British Energy's bifurcation blues

22 November 2006

UK nuclear operator British Energy’s (BE’s) improved financial performance for the six months to 1 October 2006 has been overshadowed by ageing-related boiler tube cracking at two of its stations.

EBITA (earnings before interest, taxes, and amortisation) in the first half to 1 October 2006 of £481 million ($913 million) was over double the £212 million ($402 million) achieved in the comparable period the previous year. However, the total output for the period was 31.9TWh (of which 2.9TWh came from its coal-fired station at Eggborough), down from the 33.1TWh (including 2.5TWh from Eggborough) achieved in the six months to 1 October 2005.

Announcing the results, Bill Coley, CEO of BE, commented: “While our output has been disappointing in the year to date, the first six months of 2006/7 have shown an improvement in financial performance compared to the first half last year, largely due to higher achieved electricity prices.” Even though operating costs had increased in the period to £24/MWh ($45.50/MWh), he noted, the company benefited from a realised price for the half year of £35.70/MWh ($67.80/MWh), a 43% increase compared with a realised price of £25.0/MWh ($47.40/MWh) for the comparable period.

Coley said the lower output this year reflected “higher losses from planned work.” He added: “We’ve been impacted by unplanned losses in the first half of the year and of course boiler inspection repair and boiler management strategy will impact outputs significantly in the second half year.”

As part of the boiler management strategy, the four units at BE’s Hunterston B and Hinkley Point B are expected to be brought back online at 70% of full capacity, reducing output by some 5TWh/y. In addition, statutory outages will be undertaken every two years (compared with the current three-year cycle) in order to carry out boiler inspections of these units. Including the impact of 5TWh of capped contracts, BE said it had fixed price contracts in place for approximately all of its planned output for the financial year 2006/7 at an average contract price of around £44/MWh ($83.50/MWh).

Cracking: cause and cure

In a seminar on the boiler issues, Andy Spurr, formerly BE’s deputy chief nuclear officer (CNO) and now appointed chief technical officer, said that cracking in the boiler tubes at Hunterston B and Hinkley Point B is a result of ‘creep’, which is a phenomenon that affects thermal power stations that operate at high temperatures and pressures. All four units at Hunterston B and Hinkley Point B have over 200,000 operating hours each – more than any of BE’s other AGR units. However, the particular component most vulnerable to cracking – called the ‘bifurcation’ – was redesigned at Heysham and Torness, so this issue is only of major concern at the Hunterston B and Hinkley Point B stations. Spurr noted that there have been more leaks in these four units than in the other ten of BE’s AGR units combined.

The AGR reactor core is surrounded by 12 boilers, which are contained in the steel-lined concrete pressure vessel. The bifurcations (528 per reactor) are located at the top of the boiler where access is restricted. Inspections of the bifurcations have been carried out since 1993, when the first leak occurred as a result of cracking. Since then, there have been some 20 leaks, though none have been serious enough to cause water ingress to the gas circulators.

Eddy current testing of the bifurcations is performed to determine the size and location of the cracks. The typical growth rate for cracks is about 0.1-0.2mm/y, though Spurr said that as much as 1mm/y has been observed. Spurr said that the vast majority of cracks are too insignificant to warrant repair and the rest are treated using one of four options:

  • Remelt affected area.
  • Replace the bifurcation.
  • Internal plugging.
  • External plugging.
The chosen option depends on the particular crack and bifurcation. Spurr said that plugging is not an attractive option because it can lead to the degradation of the boiler’s surface area. However, each boiler can accommodate “quite a lot of plugging” before there is any reduction in output. Asked whether replacement of the boilers was an option, Spurr said it was highly unlikely as it would be “practically, very, very difficult to execute.”

In order to reduce creep, BE has decided to reduce the operating temperature of the four units, an effective downrating to 70%. Operating at 450ºC, down from the full load temperature of 505ºC, should reduce creep by a factor of around 25. This is enough to effectively halt the progression of the cracking, allowing the company decide on a future operating strategy that balances output with ageing-related effects.

“Operating at 70% power relieves the thermal stress that drives tube cracking,” said Coley. “We will also be taking a look at the power level at which we would operate those units in the future. And it would be strictly an economic decision. For example, you can operate at higher loads and have a higher level of cracking and more frequent repairs or you can operate at a lower load and have a lower level of thermal stress on the tubes and fewer repairs. It’s strictly an economic decision.”

Coley added that the reduced two-year inspection period was also an interim measure. “We would hope that in the future, that as we get our baseline on these boilers and develop our strategy, that would move back to a three-year inspection,” he said.

Return to service

Inspections of 100% of the bifurcations have been completed at Hunterston B1 and BE said it hoped to return the unit to service (at 70% capacity) by the end of December. Further repairs are to be completed during a planned outage in the 2007/8 financial year.

Inspections are currently underway at Hunterston B2 and also at Hinkley Point B1. The latter is expected to be back online by the end of December, with Hunterston B2 returning to service by end January 2007.

For the remaining unit, Hinkley Point B2, inspections are planned for December 2006. Subject to the nature and extent of repair work to be carried out, the company expects the unit to return to service by the end of January 2007.

BE said it would be “prudent” to assume that the units will run at 70% of full capacity up to 31 March 2008, while the company develops a long-term boiler management programme. BE is due to make a decision on whether to extend the accounting lifetimes of both Hinkley Point B and Hunterston B by this date. Both stations are currently due for closure in 2011.

Roy Anderson leaves BE

Coley also announced that the company was being restructured in line with managing the AGRs of similar design. He said it now made sense to have three regional chief nuclear officers (CNOs) instead of one. “For example Hinkley Point and Hunterston are of similar design – they have the same closure dates and they also are candidates for life extension. By consolidating those two plants under one chief nuclear officer, we believe we are putting them in the position that they can focus on boiler issues, life extension, and maximise the value of the assets.” As a result, Roy Anderson has stepped down as the company’s CNO as of 17 November and three regional CNOs and a chief technical officer (Andy Spurr) have been appointed. The regional CNOs are Chris Bakken (responsible for Hunterson B, Hinkley Point B, Dungeness B); Matt Sykes (Hartlepool, Heysham1, new build technical); and Peter Prozesky (Sizewell B, Heysham 2, Torness).

Coley said that Anderson’s departure was a “joint decision with the company.” He noted that Anderson has “fundamentally completed his charge with the company. He agreed to come with us in a turnaround and I think he has done admirably well in satisfying his obligation to the company.”

Other stations

Meanwhile, both units at Hartlepool are expected to return to service in December. Repair work at the station is currently underway following a leak discovered in October in an underground cast iron pipe in the cooling water systems. And both units at Dungeness B are expected to remain offline until sometime in the next financial year as a result of issues with the operation of its fuel route “which relate to the original construction of certain components of the fuel assembly.”

However, there was good news for BE’s PWR unit, Sizewell B. The reactor achieved a continuous run of 471 days breaker to breaker. Following its largest ever statutory outage, which included replacement of the reactor vessel head and upgrade of the refuelling machine, the reactor returned to service at full power six days ahead of schedule on 21 October. Coley said that Sizewell’s operating record over the past 12-18 months “places the station among the very best pressurised water reactors, well into the first quartile in worldwide performance,” when compared with the World Association of Nuclear Operators’ performance indicators.

Investment in plant was £138 million ($262 million) for the half year, up from £102 million ($194 million) in the same period last year. As well as the Sizewell B outage, this figure includes replacement of the data processing system at Dungeness B, and cast iron pipe replacement work at Hinkley Point B and Hunterston B as part of the company’s cast iron replacement programme.




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