Saturday, May 24, 2014

Bolting For Safety at Nuclear Plants

Subtitle: The Bolts are Broken but Reactors are Safe?

[Update - 6/11/2014: Broken bolts found in 3 out of 4 cooling water pumps - see below.]

Bolts.  Again.  Nuclear reactors are safe, their proponents insist.  

"A scheduled outage for the Salem 2 nuclear plant  has been extended for an indefinite period after workers found heads of broken bolts in a key cooling pump and at the bottom of the reactor vessel."   see link   article from May 19, 2014

Salem nuclear plant is a two-reactor, pressurized water design by Westinghouse in New Jersey with the reactors starting up in 1977, and 1981.  Unit 2 is approved by NRC to run
Salem 1 and 2 Nuclear Power Plant, New Jersey
source: Nuclear Regulatory Commission
for 60 years, ending in 2040.  Here we are, 33 years into the 60 year allowable lifetime, with broken bolt heads found inside a cooling pump and at the bottom of the reactor vessel.  

Broken bolts are not a new phenomenon in nuclear plants.  Indeed, they have been recognized as a problem for decades.   A report from April, 1988, by EPRI (report EPRI NP-5769 see link) describes the bolt-failure issue.  The report was the result of a 6-year-long task force on bolts in nuclear power plants.   This report is excellent reading, for those who want to know more about nuclear power plants, their problems with something as seemingly simple as choosing a bolt and nut, and torquing them to the right amount.  As is usual with nuclear power, nothing is as simple as it seems.  Radiation weakens metal over time, resulting in stress-corrosion cracking.  Also, the bolts must resist boric acid washing.   In short, the bolts become brittle over time.  Torquing the bolts to the proper tension may be possible during a shutdown for maintenance, without popping the bolt (breaking it).  However, during the next year or 18 months of operation, the bolts may spontaneously break as the metal degrades with further bombardment by radiation.  

Salem 2 is down for what may be an extended period, while investigations are made into what bolts broke, and why, and if other bolts are also likely to break.  Broken bolts can result in many problems, some of them serious when nuclear power is the subject. 

Nuclear power:  It's not like coal, or gas, or hydroelectric.   Nuclear radiation bombards all the metal parts, weakening the metal, causing cracking, and stress-corrosion cracking.  Bolts will fail.  Joints will spring apart.  High-pressure radioactive water inside the vessels, pipes, and pumps will find the weakness and shoot out the cracks.   Small earthquakes worsen the situation, as the entire plant is jolted around, sometimes severely.  Startups and shutdowns also stress and de-stress the metal, as pressure is exerted then removed.   This has been known for decades, as the report from EPRI above shows.   

It's only a matter of time, when these reactors licensed for 60 years fall apart like a dropped egg onto concrete.  Brittle, fatigued, cracked, and metal under serious stress.  

What could possibly go wrong?  Who could possibly see this one coming?

UPDATE -  6/11/2014:  The company removed and inspected the other pumps with similar bolts and found that 3 of the 4 pumps also had bolts sheared and pieces had fallen into the pumps.  From the article linked: "PSEG Nuclear workers have found there is a complete failure of all bolts securing water-pushing impellers in three of four Salem Unit 2 reactor coolant pumps, with investigations continuing inside the last unit."   see link  -- end update

For more on nuclear reactor safety, see the articles on the Truth About Nuclear Power, at this link

Roger E. Sowell, Esq. 
Marina del Rey, California. 

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