Modeling Large Break-LOCA: In Reactor Fuel Bundle Materials Test MT-4 and MT-6A

When creating power from nuclear fission, the fuel matrix and its cladding constitute the first barrier against radioactive fission product release. Therefore a defense in depth concept requires also the comprehensive understanding of fuel rod behavior and accurate prediction of the lifetime in normal operation and in accident condition as well. Investigations of fuel behavior are carried out in close connection with experimental research, operation feedback and computational analyses. In this connection, OECD/NEA sets up the “public domain database on nuclear fuel performance experiments for the purpose of code development and validation (IFPE)”. This database includes the data set of the projects MT-4 and MT-6A analyzed in the current paper. The MT-4 test bundle simulated a 6x6 section of a 17x17 3% enriched, full-length non-irradiated PWR fuel assembly. There were 20 non-pressurized guard fuel rods to isolate the 12 central, pressurized tests rods; the four corner rods were deleted. In the MT-6A test, the 20 guard rods used in the previous tests were replaced with 9 pressurized thus, a total of 21 test rods were in MT-6A. Only limited destructive post irradiation examination was performed on these two tests. The objective of the activity is the validation of TRANSURANUS “v1m1j09” code in predicting fuel and cladding behavior under LOCA conditions using the experimental databases MT-4 and MT-6A. It is pursued assessing the capabilities of the code models in simulating the phenomena and parameters involved, such as: pressure trend in the fuel rod, cladding creep, ? to ?-phase phase transformation, oxidation, geometry changes and finally failure prediction. The analysis is aimed at having a comprehensive understanding of the applicability and limitations of the code in the conditions of the experiments. Finally, probabilistic calculations are performed to complete the analysis. The objective of the activity is fulfilled addressing the behavior of two equivalent full lengths fuel rods, one for each test., suitable for the assessment of TU code versions “v1m1j09”.