The purpose of the intervention was to discuss and review a sample of the surveillances, inspections and tests being undertaken by EDF-NGL to support their anticipated request for consent to return to service (RTS) of Reactor 3 (R3) pre-stressed concrete pressure vessel (PCPV) at Hunterston B Power Station (HNB) following the 2015 LC30 Periodic Shutdown.
This was a technical discussion regarding the intended scope of examination, maintenance and testing being conducted on the pre-stressed concrete pressure vessel under site Licence Condition 28. Some inspections and maintenance are conducted safely with the reactor at power.
NGL’s Appointed Examiner (Apex) has planned the surveillances, inspections and tests in accordance with their Branch Instructions.
Settlement and tilt survey points, E and F, have been re-established and surveyed. These survey points allow the licensee to measure any tilt of the reactor. These points were last measured in 1985, and the initial results appear satisfactory.
The tendon load tests, anchorage inspections, metallurgical examinations and tensile tests on the tendons have been completed in advance of the outage. The results from these inspections are satisfactory.
A thorough survey to determine the available number of tendons was carried out as a result of the finding of empty ducts during a previous ONR inspection. The total number of tendons was found to be 2810, instead of 2816 as stated in the safety case. Nevertheless the PCPV has enough redundancy to accommodate this reduction.
The insufficient and poor quality of the insulation of the superheater pipework is heating local areas of the external face of the PCPV to temperatures above the Station limits. The Station has planned to improve the insulation of the pipework during this outage. The APEX will inspect these areas of the PCPV during the outage to identify the impact of these temperatures on the concrete.
A Start-Up Statement, that summarises the work, will be submitted in support of the request for consent to return the reactor to service. This follows the expected process. No adverse judgements were made.
Overall, I am content with Hunterston B arrangements for the PCPV statutory surveillances and inspections under LC28 (Examination, inspection, maintenance and testing). I consider these arrangements to be adequate (IIS Rating – 3).
I conclude from the information presented at the discussion that these statutory surveillances, inspections and tests are proceeding as normal. I believe there has been an improvement to the surveillance by re-establishing the tilt survey points.
I recommend that after installing new insulation on the superheater pipework, the temperature on the external face of the PCPV is monitored to ensure that it is within the Station limits.
A forthcoming assessment report will consider whether the inspection results are consistent with the safety case once the inspections are completed and provide a recommendation on whether to support the granting of consent.