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## Incident at the Penly NPP in France

According to Handelsblatt, the German FT equivalent, EDF has admitted that a serious incident took place April 5-6 at the Penly NPP, near Dieppe.
A primary cooling pump leaked close to 100 gallons of oil, which pooled inside the containment and then caught fire around 7pm on April 5th. This resulted in an automatic reactor shutdown.
A primary cooling circuit pump(one of 4, according to EDF) then blew a seal. As the backup seals are able to withstand the 155 atmosphere pressure only briefly, it became imperative to reduce the pressure by venting some of the coolant into reservoirs inside the containment. The emergency valves for this venting failed, threatening a rupture in the primary cooling circuit.
The situation eased after some substantial leaks, starting at 600 gal/hr, falling to only 15 gal/hr before ending by 4 am April 6.

My question to the nuclear pros on this site:
Is this kind of primary pump failure not something that should be a fairly routine event, given the presence of several such pumps and can emergency valves be tested periodically just to be sure they function properly when they are needed.
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 Recognitions: Gold Member Science Advisor Do you have a link to a report? That sequence of events just doesn't sound quite right to me. There were three sets of seals in my plant and i think that French pump is similar. If i recall , that 600 gal/hr number is not much out of line for failure of single seal. It's only 10 gpm which is easily handled. And it is captured and piped into a tank that's there for that purpose. But you dont want to run very long with that failed seal. The leakage can get worse if seals overheat. And yes, all emergency equipment is tested periodically for the reason you mentioned. It would be interesting to know which valves failed.
 Admin Some news on Penly ASN - English http://www.french-nuclear-safety.fr/...enly-NPP-event http://www.french-nuclear-safety.fr/...enly-NPP-event http://www.french-nuclear-safety.fr/...enly-NPP-event IAEA - http://www-news.iaea.org/ErfView.asp...e-68bbb3af6d8c Oil fire, reactor pump leak shut down Penly Nuclear Power Plant http://www.pennenergy.com/index/powe...__reactor.html http://www.world-nuclear-news.org/RS...2_0504121.html From Handelsblatt - Französische Reaktorpanne schwerer als bisher bekannt (Reactor failure worse than previously known) http://www.handelsblatt.com/politik/...t/6536034.html

## Incident at the Penly NPP in France

The general problem with main circulation pump seals is that they are not able to withstand the primary coolant temperature and thus require constant coolant injection in between the seals to keep them cool. Loss of this injection may lead to quite large leak through the seals, if the pump does not have a specific "stand still seal system" which only few plants in the world have.

There's at least one NUREG on the generic issue, but I was unable to locate it right away - I will get back once I find it. Meanwhile - a couple of references can be found at the bottom of that page: http://www.nrc.gov/reading-rm/doc-co...9/4661857.html

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Thanks Astro.
Sounds like a bad day over there. An oil leak around noon... The motor being above the pump, an oil leak runs down onto the hot pipes (~540 degF) and smolders or burns.
Then a seal failure at 7:30PM...

 The general problem with main circulation pump seals is that they are not able to withstand the primary coolant temperature and thus require constant coolant injection in between the seals to keep them cool. Loss of this injection may lead to quite large leak through the seals, if the pump does not have a specific "stand still seal system" which only few plants in the world have.
Indeed loss of cooling wrecks them.

Our seal failures were almost always preceded by a period of unusual sensitivity of seal leakoff flow, normally something like 0.1gpm, to the temperature of that "constant coolant injection" .

So to OP - i wouldn't call seal failures "routine" . But they are not un-anticipated or particularly challenging when caught early.
They are however a real nuisance because it requires cold shutdown to repair meaning a week or two offline.
The seals themselves are rather marvels of mechanical engineering.
Their 'Achilles Heel' is dual - loss of cooling or microscopic particles in the coolant (dirt).
 There's one EPRI report containing a systematic study of MCP shaft seal failures at the US plants: http://www.osti.gov/etde/servlets/pu...8O/6675354.pdf The one report I referred to earlier ( and still haven't been able to found) went one step further in assessing ways to do away with the problem - including replacement of pumps with ones that have a mechanical (metal on metal) stand still seal, or even going the same route that BWR designers took in the late 70's by introducing wet motors in the main circulation pumps, thus completely eliminating the penetrations that require soft seals.

 Quote by jim hardy And yes, all emergency equipment is tested periodically for the reason you mentioned. It would be interesting to know which valves failed.
I am more surprised by this part:

"The emergency valves for this venting failed, threatening a rupture in the primary cooling circuit."

Valves? Plural? *All of them failed at once*?
Obviously, thy weren't properly tested for quite some time. How come?

 Quote by nikkkom "The emergency valves for this venting failed, threatening a rupture in the primary cooling circuit." Valves? Plural? *All of them failed at once*?
Yeah, apparently all at once. But they only wrote that there's a failure which prevented the valves of being opened. Not of one or more valves itself failing. Perhaps the failure wasn't at valve level, but at control level?
Similar to Fukushima Unit 1, where the IC-valves didn't fail - but the programming which controlled them.

By Handelsblatt:

 Der Zwischenfall eskalierte, als gegen 19h eine Dichtung der Pumpe platzte. [...] Die zweite und dritte Dichtung sind aber nur für den Notfall vorgesehen und können dem hohen Druck nur kurzfristig standhalten. Um ein unkontrolliertes Austreten des verseuchten Wassers zu verhindern, wird der Druck heruntergefahren. Dafür öffnet das Personal Notventile, die das Kühlwasser in Reservoirs im Reaktorgebäude ableiten. Die Lage in Penly verschärfte sich, weil die Ventile sich aufgrund einer weiteren Störung schlossen. Damit drohte ein Platzen des Primärkreislaufes, der je Pumpe 100 Kubikmeter verstrahlten Wassers enthält. The incident escalated when a pump seal ruptured at 7 pm. The second and third seal [out of three] are only provided for cases of emergency and can only withstand the pressure for a short amount of time. To prevent uncontrolled release of contaminated water, the pressure is lowered. To do this, the staff's opening emergency valves which will rerout the water into reservoirs inside the reactor building. The situation in Penly exacerbated because another failure closed the valves. This led to the threat of a rupture of the primary coolant circuit which holds 100 cubic meters of contaminated water per pump.
The translation probably sounds very stiff to native speakers. That's deliberate, I wanted to make it as accurate as possible.

 Quote by Astronuc http://www.osti.gov/bridge/servlets/purl/10191677-Lzyqbh/native/10191677.pdf
Thanks - that's the report I talked about but couldn't find.
 I may be wrong on this, but I have a vague recollection there has previously been an incident at another French plant, where they had a problem running the plant to a cold shutdown state because the letdown line had failed close, and it was therefore difficult to get borated water in. I seem to have a recollection that the letdown function might not be fully safety classified according to the French regulations. But as I said, I may be very wrong on this, so please correct me if you have more accurate information.
 There are other ways to lower PWR pressure, such as cold spray in pressurizer. Why those weren't used or did not work?

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 introducing wet motors in the main circulation pumps, thus completely eliminating the penetrations that require soft seals.
To my understanding that's how Navy plants are built. Early PWR's (eg Yankee Rowe) had same design, and probably the same pumps. It was called "canned pumps" But those six-thousand horsepower monsters on my plant would have been tough to can.

 "The emergency valves for this venting failed, threatening a rupture in the primary cooling circuit." Valves? Plural? *All of them failed at once*? Obviously, thy weren't properly tested for quite some time. How come?
I am having a hard time thinking just what 'emergency' valves one would use in that scenario.
Pressurizer sprays are the usual method of depressurization. It is conceivable that with seal failure they shut down the affected pump. With one main coolant pump shut down and both spray valves open you may not get spray flow , but that situation has to be recognized and the spray valve that comes from the idle loop closed from the control room. That's because there are scoops in two of the pump discharge lines so that velocity head pushes water up to top of pressurizer where the sprays are. On my plant the two lines shared a common showerhead inside the pressurizer. With an idle pump you can have 10% or so reverse flow, so the loop with reverse flow steals spray flow from the other one. It can steal all of it.

But spray valves are not 'emergency' equipment since they are useless without main coolant pumps runing..
Pressurizer Relief valves are last ditch depressurization method but since TMI there is reluctance to use them. We had to report every actuation of them to NRC.

That account of events, emergency equipment failing, is just not making sense to me . I suspect exaggeration there is some detail lacking and therefore await further reports.

old jim
 Recognitions: Gold Member The report as written up in the Handelsblatt was clearly not the product of someone familiar with the specifics of a nuclear plant, so it may be incomplete, even misleading, simply because the writer did not understand what was important. That said, the most recent update on Penly in Le Figaro, the leading French economic paper, is not very illuminating, with the CLIN, the semigovernmental broad based group of committees for local nuclear information, also complaining about being kept in the dark as to the accident specifics. The Handelsblatt sources may therefore be partially unofficial, which would further increase the chance of some technical misunderstanding.

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