Overview
ISO 20890-3:2020 provides internationally harmonized guidelines for hydrostatic (in-service) pressure testing of the primary coolant circuit in light water reactors. The standard defines the test technique, requirements for measuring equipment and pressure-generation systems, personnel qualifications, preparations, test performance and documentation to ensure reliable, comparable reactor coolant system (RCS) pressure tests. It notes that specific test pressures, temperatures, schedules and inspection intervals are determined by applicable national nuclear codes.
Key topics and technical requirements
- Scope of test: Integral hydrostatic system pressure tests covering pressure-retaining components of the reactor coolant circuit, with a pressure–temperature–time schedule and defined holding time followed by visual inspection for leaks.
- Test system and procedures: Development of a general test procedure (see Annex A), filling and venting the system, heating to specified test temperature ranges, controlled pressure/temperature ramps, and safe depressurization.
- Measuring equipment:
- Operational instrumentation may be used if it meets accuracy requirements.
- Pressure measurement for operation: ±1% full scale (analog) or over calibrated range (digital).
- Additional test manometer: ±0.6% full scale (analog) or over calibrated range (digital), installed per EN 837-2.
- Temperature monitoring for brittle-fracture protection: maximum discrepancy ±2 K.
- All measuring equipment must be calibratable.
- Pressure generation system: Must hold test pressure for the required duration, limit rates of change, and include emergency deactivation to prevent over-pressure.
- Personnel requirements:
- Defined qualifications for test inspectors and test supervisors (education/training and pressure-testing experience).
- Annual visual acuity validation using ISO 8596 or ISO 18490 symbols (near vision 1.0 at 0.33 m; far vision 0.63 at ≥4.0 m).
- Safety and radiation protection: Removal of insulation at representative points, minimization of radiation exposure during inspections, and definition of protection zones.
- Documentation: Calibration records, test procedures, test reports and evaluation of abnormalities.
Applications
- Routine and periodic hydrostatic integrity verifications of reactor coolant systems in pressurized water reactors (PWRs) and boiling water reactors (BWRs).
- Commissioning, post-maintenance testing, and post-event integrity assessments where system-wide pressure testing is required.
- Basis for plant procedures, regulatory submissions, and supplier/test house contracts to ensure consistent test execution and reporting.
Who should use this standard
- Nuclear power plant operators and maintenance organizations
- Inspection and testing engineers, NDT personnel, test supervisors
- Nuclear regulators and licensing bodies
- Qualification and certification bodies for pressure-testing personnel
Related standards and references
- ISO 20890 series (other parts covering in‑service inspection)
- EN 837-2 / EN 837-1 (pressure gauge selection/installation/class accuracy)
- ISO 8596 and ISO 18490 (visual acuity testing for inspectors)
- Applicable national nuclear codes for test pressures, temperatures and intervals
ISO 20890-3:2020 is essential for ensuring safe, comparable hydrostatic testing practices and clear documentation of RCS integrity in light water reactors.