Office for Nuclear Regulation

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System Based Inspection (SBI) of the TDN Reactor System, within the Magnox Reprocessing Facility of the Magnox Operating Unit, on Sellafield Ltd.'s nuclear licensed site at Sellafield, Cumbria

Executive summary

Purpose of intervention

The Office for Nuclear Regulation (ONR) undertakes all regulatory interaction with the Sellafield site licensee (Sellafield Limited (SL)) against a strategy defined by the ONR Sellafield Programme.

In accordance with that Strategy, a system based inspection (SBI) of the Thermal Denitration (TDN) reactor system within the Magnox Operating Unit was planned for June 2016. The purpose of this planned inspection was for ONR to confirm the adequacy of implementation of the licensee's safety case claims in respect of this system.

As part of each SBI, the ONR examines evidence of the adequate implementation of six pre-defined licence conditions. These licence conditions (listed below) have been selected because of their importance to nuclear safety, and are defined within the ONR's formal process for delivery of an SBI.

Interventions Carried Out by ONR

I led a two-day, on-site, SBI of the TDN reactor system within the Magnox Reprocessing facility (MRF), which is part of the Magnox OU. I was supported by an ONR chemical process specialist inspector from the Sellafield, Decommissioning, Fuel and Waste (SDFW) Programme.

The inspection comprised discussions with SL staff, plant walk downs and reviews of plant records and other documentation.

Explanation of Judgement if Safety System Not Judged to be Adequate

The TDN reactor system was judged to be adequate.

Key Findings, Inspector's Opinions and Reasons for Judgements Made

From the evidence examined during this inspection, I consider that SL has adequately implemented those claims within the facility safety case that I sampled, and which relate to the TDN reactor system.

I noted, at the time of the inspection, that the licensee was in the process of reviewing (with the intent of reducing) the safety case claims on the system inspected. I did not identify any proposed changes to the safety case claims that were of concern, and would thus merit challenge as to their rationale and/or approach to implementation.

As part of the scope of this SBI, I have considered if the safety case that is the subject of this inspection might require an ONR assessment of adequacy in a timeframe shorter than currently planned. Although the safety case documentation is structured in a manner that does not always allow efficient extraction of information by the operator, based on the evidence sampled I have no reason to recommend an early assessment of the safety case for this system.

During this inspection, it was evident that there have been a number of improvements in the operation and asset ownership of the TDN reactor system over the last two years, which, I believe, reflects the importance placed by the licensee on sustainment of Magnox Operating Programme (MOP) timescales, to which the TDN reactor system is a significant contributor.

I was unable to establish the adequacy of the licensee's response to the findings from their planned periodic inspection of a particular piece of plant equipment and related prior abnormal plant parameters. Consequently, I have raised an ONR Regulatory Issue to track the progress to completion of my request for further evidence of an appropriate close-out of their findings and the capture and implementation of learning.

I made a number of regulatory observations, all of which were accepted by SL. I also noted that the intent of the Regulatory Issue that would be raised as a result of this inspection would be to track delivery of further compliance evidence that was not available at the time of the inspection. Consequently, based on the sampled evidence, I consider that a rating of Green (no formal action) is merited for Licence Conditions 10, 23, 24, 27, 28, and 34.

Conclusion of Intervention

From the evidence sampled during this inspection, I judge that the licensee has implemented adequately the sampled claims within its safety case. Additionally, on the basis of the evidence requested and reviewed, I consider that the licensee's formal arrangements for compliance with all Licence Conditions against which I inspected are also being implemented adequately.