There are 23 nuclear power plants operating in the U.S. using the same General Electric Mark 1 reactors as the Fukushima Daiichi Unit 1 that suffered a hydrogen explosion on Saturday and then again early Monday, according to a fact sheet just released by the Nuclear Information and Resource Service, a Maryland-based nuclear power watchdog group.

This design, a General Electric Mark I, has been criticized by nuclear experts and even Nuclear Regulatory Commission staff for decades as being susceptible to explosion and containment failure.

According to NIRS, 35 of the 110 operational nuclear power reactors in the United States, are boiling water reactors (BWR). General Electric is the sole designer and manufacturer of BWRs in the United States. The BWR’s distinguishing feature is that the reactor vessel serves as the boiler for the nuclear steam supply system. The steam is generated in the reactor vessel by the controlled fissioning of enriched uranium fuel which passes directly to the turbogenerator to generate electricity.

The General Electric Mark 1 uses a smaller pressure suppression containment conceived as a cost-saving alternative to the larger reinforced concrete containments marketed by competitors.

San Onofre’s reactors are Pressurized Water Reactors (PWR) designed by Combustion Engineering. The PWRs use pressurized water as coolant instead of boiling the water directly in the containment vessel.

The reactors at Diablo Canyon, in Northern California, are also PWR’s, designed by Westinghouse.

A chilling NIRS fact sheet from 1996 essentially predicts what has happened in Japan in the last few days:

(The GE Mark I utilizes)a large inverted light-bulb-shaped steel structure called “the drywell” constructed of a steel liner and a concrete drywell shield wall enclosing the reactor vessel. The atmosphere of the drywell is connected through large diameter pipes to a large hollow doughnut-shaped pressure suppression pool called “the torus”, or wetwell, which is half-filled with water. In the event of a loss-of-coolant-accident (LOCA), steam would be released into the drywell and directed underwater in the torus where it is supposed to condense, thus suppressing a pressure buildup in the containment.

However, as early as 1972, Dr. Stephen Hanuaer, an Atomic Energy Commission safety official, recommended that the pressure suppression system be discontinued and any further designs not be accepted for construction permits. Shortly thereafter, three General Electric nuclear engineers publicly resigned their prestigious positions citing dangerous shortcomings in the GE design.

An NRC analysis of the potential failure of the Mark I under accident conditions concluded in a 1985 report that Mark I failure within the first few hours following core melt would appear rather likely.”

In 1986, Harold Denton, then the NRC’s top safety official, told an industry trade group that the “Mark I containment, especially being smaller with lower design pressure, in spite of the suppression pool, if you look at the WASH 1400 safety study, you’ll find something like a 90% probability of that containment failing.”

In order to protect the Mark I containment from a total rupture it was determined necessary to vent any high pressure buildup. As a result, an industry workgroup designed and installed the “direct torus vent system” at all Mark I reactors. Operated from the control room, the vent is a reinforced pipe installed in the torus and designed to release radioactive high pressure steam generated in a severe accident by allowing the unfiltered release directly to the atmosphere through the 300 foot vent stack.

Reactor operators now have the option by direct action to expose the public and the environment to unknown amounts of harmful radiation in order to “save containment.”

We’ve got some calls out to nuclear engineers and nuclear power watchdogs and we’ll add more details here as we get them. We’ll also be looking more closely at the design and safety of San Onofre’s reactors.

Here is the list of U.S. reactors using the GE Mark 1 design:

Reactor Location Size Year operation began

Browns Ferry 1 Decatur, AL 1065 MW 1974

Browns Ferry 2 Decatur, AL 1118 MW 1974

Browns Ferry 3 Decatur, AL 1114 MW 1976

Brunswick 1 Southport, NC 938 MW 1976

Brunswick 2 Southport, NC 900 MW 1974

Cooper Nebraska City, NE 760 MW 1974

Dresden 2 Morris, IL 867 MW 1971

Dresden 3 Morris, IL 867 MW 1971

Duane Arnold Cedar Rapids, IA 581 MW 1974

Hatch 1 Baxley, GA 876 MW 1974

Hatch 2 Baxley, GA 883 MW 1978

Fermi 2 Monroe, MI 1122 MW 1985

Hope Creek Hancocks Brdg, NJ 1061 MW 1986

Fitzpatrick Oswego, NY 852 MW 1974

Monticello Monticello, MN 572 MW 1971

Nine Mile Point 1 Oswego, NY 621 MW 1974

Oyster Creek Toms River, NJ 619 MW 1971

Peach Bottom 2 Lancaster, PA 1112 MW 1973

Peach Bottom 3 Lancaster, PA 1112 MW 1974

Pilgrim Plymouth, MA 685 MW 1972

Quad Cities 1 Moline, IL 867 MW 1972

Quad Cities 2 Moline, IL 867 MW 1972

Vermont Yankee Vernon, VT 620 MW 1973