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.
Damage initiation and propagation in composite shells subjected to impact
Abstract The paper investigates the impact-induced damage initiation and propagation for laminated composite shells under low-velocity impact. A three-dimensional eight-node non-conforming element is described to analyze interlaminar stress distribution, and progressive failure. The damage analysis is performed by using Tsai–Wu quadratic failure criterion, Tsai’s damage modes and an additional delamination formula at all Gaussian points. The damage modes considered are matrix cracking, fiber breakage and delamination. The progressive failure is expressed by reducing stiffness of the material at all failed Gaussian points. Special attention is centered on curved laminates. Impact energy threshold for the onset of damage and transient damage size are predicted for composite shells. The analyses of the flat and curved laminates are compared for discussing their different damage mechanism. In addition, the influence of the stacking sequence, the thickness and the radius of curvature on damage behavior of composite shells are studied.