Reinforced concrete (RC) shield building as the first external defense layer of AP1000 structure plays an important role in protection the population and environment when against the outer explosion. The strain rate effect of reinforced concrete was taken into consideration in the establishment of an AP1000 nuclear island structure-air-explosives fully coupled model by using the software AUTODYN. Object using damage mass as index, to infer the degree of damage. This paper studied the pressure evolution and damage mechanism. The analysis results provide valuable data on improving the anti-explosion capabilities in design based on the damage characteristics.
Most studies on nuclear power plants subjected to contact explosion have put their interests in the reinforced concrete containment vessel. Many works have been done to the dynamic response of the reinforced concrete containment under internal explosion [
In this paper, the dynamic response of the AP1000 nuclear island under a contact explosion load at different initiation positions will be discussed. This paper also aims to find the most unfavorable position for contact explosion and provide valuable data on improving the anti-explosion capabilities in design based on the damage characteristics.
The RC shield building is the first external defense layer of AP1000 structure to protect the containment vessel. The geometry of AP1000 model and boundary conditions are shown in
Considering the randomness of the contact explosion positions, multiple initial detonation positions were selected for this study. In order to describe the calculation conditions directly, the name of each part of the nuclear island and the definition of the initial angle are shown in
Autodyncontains a variety of material models. In the numerical model, the Riedel-Hiermaier Thoma (RHT) concrete strength model is used to give a description of the dynamic response characteristics of concrete [
The mesh size has a great effect on the accuracy of numerical results. The results of nuclear island frequency on three different element sizes are shown in
Therefore, it was finally decided to mesh the area around the explosive position, orifice and air intake with a mesh size of 300 mm and other areas with a size of 500 mm. In this way, the calculation efficiency could be improved, and greater accuracy of the calculation could be achieved.
Element size (mm) | 1st Frequency (Hz) | 2st Frequency (Hz) | 3st Frequency (Hz) |
---|---|---|---|
300 | 3.3169 | 3.3265 | 5.1410 |
500 | 3.3666 | 3.3771 | 5.1918 |
800 | 3.3720 | 3.3824 | 5.1848 |
evaluation index. At 5 ms, the explosive expend rapidly and formed a cavity filled with high-temperature and high-pressure gas. A elliptical crater was pre- sent on the center of the explosion source. The reinforced concrete lost carrying capacity, and the main damage area was formed. At this time, the damage is mainly induced by axial tension and compression. At 20 ms, the stress wave continues to spread around the reinforced concrete, but the energy density of concrete per area decreases rapidly. A completely damaged structural area of the structure is formed. During 20 ms and 50 ms, the completely damaged zone of the plant is no longer extended, and the decreased pressure continue to expand the area of the shallow damage zone. The maximum length of the fully damage area in the vertical and circumferential directions are 8.295 m and 12.32 m, respectively.
This section focuses on the damage degree and mode with the same circumferential angle but different heights. According to the above conclusions, it’s known that the damage degree is similar when the burst conditions are at the same height but have different circumferential angles. Therefore, this part uses condition I, II, III, IV, V as examples.
When t = 1 ms, the pressure wave is concentrated in the explosion source region, and the pressure value is symmetrical to the horizontal axis for each condition. The crater’s shape is an ellipse with the major axis in circumference, as previously explained. When t = 5 m, the pressure waves of condition I and IV are symmetrical with the horizontal direction, and the pressure wave of condition II is no longer symmetrical. The positive pressure amplitude of condition III appears in the area of the orifice near the explosion source, and the center of explosion source is under negative pressure. The stress amplitude of condition V appears in the center of explosion and the area of a 45-degree angle to the horizontal direction, presenting an obvious shear failure mode. When t = 10 ms, the damage zone of condition V continues to expand, and the crack extended along the axial direction. The reason is that the reflected pressure waves propagate to the upper and bottom boundary of the water tank, which are superimposed in the axial direction to generate secondary damage.
Consequently, our results indicate that we should pay more attention to improving the longitudinal reinforcement in the parts of the shield building and the wedge (as shown in
In this paper, we mainly focus on the pressure evolution processes and damage modes under contact explosion at five typical detonation positions. It’ clearly that the degree of damage of the contact explosion occurring in the shield building is larger than that experienced by the wedge and water tank, which indicates that the most unfavorable position under a contact explosion is located between the orifice and air intake. Through the analysis of damage characteristics more attention to improving longitudinal reinforcement in the parts of shield building and the wedge should be paid. In the parts of the water tank, longitudinal and circumferential reinforcement should be paid the same attention.
The research described in this paper was financially supported by Educational Commission of Liaoning Province of China (No. LZ2015022), the State Key Development Program for Basic Research of China (No. 2013CB035905).
Xu, Q., Cao, X.Y., Chen, J.Y., Li, J. and Cao, Y. (2017) Study on Contact Explosion Performance of Nu- clear Containment. Energy and Power En- gineering, 9, 486-494. https://doi.org/10.4236/epe.2017.94B054