Lightweight Radioisotope Heater Units• Designed to maintain temperature for

important components on deep space explorations.

• Fueled by 2.6 grams of 238PuO2 (Plutonium Oxide), LWRHUs produce one thermal watt of power for seven years after fueling.

• Approximate physical characteristics: 32 mm tall , 26 mm in diameter, and weighing 40 grams.

• LWRHUs components: 238PuO2 fuel pellet, a pure platinum powder pressed and sintered vent frit, Platinum Rhodium (Pt-30Rh) alloy cladding, three pyrolytic graphite thermal insulation tubes, and a graphite ablation shell.

What is a Lightweight Radioisotope Heater Unit (LWRHU)?

Vent Activation

LWRHUs in Space

• LWRHUs have been used on a handful of NASAs deep space explorations.

• Galileo used 120 LWRHU’s on its 14 year mission and successfully studied Jupiter and its moons.

• Cassini with its probe, Huygens, carried 117 LWRHUs to orbit Saturn and explore its rings and moons.

LWRHU Assembly ProcessAmanda Gates

LWRHU components received at INL

LWRHU fueled clad vent activated and inspected

LWRHU fueled clad assembled into graphite

components

LWRHU fueled module undergoes cement curing

process

LWRHU fueled module undergoes vacuum bakeout process to remove impurities

LWRHU fueled module shipped to customers

for integration to space vehicle/components

• Mars Pathfinder carried three LWRHUs and built technical competencies needed for designing and operating the later generations of Mars rovers.

Summer Internship Project – Develop Vent Activation & Inspection Process

• Researched and selected post vent activationvisual inspection system to ensure that the LWRHU vent is fully activated -- Aven Cyclops Digital Microscope

• Selected/designed various tooling and fixtures for ventactivation process.

INL/MIS-15-36048

Acknowledgements This work would not have been possible without the guidance of Shad Davis of the Radioisotope Power Systems Department.

Why Vent Activation is Necessary• Helium is generated by radioisotope decay. This builds pressure causing distortion and

potential failure of the LWRHU clad. The clad is the primary confinement system that prevents radioactive contamination escape. To avoid pressure buildup, a vent hole is added to the top of the clad (vent cap) after receipt at INL without penetrating the vent frit. This frit allows Helium to escape without releasing 238PuO2

How Vent is Activated • Vent activated by drilling a 0.635 mm (0.025 in) diameter hole through the fuel clad end

cap to a depth of 0.330 mm (0.014 in).Project Accomplishments• Researched and selected machine to perform vent activation drilling operation --

Cameron 214-CS Drill Press• Tested the micro drill machine to optimize cutting

speed, determine manual feed rate technique,calibrate x-y positioning for fuel clad axis location, and

determine hard stop positioning to ensure that the vent/fuel clad is not breached.