Analyzing Operator Actions During Loss of AC Power Accident with Subsequent Loss of Secondary Heat Sink (NUREG/IA-0225)

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Publication Information

Manuscript Completed: December 2004
Date Published: April 2010

Prepared by:
Iztok Parzer1, Božidar Krajnc2, Borut Mavko1

1Jožef Stefan Institute
Jamova cesta 39
SI-1000 Ljubljana, Slovenia

2NPP Krško
Vrbina 12
S1-8270 Krško, Slovenia

Antony Calvo, NRC Project Manager

Prepared as part of:
The Agreement on Research Participation and Technical Exchange
Under the Thermal-Hydraulic Code Applications and Maintenance Program (CAMP)

Prepared for:
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Availability Notice


The thermo-hydraulic analysis of plant response on total loss of AC power is very demanding and challenging job due to a number of phenomena included. Such an analysis becomes even more complicated and interesting if we include also the assumption of total loss of secondary heat sink.

In this paper we are presenting the NPP Krško specific analysis of complete loss of AC power with subsequent total loss of secondary heat sink and influence of specific operator actions. The aim of this analysis is to verify if emergency operating (EOP) or severe accident management guidelines (SAMG) procedures should be changed and if design change on pressurizer pressure relief valves (PORV) should be implemented to be able to cope with this kind of accidents better.

The analyses were performed with three different state of the art codes used at NPP Krško and IJS: RELAP5/MOD3.3, ANTHEM and MAAP4. The last two codes are used in the NPP Krško plant specific full scope simulator, one for the simulation of the design bases transients and accidents and the second for simulation of the severe accidents.

This type of analyses has been done also for the simulator validation, performed during vendor and site acceptance testing.

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