ATEX & hazardous areas T
he nuclear sector is a low risk, high consequence industry. So, while there is minimal chance of an industrial accident occurring, when one does happen, it is disastrous. To date, there have only been two nuclear plant accidents in history to be classified as a level seven event on the International Nuclear Event Scale (INES). These were the Chernobyl accident and Fukushima Daiichi accident, which saw roughly 500,000 people evacuated between them. While these are the only major nuclear accidents to have occurred in over 19,000 cumulative reactor-years of commercial nuclear power operation globally, images of the exposed reactor of the Fukushima Daiichi plant raging out of control still haunt the minds of many. A decade on, safety remains at the forefront of the agenda for the nuclear industry and all new systems and protocols for the sector are developed with that in mind. For example, the Enhanced Methodologies for Advanced Nuclear System Safety (EMEANSS) project aims to reduce the risks associated with developing new nuclear energy technologies. The four-year project brings together scientists from across the UK and India and is led by Dr Simon Middleburgh from Bangor University’s Nuclear Futures Institute. It will use experimental data and machine learning to develop sophisticated safety systems and models across key areas, such as new fuels for nuclear power generation.
By modelling the performance of new fuels, the scientists hope to improve operational efficiency and plant-wide safety. Nuclear fuels operate in some of the most extreme conditions and predicting their behaviour as they are used in the reactor is important, to ensure they remain within their safe operating parameters. While research projects like EMEANSS will undoubtedly play a key part in the evolution of plant safety in the nuclear industry, the sector remains highly regulated and engineers are often hesitant to adopt new technologies. For example, many plant managers are reluctant to adopt commercial off-the-shelf COTS products, even though they offer some key advantages.
A HIGHLY REGULATED ENVIRONMENT Every UK-based nuclear facility must follow strict regulations for the radiological protection systems used to monitor
THE FUTURE OF PLANT-WIDE SAFETY IN THE NUCLEAR INDUSTRY
No industrial sector is as highly regulated as the nuclear industry and there is none where mission-critical safety systems matter more. Safety critical systems in nuclear plants include plant control systems, radiological monitors and critical alarms, which must meet IEC 61508 safety integrity levels (SIL). Here Gary Bradshaw, director of nuclear plant safety specialist Omniflex, shares an overview of plant-wide safety systems in the nuclear industry and discusses some of the systems that are improving safety in nuclear facilities.
the levels of alpha, beta and gamma radiation in the environment. These regulations are set by the Health and Safety Executive (HSE), the Office of Nuclear Regulators (ONR) and the Nuclear Decommissioning Authority (NDA) and are designed to avoid the likelihood of accidents and minimise the major human consequences when they occur. IEC 61508 SIL ratings are crucial for this as they help plant managers identify safety critical systems that should function with or without a human operator.
In the IEC 61508 standards, four SILs are defined with SIL-1 being the least strict and SIL- 4 the most. Any system rated SIL-2 or higher must be able to act without an operator. This means systems like local alarm annunciators that require operators to acknowledge abnormal status alerts and take action can only be SIL-1 at best. However,
nuclear
facility control systems must act automatically without operator actions and, therefore, must be at least SIL-2 certified. For example, even if operators missed a high level alarm, the control system can automatically implement safety shutdown procedures regardless and avert disaster.
NETWORKED RADIOLOGICAL MONITORING Traditionally, nuclear facilities used non-networked wall- mounted radiation protection instruments to monitor alpha,
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February 2023 Instrumentation Monthly
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