Three Mile Island

1. Three Mile Island • Perhaps the most famous nuclear accident in the US • On March 16, 1979, the movie China Syndrome, based on the effect described in the last slide, was released. • 12 days later, March 28, 1979, the worst civilian nuclear accident in the US occurred at the Three Mile Island NPP on the Susquehanna River, south of Harrisburg, PA occurred.

2. Location

3. The accident • Partial core meltdown as the result of a LOCA • Main feedwater pumps failed, triggered a controlled shutdown (scram). • But the decay heat continued, with nothing to remove it • Auxiliary systems could not pump water, as their valves had been closed for maintenance (which was a violation of NRC regulations) • Pressure built up, which was released by a PORV (Pilot-operated relief valve) which opened automatically, but failed to close. This allowed coolant water to escape.

4. The accident • Plant operators had a control light that only indicated if power was applied to the valve, not if it were open or closed. The light went out when the power was cut, the operators did not know this did not mean the valve was closed. Bad design. • However, there were other instruments that told the operators something was wrong, in fact that suggested the valve was still open, but the light was out! Bad operators. • As pressure was lost, some of the coolant turned to steam and formed steam pockets (remember the high pressure is used to keep the coolant liquid at high T). This caused the coolant level in the pressurizer to look higher than it was, and the operators turned off the emergency core pumps which came on after the initial pressure loss.

5. The accident (Con’t) The tank that collected the discharge from the PORV overfilled and the sump pump in the containment building filled and sounded an alarm. This, plus abnormally high PORV T and higher than normal containment building Temperature and Pressure readings were ignored by the operators. A failure in the quench tank caused radioactive coolant to be pumped into a building outside the containment building.

6. Accident con’t • Steam bubbles in the cooling pumps caused them to cavitate and need to be shut down, with the operators believing the coolant would circulate naturally. It did not (they did not know there were steam cavities that blocked the water flow). • The top of the reactor became exposed and the steam reacted with the zirconium cladding on the fuel rods and damaged the fuel pellets, releasing more radioactivity into the coolant water. • Plant had become seriously contaminated, but it wasn’t until 165 minutes after it all began that contaminated water reached radioactivity detectors and the alarms went off. • At this point a new shift of operators came on, who noticed a problem and shut off the coolant venting via the faulty PORV valve. • Several hours later, new water was pumped into the primary cooling loop, and a backup valve was opened to relieve the pressure so the loop would fill up. Around 2pm an explosion rocked the containment building. This explosion was the result of H released when the zirconium cladding was burned off of the fuel rods. 16 hours after the start, the primary coolant loop was operating the core T began to fall.

7. Another illustration of the accident site

8. Effects of TMI • Amount of radiation released is debated, the containment building held. • Official figures indicate a small amount of radioactivity was released. • Independent measures claim radiation of 3-5 times higher than normal were detected hundreds of miles downwind of the plant. • Long term health effects on residents are hotly debated. • The valve had failed in the open position 9 previous times, and 2 other times in the closed position. • It had also previously failed at another plant. The valve company never notified its customers of the previous failure.

9. Other accidents-1980s • March 13, 1980 –- Orléans, France - Nuclear materials leak • A brief power excursion in Reactor A2 led to a rupture of fuel bundles and a minor release (8 x 1010 Bq) of nuclear materials at the Saint-Laurent NPP. The reactor was repaired and continued operation until its decommissioning in 1992. • March, 1981 - Tsuruga, Japan – Overexposure of workers • More than 100 workers were exposed up to 155 mrem/day during repairs of a NPP, violating the company's limit of 100 mrem (1 mSv) per day. • September 23, 1983 Buenos Aires, Argentina - Accidental criticality • An operator error during a fuel plate reconfiguration in an experimental test reactor led to an excursion of 3×1017 fissions at the RA-2 facility. The operator absorbed 2000 rad (20 Gy) of gamma and 1700 rad (17 Gy) of neutron radiation which killed him two days later. Another 17 people outside of the reactor room absorbed doses ranging from 35 rad (0.35 Gy) to less than 1 rad (0.01 Gy).

10. Other accidents-1980s (Con’t) • April 26, 1986 — Prypiat, Ukraine (then USSR) - Power excursion, explosion, complete meltdown • A mishandled reactor safety test led to an uncontrolled power excursion, causing a severe steam explosion, meltdown and release of radioactive material at the Chernobyl nuclear power plant located approximately 100 km north-northwest of Kiev. • May 4, 1986 – Hamm-Uentrop, West Germany - Fuel damage • A spherical fuel pebble became lodged in the pipe used to deliver fuel elements to the reactor at an experimental 300-MW THTR-300 HTGR. Attempts by an operator to dislodge the fuel pebble damaged its cladding, releasing radiation detectable up to 2 km from the reactor. • November 24, 1989 — Greifswald, East Germany - Fuel damaged • Operators disabled three of six cooling pumps to test emergency shutoffs. Instead of the expected automatic shutdown a fourth pump failed causing excessive heating which damaged 10 fuel rods. The accident was attributed to sticky relay contacts.

11. Other Accidents 1990s • April 6, 1993 — Tomsk, Russia – Explosion • A pressure buildup led to an explosive mechanical failure in a 34 m3 stainless steel reaction vessel buried in a concrete bunker under building 201 of the radiochemical works at the Tomsk-7 Siberian Chemical Enterprise Pu reprocessing facility. The vessel contained a mixture of concentrated nitric acid, U (8757 kg), Pu (449 g) along with a mixture of radioactive and organic waste from a prior extraction cycle. The explosion dislodged the concrete lid of the bunker and blew a large hole in the roof of the building, releasing approximately 6 GBq of Pu 239 and 30 TBq of various other radionuclides into the environment. The contamination plume extended 28 km NE of building 201, 20 km beyond the facility property. The small village of Georgievka (pop. 200) was at the end of the fallout plume, but no fatalities, illnesses or injuries were reported. The accident exposed 160 on-site workers and almost two thousand cleanup workers to total doses of up to 50 mSv (the threshold limit for radiation workers is 100 mSv per 5 years)

12. Other Accidents 1990s (con’t) • June, 1999 - Ishikawa Prefecture, Japan - Control rod malfunction • Operators attempting to insert one CR during an inspection neglected procedure and instead withdrew three causing a 15 minute uncontrolled sustained reaction at the number 1 reactor of Shika NPP. The Hokuriku Electric Company did not report this incident and falsified records, covering it up until March, 2007. • Sept 30, 1999 — INES Level 4 - Ibaraki, Japan - criticality Accident • Workers put uranyl nitrate solution containing about 16.6 kg of U, which exceeded the critical mass, into a precipitation tank at a U reprocessing facility in Tokai-mura Japan. The tank was not designed to dissolve this type of solution and was not configured to prevent eventual criticality. Three workers were exposed to (neutron) radiation doses in excess of allowable limits. Two of these workers died. 116 other workers received lesser doses of 1 mSv or greater though not in excess of the allowable limit.

13. Other accidents -2000s • April 10, 2003 - Paks, Hungary - Fuel damaged • Partially spent fuel rods undergoing cleaning in a tank of heavy water ruptured and spilled fuel pellets at Paks NPP. It is suspected that inadequate cooling of the rods during the cleaning process combined with a sudden influx of cold water thermally shocked fuel rods causing them to split. Boric acid was added to the tank to prevent the loose fuel pellets from achieving criticality. Ammonia and hydrazine were also added to absorb iodine-131. • April 19, 2005 — Sellafield, England, UK - Nuclear material leak • 20 tons of U and 160 kg of Pu dissolved in 83,000 L of nitric acid leaked over several months from a cracked pipe into a SS sump chamber at the Thorp nuclear fuel reprocessing plant. The partially processed spent fuel was drained into holding tanks outside the plant.

14. Other accidents -2000s (con’t) • November 2005 — Braidwood, Illinois, US - Nuclear material leak • Tritium contamination of groundwater was discovered at Exelon's Braidwood station. Groundwater off site remains within safe drinking standards though the NRC is requiring the plant to correct any problems related to the release. • March 6, 2006 — Erwin, Tennessee, US - Nuclear material leak • Thirty-five liters of a highly enriched uranium solution leaked during transfer into a lab at Nuclear Fuel Services Erwin Plant. The incident caused a seven-month shutdown and a required public hearing on the licensing of the plant. • March 11, 2011 – Fukushima - Japan