Damage limitation at Daya Bay2 May 2014
A dedicated critical component management system established at Daya Bay and Ling Ao nuclear power plants has yielded positive results. By Liu Kai
Daya Bay Nuclear Power Operations and Management (DNMC) company was established in March 2003 and manages both the two-unit Daya Bay and four-unit Ling Ao nuclear power plants. An equipment management branch of a predecessor company was established in 1998. Today, the company's equipment management branch has six divisions:
- Nuclear island systems
- Conventional island systems
- Electrical section
- Instrumentation & control section
- Reliability-centred maintenance section
- Root cause analysis group.
In 2002, systems whose poor performance generate reactor trips were identified. At that time, the most significant systems (with number of trips attributed to them since startup in 1994) were: feedwater flow control (7), power transmission (3), nuclear instrumentation (3), motor- and turbine-driven feedwater pumps (2 each), circulating water, 48V DC power supply (2) and main steam (2).
In 2003, an equipment reliability system based on INPO AP 913 (Equipment Reliability Process Implementation) was launched.
Critical component management began to improve equipment reliability in 2004. The three components of equipment reliability analysis are prevention, detection and correction. In 2005, monitoring and failure management of critical components began. A plant health committee was established in 2006, and a policy of zero tolerance for critical component failure was declared.
By 2007, some 7000 critical components had been identified at four units. Standard procedures began to be defined, including monitoring and trend analysis, a component parameters control sheet, and as-found condition reports. A CCM ageing equipment management project group issued standard procedures in 2008.
Critical component management
At this point, definition of CCM was broadened into three categories: equipment whose failure affects safety (CCM2), and equipment whose failure affects power production either as an automatic shutdown through a trip (CCM1), or through a capacity-related forced shutdown (CCM3). These additional classifications were rolled out over all four units in 2009, and in 2010 extended to Ling Ao Phase II (Ling Ao 3&4). By 2013, more than 10,400 critical components had been identified across all six units (Table 1). The CCM system has been implemented according to the flow chart in Figure 1.
Multiple management procedures have been written for critical component management. They include a general description of CCM, guidelines for critical component identification, guidelines for writing key technical points, monitoring and trending of critical components, an overview of the responsibility of the person in charge, management of critical component spare parts, management of critical component defects, critical component maintenance optimization, and implementation, and sensitive area management.
For example, equipment defect management consists of a multiple-step process. Following a degradation failure, irrelevant defects are filtered out, and then four actions are taken. First, the defects are fixed, or the defective situation is eliminated. Second, a root cause is identified. Third, reoccurrence is prevented. Fourth, the preventive step is applied to similar equipment. Then the defect report is reviewed and closed.
The programme has been successful; CCM equipment defects across the fleet of six reactors have declined to a consistently low level over the past five years (Figure 2).