Oil-Free Screw Air Compressor for Nuclear Power Plant I&C Instrument Air Supply

Safety Valve Integrity

Oil aerosols at concentrations as low as 0.01 mg/m³ can cause pneumatic valve seats to swell, stick, or fail to reseat. In a safety instrumented system, a stuck-open or stuck-closed valve directly challenges the plant protection function — an outcome that regulators treat as a safety significant failure.

Regulatory Compliance

The ONR’s Safety Assessment Principles and IAEA Safety Standards Series NS-G-1.3 both require instrument air quality to be specified, monitored, and maintained across the life of the plant. ISO 8573-1 Class 0 certification provides the documented quality benchmark that safety cases and periodic safety reviews demand.

Redundancy Architecture

Nuclear I&C instrument air systems are configured on a 2×100% or N+1 basis so that a single compressor failure — whether planned or unplanned — does not interrupt the instrument air supply header. Ever Power compressors are available in matched-set, duty/standby, or fully segregated architectures to support any nuclear single-failure criterion.

Long Service Life

A nuclear plant’s design life runs to 40–60 years, with each instrument air compressor expected to operate for 60,000+ hours across planned outage windows. The oil-free screw design eliminates lubricant degradation as a life-limiting mechanism, yielding a substantially lower lifecycle cost than oil-injected equivalents retrofitted with downstream filtration.

Safety Instrumented System (SIS) Actuation

Pneumatic SIS final elements — including process isolation valves and trip valves — rely on clean, dry instrument air to maintain their fail-safe position under power loss or logic solver command. Ever Power compressors supply the header pressure and flow stability that eliminates spurious trips due to air pressure variations, with pressure tolerance held to ±0.15 bar across the full demand range of the SIS loop.

Containment Isolation Valves

The primary containment boundary depends on air-operated isolation valves closing within defined stroke times following a containment isolation signal. Any degradation in instrument air supply quality — whether from oil fouling, moisture freezing, or pressure loss — directly threatens the leak-tightness of the containment envelope. Our redundant compressor sets maintain a live instrument air header at all times, even through planned maintenance periods using the built-in standby changeover logic.

Reactor SCRAM & Emergency Shutdown

Emergency shutdown systems — whether hydraulic or pneumatically-assisted reactor trip breaker mechanisms — demand ultra-reliable motive air supplies with defined minimum header pressures. Ever Power’s automatic standby duty changeover, combined with a receiver buffer sized to bridge the changeover transient, ensures that the SCRAM air header remains pressurised above the minimum trip valve actuation pressure throughout any credible single-compressor failure scenario.

Emergency Core Cooling System (ECCS)

ECCS accumulator charging, ECCS injection line valve actuation, and core spray initiation logic all have pneumatic elements that must function during and after design-basis events including seismic events and station blackout scenarios. Instrument air compressors supplied to ECCS-related circuits are specified with seismic qualification documentation (IEEE 344 methodology) and emergency diesel-backed power distribution — both features Ever Power’s nuclear package supports as standard options.

Zero Oil Carryover — Verified

Each unit ships with a factory-issued ISO 8573-1 Class 0 test certificate from an accredited third-party laboratory. The test report forms part of the equipment data package submitted for nuclear safety case purposes, eliminating the need for purchaser-commissioned post-installation testing before handover.

Full Documentation Package

Nuclear procurement demands material traceability, weld inspection records, FAT/SAT protocols, and operation and maintenance manuals formatted to client specification. Ever Power maintains a dedicated nuclear documentation team who produce compliant data books for ONR-regulated sites, NDA framework contracts, and EDF Energy procurement requirements — all under our ISO 9001-certified quality management system.

Seismic Qualification Available

For safety-classified instrument air applications at new-build nuclear facilities — including Hinkley Point C — Ever Power can supply compressor packages with seismic anchorage design documentation, shake-table test reports aligned with IEEE 344, and structural calculations certifying performance at the site-specific ZPA. This is rarely offered by standard industrial compressor suppliers and reflects our depth of experience in nuclear project work.

Automatic Duty/Standby Changeover

The integrated PLC control panel monitors discharge pressure and compressor health signals from both units simultaneously. A pressure drop below the low-pressure setpoint — or a fault signal on the duty compressor — triggers automatic standby start and changeover within three seconds, faster than most pneumatic header receivers deplete to minimum instrument air pressure. Changeover events are logged with timestamp for post-event review by plant engineers.

Low Lifecycle Cost

Eliminating oil means eliminating the oil separator element, inline oil-removal filters, and the scheduled oil changes that oil-injected machines require every 2,000–4,000 hours. Over a 20-year operating period at a nuclear site, the avoided maintenance cost — combined with the IE4 motor’s reduced energy consumption — typically delivers a lifecycle saving of 30–40% against an equivalent oil-injected package with downstream filtration to Class 1.

Remote Monitoring & Alarm Integration

Plant DCS integration is standard. Modbus RTU, PROFIBUS DP, or 4–20 mA hard-wired I/O outputs allow the instrument air system status — running state, header pressure, outlet dewpoint, air quality monitor alarms, and compressor fault conditions — to be annunciated at the main control room and incorporated into the plant alarm management system without additional engineering.

“The documentation pack Ever Power delivered was the most complete we have received from any rotating equipment supplier on this project. The FAT records, FMEA, and material traceability certificates all came in the correct format for our nuclear QA system without a single revision request — genuinely rare in our experience.”

— Senior Mechanical Engineer

Nuclear Engineering Contractor, Somerset

“We had a tight schedule pressure on getting the instrument air system commissioned ahead of the SIS performance testing window. Ever Power’s project manager kept pace with our programme milestones and the units arrived fully factory-tested with zero commissioning snags. The standby changeover worked first time on site testing — exactly what you need on a nuclear programme.”

— I&C Commissioning Lead

Nuclear Systems Integrator, North West England

“We replaced three ageing oil-injected compressors with Ever Power oil-free units at our AGR station. The maintenance workload dropped significantly — no more oil filter changes, no more weekly oil level checks, and the air quality monitor has not triggered a single high-oil alarm since installation. Our outage planning has improved because the maintenance scope is so much more predictable now.”

— Maintenance & Reliability Manager

EDF Energy AGR Station, Scotland

For nuclear power plant I&C instrument air in the UK, a two-stage oil-free rotary screw compressor configured as a 2×100% redundant package is the industry-standard choice. It achieves ISO 8573-1 Class 0 air purity without downstream filtration that could introduce a point of failure, and its lower maintenance profile suits the extended intervals between nuclear outage maintenance windows. Indicative pricing for a complete skid-mounted nuclear instrument air package — including integrated dryer, filtration train, control panel, and documentation — typically ranges from £85,000 to £280,000 depending on flow rate, pressure, redundancy architecture, and customisation scope. Contact our team at [email protected] for a project-specific quotation.

ISO 8573-1 is the primary international standard governing compressed air purity. For nuclear safety-grade instrument air, the applicable class is Class 0 — which defines the most stringent purity level, requiring that total oil content (including aerosol, vapour, and liquid phases) does not exceed 0.01 mg/m³. Every Ever Power oil-free screw compressor supplied for nuclear applications ships with an accredited third-party ISO 8573-1 Class 0 test certificate. Additional relevant standards include ISO 8573-7 for viable microbiological contamination and IAEA NS-G-1.3 for nuclear I&C system design, with which our equipment packages are designed to be compatible.

ONR’s Safety Assessment Principles (SAPs) and the associated Technical Assessment Guides require that instrument air quality be defined and maintained as a nuclear safety function. For a Hinkley Point C or Sizewell C specification, you should reference the EDF/NNB EPR design basis for instrument air quality and redundancy, specify ISO 8573-1 Class 0 air purity at the compressor outlet, require a 2×100% compressor duty/standby configuration meeting the single-failure criterion, and include documentation requirements aligned with the nuclear quality assurance framework (typically ISO 9001 with a nuclear supplement). Ever Power’s applications engineers can assist in developing the functional specification and equipment data sheet as part of the pre-order technical dialogue — at no charge for qualifying nuclear procurement projects.

Ever Power supplies oil-free screw air compressor packages to NDA decommissioning sites across the UK, including Sellafield, Magnox legacy sites, and Dounreay. Our nuclear documentation package — including material certificates, weld records, FAT/SAT protocols, and FMEA — is formatted to the requirements of the NDA Procurement Governance Framework and can be submitted directly to the relevant Licensed Site’s QA team. Delivery lead times for NDA replacement packages are typically 14–20 weeks from order, with expedited options available for urgent operational requirements. To discuss a specific NDA project requirement, email [email protected] with the site name, required flow and pressure, and your target on-site date.

Containment isolation valves (CIVs) are typically spring-loaded to their fail-safe position — either fully closed or fully open depending on their function — and held in the operating position by instrument air pressure against the spring. If instrument air supply pressure falls below the minimum valve actuation pressure, the valve moves to its fail-safe position. While this is by design, an uncontrolled pressure loss during normal power operation can cause spurious containment isolation, triggering a reactor trip and potentially challenging other safety systems. A 2×100% redundant oil-free compressor system prevents this by automatically starting the standby compressor within seconds of a detected duty compressor fault, maintaining header pressure continuously above the CIV minimum actuation setpoint. The pneumatic receiver volume is sized to bridge the changeover transient even in a worst-case demand scenario.

For nuclear instrument air service, Ever Power oil-free screw compressors are designed to a 20,000-hour minor service interval (air filter, inline filter elements, belt or coupling inspection) and a 40,000–60,000-hour major overhaul interval covering rotor bearing replacement and PTFE coating inspection. By comparison, an oil-injected compressor in the same application requires oil changes every 2,000–4,000 hours, oil separator element changes every 4,000 hours, and mandatory downstream oil-removal filter replacements every 6,000–8,000 hours. Over a 20-year plant life, the avoided maintenance costs for the oil-free option typically represent a saving of £40,000–£90,000 per compressor set, depending on site-specific labour rates and parts pricing. This figure does not include the cost of downstream filter failures and associated air quality incidents, which can be considerably more expensive in a nuclear context.

Yes — Ever Power oil-free screw compressor packages for EDF AGR stations are supplied with fully configurable communication interfaces. Standard options include Modbus RTU (RS-485), Modbus TCP/IP (Ethernet), PROFIBUS DP, and hard-wired 4–20 mA analogue signals for the most critical parameters: header pressure, outlet dewpoint, running/standby status, and fault alarm. For the EDF DCS environment — typically ABB System 800xA or Siemens SPPA-T3000 variants at AGR stations — we can pre-configure the Modbus register map to align with the DCS engineering database before FAT, minimising site engineering time. We have successfully commissioned DCS-integrated instrument air packages at Heysham 2 and Hunterston B, and our engineers are familiar with EDF’s grid connection and I/O tagging conventions.