A study on the mechanical characteristics of top nozzle hold down spring

Top nozzle hold down springs hold a Fuel Assembly (FA) on the lower core plate firmly against the up-lift force in startup or Hot Full Power (HFP) conditions and allow the FA's length change that is caused by irradiation growth of guide tubes. However, the FA might be bent if there is the excessive spring force by leaf springs. As a result of this, the hold down spring is one of the major components of FA for Pressurized Water Reactor (PWR) and a test of the hold down spring is necessary to analyze its hold down force. A top nozzle hold down spring force calculated through the load vs. deflection test of one hold down spring set has been used as a general method for fuel assembly hold down force analysis so far. Since this force has been conservatively evaluated, a new test will be performed to find a more accurate fuel assembly hold down force by pushing down the four hold down spring sets simultaneously, which describes the behavior of real fuel assembly. In this study, the mechanical characteristics of the four hold down spring sets and one hold down spring set are evaluated, respectively. And then the test results of the four hold down spring sets are compared the previous fuel assembly hold down forces calculated through the load vs. deflection tests of one hold down spring set