PERIC Customized NOx Online Monitoring System for Spent Nuclear Fuel Reprocessing

Overview

The PERIC Customized NOx Online Monitoring System is a purpose-built, safety-critical analytical platform engineered for continuous, real-time quantification of nitrogen oxides (NO, NO₂, and total NOₓ) in off-gas streams generated during spent nuclear fuel reprocessing operations. It operates on the principle of ultraviolet differential optical absorption spectroscopy (UV-DOAS), coupled with a chilled-dry sample conditioning architecture. This methodology enables selective, interference-resistant detection of NOₓ species without chemical conversion or catalytic reduction—critical for maintaining measurement integrity in complex, radiolytically active, and highly corrosive nitric acid–based process environments. The system is fully integrated into plant Distributed Control Systems (DCS) via standard 4–20 mA analog outputs and Modbus TCP digital interfaces, supporting closed-loop process control, alarm triggering, and regulatory data logging requirements under nuclear facility operational protocols.

Key Features

• UV-DOAS optical engine with dual-beam path design for high signal-to-noise ratio and long-term photometric stability
• Cold-dry sampling architecture: heated probe (up to 180 °C) + thermoelectric chiller (dew point ≤5 °C) + particulate filtration (≤0.3 µm) + pressure/flow regulation
• Real-time NO and NO₂ speciation with independent spectral deconvolution—no reliance on conversion efficiency assumptions
• Automatic zero/span validation capability using certified calibration gases (NIST-traceable)
• Fail-safe diagnostics including lamp intensity monitoring, optical path contamination detection, and flow/pressure anomaly alerts
• ATEX-certified enclosure option (II 2G Ex d IIB T4 Gb) and IP65-rated field housing for hazardous area deployment
• Compliance-ready firmware architecture supporting audit trails, user access levels, and electronic signature functionality per ALARP and IEC 61511 guidelines

Sample Compatibility & Compliance

The system is validated for direct analysis of hot, humid, acidic off-gas containing HNO₃ vapor, NOₓ, N₂O₄, O₂, CO₂, and trace radioactive aerosols (e.g., ¹⁰³Ru, ¹³⁴Cs). Sample matrix effects are mitigated through spectral fitting algorithms that account for water vapor and nitric acid cross-absorption in the 190–230 nm range. All wetted materials—including probe, tubing, and chiller surfaces—are constructed from Hastelloy C-276 or electropolished 316L SS to resist nitric acid corrosion at concentrations up to 12 mol/L. The system meets IAEA Safety Standards Series No. SSG-29 (Monitoring of Radioactive Effluents), adheres to ASTM D6348–21 for gaseous emission monitoring, and supports GLP/GMP-aligned data integrity practices per FDA 21 CFR Part 11 when deployed with optional secure software modules.

Software & Data Management

PERIC’s proprietary NOxView™ software provides embedded instrument control, real-time spectral visualization, and automated baseline correction. Data are timestamped with microsecond precision and stored locally (SSD) with redundant backup to networked historian systems. Export formats include CSV, XML, and OPC UA-compliant structured data for integration into PI System, DeltaV, or Foxboro DCS platforms. Audit logs record all configuration changes, calibration events, and operator interventions with immutable timestamps and user IDs. Optional cybersecurity features include TLS 1.2 encryption for remote access, role-based authentication, and firmware signing verification to prevent unauthorized code injection.

Applications

• High-tritium nitric acid recovery circuits—monitoring NOₓ generation during acid concentration and distillation
• Intermediate-level radioactive waste evaporation units—tracking NOₓ release kinetics during thermal decomposition of nitrates
• Pu purification solvent extraction off-gas treatment lines—ensuring compliance with stack emission limits per national nuclear regulatory authority thresholds
• UO₂(NO₃)₂ calcination and denitration ducts—supporting mass balance closure and process optimization studies
• Integrated monitoring for decommissioning campaigns where legacy off-gas behavior must be characterized prior to facility shutdown

FAQ

What NOₓ species does the system measure independently?
It quantifies NO and NO₂ simultaneously and directly via their unique UV absorption fingerprints; total NOₓ is calculated as the sum without requiring catalytic converters.
Can the system operate continuously in high-radiation zones?
Yes—the optical bench is shielded with borosilicate glass and lead-lined housings; electronics meet IEC 62582-2 (ED-2) for 10⁵ Gy total ionizing dose tolerance.
Is hot-wet measurement capability available?
A parallel thermal-wet DOAS configuration (without condensation) is under qualification; it eliminates dew-point-related drift but requires higher-grade optical window materials and dynamic spectral compensation algorithms.
How is calibration traceability maintained?
Certified gas standards (NO in N₂, NO₂ in air) with NIST-traceable certificates are used for initial setup and periodic verification; onboard span gas delivery is automated via solenoid-controlled manifold.
Does the system support SIL2 functional safety certification?
The core analyzer module is designed to SIL2-compliant architecture per IEC 61508; full loop certification requires integration validation with customer-specific DCS logic solvers and final element response testing.