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Unformatted text preview: NEEP 411: HW#5 Severe Accident Calculations: Structural Calculations Due: Friday, October 28 th , 2011 1. In class, we formulated a crude expression for the temperature of the pressure vessel lower head as a function of time, where time is measured after a large mass of relocated corium settles on the lower head: Here is the temperature difference between the vessel and containment air, is the initial temperature difference, = is the time constant and T = . The numbers we obtained for these values are: = 270 K, T = 1300 K and = 1.1 hr. Suppose that the lower head is subjected to a membrane stress of 100 MPa while experiencing this temperature history. The creep strain rate can be described in power law form as: where A is a temperature-dependent coefficient, n = 4 at this level of stress, the creep strain rate has units of [hr-1 ] and the stress has units of [MPa]. For the SA533B steel used for nuclear pressure vessels, an approximate expression for A(T) is: In the expression for A ( T ), T must be in [K]. The value of A o is 1.667 10- 12...
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- Fall '09