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The pipe leak is 1/3rd of a one inch pipe. Arkansas Nuclear One, Unit 1, is shut down for refueling, but Unit 2 was apparently also shut down because this impacts common Decay Heat piping. Nuclear reactors require cooling even in shutdown. Shutdown would allow the pressure to be reduced, however. Or, it may have been belatedly been shut down because of an Inoperable Emergency Generator, or both.

The leak is .25 gallons per minute x 60 or 15 gallons (57 litres) per hour. This is a big leak, especially from a small pipe. It’s almost full flow from a small tap! “Compensatory measures are in place and include an individual posted to watch the pipe in case plugging is necessary. Repairs to the pipe will be completed once pipe is able to be drained” [When is that?]. Where are the Clintons? Have Bill or Hillary been posted to watch the pipe? Have they forgotten Arkansas? That wouldn’t make a good photo op?
Arkansas One offline 29 Sept. 2016
From US NRC “events”:
UNISOLABLE LEAK ON DECAY HEAT REMOVAL PIPING DUE TO WELD FAILURE ON A 1″ COMMON PIPE

“At 2100 CDT on 09/29/16, while in Mode 6, both trains of Decay Heat (Residual Heat Removal) were declared inoperable due to a cracked weld on a 1″ common pipe. The leak developed in a USAS B31.7, Class1 pipe at a weld upstream of pressure indication isolation valve DH-1037. The leak is not isolable from the common 8-inch Decay Heat piping and encompasses approximately 1/3 [one third] of the pipe circumference.

“At the time of discovery, the unit was in Lowered Inventory with both Loops of Decay Heat in service. Subsequently, one train of Decay Heat has been secured to reduce the likelihood of crack propagation. One Train of Decay Heat remains in service providing the function of removing Decay Heat and the other train is readily available. The leakage impacts redundant equipment required to fulfill a safety function. In the current condition, both trains are required to be operable to meet Technical Specification LCO 3.9.5, Decay Heat Removal (DHR) and Coolant Circulation-Low water Level.

“This condition is reportable per 10 CFR 50.72(b)(3)(v)(B) for any event or condition that results in a loss of Safety Function associated with the Decay Heat System (Residual Heat Removal System).

“The licensee has notified the NRC Resident Inspector.”

The leak is approximately 0.25 gallons per minute and pipe pressure is 140 psi. Compensatory measures are in place and include an individual posted to watch the pipe in case plugging is necessary. Repairs to the pipe will be completed once pipe is able to be drained.
https://web.archive.org/web/20160930211009/http://www.nrc.gov/reading-rm/doc-collections/event-status/event/2016/20160930en.html

This was not reported until the 28th, almost 2 weeks after the fact:
UNIT 2 SHUTDOWN REQUIRED BY TECHNICAL SPECIFICATIONS DUE TO INOPERABLE DIESEL GENERATOR

“On September 16, 2016, at 0036 [CDT], during a 24-hour Technical Specification (TS) endurance run, the Arkansas Nuclear One, Unit 2 (ANO-2) red train Emergency Diesel Generator (EDG) became inoperable when its inboard generator bearing failed. ANO-2 TS 3.8.1.1, ‘AC Sources’, requires an inoperable EDG to be restored to service within 14 days or actions to place the unit in a shutdown condition initiated.

“It has been determined that repair options cannot be completed within the Allowed Outage Time (AOT) due to unforeseen circumstances which evolved during recovery efforts. At 0745 [CDT], ANO-2 initiated plant shutdown due to the inability to restore the red train EDG. ANO-2 will be shutdown and cooled down to Mode 5.” The licensee informed the NRC Resident Inspectors.https://web.archive.org/web/20160930230508/http://www.nrc.gov/reading-rm/doc-collections/event-status/event/2016/20160929en.html

If you think for even a second that the new nuclear power stations will be better or safer, read about Vogtle on this same page: https://web.archive.org/web/20160930230508/http://www.nrc.gov/reading-rm/doc-collections/event-status/event/2016/20160929en.html Well, they may be safer because if the pipes and pieces don’t even fit then it will be impossible for them to even operate at all! A nuclear power station which is unable to go online is obviously the safest!

ANO 1 refueling outage start Sept 23 2016
ANO 2 planned refueling outage start Feb 25 2017
https://web.archive.org/web/20160930205954/https://www.roadtechs.com/nukeout.htm
Arkansas One Unit 1 was last at 100% power on Sept. 5th 2016. Unit 2 was listed as 100% until the last couple of days, however. http://www.nrc.gov/reading-rm/doc-collections/event-status/reactor-status/2016/

In a similar case at Davis Besse “Because the cracked weld is on the common suction line to both decay heat removal pumps, it involves at least the potential for both decay heat removal pumps being lost. Consequently, FirstEnergy declared both sets of decay heat removal inoperable pending investigation of the extent of the problem and implementation of repairs.” (UCS: http://www.ohiocitizen.org/campaigns/electric/2008/ucs_brief.pdf ) See too: http://www.nrc.gov/docs/ML0806/ML080640204.pdf

The purpose of the RHR System in MODE 6 is to remove decay heat and sensible heat from the Reactor Coolant System (RCS), as required by GDC 34, to provide mixing of borated coolant and to prevent boron stratification (Ref. 1). Heat is removed from the RCS by circulating reactor coolant through the RHR heat exchanger(s), where the heat is transferred to the Component Cooling Water System. The coolant is then returned to the RCS via the RCS cold leg(s). Operation of the RHR System for normal cooldown or decay heat removal is manually accomplished from the control room. The heat removal rate is adjusted by controlling the flow of reactor coolant and component cooling water through the RHR heat exchanger(s). Mixing of the reactor coolant is maintained by this continuous circulation of reactor coolant through the RHR System.

APPLICABLE If the reactor coolant temperature is not maintained below 200°F, SAFETY ANALYSES boiling of the reactor coolant could result. This could lead to a loss of coolant in the reactor vessel. Additionally, boiling of the reactor coolant could lead to a reduction in boron concentration in the coolant due to boron plating out on components near the areas of the boiling activity. The loss of reactor coolant and the reduction of boron concentration in the reactor coolant would eventually challenge the integrity of the fuel cladding, which is a fission product barrier. One train of the RHR System is required to be operational in MODE 6, with the water level ≥ 23 ft above the top of the reactor vessel flange, to prevent this challenge. The LCO does permit de-energizing the RHR pump for short durations, under the condition that the boron concentration is not diluted. This conditional de-energizing of the RHR pump does not result in a challenge to the fission product barrier.http://pbadupws.nrc.gov/docs/ML1434/ML14342A408.pdf

https://miningawareness.wordpress.com/2016/02/14/radioactive-groundwater-contamination-at-all-us-nuclear-power-stations-pipe-failures-endanger-nuclear-power-station-cooling-systems-environment/

https://web.archive.org/web/20160930204555/http://www.nrc.gov/reading-rm/doc-collections/event-status/reactor-status/2016/20160930ps.html
https://web.archive.org/web/20160930205030/http://www.nrc.gov/reading-rm/doc-collections/event-status/reactor-status/2016/20160929ps.html
https://web.archive.org/web/20160930205330/http://www.nrc.gov/reading-rm/doc-collections/event-status/reactor-status/2016/20160928ps.html