S/G Tube Leak at IP-2

[Rodney Bauman <rodney_bauman@wssrap-host.wssrap.com>]

I find it interesting that Indian Point Unit 2 is still at 547 degrees F and
approx. 2235 psig.  I was trained (but never licensed) to operate a four loop
Westinghouse PWR, and following a steam generator tube rupture event, the
primary responsibility of the operating staff was to reduce the primary system's
pressure (and temp) to below that of the secondary system's pressure in order to
stop the primary to secondary leakage through the ruptured tube.  Our UFSAR
claimed that this process could be completed in approximately 1/2 hour following
a "design-basis" SGTR event.

Since IP-2 is still at normal operating temp and pressure, then the tube leak
must be sufficiently small such that the normal charging system is easily
compensating for the loss.  Or possibly, the primary system is equipped with
loop stop isolation valves (LSIVs) which actually work (most are not depended
upon).

The off-site release pathway for such an event is normally via the condenser
off-gas system (i.e., steam jet air ejectors) or any steam-system pressure
safety valve which may have lifted.  Once the secondary-side of the steam
generator is isolated, the only pathway for off-site release would be from the
affected steam generator over-pressurization safety valves (if ever utilized to
protect the S/G from over-pressurization).

The off-site radiological release would be comprised of mostly non-condensable
gases (e.g., noble gases) and iodine compounds.  The level of iodine released is
very dependent upon the location of tube leak within the steam generator.  A
leak below the secondary water level (i.e., underwater) results in a "scrubbing"
of the iodine and thus a much smaller release of iodine isotopes to the
atmosphere.

This is an abnormal event for which any PWR operating staff is well-trained to
deal with.  The very fact that a site or general emergency was not declared
tells me that this was not a full-blown steam generator tube rupture event and
any off-site releases were probably negligible.

Rodney Bauman, CHP, RRPT
rodney_bauman@wssrap-host.wssrap.com

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