Guide Thimble: Outer Diameter 12.0-15.0 mm, Length 4000-5000 mm

Component Specifications

Definition

A cylindrical guide thimble is a critical structural component in nuclear fuel assemblies, designed to maintain precise spacing and alignment between fuel rods while providing channels for control rod insertion and instrumentation. It ensures geometric stability under extreme thermal, hydraulic, and radiation conditions during reactor operation.

Working Principle

The guide thimble functions as a rigid tubular guide that maintains fuel rod lattice geometry through mechanical constraint, allowing control rods to move freely within its bore while withstanding axial and lateral loads from coolant flow and thermal expansion.

Materials

Zirconium alloy (typically Zircaloy-4 or ZIRLO), austenitic stainless steel (304L, 316L), or nickel-based alloys (Inconel 718), selected for low neutron absorption, corrosion resistance, and high-temperature mechanical properties.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Length	4000-5000 mm
Outer Diameter	12.0-15.0 mm
Surface Finish	Ra ≤0.8 μm
Wall Thickness	0.4-0.8 mm
Pressure Rating	15-20 MPa
Operating Temperature	Up to 350°C
Straightness Tolerance	≤0.1 mm/m

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 18279, ASTM B353, RCC-M

Parent Products

This component is used in the following industrial products

Fuel Assembly

A structural unit containing nuclear fuel rods arranged in a specific geometric pattern for controlled fission reactions.

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Engineering Analysis

Risks & Mitigation

Stress corrosion cracking
Grid-to-rod fretting wear
Dimensional deformation under irradiation
Hydride embrittlement in zirconium alloys

FMEA Triads

Trigger: Inadequate material purity or improper heat treatment
Failure: Premature corrosion or cracking
Mitigation: Strict material certification, non-destructive testing (UT, ET), and compliance with nuclear-grade standards.

Trigger: Excessive vibration or flow-induced oscillation
Failure: Fretting wear at spacer grid contact points
Mitigation: Optimized support design, anti-vibration features, and wear-resistant coatings.

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

±0.05 mm on critical dimensions, per ASME Y14.5

Test Method

Dimensional inspection (CMM), hydrostatic pressure testing, eddy current testing for defects, and neutron absorption cross-section verification.

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

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Manufacturers of Guide Thimble

Manufacturer profiles associated with Guide Thimble.

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Frequently Asked Questions

What is the primary function of a guide thimble in a fuel assembly?

It maintains precise fuel rod spacing, provides channels for control rods and instrumentation, and ensures structural stability under reactor operating conditions.

Why are zirconium alloys commonly used for guide thimbles?

Zirconium alloys offer low neutron absorption, excellent corrosion resistance in high-temperature water, and good mechanical strength, making them ideal for nuclear applications.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Guide Thimble