Incident at the Penly NPP in France

rmattila

The pump seal system for the new EPR reactor is presented in this document, on pages 16-17. The reactors at Penly are of the 1300 MWe type, i.e. third-latest of the French reactor generations, and have a somewhat different pump design. The basic principles are however more orless similar, with the exception of the SSSS which does not exist in the older designs.

tsutsuji

What is the next countermeasure one takes if all the seals go wrong ? Are there no valves that can be closed to close the loop and isolate the pump ?

rmattila

The leakage return lines between each seal can be closed, but of course there is always the top seal, above which the water will escape. The purpose of the stand still seal system in the new plants is to make the top seal mechanically tight and able to withstand harsh conditions (metal on metal). In those plants where all seals are soft (most PWRs currently in operation), the primary pressure must be lowered in order to make the leak stop if all seals have failed.

EDIT: Regarding the possibility to isolate the pumps from the loops, the VVER-440 plants (with 6 loops and a small power) have isolation valves in the loops, but they are mainly meant to enable maintenance operations, and are not qualified to function as safety devices. As far as I know, any other modern PWR does not have such isolation valves in the primary loops.

tsutsuji

It was reported that they did just that (1). And that, as a consequence, the leakage rate declined from 2300 litres per hour to 66 litres per hour (2), and the quantity of leaked water that was collected in a dedicated circuit was around 1 m³ (3). But I don't remember reading how they did that. Any idea ? Did they do anything special beyond cooling the reactor the usual way for a shutdown ?

Business daily Les Échos (3) calls the loss of more than one seal a "black scenario", where "the pump breaks up and thousands of litres of radioactive water are released into the building".

Then they say:

"This black scenario did not happen, but everything did not go as expected. This is problem number 4 [they listed the oil leak as problem No. 1, the oil fire as problem No. 2, the seal failure as problem No. 3]: two valves that were supposed to channel the primary coolant leak were unexpectedly closed. "If it had lasted longer, there would probably have been difficulties", Simon Huffeteau [the head of the ASN bureau in Caen] recognises".

Perhaps the above can help figure out which valves are those valves that went wrong.

Would the "black scenario" require radioactive releases into the environment ? Or is it "black" only because of the money it would cost ?

(1) 6 April 04:00 AM "Its [EDF's] teams managed to control it [the leak] by reducing pressure and temperature" http://www.lemonde.fr/planete/articl...1749_3244.html
(2) Interview with ASN's Director General http://www.lemonde.fr/planete/articl...1749_3244.html
(3) http://www.lesechos.fr/entreprises-s...nly-314665.php

jim hardy

here's another introductory document. Around paged 19-25 is description of how the seals work.
http://www.google.com/url?sa=t&rct=j...xHWGAmEJSLNH2A




fig 4.3.2 on page 26 shows the arrangement of seals , injection flow and thermal barrier at bottom.
i dont know which valves might have been closed or if they're even shown on that training drawing.