In a typical pressurized water reactor commercial nuclear plant, a number of components such as CRDMs, a lift rig to lift the Reactor Vessel Closure Head (RVCH), seismic restraints, missile shield, and a cooling system with large air ducts are installed on or directly over the RVCH. These components and systems are typically designed and installed individually to perform designated functions during plant operation.
During refueling outages the removal of the RVCH from the pressure vessel and its subsequent re-installation on the pressure vessel for fuel loading requires individual dismantling and reassembly of these components resulting in an expensive and time-consuming process. Prior to detensioning the RVCH from the vessel, a lengthy series of steps or detailed procedures must be followed to safely remove the head area components and to store them in their designated spaces inside containment. The procedure generally includes: removal and storage of the concrete missile shield; removal and storage of CRDM cooling ducts; removal of seismic restraints; removal of head area cables; installation of the tripod assembly over the service structure; disconnecting the vent and level indicator lines; and installation of temporary lead blankets around the RVCH. Once the refueling is complete, these procedural steps are repeated in reverse order.
Each procedure in the refueling process contributes significantly to the total cost associated with personnel time required to perform the refueling, power plant down time and consequent loss of electricity production, radiation exposure to personnel, and risks and costs associated with potential human errors. In addition, these components require a large amount of storage space inside containment raising the risk of having inadvertent contamination of work and storage areas.
To reduce the outage duration and the associated radiation exposure to the workers, the authors have designed an Integrated Head Assembly (IHA) for Callaway nuclear plant based on Mr. Baliga’s patented design as disclosed in U.S. Patents. The IHA is an assembly of all head area components integrally attached to the RVCH so that all these components can be lifted with the RVCH in one assembly (see Figure 1). The IHA also provides a forced air convection system that improves the efficiency of the CRDM cooling. The IHA reduces a significant amount of critical path time and radiation dosage during refueling outages.
Mr. Baliga’s invention has been implemented at several commercial nuclear plants in the USA (Turkey Point Units 3 and 4; Salem Units 1 and 2; DC Cook Units 1 and 2; Diablo Canyon Units 1 and 2; Davis Besse Unit 1; and Callaway Unit 1). This paper provides details of the IHA design implemented at Callaway nuclear plant in the USA.
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