Ten more years for Doel's first PWRs11 May 2016
After being scheduled for shutdown in 2015, regulators have given permission for Doel’s units 1 and 2 to operate for a further ten years. The extension comes in the midst of a long-term operation plan and new financial agreements as Corrina Thomson explains.
Sited in East Flanders, near the Dutch border, Belgium's Doel plant consists of four PWRs and employs around 800 people. Doel 1 reached criticality in 1974, unit 2 in 1975. Both are 433MWe Westinghouse two-loop PWRs. Units 3 and 4 reached criticality in 1982 and 1985, respectively.
Doel 1 was shut down in February 2015 when it reached the end of its 40-year operating life. Doel 2 had been in a maintenance outage since October 2015 and was scheduled to shut down in January 2016. These actions were in accordance with Belgian nuclear phase-out legislation. In 2003, the Belgian Chamber of Deputies had passed a bill aimed at gradually phasing out the use of nuclear power in the country from 2015. The bill ordered the shutting of reactors after 40 years of operation, and banned construction of new ones. Under current Belgian law, nuclear power is to be phased out by 2025.
However, Doel 1 and 2 have now been given a reprieve that could extend their lives by another ten years. This follows a tax agreement between parent company Engie and the Belgian government signed in December 2015 and actions outlined in Electrabel's Long Term Operation (LTO) plan, which have been approved by the Belgian Federal Agency for Nuclear Control (FANC).
Engie says it has agreed taxes for the Doel 1 and 2 extension: an annual fee of €20 million per year from 2016 to 2025. It will be paid into Belgium's energy transition fund, created under a June 2015 law. This tax agreement was signed in December 2015 and is part of an overall framework for a new nuclear contribution system. It is subject to approval by the Belgian parliament.
Engie says the agreement establishes a stable legal and economic framework, so it plans to invest €700 million in Doel for the ten-year life extensions. FANC authorised the restart of Doel 1 and 2 in December 2015 after Electrabel had completed priority actions.
Electrabel had an integrated action plan which included the priority actions, plus another series of actions to be completed between three and five years after the restart. FANC says the latter actions are continuous safety improvement, whereas the priority actions are necessary to ensure proper operation of safety-related systems, structures and components immediately.
FANC said that Doel's operators had to consider, for example, whether all equipment is still sufficiently resistant to heat, radiation and humidity. The reactor vessels had to be checked to check for hydrogen 'flakes'. Similar flaws have been found at Doel 3 and Tihange 2. The inspections showed the vessels comply with safety requirements, FANC said.
FANC then approved the restart after the priority actions were complete, Electrabel submitted a status report and inspectors confirmed that the actions had been taken.
Planned actions over the next ten years include modernisation, ageing management, stress tests and planned ultrasonic inspections of refuelling water storage tanks and piping.
A FANC assessment
Some post-Fukushima stress tests had been amended or cancelled for Doel 1 and 2 because the units were expected to close.
A reassessment resulted in a number of improvement actions in terms of organisation, hardware and procedures.
Some work has already been carried out. Upcoming actions include: additional hydraulic connections and electrical cabling (2016- 2017); new mobile pumps and diesel generators (2016); seismic strengthening of the refuelling water storage tank and adding a seismic riser refill (2018 -2019); and additional valves in the primary system containment spray pipes (2017).
FANC concluded the restart and life extension would not lead to a significant change in radiological or environmental impact. As a result, it decided that no environmental impact assessment was required for public consultation.
FANC also decided it would tighten up the operating licence for the two units to anchor the safety actions into it. It added three licence conditions. Firstly, the action plan should be implemented to the schedule described in the summary report, with any deviation approved by FANC. Secondly, all priority actions described in the action plan had to be finished before the start of long-term operation. Thirdly, prior to the start of long-term operation, Doel's operators had to submit a summary report on the long-term operations for the fourth ten- yearly safety review.
Electrabel's LTO plan was updated in 2015, and is known as the LTO synthesis report. Since the original 2012 LTO plan, ageing has been given more focus through additional inspections. Electrabel is also drawing on experience gained at Tihange 1.
The action plan is based on an operating life extension of the full ten years. This period is needed to justify the investment in Doel
1 and 2, and to maintain competent staff. For the operator, it is essential that planned investments are carried out in a stable legal and economic framework.
The operator identified over 90 actions to manage ageing effects in mechanical components and systems, including inspections, fatigue analysis, improvement and planning.
Inspection encompassed reactor lids, baffle bolts, split pins, and instrumentation penetrations below the Doel 1 reactor. Visual tests were made of feed water baffle boxes, small bore piping, bolts containing 17-4PH precipitation-hardening steel and other various small components. Ultrasonic thickness measurements were taken and components, mechanical structures and fire- resistant barriers, were inspected.
Fatigue analysis is an important issue at all nuclear plants with life extensions, and Doel was no different. Some parts had reached or nearly reached the theoretically calculated limit for fatigue.
Other improvement actions included optimising maintenance programmes for mechanical components, developing a visual inspection checklist for places such as reactor buildings, the space between primary and secondary containment, and the emergency services centre. The inspection programme of pressurised bimetallic welding and penetrations is also being increased.
Statutory inspections were carried out on mechanical systems and no significant findings were established related to ageing, according to the report.
Electrical and instrumentation and control systems underwent a comprehensive inspection and upgrade programme. Operators also have to develop and implement additional maintenance activities with the aim of controlling ageing, and document the qualification of electrical instrumentation and I&C.
Higher priority was given to conducting another extensive inspection programme, in line with the inspections that were completed between 2012 and 2015. The main inspections relate to cables and connectors, boards and circuit breakers, cabinets with relays, and electric heating resistors.
Modifications and substitutions include: 380V pump motors, valves and fans; 6kV pump motors; process control components; reactor measurement instrumentation; reactor protection systems, control room systems and alarms; pneumatic and hydraulic drives; power supplies and switches; scram breakers; non-safety-related 380V-plates and switches (replacement or retrofit); and transmitters. During the period 2012 to 2015, the 6kV takeover breakers and the central fire detection system were changed.
Components in systems with safety functions are given a classification depending on their environmental conditions. These are: 1EA - qualified for accident area (reference accident); 1EB - qualified for special environmental conditions, such as high temperature and humidity, with or without exposure to radiation; and 1Ec - qualified for a mild industrial environment.
The current components can also be divided into two different groups: components for which a formal LTO synthesis report qualification exists and components without formal qualification in the synthesis report. Components with a formal synthesis report qualification had to be checked for conformity with the rules. Any non- compliance was eliminated before the restart.
Components without a formal qualification in the synthesis report, classified as 1EA and 1EB and exposed to radiation, had to demonstrate sufficient lifespan or they were replaced.
For components 1EB without exposure to radiation, and components 1Ec, a justification is prepared based on analysis, inspection and maintenance work carried out before the restart. After the restart, these components gain formal qualification based on a technical
analysis and or qualification test, or are replaced by a new component with a formal qualification. After these actions, to be completed by 2018 or 2019, the components will have a formal synthesis report qualification and comply with the requirements.
Ageing architecture is also a feature of the LTO synthesis report, and inspection plans were expanded or modified for the extension. Ongoing actions include expanding the in- service inspection programme and inspection procedures for engineering structures.
Inspections and actions in accordance with the enhanced tracking programme, such as first baseline inspections and post-repair inspections, were highlighted; so were research on appropriate remedial actions and renovation.
In the synthesis report, Electrabel said it will operate Doel 1 and 2 in an appropriate and secure manner, and in accordance with FANC requirements on continuous safety improvement.
The foundation of this approach includes the original 2012 action plan, with four chapters of basic requirements, ageing management, draft evaluations, and management of competencies, knowledge and behaviour. Also key to nuclear safety are the evaluation of stress tests in relation to long-term operation and shutdown, and actions arising from ten-yearly safety review.
Actions that stem from the experience gained in the period 2012 to 2015, for example the ultrasonic inspection of the reactor vessels, also play an important role as well as evaluation of all planned and actual actions since 2012.
Through its integrated action plan, part of which is the LTO synthesis report, Electrabel said it maintains continuous improvement. World Association of Nuclear Operators performance indicators show that Doel 1 and 2 are still among the best quarter of all nuclear power plants worldwide today.