U.S. NRC Experience with Undervoltage Trip Attachments on Reactor Trip Switchgear
An overview of the failures of reactor trip switchgear to trip soley on loss of voltage is presented. There are three types of switchgear in reactor protection systems in pressurized water reactors in the United States. The review of the failures to date and the corrective actions taken suggest that proper maintenance and surveillance testing of existing undervoltage trip attachments on reactor trip switchgear should reduce substantially the number of failures.
UNITED STATES NUCLEAR REGULATORY COMMISSION REGION II
Northern States Power Company, a Minnesota corporation, requests authorization for changes to Appendix A of the Monticello Operating License as shown on the attachments labeled Exhibits A, and B. Exhibit A describes the proposed changes, describes the reasons for the changes, and contains a significant hazards evaluation. Exhibit B is a copy of the Monticello Technical Specifications incorporating the proposed changes.
Delaminated Prestressed Concrete Dome: Investigation and Repair
A description of the discovery of the delamination of the 3‐ft (76‐m) thick concrete dome portion of a nuclear power plant containment. An investigation was made as to the causes of the delamination, the strength of the delaminated structure, and repair techniques. Repairs were made consisting of epoxy injection of cracks in the lower 2 ft (51 m) of the dome, providing radial anchors between the lower portion of the dome and the upper “cap,” the delaminated portion, which was removed and replaced with new concrete.