Reply #17: That's right, they are FAR more oriented to public safety in Japan than in the US

[kristopher]

Care to discuss Davis Besse?



http://www.nrc.gov/reactors/operating/ops-experience/vessel-head-degradation/images.html

Reactor head hole
In March 2002, plant staff discovered that the boric acid that serves as the reactor coolant had leaked from cracked control rod drive mechanisms directly above the reactor and eaten through more than six inches<10> of the carbon steel reactor pressure vessel head over an area roughly the size of a football (see photo). This significant reactor head wastage left only 3/8 inch of stainless steel cladding holding back the high-pressure (~2500 psi) reactor coolant. A breach would have resulted in a loss-of-coolant accident, in which superheated, superpressurized reactor coolant could have jetted into the reactor's containment building and resulted in emergency safety procedures to protect from core damage or meltdown. Because of the location of the reactor head damage, such a jet of reactor coolant may have damaged adjacent control rod drive mechanisms, hampering or preventing reactor shut-down.As part of the system reviews following the accident, significant safety issues were identified with other critical plant components, including the following:
(1) the containment sump that allows the reactor coolant to be reclaimed and reinjected into the reactor;
(2) the high pressure injection pumps that would reinject such reclaimed reactor coolant;
(3) the emergency diesel generator system;
(4) the containment air coolers that would remove heat from the containment building;
(5) reactor coolant isolation valves; and
(6) the plant's electrical distribution system.

Under certain scenarios, a reactor rupture would have resulted in core meltdown and/or breach of containment and release of radioactive material.
http://en.wikipedia.org/wiki/Davis-Besse_Nuclear_Power_Station

Davis-Besse: One Year Later
Nearly one year ago, on March 6, 2002, workers repairing a cracked control rod drive mechanism (CRDM) nozzle at the Davis-Besse Nuclear Power Station in Ohio discovered a football-sized cavity in the reactor vessel head.1 Their finding is linked to two other discoveries 15 years earlier. On March 13, 1987, workers at Turkey Point Unit 4 in Florida discovered that a small leak of borated water had corroded the reactor vessel head. Their revelation prompted the Nuclear Regulatory Commission (NRC) to require all owners of pressurized water reactors,2including Davis-Besse, to take specific measures to protect plant equipment from boric acid corrosion. On March 24, 1987, the NRC learned that control room operators at the Peach Bottom Atomic Power Station in Pennsylvania had been discovered sleeping while on duty. That revelation prompted the NRC to issue an order on March 31st requiring Peach Bottom Unit 3 to be immediately shut down.3


The three findings spanning 15 years are intertwined....

http://www.ucsusa.org/assets/documents/nuclear_power/davis-besse_retrospective_030303db.pdf

The NRC and Nuclear Power Plant Safety in 2010
A Brighter Spotlight Needed


The crisis at the Fukushima Daiichi nuclear plant in Japan following the March 11 earthquake and tsunami is a stark reminder of the risks inherent in nuclear power. One of its consequences has been heightened concern about the safety of nuclear power facilities in the United States.

The Nuclear Regulatory Commission, the federal agency responsible for ensuring that U.S. nuclear plants are operated as safely as possible, gets mixed reviews in a March 2011 UCS report, The NRC and Nuclear Power Plant Safety in 2010: A Brighter Spotlight Needed. The report—the first of an annual series—was prepared and scheduled for release before the crisis in Japan began to unfold, but the disaster makes the report’s conclusions more timely than ever.

Authored by UCS nuclear engineer David Lochbaum, the report examines 14 “near-misses” at U.S. nuclear plants during 2010 and evaluates the NRC response in each case. The events exposed a variety of shortcomings, such as inadequate training, faulty maintenance, poor design, and failure to investigate problems thoroughly.

Since NRC inspections cannot reveal more than a fraction of the problems that exist, it is crucial for the agency to respond effectively to the problems it does find. The report offers examples of both effective and ineffective responses...

Download: The NRC and Nuclear Power Plant Safety in 2010 |
The NRC and Nuclear Power Plant Safety in 2010: Executive Summary |
Press Briefing on The NRC and Nuclear Power Plant Safety in 2010

http://ucsusa.org/nuclear_power/nuclear_power_risk/safety/nrc-and-nuclear-power-2010.html