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Engineering Design Project

Sample Subway – Nuclear Pressure Tube Sampling System

A remote-controlled device for retrieving metal samples from nuclear pressure tubes to assess hydrogen embrittlement.

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Overview

The "Sample Subway" is a specialized tool designed to scrape and collect a 30-80mg metal sample from the inside of a nuclear reactor pressure tube. The sample is used to analyze hydrogen levels, a key indicator of structural integrity.

Our solution operates remotely to minimize operator exposure to radiation. It features a self-sealing containment system that weighs the sample in real-time, ensuring precise collection without direct human contact.

Key Features

Remote Operation: Reduces radiation exposure for operators.
Automated Sampling: Precise scraping mechanism targets 30-80mg samples.
Real-time Feedback: Integrated load cells and sensors report status to the operator.
Fail-Safe Design: Winch retrieval system ensures the tool can be recovered if power fails.
Self-Contained Power: On-board battery system eliminates trailing cables.

Sample Subway Final Design Render — Final rendered design of the Sample Subway.

Design Process

1. Empathize

Operators in nuclear facilities work under extreme constraints: high radiation levels, limited time windows, and restricted physical access. Understanding the danger and stress of this environment was crucial. The primary user need was safety—ensuring no direct contact with the radioactive sample while maintaining operational efficiency.

2. Define

We defined the core problem: How to remotely extract a specific mass (30-80mg) from a 4-inch diameter tube, 15 feet deep, without manual intervention? The solution required a self-contained, wireless robot capable of:

Traversing the tube horizontally.
Scraping a precise sample.
Weighing it in real-time.
Returning safely, even in power failure.

3. Ideate & Concept

We explored multiple scraping mechanisms, from rotary cutters to linear scrapers. Hand-drawn sketches helped visualize the "Subway" form factor—a cylindrical carriage that could ride inside the tube.

Sample Container Diagram — Diagram showing the sample containment mechanism.

Side View Diagram — Side view diagram of the proposed form factor.

Top View Diagram — Top view diagram showing component layout.

4. Prototype & Test

We moved to CAD and 3D printing to test fit and function. The "Sample Subway" prototype integrated a high-torque DC motor for the scraper and a load cell for real-time weighing. Testing verified that our scraping mechanism could consistently achieve the +/- 9.5mg accuracy required.

Load Cell Testing — Testing setup for the load cell calibration.

Motor Mounting — 3D printed prototypes for the motor mounting plates.

Early Load Cell Test — Early load cell body implementation test.

Battery Pack Assembly — Custom 12V battery pack assembly.

Bill of Materials

A breakdown of the core components used in the prototype.

Item #	Part	Vendor	Description	Qty	Cost (CAD)
Battery and Power Delivery (PDXX)
PD01	22 awg Wire	Amazon	Wires for connecting components to circuit	1	$0.80
PD02	XT60 Connectors	Aliexpress	Connectors for battery pack	1	$1.60
PD03	16 awg Wire	Amazon	Wires for 12v components	1	$0.80
PD04	P42A Molicel Battery 21700	18650 Battery	For battery pack assembly	3	$15.00
PD05	3S Battery Management System	Aliexpress	For safety	1	$2.94
PD07	LM2596	Aliexpress	Step down buck converter, 36V/24V/12V/5V/3V	1	$0.45
Control and Logic (CLXX)
CL01	ESP32-WROOM-C3	Elegoo	Controller w/ Wifi + BT	1	$9.99
CL02	H-Bridge Motor Driver BTS7960	Aliexpress	Driving 12V motor for scraping	1	$7.41
CL03	HX711 Sensor	Aliexpress	Strain gauge for mass analysis	1	$1.80
Measurement (MXX)
M01	100g Load Cell	Aliexpress	Strain gauge to measure mass	1	$4.93
Structural Components (SCXX)
SC01	PLA - ~0.5 KG	Bambu	Filament for chassis	1	$7.99
SC02	M3 Female Threaded Insert	Aliexpress	Heat set threaded inserts for chassis	1	$0.80
SC03	M3/M4 Machine Screws	Aliexpress	Various length M3 Machine Screws	1	$1.00
SC04	608 ZZ 608RS	Aliexpress	Ball bearings	3	$1.80
Sampling Tooling Components (STXX)
ST01	MGEHR1212 + Bits	Aliexpress	Lathe Bit and armature	1	$9.28
ST02	GB37-520 7rpm 12v Motor	Aliexpress	For moving the armature with lathe bit	1	$11.28
Total					CA$77.87