Dominion sets new records30 October 2000
Dominion Energy’s North Anna 1 and Surry 1 units were refuelled during the first quarter of 2000 in outages that were scheduled back-to-back. Both outages set record low personnel radiation records.
In March 2000, North Anna power station completed a refuelling and 10-year in-service inspection outage in 27 days, 19 hours and 56 minutes, beginning on 12 March and ending on 9 April. It achieved a Dominion Energy record low personnel radiation exposure of 51.516 man-rem. The outage involved normal refuelling and maintenance activities and included a core barrel movement and lower vessel inspection. This exposure was about 40rem lower than the last two outages in the same unit. It was also 30rem lower than the previous low exposure for a North Anna outage.
No single variable was responsible for an unprecedented 37% drop from the previous low outage. The reasons for the large reduction in exposure exemplify the basic building blocks of an effective ALARA (as low as reasonably achievable) programme – lower source term, effective control of work scope and man-hours, implementation of lessons learned, and skilled and motivated workers.
Cutting dose rates
Reduction of work-area dose rates has been the focus of North Anna personnel for many years. The station continues to implement a sub-micron filtration programme to reduce the amount of corrosion products in the primary system. A tighter operating chemistry band for pH has reduced the material available for activation in the reactor core. Other efforts such as reduced cobalt, good foreign materials exclusion controls, and proactive shutdown chemistry have reduced activated materials input, while the filters maximise removal of the material that does find its way into the circuit. Strategic shielding of even lower dose-rate areas further reduced the dose rate for the workers so that on average, dose rates in the unit 1 reactor containmenthad decreased by 21% from the previous outage in 1998.
Controlling work scope does not necessarily mean eliminating work. During this outage, work scope was controlled in several ways. First, through the co-ordination of preventative maintenance, tasks such as reactor coolant pump motor and seals replacement were planned for the same pump. Snubber work was concentrated in areas that would maximise the use of shielding and scaffolding.
Secondly, work scope was controlled by systematically eliminating high dose work, without reducing safety margin. Examples are undertaking the inspection of welds in the penetration areas and safeguards building, instead of in the loop room and motor cubes. By using historical data, engineering and electrical personnel could perform motor operated valve testing from the motor control centres, instead of at the valves. Primary system check valves were satisfactorily tested using acoustic monitoring instead of the older method of disassembly and visual inspection. All of these jobs have an effect on outage exposure greater than it first appears, because less work scope leads to less scaffolding, insulation, and health physics support.
Support exposure was at a historic low this outage. Through effective control of the work scope, man-hours in the radiological control area were reduced by 16%, compared to the 1998 outage.
Reduced source term and close control of work scope were not the only causes for this successful outage exposure. Prior to the outage, personnel planned for success and post-job reviews were scanned for ways to improve every task. Tools such as the ALARA 80-Rem Outage Action Plan and the Planning Department’s outage improvement tracking system were used to capture and track many of these enhancements.
The flagship of ALARA awareness is the disassembly of the reactor head for refuelling. This job is composed of many different tasks, each with its own challenges, and it is the highest exposure job performed each outage. The crews assigned to this work have made incremental improvements to every task, outage after outage. The key to this sustained improvement is consistency within the work group. Recent years have seen a shift from a reliance on contract labour to increased use of station employees. There are several benefits to this strategy including more experience on the job, continuity in the performance of work, and a sense of ownership for the task’s success. Personnel exposure for all refuelling work declined over 25% from 1998 to 2000. It has been reduced by more than 75% since 1990. On average, repetitive job exposure dropped 28% from the previous outage.
More evidence of worker and management ALARA awareness can be seen in how jobs are planned and executed. One example is the increased use of mock-ups and prefabrication. Using these techniques, one job, pressuriser heaters cable replacement,
finished at 50% of the projected exposure. Through prefabrication and testing of the cables and ceramic insulators, the electricians and welders trained on mock-ups for most job aspects. Other mock-up activities included reactor coolant pump seals, reactor stud tensioning, and reactor head conoseals. The welding foremen and the welders performed more pre-fabrication work than in any previous outage, replacing many field welds with better-quality shop welds.
Another essential factor in ALARA awareness is close control of worker exposure, without interfering with the flow of the job. This was accomplished using a remote monitoring system (RMS). The North Anna RMS comprises telemetric digital dosimetry, an array of cameras, and audio communication in the form of radios and a hardwired communication system. It operates as a proprietary network, using telemetric dosimetry, and interfaces with a personnel radiation exposure management system. Five client personal computer workstations allow technicians remote monitoring capability from outside the radiological control area. The use of RMS allows health physics coverage with real-time data collection, without the presence of a technician in the higher dose rate areas. Levels of coverage can range from informational to full coverage of high-risk work. The benefits of the system are many, from reduced technician staffing to increased ALARA awareness for the workers.
North Anna personnel succeeded with this 51.5rem outage by following the basics of an effective ALARA programme and by developing self-motivated workers with a high ALARA awareness. This is the most difficult variable to develop, but it makes the most valuable contribution.
Surry completed its unit 1 spring refuelling outage in 23 days, 15 hours and 45 minutes, claiming a world record for a three-loop Westinghouse PWR. Exposure, at 70.151 man-rem, was a station record. Activities included normal refueling maintenance, replacing two reactor coolant pump seals, steam generator eddy current inspection on one generator, sludge lance and foreign object search and retrieval on all generators and non-destructive examination/in-service inspection activities. The exposure of 70 man-rem is 64rem below the best unit 1 outage and 8rem below the best unit 2 outage.
The reasons for success in Surry’s outage exposure mirror those at North Anna, in that all the basic parameters of an ALARA programme were implemented. The scope of work at Surry was challenging and involved a lot of detailed planning prior to the outage. Integration team meetings brought all the planning together with weekly meetings up to the outage start date to resolve emergent issues.
Pre-outage meetings focused on outage safety, scope, ALARA, and quality. Awareness was enhanced during the outage with daily newsletters and awareness boards. (North Anna also used daily outage newsletters for ALARA awareness). One board focused on daily outage exposure status and the other showed cumulative outage exposure status as a graphic. A human performance event prevention framework was brought into the pre-job briefing to identify problem areas before workeres had to enter the radiological control area to perform a task. The framework focused on task demands, work environment, individual capabilities and human nature to identify ‘error-likely’ situations and resolve issues prior to starting a task.
Source term reduction is a priority for Dominion Energy with sub-micron filtration, and effective operational and shutdown/startup chemistry programmes. The lower limit for reactor coolant activity has been reduced from 0.5 to 0.05µCi/ml prior to reactor cavity flood up. Reactor coolant piping contact dose rates continue to trend down at Surry, with a 12.3% reduction in average dose rates. Steam generator tube sheet contact dose rates were 12 rem/hr cold leg, and 10 rem/hr hot leg.
Experience and lessons learned are enhanced through resource sharing with North Anna. This exchange of personnel has been essential to the continued improvement at both stations. Personnel support is provided to each station from multiple craft areas including mechanical maintenance, welding, electrical, instrument and control, health physics, decontamination, and outage and planning.
The station uses a 90 man-rem action plan as a guideline to achieving 90 man-rem or less outages. Post-job reviews, outage critiques, operating experience reports, lessons learned, and North Anna’s post jobs and action objectives were used to develop the plan. Each major area of the outage (refuelling, steam generators, non-destructive examination/ in-service inspection) is segmented in the plan. ‘Action items’ are assigned to appropriate departments for tracking and completion. The plan provides management with an overview of action item status and is a tool to heighten interdepartmental awareness of outage item status.
The refuelling line continues to be an area with many improvements through craft involvement. Craft personnel and engineering were responsible for the approval and implementation of a new reactor cavity seal ring, which reduced installation time from 2-3 shifts to one hour and an exposure of 163 mrem. Other refuelling line improvements include eliminating the second reactor head lift for cleanliness inspection, using a new reactor head stud hoist and trolleys, and a reduction in reactor head stud cleaning. Total refuelling exposure decreased by 24% from the 1998 unit 1 outage. This continued craft effort to improve efficiency and reduce reactor disassembly and reassembly time demonstrates the personal involvement of Surry employees in the station success.
The Radiological Protection Department continues to enhance outage effectiveness by improving remote monitoring of workers. The use of telemetric dosimetry, video monitoring and audio communication has been expanded at each outage, reducing exposure. The work control centre has become a focal point of worker exposure control from outside the radiological control area. Additionally, satellite-monitoring stations have been set up in key areas such as the outage co-ordination office, ALARA office, main control room and maintenance area to allow remote monitoring of tasks of concern to each group. The operations department monitors containment sump and reactor vessel standpipe level from the main control room, so staff do not have to enter. Exposure has decreased by an average of 23% over each of the past two outages.
The engineering department successfully developed and obtained approval of risk-based in-service inspection programmes for both Surry units. These programmes allow inspections of welds in lower dose rate areas instead of high dose rate areas like loop rooms and reactor coolant pump cubicles.
Successful outage execution has a direct effect on outage exposure. This starts with outage preplanning, control of work scope and emergent work issues, reduced rework through preplanning and skilled individuals, and implementing ALARA practices from planning through execution of tasks. The elements of the ALARA programme that have been instrumental in Surry achieving a record low 70 man-rem include: an effective source-term reduction programme; a high degree of ALARA awareness and worker skill; improvement and implementation of technology; and human performance awareness and improvement.