Office for Nuclear Regulation

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Sellafield, MSSS Retrievals - Permissioning Readiness Review

Executive summary

Purpose of Intervention

The Magnox Swarf Storage Silo (MSSS) is a legacy facility on the Sellafield site that was built in the 1960’s to store Intermediate Level Waste under water and is currently assessed as one of the highest risk nuclear facilities in the Nuclear Decommissioning Authority estates. In order to safely accelerate hazard and risk reduction, Sellafield Ltd (SL) has commenced a programme of work that aims to retrieve the waste from MSSS and transport it for storage in a more modern facility at the Sellafield site.

SL has constructed Silo Emptying Plant № 2 in MSSS that will be used to extract the waste . This plant is currently undergoing inactive commissioning. Silo Emptying Plant № 2 will be brought into service on Compartment 10 for active commissioning by retrieving waste from this compartment in due course. Given the safety significance of the activities, complexity and novel nature, ONR has introduced three consecutive regulatory hold points as follows:

SL declared that it is ready to proceed beyond the first hold point. The purpose of the intervention, which was undertaken on 8th and 11th July 2019, was to inspect SL’s readiness to implement its revised safety case for active commissioning of the waste retrievals ventilation system without Silo Emptying Plant № 2.

The findings of this intervention will be used to inform ONR’s regulatory decision whether to permission the release of this hold point. This intervention was also used to hold meetings to discuss a number of matters relating to Magnox Swarf Storage Silo hazard and risk reduction.

Interventions Carried Out by ONR

Licence Condition (LC) 22: ‘Modification or experiment on existing plant’ requires the licensee to make and implement adequate arrangements to control any modification or experiment carried out on any part of the existing plant or processes which may affect safety.  ONR’s Technical Inspection Guide for LC 22 contains guidance on assessing the adequacy of the arrangements and their implementation.

This inspection focussed on SL’s implementation of its LC 22 arrangements and safety case relating to the aforementioned modification. This inspection comprised discussion with licensee staff, examination of documentation and records and a plant inspection.

This readiness inspection was undertaken to confirm that SL is prepared to implement its safety case modification and to determine that sufficient progress has been made to give regulatory confidence for ONR to subsequently permission commencement of active commissioning of the compartment 10 ventilation system without Silo Emptying Plant № 2. 

Explanation of Judgement if Safety System Not Judged to be Adequate

No safety system was inspected during this intervention.

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

Operator and maintenance instructions were sampled and found to accurately include the limits and conditions identified by the safety assessment for this modification. I found that the sampled maintenance and operating instructions had completed SL due process and were quarantined awaiting safety case implementation.

ONR identified that SL’s training did not include any reference to the limits and conditions associated with the use of one item of safety related plant. Following completion of this readiness review, SL has provided a safety case training brief. SL has confirmed that the brief will be distributed to operations staff prior to implementation of the safety case modification. I am satisfied that the brief does include an explanation of the limits and conditions associated with the use of this plant. I am content that SL has demonstrated the ability to deliver this training and consider that no further regulatory action is required.

SL aims to have 80% of each shift trained in this modification prior to safety case implementation. At the time of this inspection staff training was just short of this target. SL’s internal Hazardous Activity Readiness Review (HARR) has recorded a Category A finding concerning completion of 80% of staff training. SL’s arrangements require that HARR Category A findings are completed before to safety case implementation. I have requested SL provided evidence of HARR finding closure and consider that no further regulatory action is justified.

I interviewed the operations staff and confirmed that they had received training and were knowledgeable about the limits and conditions and hazards associated with active commissioning of the waste retrievals ventilation system. These staff were also aware of the revised emergency arrangements.  

In order to ensure completion of the plant modification, I requested that SL provides a forward action plan for the completion of the post safety case implementation activities. I have raised a regulatory issue and added this requirement to it. I have identified two further actions relating to post safety case implementation activities that I have added to this regulatory issue ..

Conclusion of Intervention

On the basis of this intervention. I am satisfied that SL has provided sufficient evidence to demonstrate, subject to completion of its identified outstanding actions  that it is ready to implement this safety case modification that will allow the commencement of active commissioning of the waste retrievals ventilation system without SEP 2. For this reason, the intervention is rated as GREEN.