ML20058Q284
| ML20058Q284 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 10/19/1993 |
| From: | Simpkin T COMMONWEALTH EDISON CO. |
| To: | Murley T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation |
| References | |
| TAC-M77540, TAC-M77541, NUDOCS 9310260128 | |
| Download: ML20058Q284 (6) | |
Text
Ccmm:nwa:lth Edisen ry 1400 Opus Place Downert, Grove, Illinois 60515 -
October 19,1993
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l Dr. T. E. Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn: Document Control Desk
Subject:
Zion Station Units 1 and 2 NRC Diagnostic Evaluation Follow-up ltems (TAC NOS. M77540 and M775M)
NRC Docket Nos. 50-295 and 50404 Reference.
(a) September 4,1990 letter from J. Taylor to J.J. O'Connor (b) November 2,1990 letter from C. Reed to J. Taylor (c) July 6,1993 letter from C.Y. Shiraki to D.L. Farrar with attached Safety Evaluation Reference (a) transmitted the results of the NRC Diagnostic Evaluation Team (DET) inspection conducted for Zion Station in 1990. Reference (b) documented the Commonwealth Edison (CECO) response to the reference (a) DET report. Reference (c) supplied a safety evaluation which outlines the staff's position regarding the licensing basis for the Zion Station service water system.
In reference (c), NRR has identified specific DET inspection issues that involve potential vulnerabilities that NRR believes could be contrary to the licensing basis for the Zion service water system. In addition, NRR expressed a concern that actions taken or planned by CECO in response to DET findings may not be entirely appropriate since the staff's position on the licensing basis for the service water system was not previously available to CECO.
CECO has completed a review of previous submittals, as well as actions taken or planned, taking into consideration NRRs position as provided in the reference (c) Safety Evaluation. Attachment
'A' provides the results of that review and indicates the additional actions that are planned.
Sincerely, NM
, W. Simpkin 250154 Nuclear Licensing Administrator Attachraent cc: J. B. Martin - Region Administrator-Rill C. Y. Shiraki - NRR Project Manager J. D. Smith - Senior Resident inspector - Zion k:nlaton/swdatwpt'1 I
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L ATTACHM ENT 'A' The following five issues were identified in the safety evaluation dated July 6,1993:
'l during postulated accident scenarios.
- b. The capability of two or three service water pumps to deliver design flow to safety related loads during postulated accident conditions had not been demonstrated.
c Valves were not adjusted to balance flow in the service water system.
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- d. Contrary to the Zion UFSAR, single valve isolation exists in at least two locations between safety and non-safety related portions of the service water system.
- e. A failure of non-safety related structures, piping, or valves could reduce flow through the safety related portions of the service water system.
i issues a, b, d, and e all involve concerns of potential vulnerabilities to specific postulated event scenarios.
To address these concerns, CECO proposes to perform analyses of four postulated event scenarios designed to encompass the potential vulnerabilities identified. The four postulated event scenarios have i
been designed in a manner consistent with current regulatory guidelines as outlined in the NRC's Inspection and Enforce. ment Manual Part 9900. CECO intends to complete these analyses no later than January 31,1994. The scenarios are as follows:
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Scenario No.1 i
-Both Units operating at power j
i iNo design basis accidents, no LOOP, no natural phenomena
-Minimum SW pumps per TS (5 pumps) l
-SW system is cross-tied between units
-SW pipe break - any location, with size defined per BTP ASB 3-1 for safety-related and/or seismic piping (for non-seismic piping a guillotine break will be assumed.)
-SW valve fails to close - stuck open
-Local / remote manual operator actions acceptable
-Achieve Hot Shutdown on affected unit (s) knlatonswdet wpt?.
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Scenario No. 2 1
-One Unit operating at power, other unit in mode 5
-No design basis accidents, no LOOP, no natural phenomena
-Minimum SW pumps per TS (3 pumps)
-SW system is cross-tied between units
-SW pipe break - (same as scenario #1)
-SW valve fails to close - stuck open
-Local / remote manual operator actions acceptable
-Achieve Hot Shutdown on operating unit, maintain shutdown unit in mode 5 Scenario No. 3
-One Unit operating at power, other unit in mode 5 l
-LOCA on operating unit, LOOP on both
-Minimum SW pumps per TS (3 pumps)
-SW system is cross-tied between units t
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-no na ura p enomena
-Single failure: active failure assumed early in transient, or passive failure (per BTP ASB 3-1) assumed later, if no active failure (same as ECCS assumptions per the 1968 SER)
-Operator action (past " hands-off time") assumed for passive failure l
-Operator action must meet " hands-off time" for early active failure
-Local / remote manual operator actions acceptable
-Achieve Hot Shutdown on operating unit, maintain shutdown unit in mode 5-6 l
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Scenario No. 4 -
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-Both Units operating at power
-LOCA on one unit, LOOP on both
-Minimum SW pumps ~ per TS (5 pumps)
-SW system is cross-tied between units
-No natural phenomena
-Single failure - active early or passive (same as scenario #3)
-Operator action must meet hands-off time" for early active failure
-Local / remote manual operator actions acceptable
-Achieve Hot Shutdown on affected unit (s)
Issue A
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'i Issue A states that the existing Zion Technical Specifications do not appear sufficient to ensure that the licensing basis for the service water system.is met at all times. One specific vulnerability identified for this issue involves a single passive failure which leads to loss of all SW pumps associated with the operating
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unit. An example was postulated where, with one unit shut down, a crack develops on the discharge pipe of the operating unit, necessitating use of pumps associated with the non-operating unit. This specific t
example falls under the analysis for scenario 2 above. Scenarios 1 through 4 are designed to encompass the various passive failure scenarios and determine if any of these scenarios result in failure of the service water system to meet its design basis.
The adequacy of the basis for the Technical Specification requirements is the central question for this issue. CECO has determined through analyses conducted to date that the ability of the service water system to satisfy this basis is dependent on service water pump flow capacity. Our analyses confirm that under certain scenarios one pump per unit is not adequate when one or two of the available pumps are of lower flow capacity. Since the DET, CECO has had administrative controls in place to ensure that adequate service water flow will be available to safety related components whenever plant conditions are such that only one service water pump could operable, as is currently allowed per Zion's Technical Specifications. These administrative controls were first in the form of a standing order and are now in place as administrative technical specifications. As described under issue B, CECO currently plans to conduct testing during the upcoming dual unit service water outage designed to show, that with the service water pumps upgraded to a new minimum flow level, two pumps will be adequate to ensure licensing basis-requirements are satisfied at all times with the existing Technical Specifications.
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Issue B l
CECO has scheduled pump pair testing designed for the upcoming Dual Unit Outage to allow evaluation of the worst case post accident service water alignment (flow available only equivalent to two pumps). A single pair of pumps will be tested and the results of the test will be evaluated. This information will then be used to validate adequacy of assumptions previously utilized. The adequacy of three pumps to deliver design flow to safety related loads will be demonstrated and reconfirmed at this time. This testing will be completed in conjunction with the flow balancing described below under issue C.
To date, three service water pumps have received pump impeller upgrades. The other three service water pump impellers are scheduled to be upgraded between now and July 1995. CECO intends to keep administrative controls in place to prevent a two pump scenario where one or two pumps could be non-upgraded service water pumps. As additional service water pumps have their impellers upgraded, they will i
be tested to ensure that they would not result in system flowrates below that determined acceptable based on the pump pair testing described above. In the event that this occurs, an appropriate engineering analysis will be completed to ensure that adequate service water flow margin exists before any administrative controls are relaxed.
Issue C i
Service water system flow balance testing is scheduled for the upcoming Dual Unit Outage. The results of j
this testing will be used to establish appropriate valve positions for service water system throttle vaives.
i The flow balancing effort will be completed in conjunction with the pump pair testing as described above under issue B. Once the proper throttle positions to balance flow are established, empirical data will be recorded and utilized with the service water computer flow model to ensure that the resulting flows to all safety-related components will be adequate. In addition, administrative controls will be established to ensure proper control is maintained over the appropriate system throttle valves.
l Issue D Reference (c) indicates that the DET identified at least two locations between safety-related and non safety-relMed portions of the service water system where only single isolation valves exist. It also states that this was contrary to the description of the system provided in the Zion UFSAR, and therefore must be evaluated as required by 10 CFR 50.59. Two locations that fit this description are at valves OMOV-SW0005 and OMOV-SW0006 (fire protection service water booster / travelling screen backwash isolation valves).
As part of our effort to address Generic Letter 89-13, CECO on September 30,1991 completed a service water system design review for Zion Station. This review contained three parts: (1) As-built walkdowns of system P&lDs, (2) a review of flood protection features, and (3) a single active component failure review.
As a result of this review, revisions to emergency procedure E-0 were made. The revisions included guidance and local actions to be taken in the event that the OMOV-SW0005 or 0MOV-SW0006 valves should fail to close.
In 1991, Zion submitted, as part of it's annual UFSAR update, corrections to section 9.6.3 which stated that, "Under emergency conditions, all essential equipment requiring cooling is supplied, while double isolation valves in each main header isolate the supply to non-essential equipment." The safety evaluation required I
by 10 CFR 50.59 was completed in support of the change to the UFSAR. This safety evaluation addressed the consequences of a failure of either 0MOV-SW0005 or 0MOV-SW0006.
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In addition,it addresses the following non-essentialloads that can only be isolated by closing manually operated valves:
1cPrime Computer AC Unit Condensers
- 2. Vacuum Pump and. Nitrogen Condenser
- 3. Various Radiation Detectors
- 4. Counting Room HVAC Condensers These non-essential loads are fed by small diameter lines (2" or less in diameter) and are within the uncertainty allowed for calculation of total service water flow requirements.
Issue E
-l The single active failure review completed per the Zion response to Generic Letter 89-13 concluded that the Zion service water system is capable of performing its intended function given a single active failure.
However, the analyses for the above scenarios 1 through 4 should confirm this conclusion and also establish the systems ability to withstand passive failures as identified above that are within the design basis for the system. Flooding scenarios have been previously analyzed and results have determined that the service water and component cooling water pumps are not vulnerable to flood damage. The passive failures assumed for the above analyses will be reviewed to ensure that they are bounded by the previously evaluated flooding scenarios.
Should the analyses for scenarios 1 through 4 show that Zion service water system is unable to satisfy its licensing basis given certain single active or passive fai!ures, necessary actions will be taken_in order to satisfy the reporting requirements of 10 CFR 50.72 and 10 CFR 50.73.
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