Following one major upgrade, processes at BNFL Springfields Building 633 are now monitored in real time, with alarms being time-stamped to a resolution of 10 milliseconds. As a result, productivity at the plant has improved markedly.
BNFL is an international nuclear energy business that employs some 23,000 people in 16 countries. Its activities span the entire nuclear energy cycle. That means everything from reactor design and fuel manufacture to power station decommissioning and clean-up. BNFL has around a 12 per cent share of the world nuclear market.
Springfields, near Preston in Lancashire, UK is the site of BNFL's fuel manufacturing operation which processes several thousand tonnes of uranium a year. It has the technology to manufacture fuel for all the major designs of nuclear reactors in use worldwide, and supplies the majority of fuel requirements for the UK's nuclear power station infrastructure.
The company's work spans fuel manufacture and uranium procurement through to recycling used fuel, transporting radioactive materials, engineering, waste management and decommissioning.
Building 633 at the Springfields site had an ageing monitoring system, along with outdated graphics and operator controls. A replacement system to interface into the existing plant instrumentation was required, and which would provide a real time alarm management function.
BNFL's team chose a network based Maxiflex and Maxilarm system supplied by Omniflex, following successful installations at other BNFL sites.
The full 633 DAS system, as it is called, comprises 19 separate Maxiflex and Maxilarm nodes connected on a 500m dual Conet network and communicating with a new plant SCADA system.
Conet is the world's most rugged LAN, allowing reliable industrial strength communications on existing plant wiring to 10km in a full peer-to-peer configuration. Capabilities for report by exception, dual redundancy and multiple network segments to suit the plant topology are features of the Conet network.
Conet networks can support up to 127 nodes, and can also be interconnected with radio, PSTN and GSM networks to provide an extremely versatile communications infrastructure.
The SCADA software is configured as a hot standby dual- redundant client/server system with five nodes all connected via Ethernet.
The alarms are generated from furnace temperatures, flows and tank levels, obtained either from digital systems hardwired into the scheme, or derived internally from analogue set points.
Maxiflex gathers remote digital and analogue inputs and interfaces to some existing intelligent controllers via RS485, using the controller's proprietary protocol.
An important point to note about Maxiflex and Maxilarm front-end I/O is that the I/O is scanned asynchronously. The conditions are then loaded into a large 'data interchange table' in the CPU memory, where it is instantly available to any other device on the network.
This allows flexible I/O routing between other nodes on the network and easy interrogation of the node data by the SCADA and DCS systems. Maxilarm nodes are also able to transmit unsolicited data, enabling the alarms to be transmitted to the SCADA system without delay. Both data transmission techniques were used in Springfield applications.
Network redundancy ensures that a separate network operates between each node, as well as between the SCADA PC's. A monitor node scans each alarm node on the network for correct and healthy communication. Failure of communication or non- detection of the node's watchdog results in a physical changeover of the network for all the nodes on the system. In addition, the monitor node alternates the networks periodically to check that they are both healthy.
Real time systems such as these have many advantages; including an ability to log and monitor 'first- up' sequences which in many instances can quickly pinpoint the true cause of alarm avalanches. They also play a major role in helping companies to achieve their preventative maintenance goals.
The installed system has already made a significant contribution to the efficiency of the plant. In particular, Maxilarm's ability to time-stamp the digital inputs to a resolution of 10 milliseconds, synchronised across the network, has been welcomed by the operators. Moreover, the system provides real-time alarm management, with the inputs being chronologically logged into the SCADA software.
"We have used data acquisition systems from Omniflex before, and have always found them very reliable," comments Springfields based design engineer Mark Williams.
"We especially like the robust Conet network which causes us very little trouble, and the system's ability to time-stamp at each point to a resolution of 10 milliseconds which has undoubtedly improved the plant's productivity."