Subject Engineering Mechanical Engineering

Question

Mechanical Engineering Study Guide Questions

2. If the fracture toughness for 304L austenitic stainless steel is determined to be 20 √ , would you expect the crack identified in Question 1 to be under elastic or inelastic stress? Would you expect the crack to grow (on set of crack extension) under the calculated conditions. Include a discussion justifying your conclusion. Disregard any material properties expected due to operational life in a high flux environment and assume steady state temperature and pressure environments.

3. In each of the situations below, identify whether the cost of reverse engineering the component is expected to be justified and whether reverse engineering of the components is appropriate. Disregard cost of manufacture when considering reverse engineering. Provide a basis for your answer.

a. A valve vendor has gone out of business resulting in no support for a critical feed system valve; if failure occurs, the power plant must be shutdown. The mean time to repair (MTTR) for the valve is six hours with materials on hand. A second vendor has provided a lead-time for a replacement valve of 15 days. Revenue lost is $1,000,000 per day while shutdown. The estimated cost of reverse engineering the valve is 14 days, at a daily cost of $500,000. The mean time between failure (MTBF) for this valve in similar applications is two failures per year.

b. A vendor for a remotely operated valve motor controller has gone out of business and no longer supports ECCS injection valve operators. A second vendor has estimated they can provide equivalent operators at a cost of $250,000 per unit, if a contract for retention of services at a cost of $100,000 annually is part of the order. The operators have technically complex and your R&D team has no experience with valve operators. The estimated cost to reverse engineer a prototype for testing is $25,000 per day for 30 days.


4. What is the dominate fuel lattice structure in operation today in PWRs? In what ways and why did the fuel lattice structures change over the past 40 years?

5. The graph below was produced during material testing of a new alloy proposed for use in a PWR reactor vessel. The operating temperature is currently 800°K with a new core design proposing to raise this temperature to 925°K to achieve an increase plant efficiency from 0.33 to 0.45. The neutron density would remain relatively constant at ~ 3 to 5 X 1022 fast neutrons/(cm2*sec). Would you agree with the recommendation to raise the operating temperature? Explain/justify your position.

6. Two identical alloy specimens are being evaluated for use in a new fuel rod design. One sample was exposed to a fast neutron flux of 9 X 1023 neutrons/(cm2*sec) at a temperature of 323°K for six weeks in a test reactor. The second sample was placed in an electrically heated oven with no fast neutron flux present at a temperature of 323°K for the same six week time period. What is the expected behavior in Charpy impact energy testing and nil ductility transition temperature (NDTT) of each of the two specimens? Include in your answer a graphic representation of a generic Charpy impact energy and NDTT curve comparing specimens over temperature.

7. Reverse engineering is a multistep process that is similar but different from classic engineering. List each step in the generic reverse engineering process, in sequence, and provide a description of each step in your own words, including any crucial elements applicable to each step.

8. Identify the primary considerations/requirements for thermal fission reactor coolant and for moderators/reflectors (i.e., make two lists, one for coolant and one for moderator/reflectors). Discuss the desired attributes and their bases (e.g., if ‘clarity’ were a desired attribute, describe what it is AND why it is a desired attribute) and provide two examples of acceptable materials for each.

9. What is the mechanism that has been identified during examinations of fuel coupons explaining ‘shadow corrosion induced’ channel bow in BWRs?

10. List and discuss four practical recommendations and guidance provided for reverse engineering.

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2. If the fracture toughness for 304L austenitic stainless steel is determined to be 20 √ , would you expect the crack identified in Question 1 to be under elastic or inelastic stress? Would you expect the crack to grow (on set of crack extension) under the calculated conditions. Include a discussion justifying your conclusion. Disregard any material properties expected due to operational life in a high flux environment and assume steady state temperature and pressure environments. (5 pts)


The crack will not grow because the calculated stress intensity is less than the fracture toughness value for the material. Since the crack is not growing, no deformation is occurring in the region of the crack tip, therefore the crack must be under elastic stress. However, given that the crack exists, at some previous time a localized stress was sufficient to cause some plastic deformation such that the crack formed and opened to its present state, so at some time in the past the crack region did experience inelastic stress....

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