ML20058D604
| ML20058D604 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 10/29/1990 |
| From: | Taylor D COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-86-003, IEB-86-3, NUDOCS 9011060180 | |
| Download: ML20058D604 (2) | |
Text
_.
) Commonwealth Edleon 1400 Opus Place
(. *'
- Downers Grove, Illinois 60515
~
October 29, 1990 p
U.S. Nuclear Regulatory Coaimission i
ATTN:
Document Control Desk Hashington, D.C.
20555
Subject:
Zion Station Units I and 2 Supplemental Response to NRC Bulletin 86-03 4
RRC..DocktLMm_50-235 and_50-304
References:
(a) NRC Bulletin 86-03 dated October 8, 1986 (b) I.M. Johnson letter to J.G. Keppler dated November 14, 1986
Dear Str:
}
Reference (a), (Bullettn), addressed a design deficiency involving the minimum flow recirculation lines of Emergency Core Cooling System (ECCS) t pumps that contain air-operated isolation valves.
That is, the loss of a recirculation flow path due to failure of an air-operated valve in the closed 1
position, could result in ECCS pump damage during a small break loss-of-coolant accident (LOCA), a steam generator tube rupture, or a main steam line break (MSLB) in which the RCS-pressure remains above the shutoff head of the ECCS pump.
The Bulletin requested that licensees determine if a single-fallure vulnerability existed in the minimum flow recirculation Itne of any ECCS pumps which could cause a failure of more than one ECCS train.
Commonwealth Edison's (CECO) initial response to this Bulletin, Reference (b), indicated that design deficiencies noted in the Bulletin did not exist at Zion Station.
However, subsequent review identified a related design deficiency in the high head portion of the ECCS system.
The Zion Station Emergency Operating Procedures (EOP) direct the reactor operator to close the charging pump recirculation flow valves if Reactor Coolent System (RCS) pressure drops below-1250 psig following a Safety Injection (SI) signal and to reopen those valves if RCS pressure subsequently rises above 2000 psig.
This is done to ensure'the maximum ECCS flow for a large break loss of cooling accident (LBLOCA), while also ensuring l charging pump recirculation flow in the event of RCS repressurization during other r
transient events which initiate SI.
In order to reopen the recirculation val' 1 upon repressurization of the RCS, the motor operated valves (MOV) must rem n energized and operable.
Because these valves are in series, a single-failure of either MOV in the closed position would result in a loss of recirculation flow, which could potentially ronder both centrifugal chargin;;
pumps inoperable.
l 9011060180 901029
't I PDR ADOCK 05000295 (l
Q PDC
.eaL l g
l
'.I..
U.S. NRC October 29. 1990 i
To preclude this single failure concern, the Zion Station E0P's were I
modified to instruct the operator to close the charging pump recirculation i
flow valves If:
- 1) RCS pressure drops below 1250 psig And
- 2) RCS subcooling is less than 25'F.
i This thange to the E0P's will assure maximum flow to the RCS during a t
In addition this-change will assure that the minimum flow valves are not closed during other SI events and thus they will not require reopening.
This in turn will eliminate the concern with ECCS pump damage resulting from i
the single failure of a charging pump recirculation. flow valve.
This E0P modifications therefore complete the action requirements for i
l Please direct any questions relating to this response to this office.
Respectfully.
.f Darrell Taylor Generic Issues Administrator cc:
A.B. Davis, Regional Administrator - RIII Senior Resident Inspector - Zion C. Patel, Project Manager - NRR 1mw/ID182 i
l
,