Using Data Acquisition to Ensure Safe and Reliable Nuclear Plant Operation

Background information

Rigorously testing Nuclear Reactor Plants (NPPs) is critical to ensure the strength, durability, and reliability of their primary systems and structural elements throughout their life cycles. Commissioning the power units of NPP includes field tests using test equipment known as Commissioning Measurement Systems (CMS). 

Engineers use these CMS tools to approve assembly design conditions and facilitate any required equipment adjustments. CMS tools measure data on operational mode behavior and “live” data for incident detection. They also assist in decision-making regarding mitigating incidents during the commissioning stage.

This case study describes how India’s largest nuclear power plant has standardized on Dewesoft’s data acquisition (DAQ) instruments to perform that testing that ensures the safety and reliability of the plant’s critical systems.

Commissioning work involves a broad range of test and measurement requirements. CMS instruments that can collect data in demanding environments are then selected. The process includes numerous tasks and priorities:

• Define the scope of the testing requirements and build a requirements list for the test equipment required. The CMS equipment must be capable of confirming the reactor plant’s strength, thermotechnical, and functional reliability.

• Publish the commissioning measurement system design and engineering documentation. This documentation includes general arrangement drawings, electrical schematics, and equipment instrumentation details. These details are developed based on critical project tasks and experience in nuclear reactor field testing.

• Develop and manufacture specialized sensors, primary lines, fixturing, protective devices, and output nodes.

• Deliver and install the primary measurement instruments, secondary lines, and measurement and processing equipment to the reactor plant.

• Write and publish operating procedures detailing project programs and methods regarding commissioned power unit specifics and specify the sequence of tests in the commissioning schedule.

• Identify bugs in documentation and systems and correct them.

• Arrange and perform reactor plant test modes and measurements.

• Provide the customer with “live” measurement data that confirms design conditions of equipment component assembly and adjustment. Provide data confirming design operational mode behavior and assist in the detection of incidents and making decisions about their elimination,

• Process and analyze measurement results with required estimates and results of monitored equipment load level and verification of design characteristics.

• Publish reports with data confirming design characteristics of strength and reliability conditions, defining the most loaded nodes and equipment units. Provide detailed data on operational mode behavior, including recommendations on operational mode optimization and using commissioning measurement systems as operational monitoring devices.

We performed these tests during reactor plant project development for Kudankulam NPP Units #3 and #6. Located in the southern state of Tamil Nadu, Kudankulam NPP is the largest nuclear power station in India. Based on a decade-long collaboration, measuring instrument vendor Dewesoft d.o.o. has been chosen as our primary CMS hardware and software provider.

Dewesoft hardware in the commissioning measurement system

The CMS performs commissioning tests and measurements on reactor plant equipment during circulation cleaning and test runs, physical and power start-up stages, and tests of the reactor power plant design. The system consists of steady-state and portable systems and devices connected to the nuclear plant’s Power Unit Process Control System (PCS).

Steady-state commissioning measurement systems provide three theme-based directions of data measurement and analysis:

• Reactor plant equipment vibrodynamical parameter monitoring systems

• Reactor plant component thermomechanical load monitoring systems,

• Reactor plant equipment thermohydraulic parameter monitoring systems.

Portable commissioning measurement systems perform vibration tests and acquire initial data on the hydraulic and mechanical characteristics of primary reactor plant equipment.

The critical components of steady-state and portable commissioning measurement systems are Dewesoft instruments. These instruments operate near the equipment under test, including severe temperature and radiation-controlled access conditions (non-occupied areas) and in the occupied CMS control room.

In general, CMSs are distributed information and measurement systems. See Figure 1 below for an illustration of a modern CMS configuration: 

The reactor containment area contains Dewesoft SIRlUS-8xSTGM universal measurement modules and SIRlUSr-8xSTG strain gauge measurement modules. Based on using two 24-bit ADCs per channel, SIRIUS® instruments have the wide dynamic range required by vibration and related physical measurements. In Figure 1, these instruments form the basis of the vibrodynamical hardware (RI VD) and dummy assembly vibrodynamic hardware (DA VD).

The reactor containment area also contains KRYPTON-16xTH temperature-measuring thermocouple modules and KRYPTON-6xSTG strain-gauge modules. KRYPTON® instruments have a wide temperature operating range of -40 to +85 °C. They are sealed against liquids, smoke, and dust and have high shock and vibration ratings. These instruments form the basis of the thermomechanical (ТМ) hardware, thermohydraulic reactor and primary circuit measurement (R&PC THM) hardware, and thermohydraulic reactor head and cavity volume (RH&CV THM) measurement hardware located in the non-occupied reactor containment area.

The commissioning measurement system Control Room contains Dewesoft SIRlUS-8xSTGM universal measurement modules and SIRlUS-8xSTG strain gauge measurement modules. These form the basis of the reactor coolant circuit vibrodynamic hardware (RCC VD) and vibronoise measurement hardware (VNM VD) shown on the left side of Figure 1. 

DewesoftX software in the commissioning measurement system

The Control Room contains the CMS’s Software and Hardware complexes (SHC) and an Automated Workstation (AW) connected to the upper unit-level system (UULS) of the process control system. These systems use DewesoftX software to acquire data from the Dewesoft hardware.

DewesoftX software controls and acquires data from SIRIUS and KRYPTON instruments. It can apply a rich set of mathematical operations to both real-time and recorded data. DewesoftX sends data to the Software and Hardware Complexes (SHC) via a “File streamer” software plugin. The software also solves current and long-term data acquisition and test result processing tasks.

The software includes open data processing mathematical models, methods, and algorithms aligned with monitored processes in terms of operational mode rates. It provides for digital signal/archive filtering, statistical processing of analog and digital data, and the parallelism and interaction of tasks solved with the commissioning measurement system software and hardware complexes.

Operators can create DewesoftX setups and save them for repeated use, saving time and resources. DewesoftX allows fovelopers and users alike to extend system functions. DewesoftX’s standard communications protocols ensure interoperability with other CMS software and hardware. 

Time-stamped DewesoftX data is backed up and synchronized with the PCS database. All measured and estimated data that defined the monitored parameters is available in numeric and graphical form. Only authorized users can access the data based on their responsibilities and data category.

CMS software consists of two components: system and application. The software undergoes setup, debugging, and testing during preliminary individual and combined tests of the corresponding commissioning measurement subsystems.

CMS software ensures the functioning of all system hardware, including calculation task solving. The software is of modular-assembly principle in which every application (module) implements a function or a set of functions. The software includes tools for creating and editing drawings, records, and operating forms.

Commissioning measurement system results

The CMS has operated at Kudankulam NPP power units #1 and #2 for the last ten years. Data that confirms the general compliance of actual parameters (vibrodynamic, thermomechanical, mechanical, and thermohydraulic) of the monitored equipment and reactor plant systems (RI, DA, RH, SRS, MCP, SG, PC, PHRS, QBIS, AGRS, RCH) to the design values was collected. We found several non-conformities with reactor plant project requirements, including:

• Higher temperature loads in the pressure compensator (PC) injection pipeline involving the DN25 quick boron injection system (QBIS) tie-in pipelines tie-in section.

• During reactor plant heating and shut-down cooling modes, we observed thermal cycles up to +55 °С at the pressure compensator injection pipe and boric acid concentration levelling in the primary circuit and pressure compensator mode.

• Justifying strength requires recording coolant thermal stratification levels in the pressure compensator connection pipeline.

• When the pressure compensator tubular electric heater (PC TEH) was in operation, there was some non-optimal pressure adjustment in the primary circuit during the reactor plant’s steady-state operation.

• During hot operational testing at Kudankulam NPP unit #1, there was some abnormal heating of the pressure compensator’s heating bundle outputs.

• There was insufficient cooling in the upper part of the pressure compensator box.

• The metal of the reactor vessel pipe area cooled by 15 to 20 °С, as detected by regular resistance thermometer readings.

• We found a lack of pneumatically actuated quick-acting valve tightness control at the DN200 pipelines. These pipelines were quick boron injection system tie-ins.

• During reactor plant heating and in “hot shut-down” mode, we measured water pipe temperature variations up to 180 °C (the reference value is 120 °C). The auxiliary feedwater may have been supplied through the main pipe by mistake. The recorded temperature difference at the pipe was 202 °С.

• When testing the Steam Generator Emergency Heat Removal System (SG HRS), the auxiliary feed water temperature was 33 °С ( the acceptance criterion was 40 to 70 °С).

• There was insufficient blowdown of steam generator header pouches. A sludge deposit in small-diameter pipelines (∅ 25 mm) caused this problem. Steam generator blowdown flows through header pouch blowdown pipelines during “burst” contamination (ion exchange resin) was stopped, resulting in ingress to the steam generator.

• Rapid heating of afterheat removal passive system (ARPS) heat exchangers when heated up to the hydraulic testing temperature and connected to the heated circuit after maintenance shutdown.

• The direction of thermal movement of the “hot legs” of the Main Coolant Pipeline (MCP) differed from the design direction.

• Feed water flow meters installed in units 1 and 2 had reading fluctuations. Ultrasonic flow meters operate stably and reliably at various NPPs; ultrasonic feed water flow measurements as a direct measurement or for regular flow meter calibration are used successfully per IAEA documentation.

• There was damage to the reactor coolant pump set (RCPS) at the number 2 impeller in unit #2. The internal surface of steam generator header number 2 had remaining unfixed damaged fasteners.

• Significant development of high-frequency harmonics (198.8 Hz) in the vibrodynamic spectrum of Unit’s #1 and #2 Main Circulation Circuit showed the need for improved analysis of the Main Coolant Pipeline’s fatigue damage.

• Operation at increased system load rates when the reactor plant was in the “cold cooldown” mode resulted in increased acoustic noise from the emergency and planned cooling systems. 

Detection of non-conformities proves the need for comprehensive CMS systems, including the Dewesoft brand measuring instruments and software described herein. Proper planning and measurement allowed us to identify problems and work toward their mitigation and elimination. 

We are satisfied that our selection of Dewesoft as our primary CMS instrument provider was good, and we look forward to many more years of cooperation together.