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The Committee on the Safety of Nuclear Installations (CSNI) Working Group on Analysis and Management of Accidents (WGAMA) initiated "The NEA Co-ordinated Programme on Steam Explosion Resolution for Nuclear Applications (SERENA)" to assess the capabilities of the current generation of fuel-coolant interaction (FCI) computer codes to predict steam explosion-induced loads in reactor situations.
The SERENA programme stemmed from concerns expressed by the CSNI Senior Group of Experts on Nuclear Safety Research Facilities and Programmes (SESAR/FAP). The group was worried by current de-emphasis of FCI research all over the world, while uncertainties still existed on some aspects of FCI.
This led to defining a programme in two phases: a purely analytical phase to assess the predictive capabilities of existing tools for reactor cases (Phase 1), possibly followed by a phase to resolve the remaining uncertainties through performing complementary analytical work and confirmatory testing (Phase 2).
Phase 1 was started in January 2002 in the form of a coordinated action, not a joint project, where each partner financed his own work and had a duration 3.5 years until mid-2005. Comparisons and analyses were performed through emails exchanges and five meetings, one by task. A technical programme committee assisted the programme co-ordinator and provided wide technical and international support to the action.
The synthesis of the findings of phase 1 is available in "OECD RESEARCH PROGRAMME ON FUEL-COOLANT INTERACTION STEAM EXPLOSION RESOLUTION FOR NUCLEAR APPLICATIONS – SERENA, Final Report - December 2006" [NEA/CSNI/R(2007)11].
One of the main findings of this programme was that in-vessel FCI would not challenge the integrity of the nuclear reactor containment, but the scenario could not be ruled out for ex-vessel FCI.
It was decided therefore that Phase 2 would be established and the OECD/NEA SERENA Joint Nuclear Safety Research Project was set up by a number of concerned member countries to resolve any uncertainties on the issues identified from Phase 1 (as a result, this joint project has also been referred to, internally, as SERENA Phase 2 or SERENA-2).
It was planned to achieve this by performing a limited number of focused tests with advanced instrumentation to examine a large spectrum of ex-vessel melt compositions and conditions. In parallel, analytical work was carried out to bring the code capabilities to a sufficient level that they may be used in reactor case analyses.
The objectives of the experimental programme were threefold:
provide experimental data to clarify the explosion behaviour of prototypic corium melts;
provide experimental data for the validation of explosion models for prototypic materials, including spatial distribution of fuel and void during the premixing, at the time of explosion and explosion dynamics;
provide experimental data for the steam explosion in more reactor-like situations to verify the geometrical extrapolation capabilities of the codes.
These goals were achieved by using the complementary features of the TROI (KAERI) and KROTOS (CEA) corium facilities, including fitness-for-purpose-oriented analytical activities. KROTOS was more suited for investigating the intrinsic FCI characteristics in a one-dimensional geometry. TROI was more suited for testing the FCI behaviour of these materials in reactor-like conditions by having more mass and multi-dimensional melt water interaction geometry.
The validation of models using KROTOS data and the verification of code capabilities to calculate more reactor-oriented situations simulated in TROI was considered a vehicle to strengthen confidence in code applicability to reactor FCI scenarios.
In parallel to the experiment, the analytical working group of the project prepared an outcome document describing the state of the knowledge regarding the main phenomena involved in steam explosion (jet break-up, melt mass and void in mixture, melt solidification during premixing and explosion phase) and organised a reactor exercise.
A concluding seminar of the SERENA project was held from 5 to 7 November 2012, hosted by CEA in Cadarache, France. It attracted 75 participants from 13 countries. Forty presentations were given covering the experimental results of SERENA programme, complementary experimental results, phenomenology and model development, lessons learnt from the reactor safety point of view and perspectives on the main conclusion of SERENA programme.
The final summary integration report of this project was issued in 2014 along with the conclusion of the seminar prepared by the session chair as "OECD/SERENA Project Report – Summary and Conclusions" [NEA/CSNI/R(2014)15].
Project participants: Belgium, Canada, Finland, France, Germany, Japan, Korea, Slovenia, Sweden, Switzerland and the United States.
Project period: 2007-2012
The distribution of this package is restricted and subject to prior approval.
For more detailed information visit http://www.oecd-nea.org/jointproj/serena.html
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Keywords: corium, experimental data, fuel coolant interaction, steam explosion.