Control Rod for Nuclear Reactors | Component Specifications

Product Specifications

Technical details and manufacturing context for Control Rod

Definition

A control rod is a critical safety component within a nuclear reactor's control rod assembly, designed to absorb neutrons and thereby control the rate of the nuclear chain reaction. Its insertion or withdrawal from the reactor core directly modulates reactor power and is essential for startup, operation, and emergency shutdown. Control rods contain materials with high neutron absorption cross-sections (neutron poisons), such as boron, cadmium, silver, indium, or hafnium. When inserted into the reactor core, they absorb free neutrons, reducing the number available to cause fission and thus slowing or stopping the chain reaction. Withdrawal has the opposite effect, allowing the reaction to proceed. The absorber material is typically boron carbide (B4C) for fast reactors, or a silver-indium-cadmium alloy (Ag-In-Cd 80/15/5) for standard pressurized water reactors (PWRs), per ASTM B827. The cladding is typically stainless steel 316L (ASTM A240) for corrosion resistance at high temperatures. Key dimensions include an outer diameter of 9.6–11.2 mm, total length of 3600–4200 mm, and cladding thickness of 0.5–0.8 mm. The absorber weight ranges from 2.5–3.5 kg, and the neutron absorption cross-section for thermal neutrons is 200–300 barns, depending on burnup. Operating temperature is 300–350 °C, and operating pressure is 15.5–16.5 MPa. Surface roughness is 0.4–0.8 µm Ra (ISO 4287), and dimensional tolerance is ±0.05 mm (ISO 2768-m). Drop time for SCRAM is 1.5–2.5 seconds, and service life is 10–15 years. These values are reference ranges; verify model-specific parameters with the legal manufacturer or supplier.

Working Principle

Control rods function by absorbing neutrons, thereby reducing the neutron population available to sustain the fission chain reaction. The absorber materials have high neutron absorption cross-sections, capturing neutrons without fissioning. Inserting the rods deeper into the core increases neutron absorption, decreasing reactor power; withdrawing them reduces absorption, increasing power. This mechanism allows precise control of the reaction rate and provides a rapid shutdown capability (SCRAM) by dropping the rods into the core under gravity. The effectiveness depends on the absorber material, rod geometry, and insertion depth.

Common Materials

Boron carbide (B4C), Silver-indium-cadmium alloy, Hafnium

Technical Parameters

Parameter	Typical range	Notes & selection driver
Absorber Material	Ag-In-Cd 80/15/5	Standard PWR alloy; B4C for fast reactorsASTM B827
Cladding Material	SS 316L	Corrosion resistance at high tempASTM A240
Outer Diameter	9.6–11.2 mm	Fits fuel assembly guide tubes
Total Length	3600–4200 mm	Reactor core height dependent
Absorber Weight	2.5–3.5 kg	Neutron worth and drop time
Neutron Absorption Cross Section	200–300 barn	Thermal neutrons; burnup dependent
Operating Temperature	300–350 °C	Coolant outlet temp
Operating Pressure	15.5–16.5 MPa	PWR primary circuit
Cladding Thickness	0.5–0.8 mm	Mechanical strength vs neutron economy
Surface Roughness	0.4–0.8 µm Ra	Reduces fouling and wearISO 4287
Dimensional Tolerance	±0.05 mm	Ensures fit in guide tubesISO 2768-m
Drop Time	1.5–2.5 s	SCRAM safety requirement
Service Life	10–15 years	Burnup limit of absorber

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

Components / BOM

Absorber Section
Contains the neutron-absorbing material (poison) that regulates the fission reaction.

Material: Boron carbide pellets or alloy
Cladding Part
Hermetically seals and provides structural support for the absorber material, protecting it from the reactor coolant environment.

Material: Stainless steel or Zircaloy
End Fittings/Connectors Part
Interface for connecting the rod to the drive mechanism or spider assembly for insertion/withdrawal.

Material: Stainless steel

Applied To / Applications

This component is essential for the following industrial systems and equipment:

Control Rod Assembly

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Manufacturers of Control Rod

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Frequently Asked Questions

What materials are used in control rods?

Common absorber materials include boron carbide (B4C) for fast reactors and silver-indium-cadmium alloy (Ag-In-Cd 80/15/5) for PWRs, per ASTM B827. Cladding is typically stainless steel 316L (ASTM A240).

What are typical dimensions of a control rod?

Outer diameter ranges from 9.6 to 11.2 mm, total length from 3600 to 4200 mm, and cladding thickness from 0.5 to 0.8 mm. These are reference ranges; confirm with the manufacturer.

How does a control rod work?

It absorbs neutrons, reducing the number available for fission. Inserting the rod slows the reaction; withdrawing it allows the reaction to proceed. This controls reactor power and enables emergency shutdown.

What is the service life of a control rod?

Service life is typically 10–15 years, depending on burnup and operating conditions. Regular inspection and testing are required to ensure performance.

Data Basis

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pressure:	7-15 MPa (PWR), 7-8 MPa (BWR)
other spec:	Neutron absorption cross-section: 100-2000 barns, Insertion/withdrawal speed: 0.1-10 cm/sec
temperature:	300-600°C (typical PWR/BWR operating range)

Control Rod

Product Specifications

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