[ RadSafe ] Releasing hydrogen to the reactor building

Franta, Jaroslav frantaj at aecl.ca
Wed Mar 30 12:53:58 CDT 2011


Thanks for the interesting post Harry,

You may have noticed that one of the units that blew its top off (Unit 4) didn't have any fuel in the reactor -- hence could not have vented hydrogen from the primary containment into the secondary containment.

Some reports suggest that the hydrogen came from the SNF pool, but I don't know for sure.

In any event, it appears that hydrogen can get into the secondary containment even if the primary containment is not vented into it (for example, Browns Ferry vents outside via a special vent pipe)

Thus it seems that hydrogen mitigation should be provided in the secondary containment, regardless of primary containment venting design -- preferably of the PAR type ("Passive Autocatalytic Recombiners"), which doesn't require any power to operate.



-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Anagnostopoulos, Harry (CONTR)
Sent: March 30, 2011 1:34 PM
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] Releasing hydrogen to the reactor building

"All in all, AMAZINGLY sturdy constructions although it seems equally
amazingly stupid to release containment pressure inside the reactor
building instead of either to the atmosphere or a tiosulphate scrubber.
But that's design, I suppose."

From my reading, it appears that the capability to vent the torus
(primary containment suppression pool) to the reactor building was a
modification that was installed in the 1990's.

Based on my experience working at a similar plant, it made sense at the
time, considering:
1. The primary containment is equipped with hydrogen re-combiners to
burn the hydrogen under controlled conditions
2. The reactor building is kept under negative pressure and is
ventilated via HEPA and charcoal filters
3. The reactor building is continuously monitored for gases

ALL of this assumes that there is electrical power available...

Now that we have seen a prolonged "station blackout" condition, I'm sure
that mods will be in order to allow emergency venting of the torus to
the plant stack (at elevation above the buildings).

It seems to me that the plant operators were faced with a difficult
decision: 1) vent the torus and risk a hydrogen explosion on the
refueling floor (equipped with metal blow-out panels) OR 2) let primary
containment pressure continue to rise until the containment burst

History will be the judge...

Harry Anagnostopoulos, CHP

"In preparing for battle I have always found that plans are useless, but
planning is indispensable."
-    President Dwight D. Eisenhower

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