. The initial results are: Walkdowns revealed no clear knock-out point for the plants, however there are preliminary hints for necessary further improvements. Investigations of templates taken from the RPV of Unit 1 were started: the results are still preliminary, but can be considered very positive; their transfer to the RPV of Unit 3 would mean that the latest safety analyses of the Unit 3 RPV are conservative. The general work program was successfully applied on the batteries as a pattern for the electrical equipment: parameters for the computer database and proposals for an effective aging management program were addressed. (author)

[en] Unit 3 and Unit 4 of NPP Kozloduy are second-generation WWER440/230 energy reactors. Unit 3 was in operation from 1980, Unit 4 - from 1982. No surveillance specimens for monitoring of RPV metal aging are available for both KNPP Units. The reactor pressure vessels rest lifetime assessment, Plant life management and Surveillance program development for the both units are presented and analyzed in this report. (author)

[en] The first PSA for the units 3 and 4 of the Kozloduy NPP has started in 1997. After the introduction of the auxiliary emergency feed water system in 1999 the PSA has been updated. In 2001 upgrading of the model is performed in in order to reflect changes in the emergency power supply systems. In order to development of the modernization program of the units 3 and 4 in 2002, an actualization of the PSA for thr inclusion of all measure, considered in the program as well as the introduction of symptom oriented emergency instructions. This actualization is to reflect the operational experience from Bulgarian reactors as well as of similar reactors in other countries