The purpose of this intervention was to undertake a system based inspection of the post trip sequencing equipment at EDF Energy Nuclear Generation Limited's (NGL's) Torness power station in line with the planned inspection programme contained in the Torness Integrated Intervention Strategy (IIS) for 2016/17.
As part of this intervention a C&I Specialist Inspector and Electrical Specialist Inspector performed a System Based Inspection (SBI) of the post trip sequencing equipment to judge the system performance against its safety function. During the inspection, for training purposes, a second C&I Specialist Inspector and a Project Inspector assisted in the inspection. Through examination of this system and associated sub-systems we performed compliance inspections against Licence Conditions LC10 (Training), LC23 (Operating rules), LC24 (Operating instructions), LC27 (Safety mechanisms, devices and circuits) and LC28 (Examination, inspection, maintenance and testing). LC34, which relates to leakage and escape of radioactive material and radioactive waste, was not considered applicable to the post trip sequencing equipment.
From the system based inspection, we judge that overall the post trip sequencing equipment meets the requirements of the safety case.
Based on the areas sampled during this system based inspection, it was found that Torness has adequate arrangements to ensure that the post trip sequencing equipment is maintained and operated in accordance with the safety case and the station's arrangements.
In summary, the outcome of the SBI of the post trip sequencing equipment was:
We were satisfied that Torness has implemented adequate arrangements for suitable training for staff with responsibilities for the specific operation and maintenance of the post trip sequencing equipment. We gave an IIS rating of green against LC 10.
We were satisfied that the safety case conditions and limits have been identified and where necessary have been incorporated into technical specifications. We gave an IIS rating of green against LC 23.
We were satisfied that adequate operating instructions were in place to support plant operations. We gave an IIS rating of green against LC24.
We were satisfied that suitable and sufficient safety mechanisms, devices and circuits (LC27) were connected and in working order to meet the requirements of the safety case and identified operating limits and conditions.
We also observed that the post trip sequencing equipment was maintained with adequate arrangements in place to meet the requirements of LC 28 and on that basis have assigned an IIS rating of green against the LC28 element of this system based inspection. However, we identified the following two areas for improvement which do not impact on the IIS rating:
We identified that a measurement was undertaken during maintenance without clear pass / fail criteria. Station provided an explanation for this and we considered it to be a minor deficiency in compliance given the issue ONR has raised with NGL fleet-wide on procedural use and adherence of C&I maintenance. An action has been placed on Torness to amend the related work instruction so that it contains realistic pass / fail criteria.
As part of the inspection we reviewed a MITS safety system review (MSSR) of the post trip sequencing equipment. It was not clear how the evidence presented in the report supported the conclusion that “PTSE reliability was satisfactory during the review period”. This was considered to be a minor shortfall. An action has been placed on Torness to amend the specification for MSSRs to ensure that conclusions regarding the adequacy of the relevant system are fully justified.
The intervention was performed in line with ONR's guidance requirements (as described in our technical inspection guides) in the areas inspected.
In addition to the above, the nominated site inspector, supported where required by specialist inspectors, undertook follow-up inspection activities in connection with control & instrumentation and electrical issues previously identified, and with the unplanned reactor 1 trip caused by adverse weather (marine) conditions. The nominated site inspector also participated in a routine emergency arrangements review meeting.
After considering all the evidence examined during the sample inspection undertaken against LCs 10, 23, 24, 27 and 28, we considered that the requirements of the safety case have been adequately implemented at Torness, with a rating of green assigned against licence conditions 10, 23, 24, 27 and 28.
There are no findings from this inspection that could significantly undermine nuclear safety. At present, no additional regulatory action is needed over and above the planned interventions of Torness power station as set out in the Integrated Intervention Strategy, which will continue as planned.