ML17334A732
| ML17334A732 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 06/05/1998 |
| From: | Roe J NRC (Affiliation Not Assigned) |
| To: | Congel F NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| References | |
| NUDOCS 9806110059 | |
| Download: ML17334A732 (9) | |
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t Uvn'EO Salas NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 2055'r0001 June 5, 1998 gO g/g FROM:
MEMORANDUMTO:
Frank J. Congel, Director Incident Response Division, AEOD Jack W.
Actin c or Division actor Program Management, NRR
SUBJECT:
ABNORMALOCCURRENCE INPUT Your memorandum dated January 27', 1998, requested assessments and writeups for events which may be reportable as abnormal occurrences (AO) or "Other Events of Interest" for the first quarter for fiscal year 1998. Although the events identified in the memorandum did not include events under NRR's purview, we considered an additional issue.
An inspection at Coolin S st D.C. Cook disclosed a number of problems related to the operabilit fth E
ing ys em (ECCS).
Initially,several of the problems were perceived to make the ECCS inoperable, thereby jeopardizing both fuel and containment inte rity. At that t'onsiderin the Coo g
e Cook issue to be a potential AO. Subsequent analysis showed that the ECCS gri a
ime we were was not inoperable and the issue was no longer considered a potential AO. We are providing an assessment of the event and basis for our decision.
You may also wish to consider the event as criteria are developed for "Other Events of Interest."
Our considerations utilized the final abnormal occurrence criteria approved by the Commission f
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SYNOPSIS A design inspection was conducted at the D.C. Cook Nuclear Power Plant by the Special Inspection staff of NRR from August 4 through September 12, 199T. One purpose was to evaluate the capability of the Residual Heat Removal system, the associated ECCS, and the bases th i
Component Cooling Water system to perform the safety functions requ d b th '
s, eir adherence to their design and licensing bases, and the consistency of the as-built configuration and system operations with the Updated Final Safety Analysis Report.
During the recirculation phase following a postulated loss-of-coolant accident (LOCA), spray nozzles deliver water from the containment spray system to the lower containment in an annulus area beneath the ice condenser.
The inspection team found th t th I
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no provide a flow path for the spray water to get from this annulus area to the containment sump.
As a result, cooling water from the spray system could not promptly return to the "y2-
Contact:
W.F. Burton, NRR 301<15-2853
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Frank J. Congel containment sump, and thereby could potentially reduce the available net positive suction head for operation of the spray pump and cause pump cavitation with eventual pump failure. Both units were shut down as a result of this deficiency.
In addition, as a result of flow bias errors and level instrument uncertainties associated with the refueling water storage tank (RWST),
manual switch over of the ECCS pump suctions from the RWST to the containment sump could occur before the assumed amount of water had become available in the sump to support pump operation.
However, by explicitly incorporating a conservatism, i.e., adding the calculated volume ofwater known to result from melting ice to the sump inventory, vortexing and pump cavitation could be avoided.
Also, fibrous material, which was to have been removed from containment, was found to be installed on the electrical cable trays inside the containments of both units. This material could be postulated to dislodge during a LOCA and potentially block greater than 50 percent of the containment sump screens.
In addition, some clearances around the edge of the sump screens were found to exceed the limitof 1/4", thereby allowing particles greater than 1/4" to enter the cooling system and potentially bio'ck the recirculation throttle valves.
Any of these deficiencies could have potentially-created a common cause failure of the recirculation system to circulate water due to insufficient water reaching the sump or clogging of the recirculation throttle valves., Although.the deficiencies were initiallyconsidered safety significant from a design and procedural perspective, subsequent analysis showed that the identified deficiencies did not r'esult in an actual major reduction in the degree of protection of the public health or safety.
Therefore, NRR believes this issue warrants a classification as an "Other Event of Interest."
I Another issue was identified at Cook regarding the ability of the containment ice baskets to reduce containment pressure during a LOCA. The attached highlight provides additional details.
details.
We are evaluating this additional issue to determine whether the totality of containment issues meets the AO or Appendix C criteria..
~UO Centra~ e PUBLIC H. Karagiannis W. Burton J. Carter E. Adensam J. Hickman PECB R/F DOCUMENT NAME: G:(WFBIAO To receive a cop of this document, indicate in the box C=Cop w/o attachment/enclosure E=Cop with attachment/enclosure N = No cop OFFICE NAME DATE PECB" WBurton 03/24/98 PECB*
RDennig 03/25/98 PECB*
J Carter 03/24/98 (A)D:DRPW*
EAdensam 05/06/98 C:PECB*
JStolz 05/1/98 (A) 'PM J
o GAP /98 OFFICIALRECORD COPY
tI I
Frank J. Congel containment sump, and thereby could potentially reduce the available net positive suction head for operation of the spray pump and cause pump cavitation with eventual pump failure. Both units were shut down as a result of this deficiency.
In addition, as a result of flow bias errors and level instrument uncertainties associated with the refueling water storage tank (RWST),
manual switch over of the ECCS pump suctions from the RWST to the containment sump could occur before the assumed amount ofwater had become available in the sump to support pump operation.
However, by explicitly incorporating a conservatism, i.e., adding the calculated volume ofwater known to result from melting ice to the sump inventory, vortexing and pump cavitation could be avoided.
Also, fibrous material, which was to have been removed from containment, was found to be installed on the electrical cable trays inside the containments of both units. This material could be postulated to dislodge during a LOCA and potentially block greater than 50 percent of the containment sump screens.
In addition, some clearances around the edge of the sump screens were found to exceed the limitof 1/4", thereby allowing particles greater than 1/4" to enter the cooling system and potentially block the recirculation throttle valves.
Any of these deficiencies could have potentially created a common cause failure of the recirculation system to circulate water due to insufficient water reaching the sump or clogging of the recirculation throttle valves. Although the deficiencies were initiallyconsidered safety significant from a design and procedural perspective, subsequent analysis showed that the identified deficiencies did not result in an actual major reduction in the degree of protection of the public health or safety. Therefore, NRR believes this issue warrants a classification as an "Other Event of Interest."
Another issue was identified at Cook regarding the ability of the containment ice baskets to reduce containment pressure during a LOCA. The attached highlight provides additional
'etails.
details. We are evaluating this additional issue to determine whether the totality of containment issues meets the AO or Appendix C criteria..
N Central File PUBLIC H. Karagiannis W. Burton J. Carter E. Adensam J. Hickman PECB R/F DOCUMENT NAME: G'<WFBNO To receive a cop of this document, indicate in the box C=Cop w/o attachment/enclosure E=co with attachment/enclosure N = No cop OFFICE NAME PECB*
WBurton PECB'Dennig PECB*
JCarter (A)D:DRPW'Adensam C:PECB'Stolz (A 'PM DATE 03/24/98 03/25/98 03/24/98 05/06/98 OFFICIALRECORD COPY 05/1/98 P
/98
" PRIORITY ATTENTI EQUIRED MORNING REPORT HEADQUARTERS APRIL 30, 1998 D
MR Numbers H-98-0066 qt NRR DAILY REPORT ITEM SIGNIFICANT EVENTS Sub ect: Ino exable Ice Condensers at DC Cook Units 1
R 2 Classified As A Si ificant Event The NRR/AEOD/RES Events Assessment Panel on April, 7, 1998, classified the inoperability of the ice condensers at the DC Cook nuclear power plant as a Significant Event for the Performance Indicator Program.
The significant event classification was based on the breakdown of the licensee's program for assuring continued operability of the ice condensers to perform their design function of maintaining post-LOCA containment pressure within the design basis.
The ice condenser inside the containment of each DC Cook unit is composed of 1944 baskets, each 12 inches in diameter and 48 feet tall, filled with ice. Post-accident steam released from the reactor coolant system flows into the ice condenser where much of its heat energy is removed by direct contact with the ice, such that the steam is condensed back into water.
This effect reduces the pressure inside containment to within design limits.
NRC and licensee inspection activities in January, February and March 1998 showed several conditions that raised questions concerning the operability of the ice condenser:
In both units, 10 - 20
. of the steam flow passages between baskets were blocked by frost and ice lower portions of some ice baskets were devoid of ice
- the bottoms of some ice baskets had been structurally damaged, and testing indicated that these baskets might be unable to maintain their structural configuration under accident conditions
- screws were missing from section couplings and lower rims of the baskets the licensee reported that trash, such as plastic, wire and wood, had been frozen into the ice; it was collected when ice was melted from some of the baskets, and might have caused pluggage of the containment sump screens when the ice melted following a loss-of-coolant accident the licensee had been selecting a non-representative sample of ice baskets when performing ice,weight surveillances The licensee plans to melt out the ice from both ice condensers and make the necessary repairs.
NRC Region III has issued Inspection.Report 50-315/98005(DRS);
50-316/98005(DRS) dated April 10,
- 1998, which addresses the NRC inspection activities related to these ice condenser matters.
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'EADQUARTERS RNING REPORT
~ MR Number: H-98-0066 (cont.)
PAGE 2
APRIL 30, 1998 There are seven other nuclear power reactors with ice condenser containments operating in the United States. All are located in NRC Region II and have been alerted to the problems at DC Cook. Region II is developing an ice condenser inspection plan for application to those plants.
Contact:
James
- Gavula, Region III (630) 829-9755 E-mail:JAG1nrc.
gov John Stang, NRR/DRPW/PDIII-2 (301) 415-1345 E-mail: JFS2nrc.gov Robert A. Benedict, NRR/DRPM/PECB (301) 415-1157 E-mail: RAB1nrc.gov