The Office for Nuclear Regulation (ONR) undertakes all regulatory interaction with the Sellafield site licensee (Sellafield Limited, SL) against a strategy defined by ONR's Sellafield, Decommissioning, Fuel and Waste Programme. In accordance with that Strategy, a System Based Inspection (SBI) of the electrical and back-up systems within the High Level Waste Plants (HLWP) was planned and undertaken in February 2017. The purpose of this inspection was for ONR to examine whether the licensee's safety case claims in respect of this system have been adequately implemented.
This inspection comprised an examination of the electrical system within the HLWP, which transforms HV power received from the site electrical network into various low voltages that are distributed via a network of switchboards and electrical cables to plant equipment. Reliable supplies of electrical power are needed to support the Highly Active Liquor (HAL) vitrification process. The continued processing of HAL into an immobile, vitrified product is a key aspect of Sellafield's hazard and risk reduction activities.
ONR's System Based Inspection process examines evidence to determine compliance against six key licence conditions (LCs). These licence conditions (listed below) have been selected in view of their relevance to ensuring nuclear safety and in providing a structured approach to determining whether the safety case has been implemented adequately through the system being inspected.
I carried out this SBI of the HLWP Electrical System over the course of two days and carried out intelligence gathering meetings on a further additional day. I was assisted with technical support from an external consultant with expertise in the field of electrical engineering and also by a number of ONR Inspectors, including an ONR Electrical Specialist Inspector. I was also supported on this inspection by SL staff from the internal regulatory function. The inspection comprised discussions with SL staff, physical viewing and inspections of targeted Structures, Systems and Components, and reviews of SL's records and other safety documentation.
I judge the safety case supporting this system to be adequately implemented.
Based on the areas I targeted and the related evidence I examined during this inspection, I consider that SL has adequately implemented those safety case claims that relate to the HLWP Electrical System. As such, I awarded inspection ratings of Green (No Formal Action) for LCs 10, 23, 24, 27, and 28.
I have not awarded any rating for LC34 as a result of this inspection, since I judged this licence condition was not sufficiently relevant to the system under consideration.
In the course of my inspection I did not identify any significant concerns with the adequacy of the licensee's safety case for this system that would necessitate an earlier than planned assessment by ONR.
The SL personnel involved in the inspection were knowledgeable, professional and demonstrated good situational awareness throughout. I also considered the general condition of electrical equipment and associated plant rooms that I observed to be to a high standard. However, I raised one minor regulatory issue as a result of this inspection, although this does not detract from my overall inspection conclusions. This relates to redundancy and diversity considerations for an electrical supply from a switchboard, which will be followed up during ONR's future routine regulatory engagements.
I consider that SL has adequately implemented those safety case claims that relate to the HLWP Electrical System and has a good understanding and control of the physical condition of the Structures, Systems and Components reviewed during this inspection.