Changes to control and instrumentation (C&I) system architecture, including: -Addition of a non computerised C&I safety back up system; -Introduction of one way network communication from the protection system to lower classified systems; and -Introduction of Class 1 displays and manual controls and indications in the main control room and remote shutdown station.
Additional reactor protection system trip signals, such as: -A high neutron flux trip -A high axial offset trip -A hot leg high pressure trip -A reactor coolant pump low speed trip.
Automation of certain actions such as: – Activation of the emergency boration system in the event of a steam line break; – Isolation of pipework in the event of leaks to prevent flooding; and – Actuation of the emergency feedwater system on detection of low steam generator pressure.
Improvements to the spent fuel cooling pond, including: – Removal of several penetrations and openings in the spent fuel pool to increase the robustness of the structure – Installation of protection (such as penetration covers, secondary containments etc) to prevent leaks from spent fuel pond penetrations; – Improvements to the cooling water supply systems to the spent fuel cooling pond; and Changes to SFP fuel handling procedures.
Upgrade of the safety classification of numerous structures, systems and components (SSCs) that are important to safety including: -Parts of the C&I systems; -The primary circuit safety injection accumulators; -The Ultimate Diesel Generators (UDG); -The electrical earth system; -The actuation signals for: – Starting the UDGs; -Starting the Primary Depressurisation System (PDS); -Closing the diverse full load Main Feedwater Isolation Valves; -Actuation of the Emergency Boration System (EBS).
Other modifications that provide additional diversity, defence in depth, or other safety improvements such as -Provision of additional diversification in the electrical power supplies to key components to reduce the probability of common cause failure; -Modification of the primary circuit pipework to facilitate through life inspection; Strengthening part of the civil structure to improve protection against potential dropped loads near the reactor primary circuit; -Upgrading the heating and ventilation support systems which play an important role in cooling essential safety systems such as C&I; -Providing a diverse heating and ventilation system; -Upgrading the control systems for the main and diverse heating and ventilation systems; -Improvements to the system for detecting small steam generator tube leaks; and -Reassessment of the irradiation embrittlement surveillance scheme to take account of the effects of the heavy reflector inside the UK EPR reactor pressure vessel.
Post-Fukushima reviews: Directly as a result of the Fukushima lessons learnt review, EDF and AREVA identified five design change proposals, covering 16 resilience enhancements, that include the following: -Improved flood protection for emergency electrical supplies (both AC and DC); -Extension of the capability and autonomy of emergency electrical supplies (both AC and DC); -Identified connection points for proposed mobile diesel generators; -Addition of SFP instrumentation into the severe accident management C&I systems; -Identification of a reserve ultimate water supply: and -Delivery of water via mobile pumps for SFP make up and containment pressure control.
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