Cracks in bricks might not be a traditional headline grabber but the fracturing of these particular bricks are really rather important and worrying.
Following the enforced closure of the Heysham and Hartlepool nuclear reactors by EDF Energy because of boiler problems, their Hunterston B power station, one of the 14 AGR reactors they operate, has been found to have cracks in the bricks that constitute the reactor core. That is not good news.
Hunterston B, like all of the UK nuclear fleet is old, 38 years old in fact, and had been expected by its owner to be operating well into the 2020s, this finding however has now called that expectation in to question.
Whilst the company claims there is no immediate danger from the damaged bricks, the long-term viability of the plant is open to question.
The plant had been expected to be shut down by 2011; this was subsequently extended to 2016 and before the cracked bricks, a further extension to 2023 was expected to be in the pipeline.
Reacting to the findings, Colin Weir, Hunterston B’s Station Director said:
“During the current Hunterston outage, we found two bricks with a new crack, which is what we predicted during Hunterston B’s lifetime as a result of extensive research and modelling.
“It will not affect the operation of this reactor and we also expect that a few additional cracks will occur during the next period of operation.
“The small number of cracked bricks found during routine inspection is in line with our expectations, the findings have no safety implications and are well within any limits for safe operation agreed with our regulator.”
Bricks play a crucial role in nuclear reactors, in this instance at Hunterston B, 6,000 graphite bricks constitute the ‘stack’ around the reactor core that degrade as they become increasingly exposed to radiation.
Once cracks appear, though not a sign of a critical problem, the structure can be weakened as the bricks lose weight and can become distorted and if as a result the stack shifts out of place, the essential cooling flows for the reactor core could become blocked and ultimately cause it to overheat.
Reacting to the finding the Office of Nuclear Regulation (ONR) said:
“ONR specialists will be monitoring this work closely over the next few months to inform our regulatory position in this area.”
The ONR, following lobbying by EDF Energy had already agreed to their request to increase the average weight loss limit of the bricks from 6.2% to 8% and the company in light of the latest finding is expected to push for the limit to be raised once again to 11% in order to safeguard the future of their nuclear fleet.
However John Large, a Nuclear Consultant, commented that:
“EDF has been trying to cure this problem. It’s a generic problem. You can’t confidently say that these reactors will pass a safety review.”
This latest setback to EDF Energy’s fleet comes at a time when the Heysham and Hartlepool reactors are still offline and their future restart will see output limited to between 75% and 80% of normal operating limits for at least two years. The problem boilers would then be subject to further modifications in order to enable them to get back up to full power.
Whilst the safety considerations inherent in this decision will be welcomed the increased risk of power shortages will be less celebrated. Already the absence of the plants from the network have placed significant constraints on the system, with the impending winter season and the belated and sub-optimal return of the plant, the potential for demand and supply imbalance will continue.
The thirty year old reactors Hartlepool and Heysham have a capacity of 2.3GW and alone account for 4% of peak winter demand, operating at 25% below capacity will mean that 1% of winter peak will be unavailable for the foreseeable future, a level that places the demand supply balance very much in doubt even in a nominally benign winter.
Demand and supply margins were already forecast to dip as low as 2% in winter 2015/16, but a series of unexpected closures to coal and gas plants and the nuclear shutdowns has brought these problems forward to 2014/15.
Unsurprisingly given the track record of nuclear plant problems, the restart of the reactors has already been delayed, from the end of October to the end of November and now to the end of December, returning to limited capacity operate almost 2 months through the traditional winter season.
Announcing the further delays and limited operation EDF Energy said:
“As boiler spine defects can only develop into cracks at very high temperatures, two reactors at Hartlepool and one at Heysham 1 could be returned to service at 75%-80% power to reduce the temperature to which the boiler spines are exposed”.
At the time the cracking was discovered the ONR said that whilst the likelihood a worst-case scenario emerging was “extremely low”:
“The potential worst consequences of water entering the reactor vessel is an over-pressurisation of the reactor which could result in lifting of the reactor pressure relief valves. If this was to occur co-incidentally with fuel damage then there could be a direct path to the environment and a release of radiation”
Whilst the worst case scenario may have been avoided, and a return to operation is confidently predicted, the ONR have reacted to the on-going supply constraint by granting Magnox’s 490MW Wylfa-1 nuclear power unit a generation life extension until the end of 2015 so as to help ease the coming winter’s capacity crunch.
Wylfa-1 is the UK’s oldest nuclear reactor and was due to be taken off line this winter but ONR’s decision to extend its lifetime was accompanied by the statements that:
“[Our] comprehensive assessment [of the site showed] no issues of nuclear safety significance”
However this decision merely delays Wylfa’s closure for 12 months with early defueling and decommissioning work to follow until 2024 thereafter. With almost all the existing nuclear plants operating in the UK due for closure by 2023 the backdrop of a demand and supply imbalance is unlikely to go away any time soon.
The ONR’s Deputy Chief Nuclear Inspector Mark Foy said:
“Although the periodic review will not be considered complete until the licensee has delivered an agreed programme of work to address certain areas identified for improvement, our assessment has identified no issues of nuclear safety significance that could impact power generation at Wylfa to the planned end date of December 2015, and the subsequent defueling and early decommissioning operations until 2024.”
As if the window on the nuclear industry didn’t need any more blurring, the recent green light from the EU for EDF’s Hinkley Point C new build reactor is to be investigated by the National Audit Office (NAO) as to whether it represents “value for money”.
Indeed what was seen as a critical saviour for the UKs on-going and growing demand and supply imbalance is now the subject of challenge from within, having already survived EU scrutiny.
Announcing their investigation the NAO said:
“Our work will cover the Department of Energy and Climate Change’s commercial approach to securing this deal and the proposed terms of the contract, to report to parliament on value for money and the resulting risks which the Department must manage”.
“We will also wish to identify lessons learned to inform decisions on future ‘contracts for difference’”.
A DECC spokesperson countered:
“This month the [EU] commission agreed that Hinkley represents a good deal for both bill-payers and investors. It’s perfectly ordinary for the NAO to look into large investment contracts and we will be working with them as we move closer to finalising the contract. We will not go ahead with any contract unless it is good value for money.”
It’s almost as if the industry is willing for black outs this winter.