Nuclear Energy Agency Online Bulletin

May 2000

Nuclear safety information

The CSNI Workshop on Advanced Thermal-hydraulic and Neutronic Codes: Current and Future Applications was held in Barcelona on 10-13 April 2000. The workshop was organised in close co-operation with the Spanish Nuclear Safety Council (CSN) and the Polytechnic University of Catalonia (UPC). The meeting was also co-sponsored by the Spanish utility UNESA. In total, more than 100 participants attended form 22 countries and 3 international organisations.

The agenda of the workshop consisted of 45 invited papers, which were divided into eight technical sessions. Each day was concluded by a discussion session summarising papers presented that day. At the end of the workshop there were three parallel discussion sessions covering various aspects of the thermal-hydraulic (TH) codes, such as coupling of TH and neutronic codes, use and applications of best-estimate codes, future R&D in TH modelling and numerics, etc.

Significant advances have been made in the coupling of thermal-hydraulic and neutronic codes since the 1996 Annapolis workshop, as reflected in the increased number of papers that dealt with those aspects. Steady progress has also been made in the development of improved numerical schemes that will enhance robustness of code solution capability. Major advances have been made since the 1996 Annapolis workshop to develop user support tools to assist both front-end input deck preparation and verification and user run-time interaction.

The presented papers are available in the form of hard copies ( Conclusions and recommendations from the workshop are in preparation.

The eleventh meeting of the OECD Support Group on VVER-440/213 Bubbler Condenser Containment Safety was held in the Berlin offices of the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH on 4-5 April 2000. It reviewed the main results of the European Commission PHARE/TACIS Bubbler Condenser Experimental Qualification Project as well as other activities underway in this field. It discussed remaining issues and made recommendations regarding future developments. A brief report on the status of the bubbler condenser containment system for reactors of the VVER-440/213 type will be prepared.

As a follow-up to the SESAR-FAP and CSNI recommendations, a technical expert meeting on severe accidents (SA) facilities and programmes was held at the NEA at the beginning of March. The intention of the meeting was to define priorities and possible programmes to be conducted at key SA facilities under OECD/NEA sponsorship. Two proposals were discussed at the meeting.

The first one, denominated MASCA project, focuses on in-vessel retention, i.e. on the capability of LWR vessels to retain the molten core during the progression of a severe accident. The project is scheduled to run for three years and the experimental work is to be carried out at the Kurtchatov Institute, near Moscow.

The second proposal addresses ex-vessel phenomena, in particular the molten core-concrete interaction and the coolability of the molten core after spreading on the containment basemat. The tests are to be carried out at the Argonne National Laboratory in the USA, but the matrix and schedule are still to be refined. The capability of two other facilities, one using simulant techniques for SA investigations (in Sweden), the other one equipped for fuel-coolant interaction (in the USA), were discussed at the meeting.

A new periodic report entitled Nuclear Power Plant Operating Experiences from the IAEA/NEA Incident Reporting System: 1996-1999, which highlights important lessons learned from events reported to the IRS over the period of July 1996-June 1999, is now available. A total of 342 events were reported by the participating countries during this time. Several areas were selected in the report to show the range of important topics available in the IRS. These include several different types of failure in a variety of systems, as well as experience of human errors in combination with system failures.