Session: 02-13: Structural Evaluation, Performance Assessment, Multiphysics Coupling - III

Paper Number: 134397

134397 - Investigation on Burst Behaviors of Cr-Coated Cladding Under Simulated Loca Conditions 

Abstract: 

     Loss of coolant accident (LOCA) is one of severe design basis accidents. At the moment of LOCA, the coolant water of the primary loop leaks rapidly, accompanied by a sharply drop in the pressure in the reactor core. Therefore, the fuel rod is not cooled sufficiently, which makes the cladding temperature rise rapidly. At the same time, the release of fission gases from the fuel to the cladding and the swelling of fuel pellets gradually increase the internal pressure. Due to the internal and external pressure difference, the cladding will creep, swell, and even burst, which results in the inner surface being exposed to high-temperature steam, accelerating the zirconium-water reaction. In addition, the bursting behaviors may well cause the bending and deformation of the cladding tube, deteriorating the coolant channels. Therefore, it is necessary to study intensively the bursting behaviors of the fuel cladding, especially the new claddings.

     The deficiency of the zirconium-based fuel cladding in resisting severe loss of coolant accidents (LOCA) was exposed in the Fukushima accident, and promoted the development of accident-tolerant fuel (ATF). The purpose of ATF cladding is to improve the safety margin in LOCA by reducing the cladding oxidation rate, and hydrogen generation rate, delaying or reducing the cladding rupture and reducing the cladding deformation. After more than 10 years of continuous technical exploration, Chromium (Cr) coated zirconium cladding has become the main technical route that will be put into commercial application in the near future. As a promising candidate fuel cladding, Cr coated fuel cladding usually is compared with uncoated fuel cladding in terms of corrosion resistance and mechanical properties. The extensive studies of Cr-coated and uncoated claddings show that Cr coating cladding has a positive effect on improving the corrosion and oxidation resistance of the fuel cladding. However, the resistance to burst of Cr coated fuel cladding have not been studied intensively in simulated LOCA condition. In current study, the burst behaviors of Cr coated zirconium claddings in thickness of about 15μm and uncoated zirconium claddings were systematically investigated under simulated LOCA conditions. The initial internal pressures are 2-10MPa and the heating rates are 14 ℃/s and 28 ℃/s. The effects of initial internal pressure and heating rate on the morphology, burst temperature, burst pressure, and opening geometry were analyzed, and the main conclusions are as follows:

1）At the same heating rate, the higher the internal pressure of the cladding, the shorter the bursting time, and the lower the bursting temperature.

2) At the same initial internal pressure, the higher the heating rate, the shorter the bursting time, but the higher the bursting temperature.

3) In the current experimental setup, the superheated steam was prepared prior to the burst test. The about 2-hours steam production process caused the fuel claddings oxidation, especially the uncoated cladding because of its weaker oxidation resistance. The pre-oxidation may strengthen the uncoated claddings. Therefore, the uncoated cladding shows a little longer burst time, higher burst temperature and smaller opening geometry compared with uncoated cladding under the experimental condition.

Presenting Author: Zhengang Duan Chongqing University

Presenting Author Biography: Zhengang Duan, Ph.D, associate professor at Chongqing University and major in Evaluation on the service behaviors of Nuclear material.

Authors:

Zhengang Duan Chongqing University
Bo Yuan Chongqing University
Qinglong Wen Chongqing University
Kang Chen Chongqing University