Quick-fit outage hatch15 August 2011
An Indian Point team has engineered a containment hatch closure plug that takes less than 30 minutes to install
Units 2&3 of Entergy’s Indian Point Energy Centre in Buchanan, New York were two of the first Westinghouse four-loop PWRs built in the USA; they began operation in 1974 and 1976.
The US nuclear industry has recently examined outage safety, and the ability to close all openings to the outside atmosphere in the containment building. One particular issue relates to potential safety threats during shutdowns as a result of loss of shutdown cooling systems. There were nine losses of shutdown cooling in 2008, and eight in 2009, six of which were preventable, according to the Institute of Nuclear Power Operations. If the reactor coolant were allowed to boil, coolant would gradually be lost until the fuel rods were exposed, releasing radiation. In 2009, INPO recommended a number of outage practice improvements, including being able to close containment during a loss of shutdown cooling prior to the reactor coolant system boiling (SOER 09-1). In PWRs, the reactor coolant system is drained below the reactor vessel flange for head detensioning early in the outage. In this condition, if shutdown cooling were lost, boiling would occur in less than 30 minutes.
During reactor shutdowns, the Indian Point reactor containment can be opened with a 16 ft by 14 ft (4.9 m by 4.3 m) hatch to relay equipment, materials and services. This hatch—which was never designed for speed—takes four hours to close.
So station staff have devised, manufactured and tested a plug that can be fitted in less than 30 minutes. The reinforced aluminium disc slides into the containment penetration from outside, and braces against two reinforced concrete missile shield pillars. It is designed for 5 psid and has a safety factor of two. Two redundant inflatable seals (maximum 150 psi) in the edge of the disc close the one-inch (22.5 mm) clearance gap between disc and hatch sleeve.
A dedicated forklift truck carries the 6.2 ton equipment hatch closure plug close to its final position, where a team of workers push it into its final position (it rolls on integral dolly wheels). Backstops prevent it from being inserted too far inside the penetration. Workers raise and level the plug inside the penetration using two manual hydraulic jacks. Six diagonal bracing legs are extended to corners of missile block columns. An integral manifold connects to a compressed air line and inflates the seals, and enables a pressure drop test.
Early design discussions began in April 2009. Contractor Shaw began to modify the equipment hatch sleeve to accommodate the plug in January 2010. The plug was fabricated under direction of Wisconsin-based Mechanical Research & Design by a local yacht builder, and delivered to site in March 2010, after site staff had received classroom training. Plug design, stress report, fabrication and delivery cost a total of $380,000.
The plug was used successfully for the first time on 10 March 2010 during the plant’s spring outage. During the outage, it saved 106 hours of critical path time, valued at $5 million, and 1 Rem of dose.
Joe Goebel, Indian Point assistant outage manager, said:
“When compared to the existing equipment hatch this hatch plug is significantly easier to install and seal the equipment hatch penetration. It reduced, and in some cases, eliminated, human performance traps—with time pressure, distractions and other activities in the physical environment, it worked great.”
Other team members involved included senior outage scheduler Tom Odell, engineering lead CH Yeh, Steve Traditi of the dry cask team, Jack Arcate of maintenance support and Andrew Stecker of Mechanical Research & Design Inc.