ML20029E133
| ML20029E133 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 05/13/1994 |
| From: | Marsh W SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-94-001, IEB-94-1, NUDOCS 9405170047 | |
| Download: ML20029E133 (7) | |
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,,W Southern California Edison Company it') PARKE M fsT RE ET IRVINE^, CAL IF OnNI A 9271st May 13, 1994 WAULHC WRSH m,m,,
MANAGE f4 t JF M M ;L E AF4 f tLOUL ATOFly AF F AiWe (714) 4G4-4403 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C.
20555 Gentlemen:
Subject:
Docket No. 50-206 Response to NRC Bulletin 94-01 San Onofre Nuclear Generating Station, Unit 1 This letter provides Southern California Edison's (SCE) response for San Onofre Nuclear Generating Station, Unit 1 (SONGS 1) to NRC Bulletin 94-01,
" Potential Fuel Pool Oraindown Caused by Inadequate Maintenance Practices at Dresden Unit 1."
The bulletin informed licensees about the rupture of a service water line inside containment as a result of freeze damage at Dresden 1.
The event focused attention on the potential for drainage or siphoning of spent fuel. pool water at permanently shut down nuclear plants.
The bulletin requests certain licensees with permanently shut down plants to:
(1) take the actions identified in the bulletin, (2) notify the NRC of the schedule for completion of the actions, and (3) submit a report which confirms the completion of the actions.
SCE has performed the requested actions for SONGS 1 and is submitting this letter as confirmation of their completion.
The responses to the four requested actions are detailed in the enclosure and are summarized as follows:
The adequacy of the design and operability of the structures and systems associated with storage of spent fuel in the unit's spent fuel pool was recently re-reviewed by SCE, and approved by the NRC in Amendment No. 155 (dated December 28,1993), as part of the evaluation of the Permanently Defueled Technical Specifications.
The mild climate in the vicinity of San Onofre means that SONGS 1 need not rely on heating and ventilating systems to preclude cold-induced equipment damage.
-1 The spent fuel pool is designed to eliminate the possibility of fuel j
uncovery, in part, by locating potential siphon and/or drainage paths appropriately above the stored fuel.
Procedures are in place at SONGS 1 to adequately monitor spent fuel pool water inventory.
9405170047 940513 PDR ADOCK 05000206 o
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Document Control Desk Based on the responses to the actions, the design and operability of the SONGS 1 spent fuel storage facility is adequate to provide reasonable assurance of safe, long-term storage of spent fuel.
Therefore, no further actions are required on this matter for SONGS 1.
Very truly yours, lE3 0 $
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, persono!1v brown to me to be the person whose name is subscribed to the within instrument and acknowledged to me that he executed the same in his authorized capacity, and that by his signature on the instrument the person, or the entity upon behalf of which the person acted, executed the instrument, WITNESS my hand and official seal.
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L. J. Callan, Regional Administrator, NRC Region IV K. E. Perkins, Director, Walnut Creek Field Office, NRC Region IV M. K. Webb, NRC Project Manager, San Onofre Unit 1 Louis Carson, Regional Project Inspector, San Onofre Unit 1 R. F. Dudley, Section Chief, Decommissioning Section 1
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NRC Bulletin 94-01 Responses for SONGS 1 Action 1 Verify.that the structures and systems required for containing, cooling, cleaning, level monitoring, and makeup of water in the spent fuel pool (SFP) are operable and adequate, consistent with the licensing basis, to preclude high levels of radionuclides in the pool water and adverse effects on stored fuel, the SFP, fuel transfer components, and related equipment.
Response
The adequacy of the design and operability of the structures and systems associated with storage of spent fuel in the unit's SFP was recently reviewed by SCE as part of Amendment Application No. 211, dated May 12, 1993.
That application proposed Permanently Defueled Technical Specifications (PDTS).
The NRC approved the PDTS in Amendment No. 155, dated December 28, 1993, as being adequate to ensure spent fuel can be safely stored in the SONGS 1 spent fuel storage facility. The design of that facility is summarized below.
The SONGS 1 SFP is a safety-related, seismic category A structure. The SFP is constructed of reinforced concrete and is lined with stainless steel.
The SFP consists of the fuel storage area containing the storage racks and spent fuel, an upender area where fuel is received from containment, and the shipping cask area where spent fuel is loaded for shipment.
A weir is located between the fuel storage area and the upender and cask loading areas.
The design of the weir is such that in the event of a transfer tube failure or a pool liner failure in the upeader or cask handling areas, the pool would not drain below the stored fuel assemblies. Approximately one foot of water would remain above the fuel if such an event were to occur.
The fuel transfer tube connects the SFP upender area directly with the reactor refueling cavity inside containment. The tube is constructed of reinforced concrete and is lined with stainless steel. A safety-related valve is maintained closed in the SFP end of the tunnel.
The tube is sealed with a leak-tight flange on the containment side.
As shown in Figure 1, the lowest SFP piping penetration is located I
approximately 13 feet above the spent fuel. The SFP pump normally takes suction from near the top of the pool.
The cooled water is discharged into the pool about 12 feet below the normal water level. A low level suction is l
available for the SFP pump to drain the pool to within approximately 13 feet above the top of the stored fuel assemblies.
The lower suction is isolated by-a seismic, locked-closed valve which is not used (opened) during fuel movement activities. The pool cannot be drained below this level (plant elevation 28 feet) with any permanently installed piping.
The spent fuel storage racks are designed to maintain k,g 5 0.95 when the SFP is fully loaded with new fuel and filled with unborated water.
The SFP has the capability to store 216 spent fuel assemblies.
The pool currently L
NRC Bulletin 94-01 R sponses for SONGS 1 Fuel Storage Building -
Operating Deck EL 42' - 0*
EL 40' - 3*
i, Pipe Penetrations Minimum Level
, ',-Required by t EL 39' - 4" - / - - - n-
- 4. EL 39' - 1 " - < - - - e-Technical Specifications s :
(. EL 29' - 6" - / - - - e--
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h Spent Fuel y Top of Weir Pool
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/ EL 16' - 0"
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EL 15' - 1" Top of Spent Fuel Assembly 'A ll h
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EL 2' - 0*
EL 3' - D" _ _ _
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Spent Fuel Fuel Transfer Storage Racks Tube t EL 5' Cask Handling Area (Top of Rack EL 15'- 3.5")
Figure 1.
Schematic Diagram of SONGS 1 Spent Fuel Pool.
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l NRC Bulletin 94-01 Responses for SONGS 1 i
contains 207 spent fuel assemblies, including four mixed oxide assemblies.
The maximum k,,, calculated for a fully loaded SFP, unborated water, and worst case conditions is 0.896 which is less than the 0.95 design k,rr.
The fuel array currently stored in the SFP is significantly less reactive than that assumed by the conservative k,,, design calculation.
Separate leak-detection wells are provided for the SFP and the fuel transfn tube.
The wells are designed to collect leakage from any part of the SFP liner and the fuel transfer tube liner. The SFP water level is monitored daily in accordance with PDTS D4.1.
PDTS D3.1.2 requires a minimum SFP water level of plant elevation 40 feet 3 inches which yields at least 25 feet of water above the fuel assemblies. SFP water level is typically maintained l
above 40 feet 6 inches.
Makeup water to the SFP is normally provided by the Primary Plant Makeup Tank by aligning the Primary Plant Makeup pumps to the SFP cooling water return line. Makeup water is also available in the seismic category A Auxiliary Feedwater Storage Tank (AFWST). Since a piping connection is not available between the SFP and the AFWST, a flexible, non-collapsible hose is provided to gravity feed water into the SFP.
PDTS D3.2 requires the AFWST to be operable with a minimum water level of plant elevation 50 feet 9 inches.
This ensures that at least 50,000 gallons of water is available for oravity feed into the SFP. The AFWST water level is surveilled once per seven days (PDTS D4.2).
The SFP cooling and cleanup system removes fission product decay heat and maintains SFP water clarity and purity. An SFP cooling train includes an SFP cooling pump, SFP heat exchanger, Component Cooling Water (CCW) pump, CCW heat exchanger, and Saltwater Cooling pump.
The train is classified as non-safety related with the exception of those safety-related components required to maintain the SFP pressure boundary.
The SFP water temperature is required to be maintained less than 150*F, with at least one SFP cooling train maintained functional (PDTS D3.1). The term functional is defined in the PDTS as being capable of performing its intended function and maintained in accordance with good engineering and maintenance practices for commercial grade equipment.
SFP cleaning is provided by a filter in the SFP cooling line, ion exchangers in the liquid radwaste system, and a water skimmer system. SFP water chemistry (PDTS D3.1.3).
is also controlled to maintain chloride and fluoride levels below 0.15 ppm The water chemistry is verified once a month (PDTS D4.1).
The SFP water is currently sampled and analyzed on a weekly basis'for chlorides, fluorides, pH, conductivity, sulfates, boron, and activity and l
monthly for total organic carbon. j
NRC Bulletin 94-01 Responses for SONGS 1 Action 2 Ensure that systems for essential area heating and ventilation are adequate and appropriately maintained so that potential freezing failures that could cause loss of SFP water inventory are precluded.
Respon_s.e i
As described in Section 2.3 of the Updated Final Safety Analysis Report, the general climate at SONGS is quite mild due primarily to the influence of the-Pacific Ocean.
The average daily maximum and minimum temperatures for the coolest month, January, are 65'F and 46*F, respectively.
The extreme minimum j
temperature used for general plant design is 36*F.
The lowest recorded temperature of 33.1*F occurred on January 25, 1975. Significant snow accumulation and freezing rain have not been recorded at a coastal location in Southern California.
Therefore, conditions which could result in the freezing of equipment and its subsequent failure are not likely for SONGS.
Action 3 Ensure that piping or hoses in, or attached to, the SFP cannot serve as siphon or drainage paths in the event of piping or hose degradation or failure or the mispositioning of system valves.
Response
As discussed in the response _to Action No. 1, the SFP piping penetrations are located to ensure the stored fuel would remain covered with water even in the event of a piping failure.
The SFP cooling suction is at the top of the pool.
The return line is located at plant elevation 28 feet which ensures the fuel would be covered by approximately 13 feet of water if the SFP were to drain l
due to a pipe failure.
These SFP design features were reviewed by the NRC during the Systematic Evaluation Program and determined to be acceptable (NRC letter dated December 7, 1982).
A flexible non-collapsible hose is used to transfer water from the AFWST to the SFP if the Primary Makeup Tank is unavailable. When the hose is in use, the hose is secured in place, by procedure, near the SFP water surface and is administrative 1y controlled to maintain the SFP water level at or above plant elevation 40 feet 3 inches as required by the PDTS. Hoses are also available to allow the use of a CCW heat exchanger if the SFP heat exchanger was unavailable. These hoses have never been used.
Even if these hoses were in use, a break or siphon could not drain the SFP below plant elevation 28 feet since the normal pool piping penetrations would be used.
Plant procedures are maintained and followed to ensure these pipes and hoses do not become drainage paths.
Postulated SFP piping failures have been evaluated by the NRC and determined to be acceptable.
Temporary hoses or pipes would be controlled under existing administrative controls for temporary plant changes and could not be attached at an elevation below those addressed above.
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NRC Bulletin 94-01 Responses for SONGS 1 Action 4 Ensure that operating procedures address conditions and observations that could indicate changes in SFP level and address appropriate maintenance, calibration and surveillance of available monitoring equipment. This should include any leak detection systems.
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Response
SONGS 1 is being maintained in accordance with the PDTS which specify limits for SFP water level, water temperature, and water chemistry. Operations procedures include routine surveillances to monitor SFP water level and leakage and evaporation rates. Operations procedures also provide actions to be taken if parameters are off normal.
The SFP water level indication and SFP liner and fuel transfer tube leak detection wells are passive, requiring no j
routine maintenance.
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