[en] This executive summary presents the main topics of the workshop on Debris on Emergency Coolant Recirculation, which was held from 25 to 27 February 2004 in Albuquerque. The background of the workshop, the specific purposes of the workshop are detailed, as the scope and technical content and the attendance. This summary provides also a presentation of the main findings and recommendations on future research programs. (A.L.B.)

[en] In the framework of research of researches related to the PWR sump clogging in Usa, the author presents the history of GSI-191 (assessment of debris accumulation on PWR sump performance), the research to date (technical assessment, regulatory guide and evaluation guidance, model validation), the current and planned tests (chemical effect and calcium silicate tests, latent debris and downstream effect tests, integrated chemical effect tests, EPRI coatings study). (A.L.B.)

[en] The NRC is following a well-established regulatory process to resolve a complex safety issue. The two-pronged approach first evaluates near-term compensatory measures designed to reduce risk, and second ensures that a thorough analysis of the condition has been made and that any necessary modifications have been taken to resolve the issue. This regulatory framework achieves the goals of maintaining safety. (author)

[en] The paper includes the description of separate effect test facilities used for investigations with regard to the fragmentation and the transport behaviour of different insulation materials in multi-dimensional aqueous flow. The instrumentation of the rigs is specified, in particular modern digital image processing technologies. First experimental results are shown and discussed generated at three acrylic glass test facilities. The experimental data could use for CFD-modelling and validation. (authors)

[en] Under normal operation, nuclear reactor fuel is cooled by water circulating in the primary circuit. In the case of a loss-of-coolant accident, the reactor is stopped automatically. Residual fuel heat must then be evacuated, typically by use of a safety injection system and a reactor containment spray system. These systems are fed with water recovered from the bottom of the containment through sumps. However, because this water may contain debris (insulating material, concrete particles, paint), sumps are equipped with strainers. These strainers may become clogged, preventing emergency coolant recirculation. This could in turn lead to reactor core overheating, or melting in the most extreme circumstances. Participants at the workshop discussed the most recent research and developments in this field, as well as proposed and implemented solutions. These proceedings contain the papers presented at the workshop as well as a summary of the discussions that took place. (author)

[en] Assessment of the operational characteristics of the filtration function used during the recirculation phase of safety injection system (ECCS) and containment spray system (CSS) in the event of a break of the primary system in the containment has been performed by the 'Institut de Radioprotection et de Surete Nucleaire' for the French pressurised reactors (58 reactors) in particular the CPY series, 900 MWe pressurised water reactors (30 reactors) designed according Regulatory Guide 1.82 (Rev. 1)

[en] Pressure drop calculations across a LOCA induced fibrous debris bed have been successfully demonstrated to be accurate using the NUREG/CR-6224 semi-theoretical head loss correlation. One of the critical parameters needed for the NURE/CR-6224 correlation to predict the pressure drop across a fibrous debris bed are the characteristics of the debris constituents (density and characteristic size). This paper provides a brief description of the NUREG/CR-6224 head loss correlation and presents suggested debris characteristics of typical sources of debris found in American nuclear power plants for use in the correlation. (authors)

[en] After the Barsebaeck 2 strainer clogging incident from 28 July 1992, a short term and a long term action programme was initiated by the Swiss Federal Nuclear Safety Inspectorate to resolve the strainer clogging issue. The issue was closed in 1994 based on implemented modifications of suction strainers (flow area largely increased by a factor of 7 to 30) for BWRs and the approval of the strainer design based on plant specific analysis for PWRs. The key parameters used in the plant specific analysis are still surveyed within the plant specific ageing programme. The work presented here was performed mainly between 1992 and 1994 for the resolution of the clogging issue. (author)

[en] The potential for LOCA-generated debris to degrade PWR ECCS performance during recirculation has gained international industry and regulatory attention. Many US PWR owners are still in the early stages of determining the significance of this issue for their particular plants. For a sizable number of these plants, resolution of the ECCS debris blockage issue will require a combination of analytical evaluation, changes to operating or maintenance protocols, and modifications or additions to some plant components. This paper provides an overview of site-specific ECCS debris blockage solutions anticipated to be used by US PWRs. The overview begins with a brief review of the variability in containment floor and ECCS sump configurations found in the US PWR fleet. With this variability in mind, discussion then focuses on the several different resolution modes that may be brought to bear on the ECCS debris blockage issue. Finally, a variety of factors that owners must consider in order to select an optimal means of resolution are surveyed. (authors)

[en] After the Barsebaeck 2 strainer clogging incident from 28 July 1992, a first review of the design features of a Mark I containment and the thermal insulation typically employed revealed a potential for the transportation of larger amounts of insulation into the wet-well (torus) of the containment during a LOCA. Although Switzerland took a quick decision to increase the strainers of all BWRs till the end of 1993 (as it was performed by the Swiss Utilities) for the meantime it was necessary to develop tools for assessing the effectiveness of accident management actions proposed by the utilities for the existing (old strainer) design. Among others tools a simple evaluation model for assessing the transport velocity of insulation debris caused by the suction of operating strainers was developed, which was applied for a BWR with a Mark I containment and can as well be applied for sump pool conditions of a PWR (submerged sump strainers). (author)