Photos: SFP testing. Left: fuel assembly after a Zr fire; right: fire ignition test. SNL/USNRC.
The goal of the Sandia Fuel Project was to provide experimental data relevant for hydraulic and ignition phenomena of prototypic water reactor fuel assemblies in spent fuel pool (SFP) under complete loss-of-coolant accident for direct validation of severe accident computer codes and to reduce modelling uncertainties.
Previous analyses indicated that fuel assemblies could ignite and the fire could radially propagate in a complete loss-of-coolant accident:
Hence, there was a need for qualified data obtained in representative PWR fuel configurations to confirm the results of the analyses. The performed experiments focused on a highly detailed thermal-hydraulic characterisation and zirconium fire propagation in a full length commercial pressurised water reactor (PWR) 17x17 fuel assemblies.
The project provided collaborative exchange of information on severe accident modelling based on both the PWR and BWR experimental data which resulted in increased knowledge that can be used in regulatory programmes and future research.
The project ran for three years and was conducted in two phases.
Phase 1 focused on axial heating and burn propagation. A single full-length 17×17 PWR test assembly was constructed with a prototypic fuel skeleton and zirconium-alloy cladding heater rods. The test assembly was completely insulated to model boundary conditions representing a “hot neighbour” loading pattern, which is a typical bounding scenario. Phase 1 started with separate effect tests, where the assembly hydraulic and thermal-hydraulic responses were characterised in two different-sized storage racks. This phase concluded with an ignition test using the larger rack cell to determine where in the assembly ignition first occurs and the nature of the burn in the axial direction of the assembly.
Phase 2 addressed axial and radial heating and burn propagation, including effects of fuel rod ballooning. Five full-length 17x17 PWR test assemblies were constructed in a 1x4 configuration where the centre fuel assembly was electrically heated and the four surrounding assemblies were unheated. The centre assembly was of the same heated design as used in Phase 1. The four unheated peripheral assemblies were incorporating prototypic cladding tubes and end plugs. Two of the peripheral fuel assemblies were constructed with pressurised rods that ballooned when sufficiently heated, and the other two fuel assemblies were constructed with vented rods that did not balloon. These boundary conditions experimentally represent a “cold assembly” situation imitating the situation of a recently off-loaded assembly surrounded by much older ones and thus lower decay heat assemblies, which complements the bounding scenario covered by Phase 1. Similarly, this phase started with separate effect tests, including hydraulic and thermal-hydraulic characterisation. Ignition of the Zircaloy was first observed in the centre fuel assembly, the cladding fire also propagated transversely into the peripheral assemblies across the entire cross section of all of the peripheral assemblies. All five fuel assemblies were completely consumed as a result of the Zircaloy cladding fire.
The project results and outcomes are described in detail in two NUREG reports (NUREG/CR-7215, "Spent Fuel Pool Project Phase 1: Pre-Ignition and Ignition Testing of a Single Commercial 17x17 Pressurized Water Reactor Spent Fuel Assembly Under Complete Loss of Coolant Accident Conditions." (nrc.gov) and NUREG/CR-7216, "Spent Fuel Pool Project Phase II: Pre-Ignition and Ignition Testing of a 1x4 Commercial 17x17 Pressurized Water Reactor Spent Fuel Assemblies Under Complete Loss of Coolant Accident Conditions." (nrc.gov)).
Phase 1 test results have been used for an international benchmark exercise to evaluate and compare the predictive capabilities of computer codes concerning the ignition testing of PWR fuel assemblies (M. Adorni et al. Nuclear Engineering and Design 307, 418 (2016). DOI: 10.1016/j.nucengdes.2016.07.016).
Since then in the field, a Status Report on Spent Fuel Pools under Loss-of-Cooling and Loss-of-Coolant Accident Conditions and a Phenomena Identification and Ranking Table on R&D Priorities for Loss-of-Cooling and Loss-of-Coolant Accidents in Spent Nuclear Fuel Pools have been completed discussing future research opportunities regarding spent fuel pools accidents.
The project data package is available at SFP, Experimental data relevant for hydraulic and ignition phenomena of prototypic water reactor fuel assemblies (oecd-nea.org) upon request to the NEA data bank.
Spent Fuel Pool Project Phase I: Pre-Ignition and Ignition Testing of a Single Commercial 17x17 Pressurized Water Reactor Spent Fuel Assembly under Complete Loss of Coolant Accident Conditions, S.G. Durbin et al. NUREG/CR-7215 (2016).
Spent Fuel Pool Project Phase II: Pre-Ignition and Ignition Testing of a 1x4 Commercial 17x17 Pressurized Water Reactor Spent Fuel Assemblies under Complete Loss of Coolant Accident Conditions, S.G. Durbin et al. NUREG/CR-7216 (2016).
OECD/NEA Sandia Fuel Project phase I: Benchmark of the ignition testing, M. Adorni et al. Nuclear Engineering and Design 307, 418 (2016).
Czechia, France, Germany, Hungary, Italy, Japan, Norway, Korea, Spain, Sweden, Switzerland, United Kingdom and United States.
July 2009 - February 2013
USD 5.2 million