Original scientific paper
External Reactor Vessel Cooling Evaluation for Severe Accident Mitigation in NPP Krško
Mario Mihalina
orcid.org/0000-0002-3673-348X
; Nuklearna elektrana Krško Vrbina 12, 8270 Krško, Slovenija
Srđan Špalj
; Nuklearna elektrana Krško Vrbina 12, 8270 Krško, Slovenija
Bruno Glaser
; Nuklearna elektrana Krško Vrbina 12, 8270 Krško, Slovenija
Abstract
The In-Vessel corium Retention (IVR) through the External Reactor Vessel Cooling (ERVC)
is mean for maintaining the reactor vessel integrity during a severe accident, by cooling and retaining
the molten material inside the reactor vessel. By doing this, significant portion of severe accident
negative phenomena connected with reactor vessel failure could be avoided.
In this paper, analysis of NPP Krško applicability for IVR strategy was performed. It includes
overview of performed plant related analysis with emphasis on wet cavity modification, plant’s site
specific walk downs, new applicable probabilistic and deterministic analysis, evaluation of new
possibilities for ERVC strategy implementation regarding plant’s post-Fukushima improvements and
adequacy with plant’s procedures for severe accident mitigation.
Conclusion is that NPP Krško could perform in-vessel core retention by applying external
reactor vessel cooling strategy with reasonable confidence in success. Per probabilistic and
deterministic analysis, time window for successful ERVC strategy performance for most dominating
plant damage state scenarios is 2.5 hours, when onset of core damage is observed. This action should
be performed early after transition to Severe Accident Management Guidance’s (SAMG). For loss
of all AC power scenario, containment flooding could be initiated before onset of core damage within
related emergency procedure. To perform external reactor vessel cooling, reactor water storage tank
gravity drain with addition of alternate water is needed to be injected into the containment. ERVC
strategy will positively interfere with other severe accident strategies. There are no negative effects
due to ERVC performance. New flooding level will not threaten equipment and instrumentation
needed for long term SAMGs performance and eventually diluted containment sump borated water
inventory will not cause return to criticality during eventual recirculation phase due to the lost core
geometry.
Keywords
in-vessel corium retention; external reactor vessel cooling; severe accident management
Hrčak ID:
199648
URI
Publication date:
1.9.2017.
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