By Walt Muskopf, RRVCH Project Manager, Ameren; and Mike Epling, Project Manager, AREVA Inc.
Replacing heavy equipment is one way utilities can extend the life and increase the reliability of their existing nuclear plants. As part of investing in its Callaway Energy Center, Ameren Missouri worked with AREVA Inc. to replace the reactor vessel closure head (RVCH) during a scheduled outage in fall 2014. The Callaway Replacement RVCH project was accomplished safely, on schedule, within budget and below radiation dose goals. AREVA and Ameren Missouri capitalized on the extensive operating experience of the many previous domestic replacement RVCH projects.
|Replacement reactor vessel closure head during fabrication at Equipos Nucleares SA in Santander, Spain.|
Evaluating the Need
Ameren Missouri made the decision to replace Callaway’s RVCH to reduce susceptibility to alloy 600 stress corrosion cracking in the original reactor vessel closure head. After a thorough operational risk avoidance evaluation, a full replacement was deemed the best path forward. Replacing the RVCH would improve pressure boundary degradation, subcomponent degradation and control rod drive mechanism (CRDM) ventilation system reliability. Callaway decided to implement an AREVA integrated head assembly (IHA) because it will save 48 hours of critical path time and 3,000 mR of dose during future refuelings.
Manufacturing Specialized Equipment
Ameren Missouri selected AREVA to manufacture, transport and install the replacement RVCH at the Callaway plant, in part, due to the company’s reputation for safely manufacturing and delivering nuclear plant components. The Callaway project had a five-year lead time for fabrication of the replacement RVCH and IHA.
AREVA manufactured the CRDMs, which control the movement and position of control rods in the reactor core, in Jeumont, France. At the same time, AREVA’s material procurement and manufacturing team in Saint-Marcel, France, provided project management and oversight of the manufacturing of the RVCH at Equipos Nucleares SA (ENSA) in Santander, Spain.
The IHA was fabricated in Richmond, Virginia. and shipped via truck to the Callaway site. Fabrication included a full trial build of the IHA. This was completed along with a full-flow CRDM ventilation system test, including mock-up CRDMs and insulation. This first-of-a-kind evolution demonstrated acceptable ventilation system performance prior to shipment, including fan flow, damper position and fan vibration. AREVA also used photogrammetry to perform a virtual fit-up of the IHA to the RVCH and the Callaway reactor vessel and reactor cavity, ensuring the components fabricated in Virginia and Spain would work together during installation in Missouri.
Transporting More Than 140 Tons of Equipment
Following completion, the new RVCH underwent a five-week journey from the manufacturing site in Santander, Spain, to its final home at Ameren Missouri’s Callaway Energy Center. The fully assembled component weighed 288,170 pounds or more than 140 tons. This posed unique challenges in shipping and transporting the RVCH on its transatlantic and river journeys.
The replacement RVCH departed the ENSA Fabrication Facility in Spain on April 22, 2014, on a freighter, arriving in New Orleans, Louisiana, on May 14. The component was transferred from the ship to a barge, which carried it on a journey up the Tombigbee, Mississippi and Missouri rivers.
When it reached the Callaway barge slip, the RVCH was offloaded using a Bigge Goldhofer, a heavy equipment transporter that transferred the component to the Callaway site. State inspections were required prior to moving the RVCH its final seven miles along state roads. That short distance required more than four hours to complete, and the RVCH arrived at the Callaway Energy Center on May 30.
However, the journey wasn’t finished. The replacement RVCH still needed to be offloaded from the Bigge Goldhofer and moved into the head assembly building to prepare for installation. AREVA’s component repair and replacement (CR&R) crew removed all the bolts from the shipping frame to facilitate the upending process, placing it in a vertical position to install the IHA. The RVCH was then successfully transferred into the head assembly building, joining the four IHA sections.
|The RVCH arrives at the Callaway Energy Center.|
Preparing for a Safe and Efficient Installation
The Callaway project included all new components for the replacement RVCH; no items were transplanted from the original to the replacement head. This allowed pre-outage installation of much of the new equipment, which saved at least 150 hours of work during the outage.
Onsite pre-outage work began in July 2014 when the AREVA/Ameren Missouri team installed two of the four IHA sections: the dome reflective insulation, CRDM magnetic jacks (coil stacks), CRDM ventilation dummy cans and digital rod position indication system sensors. Seismic spacer plates were also installed between the CRDMs to act as a “cheese plate,” a type of support structure used in other replacement RVCH projects. AREVA and Biggie Goldhofer designed the down-ending and lifting frame to interface with the CRDM seismic plates to support the installed equipment during down-ending, horizontal transport through the containment equipment hatch and upending in containment. All told, this was a first-of-a-kind process.
The remaining two sections of the IHA were thoroughly prepared for transport and installation in containment by pre-installing the more than 150 head area cables, maintenance hoists and much of the head vent line and level indication piping. Pre-outage work also included third-party review of heavy rigging documents and resolution of comments. Testing of the CRDM coil stacks and rod position indicator sensors was also conducted to minimize the risk of “infant failures.”
|The new Callaway reactor vessel closure head after installation|
Successfully Completing Installation and Restart
The replacement outage began on October 11, 2014. Callaway performed an integrated leak rate test at the beginning of the outage, after which the replacement RVCH activities commenced. Demolition of the original RVCH took place first. Extensive planning of the removal of demolition products, including the 120-ton concrete missile shield, avoided delays seen at other sites. Other best practices used in the demolition included:
- Cross-utilizing AREVA’s refueling head area maintenance crew and AREVA’s CR&R division crew to improve efficiency.
- Leaving the original rod position indicator sensors, magnetic jacks, dummy cans and lower ventilation shroud on the original RVCH during its removal from containment.
- Including dedicated scaffold builders on the pre-outage team.
- Loading waste Seavans with scaffolding or other support equipment to minimize the number of Seavans being moved to and from containment. At times, three Seavans were placed in containment to be filled with waste items.
- Using computer-aided design software to animate loading of all waste Seavans.
- Adding a former radiation protection supervisor to the team to coordinate radwaste and radiation protection interfaces. The project team also contracted with Energy Solutions to provide radiation shipping personnel and with Bartlett to provide additional radwaste and radiation protection technicians.
- Utilizing a dedicated logistical support team to coordinate movement of items from stores and the head assembly building to containment laydown. A script for each large demolition piece was created to ensure accurate communication between shifts.
- Establishing site-wide seminars to communicate the project sequence to site personnel. This included an animation of the replacement RVCH project sequence in containment.
It took 18 days to fully remove the original RVCH from containment.
Once the replacement RVCH was placed in containment, the radiation protection team established a “clean area,” including the equipment hatch. This allowed workers to access the work area through the equipment hatch in order to complete construction in containment, but in a non-contaminated area. This reduced the time required to prepare the equipment for placement of the RVCH on the reactor vessel. This was completed on November 11, 2014.
Final assembly was completed by Nov. 18, including operating temperature and pressure walk-downs. Subsequently, extensive rod movements were performed for CRDM corrosion mitigation and operational risk reduction. After only 42.5 days, Callaway returned to service on Nov. 22, ahead of the original schedule. “As low as reasonably achievable” performance was excellent, as all activities were performed for 11,595.4 mR total personnel dose. There were no significant issues during installation and no U.S. Nuclear Regulatory Commission inspection findings.
Looking to the Future
As a critical replacement, the approximately $150 million investment will ensure the continued safe and reliable operation of Ameren Missouri’s Callaway Energy Center, which is recognized as one of the safest and highest performing non-carbon producing generating centers in the United States. Installation of the new reactor vessel head represents one investment that Ameren Missouri is making on behalf of customers for cleaner air and renewable energy while upgrading outdated and aging infrastructure to create a more dependable grid. The Callaway Energy Center generates about 20 percent of the electricity supplied to Ameren Missouri’s 1.2 million customers.
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