Office for Nuclear Regulation

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Graphite / Hinkley Point B

Date released
7 March 2018
Request number
201802377
Release of information under
Freedom of Information Act 2000

Information requested

I am applying under the FOI Act for the results of the fuel and control channel inspections undertaken during the outage at Hinckley B specifically

i) the number and location of cracked graphite blocks,

ii) identifying these to be a) radial, b) axial and c) keyway slot fractures or cracks,

iii) the reduction of the axial and radial residual strengths of the moderator ore as a result of the existence of cracked - a), b) and) foregoing,

iv) the results of i), ii) and iii) foregoing as found by inspection compared to the model predictions for the moderator core;

v) and if, as a result of i), ii) and iii) foregoing there has or will arise a need to revise the seismic hazard pga.

I would also like to be told if it is the intention to permit Unit B1 Hinkley Point to recommence criticality and power operation at the completion of the EDF outage and before the results of the inspection have been analysed and submitted to ONR.

Information released

Questions i) and ii):

I am applying under the FOI Act for the results of the fuel and control channel inspections undertaken during the outage at Hinckley B specifically

i) the number and location of cracked graphite blocks,

ii) identifying these to be a) radial, b) axial and c) keyway slot fractures or cracks,

ONR’s response:

The last outage to conduct inspection of graphite core at Hinkley Point B (HPB) was performed in February 2018 in Reactor 3 when 26 fuel channels were inspected.

The results of the inspection are:

The total number of observed cracked bricks in HPB Reactor 3 are:

Question iii):

I am applying under the FOI Act for the results of the fuel and control channel inspections undertaken during the outage at Hinckley B specifically the reduction of the axial and radial residual strengths of the moderator ore as a result of the existence of cracked - a), b) and) foregoing,

ONR’s response:

The residual strength of the graphite in a core with cracks is the same as that in a non-cracked core of similar age. The problem that cracked bricks present to the core is that they may allow more freedom of movement of the core structure, particularly during faults such as an earthquake. This potential behaviour is what EDF model to support their safety case. Currently the number of cracks revealed by inspection of HPB Reactor 3 has been shown to have no effect on how the core moves. The total numbers of cracks in the HPB Reactor 3 core, including those found during this inspection is determined to be: 49 axial bore cracks and 98 circumferential bore cracks.

Question iv):

I am applying under the FOI Act for the results of the fuel and control channel inspections undertaken during the outage at Hinckley B specifically the results of i), ii) and iii) foregoing as found by inspection compared to the model predictions for the moderator core;

ONR’s response:

EDF’s model predictions made prior to the outage predicted that ‘five new circumferential cracks as the most likely outcome, with a range from 1 to 10 being totally in line with expectations’.

In terms of bore initiated axial cracks ‘the most likely outcome to be one new crack, with no new doubly-cracked bricks’. In terms of keyway root cracks none have yet been observed at HPB. EDF’s model predictions prior to the outage were that the most likely outcome was that zero keyway root cracks would be observed.

Question v):

I am applying under the FOI Act for the results of the fuel and control channel inspections undertaken during the outage at Hinckley B specifically if, as a result of i), ii) and iii) foregoing there has or will arise a need to revise the seismic hazard pga.

I would also like to be told if it is the intention to permit Unit B1 Hinkley Point to recommence criticality and power operation at the completion of the EDF outage and before the results of the inspection have been analysed and submitted to ONR.

ONR’s response:

The seismic withstand requirements for the core will not be revised and must be demonstrably met by the safety case.

HPB Reactor 3 has returned to service following completion of the EDF outage. ONR has put in place arrangements at HPB and Hunterston B that all graphite core inspection results should be submitted to ONR prior to restart and that EDF must consult ONR before restarting the reactor. EDF must also produce a safety case shortly after restart justifying the full period of operation of the reactor up to its next inspection. In the case where keyway root cracking has been observed in the reactor this safety case must be produced and submitted to ONR within 60 days of restart.

Exemptions applied

N/A

PIT (Public Interest Test) if applicable

N/A