The Office for Nuclear Regulation has today published its assessment of the Periodic Safety Review (PSR) for two of Britain’s nuclear power stations, alongside an update of EDF Energy Nuclear Generation Ltd’s (EDF) revised graphite core safety case. Following a high level of interest in graphite core aging in AGR reactors ONR, the nuclear safety and security regulator, has taken the step to announce its conclusions As part of its robust and extensive inspection and assessment regime, ONR confirms that EDF has carried out an adequate Periodic Safety Review for the Hunterston B power station in Ayrshire and Hinkley Point B power station in Somerset. ONR has also accepted EDF’s revised graphite core safety case for both sites, but has included a number of recommendations as part of this acceptance. These significant assessments were directly relevant to our decisions in relation to the PSR. The revised safety case provides new limits and conditions of operation in response to keyway root cracking of the graphite in the core, which is an expected part of the aging process as reactors get closer to their end of life. Acceptance of the safety case is also reliant on a revised inspection and monitoring strategy. Dr Richard Savage, Chief Nuclear Inspector said: “From our extensive review of the safety case processes and procedures, we confirm that EDF has justified future operations for the period through to end of generation (currently 2023) and defueling activities to 2027. “However, ONR’s confirmation is subject to their operations being supported by a detailed understanding of the condition of the core at each reactor must undertake regular inspections and assessment of the graphite cores to demonstrate that it remains within the limits and conditions defined in the safety case.
ONR 24th Feb 2017 read more »
The UK’s Office for Nuclear Regulation (ONR) has published its assessment of the Periodic Safety Review (PSR) for Hunterston B in Ayrshire and Hinkley Point B in Somerset, alongside an update of EDF Energy Nuclear Generation’s (NGL) revised graphite core safety case. Hunterston B and Hinkley Point B are Advanced Gas-cooled Reactors (AGRs) that both started up in 1976 and are scheduled to close in 2023. In a statement on 24 February, ONR confirmed that EDF had carried out an adequate PSR for the two plants – HNB and HPB – and said it had accepted EDF’s revised graphite core safety case for both sites, but had included recommendations as part of this acceptance. The ONR said in its report the fundamental nuclear safety requirements of the graphite core are affected by the two principal ageing and degradation mechanisms affecting the HPB/HNB graphite bricks; graphite weight loss and irradiation induced dimensional change. The stresses within the graphite bricks later in life can result in cracks originating from the key-ways on the periphery of the bricks, known as key-way root cracking (KWRC). This is of nuclear safety concern because it potentially affects the functioning of the keying system of the core, which holds the bricks in alignment, the regular said. Along with the graphite weight loss, the progression of KWRC will probably determine the lifetime of the reactors, it added. A significant nuclear safety concern for operation beyond the onset of KWRC was the ability to safely shutdown the core during a seismic event. ONR said that, in addressing the concern, NGL identified and implemented a series of “reasonably practicable modifications” to the plant, such as establishing diverse shutdown capability of the core, in order to support plant life extension. Inspection will “play a crucial role in supporting the period of safe operation of the reactor in late life,” the regulator said, adding that certain improvements are necessary, such as the development of a capability to measure the condition of control rod channels. NGL should develop improved inspection and monitoring technology; in particular equipment capable of performing visual inspection and dimensional measurements of control rod channels, it said.
World Nuclear News 1st March 2017 read more »