Publication Laka-library:
Kozzloduy: A risk too far? (1995)
| Author | Greenpeace Int. |
| Date | October 1995 |
| Classification | 2.30.9.90/01 (BULGARIA - FACILITIES) |
| Front | 
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From the publication:
Alternatives to operating the Kozloduy Nuclear Power Station 1.0 Introduction to Kozloduy Nuclear Complex "With 6 out of71eading accident indicators below average, operation of the Kozloduy nuclear power plant is truly a high-stakes gamble. " Most Dangerous Reactors: a World-wide compendium of reactor-risk assessments, Jensen, Love and Falmer, U.S. Department of Energy, May 1995. Earlier this month the Bulgarian authorities restarted the oldest unit of its Kozloduy nuclear power plant. It was decided to restart the plant despite objections from Western Governments, the European Commission and Western European safety organisations who have previously condemned the plant as failing to meet Western safety standards. As a result one of the main western contractors at the site, Electricite de France, are now proposing to withdraw their personnel. The re-start of the reactor is a real threat to the environment of Europe, as tests have not been undertaken which prove that the pressure vessel, which surrounds the radioactive core, can function as required. The Kozloduy station was the first to receive finance from the European Union and the G7's Nuclear Safety Account to upgrade safety at the station. Therefore the failure of the Bulgarian authorities to follow the advice of Western agencies sends worrying signals for all nuclear programmes in the region. Bulgaria operates six reactors at its Kozloduy nuclear power plant - four first generation VVER 440 - 230s, and two VVER 1000 reactors (third generation). The first unit started operating in 1974. The VVER 440 is a pressurised water reactor (light water cooled and moderated, with two cooling circuits). Its radioactive core contains approximately 40 tonnes of slightly enriched uranium fuel. Two reactors are always constructed within one building (twin unit plant). As in all pressurised water reactors, the integrity of the reactor vessel (the structure surrounding the core) is of prime importance. Its rupture cannot be controlled which can lead to a catastrophic accident. These reactor vessels are circumscribed by welded seams, which, on the model 230 reactors, are of particular concern due to the level of impurities in the steel and lack of protection against corrosion inside the pressure vessel. In the case of Kozloduy and other early VVER 440-230s, the steel in the pressure vessel has levels of phosphorous contamination four times that acceptable in France, according to experts from the French nuclear safety agency (IPSN). During the routine operation of any reactor neutrons are produced which bombard the wall of the pressure vessel. In the 230 model, when compared to most Western reactors, there is only a small distance between the fuel and the pressure vessel wall, which results in increased neutron bombardment of the steel. The process leads to the embrittelling of the steel and is accelerated in the 230 models by the presence of phosphorous. Embrittled steel is less able to deal with stresses and strains as it is less flexible. More alarming, the steel is less able to recover from thermal shock, which can occur when coolant is lost from the primary circuit.
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