Office for Nuclear Regulation

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Readiness Inspection for Trial Movement of Unbottled Failed Fuel from HNB to Sellafield (Alternative Failed Fuel Disposal - AFFD Project)

Executive summary

Purpose of intervention

The purpose of this intervention was to undertake Licence Condition (LC) compliance inspection at EdF Energy Nuclear Generation Ltd’s (NGL’s) Hunterston B (HNB) power station.  This was a reactive inspection under LC 22 (‘Modification or Experiment on Existing Plant’) involving NGL’s readiness to conduct a trial shipment of unbottled failed fuel from the station to Sellafield.  This inspection was performed jointly with an inspector from the Scottish Environmental Protection Agency (SEPA).

The Office for Nuclear Regulation (ONR) has been seeking a reduction in the failed fuel backlog across NGL’s Advanced Gas Cooled Reactor (AGR) fleet; particularly since the reprocessing plant for the fuel at Sellafield is due to close circa 2018.  The licensee has accordingly been involved in extensive work to address the issue and from optioneering studies has concluded that a combination of measures will be required to solve the problem.

Interventions Carried Out by ONR

Failed AGR fuel is considered to be fuel where the fuel cladding is no longer intact.  Fuel failures whilst infrequent, typically occur in only a small number of fuel pins in a given fuel element and then in only one or two fuel elements in the fuel assembly.  Currently, the fuel must be bottled in the station’s irradiated fuel dismantling facility - IFDF (to restore a secondary containment barrier during transport), prior to transfer to Sellafield for reprocessing.  Only one plant at Sellafield (the forensic examination facility) is capable of receiving and processing the bottled fuel, which creates a backlog problem.

One possible measure to address the problem is for the failed fuel to be shipped to Sellafield unbottled, since the fuel could then by-pass the forensic examination facility and pass directly to pond receipt, dismantling and reprocessing.  A trial of this route has been proposed and the licensee has carefully reviewed all its fuel failures across the AGR fleet, to identify (amongst other factors) a fuel assembly posing the lowest risk for the trial (i.e. a fuel assembly with a known small failure site).  The chosen fuel assembly for the trial is located at HNB.

Since the proposed trial poses both safety challenges and potential environmental challenges I elected to sample the arrangements in relation to the licensee’s safety case and Best Practical Means (BPM) assessment.  This inspection involved working closely with the SEPA, as part of the overall readiness of the licensee to conduct the trial (which is due to take place in early 2015).

Explanation of Judgement if Safety System Not Judged to be Adequate

No safety system inspection was undertaken, hence this is not applicable.

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

The licensee provided a useful summary of the status of all the project related safety case documentation, including confirmation that it had completed their due process.  I am broadly content with the licensee’s progress in this area but will hold further discussions with my ONR Radioactive Materials Transport (RMT) colleagues, with respect to a potential threat posed to the projected shipment date flagged by the licensee.

I sampled documents provided by the licensee which gave me confidence that the licensee has a well-established baseline for pond chemistry, activity etc. and will be conducting enhanced sampling using a well proven procedure.  The licensee’s proposals for enhanced sampling appeared sensible and comprehensive.  I was hence content with the licensee’s current operating instructions in the areas sampled.

I sampled the licensee’s three key Quality Plans relating to the failed fuel export and found these to be well written stepwise documents, with appropriate hold points and sign off requirements.  I suggested a number of minor enhancements to the documents, which the licensee readily accepted for action.  Overall I was satisfied with the management arrangements the licensee has in place for the project.

Since the project has a potential to increase radiation doses to station personnel, I paid particular attention to this area during the inspection.  The licensee addressed all my challenges to my satisfaction and has, in my view, demonstrated that any increase in dose accrual due to the trial will be minimal and that adequate processes are in place to manage and control any such additional dose accrual.  I did, however, advise the licensee on some additional defence in depth measures it could prudently take and the licensee agreed to provide further consideration to this advice.

I am satisfied that the arrangements and their implementation for LC22 are to an adequate standard and have rated this element of my inspection through the IIS as 3 (adequate).

The intervention was performed in line with ONR’s guidance requirements (as described in our technical inspection guides) in the areas inspected.

Conclusion of Intervention

From the discussions with key licensee personnel on the station and documentation sampled it is my opinion that the licensee is in a suitable state of readiness to safely undertake this trial, which ONR views as being of importance in the licensee satisfactorily managing its current backlog of failed fuel.