Abstract: During severe accident in PWRs,the cladding oxidation with steam in the core is very important to the accident process.When oxidation time is long,or oxidation occurs in steam starvation conditions,the parabolic rate correlations based on experiments are restricted,which impacts the prediction of cladding failure,hydrogen production,and temperature.According to Fick’s laws,a cladding oxidation model in a wide temperature range based on diffusion equations is developed.The developed oxidation model has a wider applicability than those parabolic rate correlations,and can simulate long-term experiments well.The restricted assumptions of short-term oxidation time and enough steam environment in the core implemented by those parabolic rate correlations are removed in the model,therefore this model perfectly fit for long-term and steam starvation conditions which are more realistic during a severe accident.This model also can obtain detailed oxygen distribution in the cladding,which is helpful to simulate the cladding failure in detail and develop advanced cladding failure criteria.