10 exam-style questions with answers and explanations, straight from our 1,030-question bank. Tap an answer to check yourself. When you're ready, take the scored version in the free practice test.
The PE-N exam has 85 questions and runs 8 hours 30 minutes.
These 10 free PE-N questions are organized by exam domain, so you can see how each part of the Principles and Practice of Engineering - Nuclear (PE-N) blueprint is tested. Reveal the answer and explanation under each question.
A gamma-shield survey agrees with the design calculation across a concrete wall except for a narrow high-dose region aligned with a straight cable conduit. The conduit must remain usable. Measurements away from its axis fall sharply, and a second calibrated instrument reproduces the pattern. The shielding modification should primarily:
Correct answer: D - Add overlapping shield baffles that eliminate the direct radiation path through the penetration.
An environmental laboratory records 1,000 gross sample counts in 10 minutes and 900 background counts in a separate 10-minute measurement. Both measurements follow independent Poisson statistics, and other uncertainties are negligible. Quantitative reporting requires a relative one-standard-deviation counting uncertainty of no more than 20% for the net count rate. Which assessment of this measurement is correct?
Correct answer: B - Net rate: 10 counts/min; uncertainty: about 44%; the precision requirement is not met.
A radiation worker at an NRC-licensed facility declares her pregnancy in writing. An assessment that includes external exposure and internal uptake projects a total embryo/fetus dose of 1.8 mSv over the entire pregnancy, with approximately uniform monthly exposure. Existing controls are ALARA, credible abnormal exposures have been reviewed, and no more restrictive site requirement applies. Which assignment decision is consistent with 10 CFR 20.1208?
Correct answer: C - Continue her duties with pregnancy-specific dose monitoring and effective exposure controls.
Following an extended low-power period, an irradiated fuel rod undergoes a rapid power ramp. Fuel analysis predicts closure of the pellet-cladding gap and a sharp increase in cladding hoop stress. Coolant conditions remain normal, calculated boiling margin stays above its acceptance limit, and examination finds neither appreciable external wall thinning nor grid-contact wear. The failure investigation should focus first on:
Correct answer: B - Pellet-cladding interaction during rapid fuel-pellet expansion
A fuel procurement campaign must deliver 1,200 kg of uranium enriched to 4.00 wt% uranium-235. The available feed contains 10,000 kg of uranium at 0.711 wt% uranium-235, and the enrichment contract specifies a tails assay of 0.300 wt%. Neglect process losses; all masses refer to uranium, not uranium hexafluoride. Which product estimate and procurement decision follow from the material balance?
Correct answer: D - About 1,110 kg of product; additional feed is required.
A pressurized water reactor develops a falling pressurizer level despite increased charging flow. Radiation rises in the secondary side of one steam generator, whose water level also increases without a feedwater change. Containment sump level and containment radiation remain at baseline. The primary system remains at substantially higher pressure than the secondary system. Which failure best explains this combination of indications?
Correct answer: C - A steam-generator tube leak into the secondary system
After a PWR trip and complete coolant-pump coastdown, the reactor coolant loops remain water-filled and subcooled. The elevated steam generators retain water and a controlled steam-release path, and forward loop flow settles at a low but nonzero value. Core outlet temperature remains above inlet temperature while average primary temperature decreases. With no other heat-removal path operating, which conclusion is justified?
Correct answer: A - Buoyancy-driven circulation is carrying decay heat to the steam generators.
After several weeks at steady full power, a thermal reactor is shut down. Reactivity calculations corrected to the same fuel temperature, moderator conditions, and control configuration show an increasingly negative poison contribution for several hours, followed by recovery over the next two days. For part of this interval, available excess reactivity is insufficient for restart. What accounts for this temporary loss of restart capability?
Correct answer: A - Iodine-135 continues producing xenon-135 after neutron absorption of xenon largely ceases.
In a uranium-fueled thermal reactor, fuel temperature rises before moderator temperature or density changes appreciably. The resulting Doppler feedback is negative. In four-factor terminology, the dominant mechanism is:
Correct answer: A - A decrease in resonance escape probability as uranium-238 resonance absorption increases.
A loss-of-coolant accident evaluation for a Zircaloy-clad light-water reactor subject to 10 CFR 50.46 predicts a peak cladding temperature of 2,100 degrees F, maximum local cladding oxidation of 14%, and hydrogen generation equal to 0.7% of the regulation's theoretical full-reaction amount. Core geometry remains coolable. Initial reflood succeeds, but the recirculation analysis predicts sump blockage that stops core cooling while decay heat removal is still necessary. Which result prevents acceptance of the ECCS performance?
Correct answer: C - The loss of sustained core cooling during the recirculation phase
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