The objective is to investigate fuel and cladding integrity under LOCA and off-normal temperature transients.

A large experimental program related to fuel rod behavior in LOCA transients will be performed. In particular, the work will concentrate on fuel fragmentation, relocation and dispersal of fuel, the fuel and cladding performance in non-safety related off-normal temperature transients and also fuel rod resistance to axial load during a LOCA transient.

The task is divided in 3 subtasks:

Subtask 1.1 Fuel fragmentation and dispersal

The objective is to investigate and quantify thresholds for fuel fragmentation and to improve the understanding of involved mechanisms.

The following parameters will be investigated to determine the impact of fuel fragmentation and dispersal: burnup, cladding strain, temperature, gas pressure & plenum volume, microstructural effects

Subtask 1.2 Off-normal temperature transients

The objective is to investigate and evaluate fuel rod integrity and cladding resistance to off-normal temperature transients.

An experimental study of overheating tests on fuel rods, rapresenting various scenario at the NPP, with characterization of tested rods by PIE and mechanical testing will be performed. In this way we can identify how the cladding mechanical properties are affected by operational off-normal transient. Also the spent-fuel-pool by overheating in air-stream mixture will be considered.  The experiments will lead to support the definition of a criteria to classify fuel as damaged or undamaged and consequences for back-end handling.

Subtask 1.3 Axial load

The objective is to evaluate the resistance of fuel rods to axial loading during a LOCA transient.

An experimental program where the fuel rod resistance to axial load will be studied by series of integral axial load tests on fuel rods with characterization of tested rods by PIE. Tests will be performed on fuel rod segments with different burnup to investigate factors such as oxidation and hydrogen content from operation and fuel cladding bonding. ECR limits to failure and fuel dispersal after an axial failure will also be measured

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Per Magnusson