Plant-Wide Safety Critical Systems: The Future of Plant Safety

Gary Bradshaw, Director Of Nuclear Plant Safety Specialist Omniflex, Discusses How New Plant-Wide Safety Critical Systems Improve Operator Response Times And Event Analysis Capabilities.

The nuclear business is the most tightly regulated and the one in which mission-critical safety systems are most important. Plant control systems, radioactive monitors, and critical alarms are examples of safety-critical systems that must adhere to IEC 61508 safety integrity levels (SIL).

Bradshaw provides a summary of the safety measures used in the nuclear sector in this article and talks about some of the technologies that increase security in nuclear sites.

The Risks Associated With Nuclear Plant Disasters Underline The Requirement For Safety-Critical Systems.

The nuclear industry is one with minimal risk but high consequences. Therefore, even if there is a small possibility that an industrial disaster may occur, when it does, it is terrible.

Only two nuclear plant accidents in recorded history have been rated as level 7 events by the International Nuclear Event Scale (INES). These were the Fukushima Daiichi tragedy and the Chernobyl disaster, which together forced almost 500,000 people to flee their homes.

Despite the fact that there have only been two other significant nuclear accidents in the more than 19,000 reactor years of commercial nuclear power operation worldwide, images of the Fukushima Daiichi plant’s exposed reactor exploding out of control are still fresh in many people’s minds.

After ten years, the nuclear industry’s top priority is still safety, and all new plant-wide safety systems and practices are created with that in mind.

For instance, the project Enhanced Methodologies for Advanced Nuclear System Safety (EMEANSS) seeks to lessen the dangers connected with the creation of novel nuclear energy technology.

Scientists from the UK and India are involved in the four-year study, which is being directed by Dr. Simon Middleburgh of Bangor University’s Nuclear Futures Institute. It will develop advanced safety-critical systems and models spanning important domains, such as novel fuels for nuclear power generation, using experimental data and machine learning.

The scientists want to increase overall plant safety and operating efficiency by modeling the performance of new fuels. To make sure they stay within their safe operating boundaries, it is crucial to predict how nuclear fuels will behave as they are consumed in the reactor. Nuclear fuels operate in some of the most severe environments.

The development of plant safety in the nuclear business will surely be significantly influenced by research initiatives like EMEANSS, although the industry is still heavily regulated, and engineers are frequently unwilling to adopt new technologies. For instance, despite the fact that commercial off-the-shelf (COTS) goods have several important advantages, many plant managers are hesitant to use them.

The Nuclear Business Is Subject To Strict Regulations.

Every nuclear power plant in the UK is required to adhere to stringent rules on the radiological protection systems that are used to check the ambient alpha, beta, and gamma radiation levels.

The Nuclear Decommissioning Authority (NDA), the Office of Nuclear Regulators (ONR), and the Health and Safety Executive (HSE) are responsible for establishing these rules. They are made to reduce the chance of accidents and their severe human repercussions when they do happen.

In order to identify plant managers’ safety-critical systems that must operate with or without a human operator, IEC 61508 SIL ratings are essential.

Four SILs are specified by the IEC 61508 standards, with SIL-1 being the least stringent and SIL-4 being the most stringent. Any system rated SIL-2 or higher needs to be capable of operating without a human being. Only SIL-1 is possible for safety-critical systems like local alarm annunciators, which need operators to notice abnormal status signals and take action.

However, nuclear facility control systems must be at least SIL-2 approved and must operate autonomously without operator intervention.

Safety systems, for instance, can automatically carry out safety shutdown processes and prevent tragedy even if operators ignore a high-level alarm.

Radiological Monitoring Over A Network

Nuclear facilities have historically monitored alpha, beta, and gamma levels with non-networked wall-mounted radiation protection devices.

The monitor would recognize a high-level radiation alert or an instrument failure and sound a local alarm. However, networking of radiological protection systems became the norm in order to adhere to the stringent operational criteria set forth by the industry. To accomplish this, the industry has to contend with exorbitant expenses and disruptions when installing, networking, and testing devices.

This is due to the fact that each safety-critical system for the entire facility was custom built, requiring a sizable quantity of new cabling and a qualified wireman to install and test each component of the system. It would take months to perform and approve this job, and then it would need to be done again whenever repair was needed or an instrument had to be moved to a new facility area.

It was not practical to employ conventional techniques when the National Nuclear Laboratory (NNL) was charged with installing 130 data collection points to link significant numbers of radiation safety instruments at Sellafield’s nuclear plant. It would have taken months to finish and cost a lot of money to install and cable.

Together with Steve Parkin, senior project manager at NNL, Omniflex developed the RPN1 radiation monitor interface device to address these issues.

A gateway device called the RPN1 was created to make it easier to aggregate data from different radiation protection monitors using RS485 communications ports. It links them to the SCADA system for the plant. It is a commercial off-the-shelf (COTS) solution that can be set up quickly, saving tens of thousands of man hours of labor, and does not require running kilometers of pricey power cables to each display.

Additionally, it is standardized to satisfy ISO 9001 quality standards, so no additional third-party inspections are required during installation or testing.

By installing the RPN1 throughout the Sellafield plant, NNL was able to cut expenses by over £1 million, guarantee that staff time spent in active areas was drastically reduced, and hasten the delivery and active service of the safety system. The units are designated for use on new projects scheduled over the following five years and have since been deployed on other Sellafield site developments.

The RPN1’s technological advances helped Omniflex earn the 2016 Nuclear Decommissioning Authority Innovation Award.         

How Can Radioactive Waste Be Properly Stored?

The secure storage of radioactive waste is the final aspect of nuclear plant safety to be highlighted. Different types of garbage call for various container types, as well as various sets of crucial factors that need to be watched.

Nevertheless, all nuclear waste is extremely dangerous and needs to be handled with caution regardless of kind. In severely hazardous environments, sensors and other electrical equipment in waste storage places must function for decades. They also need to have a power source that lasts for decades without requiring human intervention.

Sellafield Ltd. most recently requested that the Nuclear AMRC provide new smart sensor technologies for waste monitoring in order to enhance its capacity to keep track of the state of waste containers that are being stored for an extended period of time. The project’s main objective was to create new sensors to guarantee the long-term security of radioactive waste from the UK’s early nuclear program.

Data on the state of the trash after decades of storage are provided by the new sensor safety system. Each year, Sellafield Ltd. creates tens of thousands of nuclear waste containers, all of which need to be stored on-site. Sellafield is required to show that, throughout the course of this storage time, in situ monitoring has shown that the waste, the container, and the store are changing as anticipated.

The nuclear industry must keep innovating and creating new, plant-wide safety-critical technologies if it is to avoid high consequence mishaps in the future like Chernobyl and Fukushima Daiichi.

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