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[en] The rewetting of the overheated water cooled nuclear reactor fuel rods after a Loss-of-Coolant-Accident, which is defined as the re-establishment of a water film on the hot rod surfaces, is an important process for the safety of nuclear reactors. Several water experiments have been carried out to investigate the rewetting phenomena and to predict the liquid film behaviour either at atmospheric conditions or in a steam environment. The present paper describes the experimental work aimed at studying the wet front propagation along a stainless steel fuel rod in a top-flooding saturated water-steam environment in the pressure range 1-7 bar, under various initial wall temperatures up to 550⁰ C and at a liquid flowrate of 1 l min₁. Following the experimental results a correlation has been derived to predict the rewetting rate as a function of pressure and initial wall temperature. This correlation agrees well with formerly proposed correlations at higher pressures, thus permitting to extend their validity down to the pressure of 1 bar. Furthermore, a numerical method is introduced to experimentally evaluate the wet front position along the rod.(author)

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[en] The main object of this study is to perform thermal-hydraulic analyses of small (1 % of cold leg flow area), intermediate (30%). and large (100%) break loss of coolant accident (LOCA) of AP600 reactor system. Detailed examination ot AP600 thermal-hydraulic parameters during these transients is covered. Behaviour ot the system components under accident conditions is observed. Sufficiency and effectiveness of the passive safety systems are evaluated. TRAC-PF1 which is a best -estimate ode is used for for Ihe transient analyses. A detailed model is established to describe the AP600 features.Control of the system components is achieved by specifying proper setpoints, boundary and initial cconditions. It has been determined that the performance of the AP600 system in LOCA cases is satisfactory. It is observed that for small and intermediate breaks the system is succesfully depressurized without any core uncovery, and that the peak clad temperature do not exceed the steady-state values. For the design basis large break LOCA, the peak clad temperature during the accident is 1239 K which is below the design limit of 1477 K

[en] Full text: One of the major design basis accident is loss of coolant accident (LOCA). This accident is characterized by high sheath temperature and rapid depressurization of coolant. One of the ECCS acceptance criteria for this type of accident is for all LOCA events the release of radioactive material from the fuel in the reactor shall be limited such that the calculated radiological consequences at exclusion zone boundary are within acceptable limits for accidents as specified by AERB. The assessment of above criteria requires the estimation of fuel failure. Two phenomena which cause fuel failure during such condition are oxygen embrittlement and clad ballooning. Oxygen embrittlement is assessed by the amount of oxidation. Failure due to ballooning is analysed by calculating stress and strain on the clad and comparing with ultimate burst stress. Failure data generated by analysing these two phenomena are used in assessing damage on fuel. This paper discusses the criteria of fuel failure followed by various regulating agencies or countries along with Indian criteria. This paper also discusses the damage phenomena along with detailed method of assessment of fuel failure during LOCA

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[en] Conclusions: Proposed V-1 ALS can cope with 2 x DN 500 DBA. Work on V-1 ALS able to cope with DN 200 DBA and to mitigate DN 500 BDBA will have been finished by April 1994. Further leaktightness improvements are going on on the V-1 HZ boundary during outages with the aim to reduce the existing leak rate by 50%

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[en] 1) Introduction: Summary of system technology and reactor protection equipment. 2) Definitions. 3) LOCA: a) blowdown and refilling phase; b) jet and reaction forces; c) flow and heat transfer behavior in the core; d) behavior of the heater rods; e) core melting. 4) Protection against and during LOCA: a) general measures; b) break of a primary coolant pipe; c) break of a small pipe; d) break of a secondary pipe. (orig.)