Office for Nuclear Regulation

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WEP Gamma Monitoring and Structural Containment Systems Inspection

Executive summary

Purpose of intervention

The primary purpose of this intervention was to carry out a System Based Inspection (SBI) of the gamma monitoring and shielding system in Sellafield Ltd’s (SL’s) Waste Encapsulation Plant (WEP).  WEP grouts drums of Intermediate Level Waste arising from the reprocessing of fuel in THORP. This inspection forms part of ONR’s rolling five year programme of SBIs focussing on the systems on the Sellafield site most important to safety.

In addition, meetings were held with all four operational units covered by ONR’s Sellafield Programme Plan 1 (Plutonium Management Facilities North (PMF(N)) and South (PMF(S)), Encapsulation and Effluent plants) to gather data on SL’s major project work and Long Term Periodic Review (LTPR) submissions to inform the production of a five year intervention plan.

Interventions Carried Out by ONR

Interventions carried out by ONR were as follows:

Our inspections looked at SL’s compliance with the following Licence Conditions (LCs):

The inspections were conducted against the ONR’s Safety Assessment Principles (SAPs) and relevant Licence Condition guidance. They comprised a review of relevant safety documentation and operational records, a physical inspection of the plant and discussions with relevant facility personnel.

Explanation of Judgement if Safety System Not Judged to be Adequate

N/A.  The gamma monitors and cell civil structure were judged to be adequate.

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

There is a site-wide gamma monitor replacement programme underway, where obsolete AGM3 gamma monitors are being replaced with modern Lab Impex models.  SL advised that the WEP gamma monitor replacement programme was at the forefront of this programme and the facility upgrade is now over 90% complete.  This claim was consistent with the large number of new Lab Impex monitors which were observed on the plant. There was evidence of good practice in the setting up and use of the monitors.

Based on the sample of the civil engineering aspects of the concrete cell containment structure, the containment of the WEP cells was judged adequate. This is because of the robustness of the cell construction and that any spillages of acidic liquors or process spillage can be removed from the cell sump. Even if this removal failed and the civil containment structure was tested, there is sufficient robustness in the construction and condition of the WEP cell to meet the safety function as detailed in the safety case.

Overall we judged the safety systems we inspected to be adequate in meeting their required safety functions.  However, compliance with LC10 was rated as 4 (Below Standard) in view of the evident variability in the quality of SL’s records, together with a few examples of poor standards of work where improvements could be made. The issues revealed by our inspection were however not considered sufficient to alter our judgement that the safety system is adequate. Regulatory issues were raised to track SL’s addressing of the shortfalls.

Discussions with the Plan 1 operational units centred on a number of significant risk reduction projects currently in process, particularly in the PMF(N) facilities where projects worth approximately a hundred million pounds are scheduled to improve the B209 building ventilation, replace the obsolete electrical distribution system and undertake other risk reduction modifications to the facility. There are also a significant number of LTPR submissions with decision dates in 2015 across all four of the operating units. This information we gathered will be considered to help develop our Plan 1 programme strategy.

Conclusion of Intervention

The shielding and gamma monitoring system is adequate when considered against ONR guidance and the facility safety case.

Some minor regulatory issues were raised and these will be taken forward as part of normal regulatory business.