The paper presents the MAAP 4.07 analysis of containment heat removal after reactor vessel failure resulting from the initial Station Blackout (SBO) accident. The accident is analysed considering ...mitigation measures for heat removal from the containment using alternative equipment (Alternative Residual Heat Removal (ARHR) pump and heat exchanger (ARHX) and, also, Alternative Safety Injection (ASI) pump). The mitigation actions are taken according to NEK Severe Accident Mitigation Guidelines (SAMG).
There are several possibilities to remove the heat from the containment once the reactor vessel fails and, for all of them, the necessary condition is to have the sufficient source of water (Residual Water Storage Tank (RWST), Alternative Boron Water Tank (ABWT) or other) and the appropriate heat exchanger available. Two options are presented within this paper:
1. Injection to the Reactor Coolant System (RCS) using ASI pump and recirculation (sump to RCS) through ARHR system via ARHX,
2. Spraying the containment through Containment Spray (CI) system using ARHR pump and, then, recirculation (sump to spray) through CI and ARHR systems via ARHX.
The results show that the containment heat removal can be done with either of analysed ways if the water is provided for recirculation (assumed containment level 3.9 m ~ 760 m3). However, with the fact that the reactor cavity is not flooded, the cooling using ASI will initially result in considerable containment pressure increase because the water is spilled through the RCS over the hot molten core debris. Therefore, it must be stated that the preferable way of containment pressure reduction, once the vessel has failed, is by using the containment spray. On the other hand, if RWST is not available, then the initial water delivery cannot be made from ABWT via CI system because this option does not exist. It shall also be pointed out that, if the active containment heat removal is started early enough, the Passive Containment Filtered Vent System (PCFVS) opening would be prevented and no fission products shall be released to environment.
The paper presents the RELAP5/mod3.3 analysis of natural circulation cooldown with one inactive loop for Nuclear Power Plant Krško (NEK). The aim of the analysis is to determine the limiting cooldown ...rates during operator recovery actions to minimize the effect of flow stagnation in inactive loop. Since this is typical asymmetrical transient, the RELAP5/mod3.3 NEK model with split reactor vessel model was developed (models of the reactor vessel and core were axially divided in two parts) and used for this analysis. The several transients of cooldown, with one inactive loop, for different time after shutdown (different decay heat) were performed. The extreme conservative assumptions were applied for the analyses, i.e. the complete loss of feedwater (FW) and auxiliary feedwater (AF), including turbine driven (TD) AF pump, and the cooldown has started after the SG is completely dry (inactive). The analyses show that the cooldown rate shall be significantly reduced, and, based on the results the procedure ES-0.2 “Natural Circulation Cooldown” was modified.
U tekstu se iz politološke perspektive razmatraju nastanak i osnovne karakteristike nuklearne politike u bivšoj Jugoslaviji te sudbina nuklearnog programa u samostalnoj Sloveniji. Komentira se uloga ...centralnih aktera u kreiranju energetske politike kao i oblici legitimiranja njihova djeloČvanja. Posebno se analizira djelovanje transformiranih i pojava novih aktera (antinuklearni pokret) te njihove legitimacijske strategije. Razmatra se i promjena u simboličkoj percepciji nuklearne energije u transformiranoj političkoj areni, pri čemu se posebno komentira situacija oko nuklearne elektrane »Krško«.
