ML20140F627

Discusses Snp 1 RCS Partial Drain Down

ML20140F627
Person / Time
Site:	Sequoyah
Issue date:	03/29/1997
From:	Blanch P AFFILIATION NOT ASSIGNED
To:	Zwolinski J NRC (Affiliation Not Assigned)
Shared Package
ML20140F623	List: ML20140F619 ML20140F627 ML20140F632 ML20140F635 ML20140F647
References
NUDOCS 9706130172
Download: ML20140F627 (1)

Text

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1 I

. ; From:

PAUL BLANCH <PMBLANCH@ix.netcom.com>

To: WND2.WNP3(jaz)

Date: 3/29/97 4:56am 1

Subject:

SEQUOYAH 1 RCS PARTIAL DRAIN DOWN

]

3/29/97 John A. Zwolinski, Deputy Director Division of Reactor Projects-1/11 Office of Nuclear Reactor Regulation Washington DC 20555-0001 1

John: ' I l

l received the following last week.

SEQUOYAH 1 RCS PARTIAL DRAIN DOWN. On 3/23/97,in preparation for = reactor vessel disassembly, operators started to reduce the RCS = inventory from 56 % to 25 % Pressurizer level by procedure using the = cold calibrated instrument. After a half hour, operators noticed I the = cold calibrated Pressurizer levelindication had stopped decreasing = and was steady at about 34 %. The hot calibrated Pressurizer level = indications were 0 %, but were not required {

i to be monitored by = procedure. The operators observed Reactor Vessel Level Indication at = '

92 %, and stopped the drain evolution upon realizing the level = discrepancy and initiated filling. It was determined the RCS level = bad drained to approximately 3 feet above the top of l the Reactor =

Vessel flange. This represents about 4000 gallons drained below the = intended amount.

Shutdown cooling was not affected during the event. =

The licensee identified the reference leg for cold calibrated =

Pressurizer level instrument was not filled and is investigating the = root cause. [NRC Headquarters Report]

This appears to be the same problem I identified in 1989 at Millstone =

Unit 3. Westinghouse also identified this problem in February of =

1988. Bill Russell determined this not to be a problem in 1992. This = appears to be related to inoperable cold condensate pots. The full =

Commission refused to require any plants to conduct an operability = determination.

I suspect that the licensee and the NRC will find that the condensate = pot was cold and no make-up was being supplied to keep the reference = leg full. As a result of minor leakage, the reference leg slowly lost = level. This was not detected as the cold calibrated pressurizer level

= is not used during normal operation. This is the same problem = identified on Millstone Unit 3 when 2 out of 3 reference legs lost = level.

At one time OlG was investigating this as it related to the BWR=B9s = but we mutually agreed to cease the effort because the outcome was = likely to be similar to the Rosemount investigation. I was given = assurance by the NRC Staff that this issue was properly closed out

= for both BWR=B9s and PWR=B9s.

If you need any help in identifying the root cause of this problem, = give me a call.

Sincerely, 9706130172 970611 PDR ADOCK 05000327 P PDR