ASME Section I primarily applies to:

• A. Nuclear reactors
• B. Power boilers generating steam for power generation
• C. Heating boilers
• D. Portable pressure vessels

Answer: (B)

ASME Section I focuses on the construction of power boilers, specifically boilers that generate steam at high pressure for power generation or for process steam in industrial settings. This section sets the rules for design, materials, fabrication, inspection, testing, and stamping of those high‑pressure steam systems, ensuring they can safely produce the needed energy.

That’s why the correct idea is that Section I principally applies to power boilers used for generating steam for power generation. Other areas are governed by different parts of the code: nuclear reactor components are covered by a section dedicated to nuclear facilities, heating boilers fall under the section for low‑temperature or low‑pressure heating boilers, and portable pressure vessels are addressed in other sections that cover pressure vessels rather than power boilers.