Office for Nuclear Regulation

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Highly Active Storage Tanks (HAST) Cooling system

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.  The strategy includes planning inspections focussing on the systems on the site most important to safety.

Under these plans, an inspection of the High Active Liquor Evaporation and Storage (HALES) cooling system was planned for December 2014.  The purpose of this inspection was for the ONR to consider the adequacy of implementation of those safety claims made against the HAST (High Active Storage Tank) cooling system within the HALES facility.

Within this system based inspection, we examined evidence  of SL’s compliance with the following licence conditions (LCs):

Interventions Carried Out by ONR

We carried out a two-day, on-site team inspection, delivered by the ONR local site inspector, with support from two representatives from Sellafield Ltd Internal Regulation, two representatives from ONR Human Factors inspection team and two AMEC specialists working for ONR under contract. 

Explanation of Judgement if Safety System Not Judged to be Adequate

This Safety System was judged adequate.  This is despite my awarding of Below Standard IIS ratings for three of the Licence Conditions we inspected.  In all cases, I judged the shortfalls we saw were not significant enough to warrant rating the overall safety system as inadequate.

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

I judged, from the evidence provided, that there is a clear link between the sampled safety claims for this system and the operating documentation in use within the facility, and that relevant actions within within that operating documentation have explicitly referenced those overarching claims.  As a result, taking into consideration specific findings against each Licence Condition (LC) detailed below, I judge that the HALES cooling system fulfils its safety duties, in line with the safety case.

I judged that the plant operator we interviewed was suitably knowledgeable and competent in regard to the normal operation of the plant, but that there were shortfalls in awareness against response to changes in plant condition.  As a number of these sampled responses are claimed within the safety case, I consider that a below standard IIS rating for LC10 is therefore appropriate. 

I considered that the sampled Operating Rule for HAST temperature was not clearly defined in accordance with relevant good practice, prompting a below standard IIS rating for LC23. However, I judge that a combination of engineered alarms and operator actions would provide an effective response following any unplanned increase in temperature of the Highly Active Liquor (HAL).

Whist generally the operator instructions we sampled were coherent, concise and cohesive, there were examples found where I felt the level of detail led to a disproportionate reliance on the plant operators’ knowledge.  However, the licensee has recognised this and, in most areas, is undertaking sufficient remedial activities, and I thus consider that an adequate IIS rating is merited. 

Overall, the majority of safety mechanisms sampled were in good working order, appropriately controlled, adequately maintained and correctly identified within relevant plant operating documentation.  However, there were safety mechanisms that had not been maintained to the standard expected, with some evidence of subsequent impact on their performance.  I judged that this observed deficiency merited a below standard rating for LC27.

Maintenance and testing of the system is, based on the inspected sample, appropriate to the function and condition of the relevant component(s), and is effectively controlled and recorded.  Therefore, an adequate IIS rating of 3 (Adequate) has been recorded against LC28.

I judged that the plant areas we inspected are currently being maintained to an adequate standard, and that plant husbandry and leak management approaches ensure that, should leaks occur, they would be identified and rectified within appropriate timescales.  Therefore, an adequate IIS rating of 3 (Adequate) has been recorded against LC34.

Conclusion of Intervention

From the sample inspected, I judge that the safety case for the HALES HAST cooling system has been adequately implemented. 

With the exception of specific shortfalls in relation to LC10, LC23 and LC27 (for which related ONR Regulatory Issues have been either raised or updated to address the shortfalls identified here), the compliance with all other inspected LCs was also judged to be adequate. 

My inspection noted a number of minor observations.  These were shared with, and accepted by, the licensee during my inspection feedback.