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Osthammar, Sweden

Karlsson A.,Forsmarks Kraftgrupp AB | Frisk M.,Risk Pilot AB | Hultqvist G.,Havsbrus Consulting
PSAM 2014 - Probabilistic Safety Assessment and Management | Year: 2014

Benchmarking is an important activity in order to eliminate unjustified differences between PSA models and enable harmonisation. It could also be used in order to understand plant differences. As part of the BWR-club PSA activities benchmarking of bottom LOCA during outage, reactor level measurement and dominating initiating events have been performed. Modelling of bottom LOCA during outage varies between the BWR-club members and work performed within the BWR-club aims at compiling and understanding these differences. When it comes to reactor level measurement modelling varies from a more detailed modelling to more of a "black box" approach. Information has also been collected from the BWR-club members regarding dominating initiating events in their PSA studies. The initiating event frequencies, scope of the PSA studies and risk importance of different initiating events vary between the BWR-club members and work has been performed compiling and understanding these differences. BWR-club reports have been issued for bottom LOCA during outage and reactor level measurement, while the benchmarking of dominating initiating events is yet to be finalised. Source

Agency: Cordis | Branch: FP7 | Program: CSA-CA | Phase: Fission-2013-2.1.2 | Award Amount: 4.04M | Year: 2013

The Fukushima nuclear accident in Japan resulted from the combination of two correlated extreme external events (earthquake and tsunami). The consequences (flooding in particular) went beyond what was considered in the initial NPP design. Such situations can be identified using PSA methodology that complements the deterministic approach for beyond design accidents. If the performance of a Level 1-Level 2 PSA concludes that such a low probability event can lead to extreme consequences, the industry (system suppliers and utilities) or the Safety Authorities may take appropriate decisions to reinforce the defence-in-depth of the plant. The project ASAMPSA_E aims at identifying good practices for the identification of such situations with the help of Level 1-Level 2 PSA and for the definition of appropriate criteria for decision making in the European context. It offers a new framework to discuss, at a technical level, how extended PSA can be developed efficiently and be used to verify if the robustness of NPPs in their environment is sufficient. It will allow exchanges on the feasibility of extended PSAs able to quantify risks induced by NPPs site (multi-units reactors and spent fuel pools, modelling impact of internal initiating events, internal and external hazards on equipment and human recovery actions ).

Agency: Cordis | Branch: FP7 | Program: CSA-CA | Phase: Fission-2007-2.1-03 | Award Amount: 2.11M | Year: 2008

The objective of this coordination action is to develop best practice guidelines for the performance of Level-2 PSA methodologies with a view to harmonization at EU level and allowing a meaningful and practical uncertainty evaluation in a Level-2 PSA. Speficic relationships with community in charge of nuclear reactor safety (utilities, safety authorities, vendors, research or services companies) will be established in order to define the current needs in terms of guidelines for level 2 PSA development and applications. A technical group of level 2 PSA experts from project partners will propose guidelines for a limited-scope and a full-scope L2 PSA based on practical experience of each partner. Elaboration of this guidelines for operating plants will be the main activity of this coordination action. This guideline will be discussed with End-Users community and their opinion will be taken into account in the final version. The applicability of such a guideline for future reactor (Gen IV) will be also examined.

Amft M.,KTH Royal Institute of Technology | Amft M.,Forsmarks Kraftgrupp AB | Walle L.E.,Norwegian University of Science and Technology | Ragazzon D.,Uppsala University | And 5 more authors.
Journal of Physical Chemistry C | Year: 2013

We show that the formation of the wetting layer and the experimentally observed continuous shift of the H2O-OH balance toward molecular water at increasing coverage on a TiO2(110) surface can be rationalized on a molecular level. The mechanism is based on the initial formation of stable hydroxyl pairs, a repulsive interaction between these pairs, and an attractive interaction with respect to water molecules. The experimental data are obtained by synchrotron radiation photoelectron spectroscopy and interpreted with the aid of density functional theory calculations and Monte Carlo simulations. © 2013 American Chemical Society. Source

Anglart H.,KTH Royal Institute of Technology | Alavyoon F.,Forsmarks Kraftgrupp AB | Novarini R.,KTH Royal Institute of Technology
Nuclear Engineering and Design | Year: 2010

The present paper deals with a theoretical analysis of the spray cooling of a Reactor Pressure Vessel (RPV) head in a Boiling Water Reactor (BWR). To this end a detailed computational model has been developed. The model predicts the trajectories, diameters and temperatures of subcooled droplets moving in saturated vapor. The model has been validated through comparison with experimental data, in which droplet temperatures were measured as functions of the distance that they cover in saturated vapor from the moment they leave the sprinkler outlet to the moment they impact on the RPV head inner wall. The calculations are in very good agreement with measurements, confirming the model adequacy for the present study. The model has been used for a parametric study to investigate the influence of several parameters on the cooling efficiency of the spray system. Based on the study it has been shown that one of the main parameters that govern the temperature increase in a subcooled droplet is its initial diameter. Comparisons are also made between conclusions from the theoretical model and observations made through flow and temperature measurements in the plant (Forsmark 1 and 2). One of these observations is that the rate at which the RPV head temperature decreases on the way down from hot to cold standby is constant and independent of the sprinkling flow rate as long as the flow rate is above a certain minimum value. Accordingly, the theoretical model shows that if one assumes that the cooling of the RPV head is through a water film built on the inner wall due to sprinkling, the heat removal rate is only very weakly dependent on the sprinkling flow rate. © 2008 Elsevier B.V. All rights reserved. Source

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