In accordance with ONR’s Sellafield Strategy, ONR is assessing the adequacy of the systems at Sellafield Ltd (SL) that are most important to safety against the requirements of the relevant plant safety cases. ONR has implemented a 5 year rolling plan to ensure that these systems are inspected at least once during each 5 year period. The primary part of this intervention (in line with this plan) was to inspect the Thermal Oxide Reprocessing Plant (THORP) Reagent and Chemical Safety System.
ONR also carries out a programme of routine Licence Condition (LC) compliance inspections to assess the implementation of SL’s arrangements. As part of this intervention I carried out a planned inspection of THORP’s implementation of LC22 (the control of modifications or experiments on existing plant). LC22 was selected for inspection in view of the importance to nuclear safety of controlling modifications at THORP.
ONR carried out a 4 day inspection between 08 – 11 December 2014 utilising specialist inspectors from the following technical disciplines:
The scope of this inspection was to identify and sample SL’s arrangements for ensuring the robustness of claims made on the Product Purification (PP) cycle chemical and reagent safety system within the THORP safety case.
This involved reviewing the applicable safety case claims and sampling that they had been adequately implemented on the plant.
ONR assessed compliance with the following Licence Conditions (LCs) for the THORP reagent and chemical safety system using the applicable ONR inspection guidance:
I also carried out a routine licence compliance inspection to assess the adequacy of SL’s implementation of its arrangements for compliance with LC22. Amongst other duties, LC22 requires SL to make and implement adequate arrangements to control any modification or experiment on existing plant or processes that may affect safety.
In addition I held several information-sharing sessions with THORP to discuss areas of current regulatory focus:
n/a - I judge the safety system to be adequate; the issues that led to the rating of LC24 as below standard (see below) are not significant enough to imply that the THORP PP cycle reagent and chemical safety system does not adequately fulfil the requirements of the safety case.
In my assessment of licence condition compliance for the reagent and chemical safety system, I judge that compliance with LCs 10, 23 and 28 was adequate. However I considered that LC24 (Operating Instructions) deserved a rating of 4 – below standard due to the fact that although fundamental requirements are met, some specific procedural weakness along with examples of failure to follow procedures were observed. I have not raised a new Regulatory Issue (RI) however, as this is already covered by an existing RI.
I also considered that SL’s compliance with LCs 27 and 34 deserved IIS ratings of good due to the fact that in the sampled areas THORP appeared to be exceeding guidance requirements.
During the systems inspection I identified that acid quality meters associated with the PP cycle (designated by SL as Safety Related Equipment, SRE) had been degraded/unavailable for an extended period. Although SL had carried out an appropriate safety assessment, I consider that increasing the visibility of unavailable SRE may reduce the unavailability time of such equipment and so I have raised a RI for THORP to review how degraded/out of service SRE is tracked.
Although I concluded that the PP cycle reagent and chemical safety system adequately fulfils the requirements of the safety case, I observed that the safety case may not fully capture all the chemical checks across the site, such as those at the Inactive Tank Farm which contribute to ensuring the correct chemicals are delivered to THORP. As such I consider it important that SL completes the existing regulatory action requiring it to review the extant THORP safety case to ensure that the risks of importing incorrect chemicals are fully considered.
Based on my inspection in the second part of this intervention, I consider that modifications or experiments on existing plant at THORP are adequately controlled; however I did note that there may be opportunities for improvements in the clarity of the site-wide LC22 compliance arrangements, specifically in how modifications are categorised.
In regard to emergency arrangements, THORP has put into place what appears to be a comprehensive improvement plan which if effectively implemented should lead to significant improvements in THORPs overall emergency preparedness capabilities.
Following discussions with SL regarding the PP1 event in August, where process liquor was inadvertently misrouted, I have concluded that while the safety case was not challenged I consider that this event potentially represents a shortfall in compliance with LC24 – Operating Instructions. As such I will assess the significance of the event by applying ONR’s Enforcement Management Model to determine if and what further enforcement action may be appropriate and will record this in a Project Assessment Report (PAR).
I judge that, based on the sampling completed, the THORP PP reagent and chemical safety system adequately fulfils its safety case requirements.
I am satisfied that that the rating of LC24 as below standard relates to issues that are not significant enough to consider that the THORP PP reagent and chemical safety system does not adequately fulfil the requirements of the safety case.
With regards to LC22 compliance, I consider that that an IIS rating of 3 - adequate is appropriate, due to the fact that while I consider that modifications are being adequately controlled there exists some areas for improvement under ALARP.
THORP is making good progress in developing what appears to be an effective plan to improve its emergency response capability.
ONR will apply the Enforcement Management Model to determine if and what further enforcement action may be appropriate in response to the PP1 feed misrouting event.