Three Mile Island Reactor Shuts Down Unexpectedly

From NBC News (9/20/2012):

A reactor at Three Mile Island, the site of the nation’s worst nuclear accident, shut down unexpectedly on Thursday afternoon when a coolant pump tripped and steam was released, the Nuclear Regulatory Commission told NBC News.

The system tripped when "the pump stopped operating and created a power/flow imbalance," said NRC spokesman Neil Sheehan.

The plant responded as designed and is stable with no impact on public health or safety, added NRC spokeswoman Diane Screnci.

If any radiation was in the released steam, Screnci said, it would be below detectable levels.

Exelon, the plant operator, said in a statement that "during the shutdown, steam was released into the atmosphere, creating a loud noise heard by nearby residents."

A NRC inspector based at the plant "responded to the control room immediately after the reactor trip to independently assess control room operators' response to the event and ensure safety systems were functioning as designed," Sheehan said. "He did not identify any immediate concerns with operator or equipment performance."

Plant operators were not yet sure what caused the problem.

"Once the reactor is sufficiently cooled down, plant personnel will be able to access the containment building and troubleshoot the problem," Sheehan added.

Located about 12 miles south of Harrisburg, Pa., Three Mile Island in 1979 saw a partial meltdown of one of its nuclear reactor cores. Small amounts of radiation were released into the environment when the reactor core lost cooling water, exposing the highly radioactive fuel rods.

A presidential commission later said the accident was "the result of a series of human, institutional and mechanical failures."

Several thousand people claimed they had suffered ill health effects from radiation, but their lawsuit was rejected by a federal court in 1996 with the judge concluding they had not proved their case.

Various assessments by the government and nuclear industry have concluded no radiation-related deaths or illnesses resulted from the accident.

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Photos of TMI Corium from Japan Atomic Energy Agency

JAEA published the photographs of the corium from the Reactor No.2 from the Three Mile Island nuclear accident in 1979.

Asahi Shinbun (3/7/2012) reports that the 60 samples of the TMI corium have been kept at JAEA since 1991. The samples, weighing 3 kilograms, were given to JAEA by Idaho National Laboratory as part of the international research collaboration.

According to Asahi, JAEA is planning to re-evaluate the samples as part of the basic research for decommissioning the reactors at Fukushima I Nuclear Power Plant.

Cross section of a corium sample, with the surface oxidized to show colors. Green is uranium dioxide. Brownish part is metals like zirconium, iron, nickel melted together (according to Asahi):

Cross section of a small 1-mm corium grain. Whitish color is where uranium and cladding melted and mixed (according to Asahi):

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Japan's NISA Was Asking for NRC Legal Info and Advice in April 2011 Regarding TMI

An interesting titbit from Enformable, going through the NRC document.

From: Bloom, Steven
Sent: Wednesday, April 20, 2011 8:04 AM
To: bannai-toshihirowmeti.go.jp
Cc: Foggie, Kirk; Emche, Danielle
Subject: NISA Request

Dear Bannai-san,

Below is the response I have gotten from our legal staff regarding your request on legal issues related to TMI:
Strictly speaking, as far as we know, the NRC did not take any action by rule which would deem legal and justified any responsive action taken by the TMI licensee at the time of and immediately following the 1979 accident.

However, the NRC did adopt new regulations in 10 CFR 50.54(x) and (y) to ensure that licensees would be able to take timely and necessary action even though such action would be in violation of the plant’s technical specifications, license conditions or other regulatory requirements. The final rule for these provisions is 48 FR 13966 (April 1, 1983). A copy of the SOC for the final rule is attached. Our legal view is that this regulation may be applied only when the licensee action is needed to avoid imminent radiological harm the general public, i.e., in quickly emerging situations where fast action is needed to avoid radiological harm to the general public. The staff’s practice has been more lenient, however, despite OGC’s interpretation.

If you have any questions, please let me know.

Thank you,
Steve

Steven Bloom, International Relations Specialist
International Cooperation and Assistance Branch (ICA)
301-415-2431
O-4F4
M/S 0-4E21

The original emails (scanned) is at the Enformable site.

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