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Re[2]: Palo Verde
This does not sound so unfamiliar. It is not too uncommon to
accidentally shorten and twist a bundle or two due to locating-pin
misalignment during the setting of the upper internals. It is easy to
visualize a twisting action occurring when attempting to squash such a
long object with slender structural elements with little resistance to
horizontal deflection.
Root cause...good money says that the last time they lifted the upper
internals, they moved laterally when they should have only been
lifting upwards and bent some locating pins. When the upper internals
were reset, the pins do not line up and that is how bundles become
shortened slightly and possibly twisted(about the same length as the
pin). I would think the amount of shortening/pin length would be an
inch or less. I've never seen the pins that close and don't have any
immediate figures or drawings, so the length is a guestimate.
Second thought would be that the lower locating pins did not line up
properly when the bundle was put in on core reload causing the bundle
to sit a little higher than usual. The upper internals squashed the
bundle and distorted the lower pins/bundle support and this is why
they can't pull it out. A distorted grid strap may also be catching
on an adjacent bundle and add to or cause the same effect.
The amount of gas/fission producets that could be liberated from the
damage of one fuel should be insignificant for that volume and
immeasurable after being diluted by containment ventilation and the
vent stacks (approx. 200,000 cfm) leaving the building. I'm sorry but
I don't have a concentration magnitude, but the volume of gas in a
bundle would have to be 500 ml or less.
The only other concern would be to the site itself with the hopes of
not spilling fuel pellets into the bottom of the core. It would
certainly be a hassle have to worry about possibly lifting out the
lower internals to get to any that may fall through the lower support
plate.
This is what they make cool underwater cameras for. Perhaps they
could place a covering over the area of the lower support plate where
the bundles have been removed (metal screen to handle thermal and
other environmental stuff) to minimize the possibility of pellets
falling throught the lower support plate. Can't quite remember the
size of the flow holes in the lower support plate, but I would
certainly think they would be large enough for the pellets to fall
through. They could then use a "porta-power" type device (hydrolic
duck bill) attached to the end of one of their wonder fuel handling
rods and wedge it under the lower support plate for the bundle. They
could jack they bundle off of the lower support plate while they lift
the bundle with ordinary means. This would put the additional forces
between the lower support of the bundle and the lower internals and
not to the semi-mechanically fragile bundle itself. They could
probably try the jacking first without the screen and evaluate as they
go. Such a rig would only take a shift or two to to make up in
high-dollar nuclear world time.
That last paragraph of babbling just turned on a light bulb in my head
and I think I'll call Palo Verde myself...
I would not want to ask the fine folks at Palo Verde how much critical
path time they are losing due to this problem ($$$/day)
Total risk to the public...certainly orders of magnitude less than
that from drinking 8 oz. of tap water.
Glen Vickers
HP, Nuclear Power Generation
BRZGV@ccmail.ceco.com
Usual disclaimer...
______________________________ Reply Separator _________________________________
Subject: Re: Palo Verde
Author: radsafe@romulus.ehs.uiuc.edu at INTERNET
Date: 4/1/96 3:10 PM
At 06:00 AM 4/1/96 -0600, you wrote:
>
>I heard a report on the radio, this morning that there are some stuck fuel
>rods at a Palo Verde unit. I'd appreciate it if someone knowledgable would
>led RADSAFE know more about what's going on.
>
PNO-IV-96-016: DAMAGED FUEL ASSEMBLY FOUND DURING CORE DEFUELING
NRCPNO PNO1996 49616PN.TXT
-1- March 28, 1996
PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PNO-IV-96-016
This preliminary notification constitutes EARLY notice of events of POSSIBLE
safety or public interest significance. The information is as initially
received without verification or evaluation, and is basically all that is
known by Region IV staff in Arlington, Texas on this date.
Facility Licensee Emergency Classification
Arizona Public Service Co. Notification of Unusual Event
Palo Verde 2 Alert
Wintersburg,Arizona Site Area Emergency
Dockets: 50-529 General Emergency
X Not Applicable
Subject: DAMAGED FUEL ASSEMBLY FOUND DURING CORE DEFUELING
On March 24-25, 1996, with Palo Verde Unit 2 in a refueling outage, the
licensee experienced difficulty in removing fuel assemblies located in the
southeast quadrant of the core. Adjacent Fuel Assemblies A06, A07, A08, and
B07 could not be removed due to the refueling machine reaching the cut off
load limit of 1600 pounds. The licensee continued with defueling operations
in the remainder of the core and used a video camera to observe the condition
of the stuck assemblies.
Using video camera, the licensee observed damage to Fuel Assembly A07.
Specifically, the top of Assembly A07 was approximately 0.7 inch lower than
adjacent assemblies, the grid straps for Assembly A07 were lower than adjacent
assemblies, the lower end fitting for Assembly A07 was damaged, and
approximately seven fuel rods were protruding from the bottom of the assembly.
No damage to the fuel rods was observed, and the licensee had no indication
of Unit 2 fuel failures prior to starting the refueling outage. No damage to
fuel Assemblies A06, A08, and B07 was observed. Subsequently, the licensee
was successful in removing Assemblies A08 and B07.
The licensee formed task groups to develop plans for removing the last two
assemblies, to assess radiological consequences of fuel rod failure, to
inspect the reactor upper guide structure, and to determine a root cause for
the damage.
The licensee observed damage to the upper guide structure in the area where
fuel Assembly A07 was located. The licensee has preliminarily concluded that
the upper guide structure transmitted a load to the fuel assembly during the
core assembly from the last outage. The load was transmitted by the assembly
guide tubes to the lower end fitting, resulting in damage to the end fitting
and compression of the fuel assembly.
On March 26 and 27, conference calls between NRR, Region IV, and the licensee
were held to discuss the licensee's plan for removing the fuel assemblies.
The licensee stated that they believed the damaged fuel assembly is structurally
intact. Reactor coolant chemistry is normal and there is currently no other
indication of cladding damage on Assembly A07. The licensee indicated that
an assembly removal procedure was developed which included the use of cameras
to monitor the assembly and include contingency actions should fuel rods be
observed to slip during removal. The licensee manufactured a cover to hold
and capture the protruding fuel rods of Assembly A07. The licensee also
discussed radiological consequences of fuel rod failure, actions for
monitoring radiological conditions, and plans for protecting personnel
involved in the removal operation. On March 27, the licensee approved the
use of an alternate procedure under 10 CFR 50.59 to remove Assembly A07 using
the modified fuel handling tools. The licensee plans to attempt to remove
Assembly A07 on March 28, 1996.
On March 26, NRR approved an emergency Technical Specification change to
allow the licensee to increase the refueling machine cut off load limit for
Assembly A06 from 1600 pounds to 2000 pounds. The change does not apply to
damaged Assembly A07, which is limited to 1600 pounds. On March 27, Assembly
A06 was successfully removed from the core without incident.
Palo Verde Unit 2 was using fuel manufactured by Combustion Engineering. The
licensee was not going to reuse Assembly A07 for the next fuel cycle.
Combustion Engineering has been contacted and has a fuel expert on site.
Region IV dispatched a Branch Chief to the site on March 26, 1996, to assist
the resident inspector followup and Unit 2 outage issues. Additionally, two
resident inspectors continue to monitor Units 1 and 3 which are operating at
full power.
The state of Arizona has been informed.
Region IV received notification of this occurrence by telephone from the
resident inspectors to the Walnut Creek Field Office at 7:30 a.m. (PST) on
March 25, 1996. Region IV has notified NRR, OEDO, and PAO. This information
herein has been discussed with the licensee and is current as of 10:30 a.m.
(PST) on March 28, 1996.
Contact: D Kirsch J. Kramer
(510)975-0290 (602)393-3638
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