Office for Nuclear Regulation

Sellafield WEP Feed Stream Interlocks SBI

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.  That strategy includes a number of inspection plans, within which the requirement for a System Based Inspection (SBI) at the Waste Encapsulation Plant (WEP) facility in February 2015 was identified.

The WEP facility receives a number of feed streams from Sellafield’s THORP fuel reprocessing plant. These include acidic feeds arising from fuel dissolving and treatment process and alkaline slurries from the centrifuge and scrubber systems. These slurries contain significant quantities of radioactive Carbon 14 (C14) and Iodine 129 (I129). If these feed streams are inadvertently mixed, C14 and I129 could be released in a gaseous form which would pass straight through the particulate filtration provided on the stack discharge flow and so be released directly to the atmosphere.

Hence, the purpose of this inspection was for the ONR to confirm the adequacy of implementation of the safety case made for the interlock system installed to prevent inadvertent mixing of these feeds.

As part of this SBI, we examined SL’s compliance with the following licence conditions (LCs):

Interventions Carried Out by ONR

We carried out a three-day, on-site team inspection, delivered by ONR’s WEP site inspector, one representative from the Sellafield Limited Internal Regulation, and two specialists sourced from a technical support contractor.  In our inspection we received presentations from SL experts, interviewed SL staff, inspected SL’s instructions, records and other plant documents and inspected relevant parts of the WEP facility. 

Explanation of Judgement if Safety System Not Judged to be Adequate

This Safety System was judged to be adequate.

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

The key findings of my inspection were;-

Conclusion of Intervention

The WEP feed stream interlock system is considered adequate.

I awarded IIS ratings of 3 (Adequate) against LC 23 (Operating rules), LC 27 (Safety mechanisms, devices and circuits) and LC 28 (Examination, inspection, maintenance and testing).  However, in view of the findings above, I awarded IIS ratings of 4 (Below Standard) against LC 10 (Training), LC 24 (Operating instructions) and LC 34 (Leakage and escape of radioactive material and radioactive waste).

I have raised Regulatory Issues to cover these matters which I will follow up as part of normal regulatory business.