Elastic-plastic Analysis Of A Rector Pressure Vessel With A Axial Semi-Elliptical Surface Crack

The reactor pressure vessel(RPV) usually works under high pressure and temperature environment, and it often been affected by thermal shocks which caused by some incidental events, such as a pipe breaking in the primary pressure circuit. In most the case, RPV with one or more cracks, especially a surface crack. During thermal shocks, temperature gradient and pressure load would cause high tension stress in the inner surface of vessel, which becomes the driving force of cracks extension. Therefore, the integrity of RPV is a very important issue during the nuclear plant running and its lifetime extension, and much more attention should been paid to the integrity of RPV under pressured thermal shocks, which decides whether the plant can run safely. Fracture toughness is usually used to assess the integrity, which is related to the constraint level of the crack front. Therefore, considering the constraint effect is of great significance when study the fracture behavior. On the international,the mature two-parameter analysis methods include K-T, J-Q and J-A2. The safety assessment methods to the vessel during its lifetime include stress intensity factor criterion, design curve of crack tip opening(CTOD) displacement method, calculation method of J-integral put forward by American California electric power research institution(EPRI) and R6 failure assessment chart method put forward by English central electricity generating bureau(CEGB). R6 method has been applied to safety assessment of structures with defects, and it has three forms failure, namely fragility fracture, plasticity fracture and elastic-plastic fracture. The two criterion of R6 failure is to express the three forms fracture assessment in one drawing.This paper is to use J-A2-Tz three parameters method to analyse the fracture behavior of RPV, with a axial surface semi-elliptical crack, by considering the elastic-plastic material properties. By combining with practice and making some reasonable assumption, using 3-D finite element model to analyse the constraint effect and put forward the method of its integrity assessment.The main content is consist of the two sections:(1) Constraint effect. Both the regular and pressured thermal shocks environment are analysed. Based on the elastic-plastic theories, J-A2-Tz three parameters method is used to quantify in-plane and out-of-plane constraint effect of RPV crack front, by considering the temperature effect. Analysed the effect of aspect ratio(a/c), strain hardending exponent(n) and thermal shocks time history on crack front J-integral, constraint parameters A2 and Tz respectively.(2) Integrity assessment. Considering crack front constraint effect of the PRV under pressured shocks, based on R6 two parameters criterion, using J-integral and A2,which are related to the pressured thermal shocks time history, develop its corresponding criterion and put forward the failure assessment curves and the assessment method of fracture reliability.The paper is to use J-A2-Tz method to analyse the RPV with a semi-elliptical surface crack, by considering both in-plane and out-of-plane constraint effect. The results show that: The most deepest point is the serious point, which under high loading and high constraint level in both the regular and pressured thermal shocks environment. The integrity of RPV subjected to pressurized thermal shocks is performed. The analysis data and related conclusions provide great convenience to study PRV, which can be applied into practice to conduct work.