ML20029E460
| ML20029E460 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco, 07200011 |
| Issue date: | 05/12/1994 |
| From: | Redeker S SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Weiss S NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-94-001, IEB-94-1, MPC&D-94-043, MPC&D-94-43, NUDOCS 9405180343 | |
| Download: ML20029E460 (10) | |
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SACRAMENTO MUNICIPAL UTILITY DISTRICT 9R O.
Box 16830. Sacramento CA 95852-1830, (916) 452 3211 AN LLECT HIC SYSTEM SLHVING rHE HEARI OF CAllFORNIA May 12, 1994 MPC&D 94-043 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Docket No. 50-312 Rancho Seco Nuclear Station License No. DPR-54 DISTRICT RESPONSE TO NRC BULLETIN 94-01 Attention: Seymour Weiss Enclosed is the District's response to NRC Bulletin 94-01, " Potential Fuel Pool Drain-Down caused by Inadequate Maintenance Practices at Dresden Unit 1," in accordance with 10 CFR 50.54(f).
f The Rancho Seco nuclear plant is a single unit, permanently shutdown facility with a dedicated staff of over 100 workers focused on closing and eventually decommissioning the facility in a 1
safe and controlled manner. The number one priority at Rancho Seco is to safely store the spent fuel, currently located in the spent fuel pool. The District plans to move the spent fuel into the proposed Rancho Seco Independent Spent Fuel Storage Installation (ISFSI) by 1998.
Since permanent plant shut down in June 1989, the District has had the necessary programs, personnel and management oversight in place at Rancho Seco to ensure continued safe maintenance of spent fuel during the Permanently Defueled Mode (PDM).
Members of your staff requiring additional information or clarification may contact Jerry Delezenski at (916) 452-3211, extension 4914.
Sincerely,
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Steve Redeker Manager, Nuclear Plant Closure Enclosure cc: L. J. Callan, NRC, Arlington, Texas T. Markley, NRC, Rockville 9405180343 94031,
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J DISTRICT HEADQUARTERS I ! 6201 S Street, Sacramento CA 95817-1899 4
DJSTRICT RESPONSE TO NRC BULLETJN 94-01 Requested Action #1 Verify that the structures and systems required for containing, cooling, clet. iing, level monitoring, and make-up of wa'er in the 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.
District Resnonse:
CONTAINING The Spent Fuel Pool (SFP) is a reinforced concrete rectangular open tank with a stainless steel liner, located in the Fuel Storage Building (FSB). The SFP is completely lined with stainless steel plates for leak tightness. The District purchased the SFP liner as Quality Assurance (QA) Class 1 and continues to maintain this component as QA Class 1 during the Permanently Defueled Mode (PDM). The SFP is designed to hold up to 1080 spent fuel assemblies and to withstand external inDuences, particularly seismic conditions. The SFP is maintained functional through implementation of the various site programs, including the chemistry control and maintenance, SFP leak detection, SFP level maintenance and monitoring, corrective action, and 10 CFR 50, Appendix B, QA programs.
The FSB is a QA Class 1, reinforced concrete structure that contains the SFP and has a super structure with concrete walls and steel roof system. The FSB is designed to withstand the design basis seismic loads and other applicable loads without loss of function.
COOLING & CLEANING l
The Spent Fuel Pool Cooling System (SFC) heat removal design capacity is large enough to handle a full SFP (1080 fuel assemblies), which includes a freshly discharged core (177 assemblies decayed 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> with a 9 day core discharge time).
Rancho Seco is only storing 493 irradiated fuel assemblies, and the reactor has not operated since June 7,1989. The current SFP heat load is well within the SFC heat removal design capacity. Rancho Seco has not modined the SFC or retired any ofits components from service since permanent plant shutdown. The SFC consists of(1) a cooling loop, including the SFP, pump, cooler, piping, and valves, (2) a purincation loop, including the SFP demineralizer pump, Glter, ion exchanger, piping, and valves, j
and (3) a skimmer loop, which is valved into the purincation loop.
Decay heat generated in the SFP is removed by recirculating SFP water through the SFP cooler. The SFP puriGeation system is tied into the cooling loop downstream of the cooler. The purincation system keeps the water clean and removes residual ionic radionuclides present in the SFP. A fraction of the total SFC How is diverted through the purification system, passed through the Glter and ion exchanger, and returned back to the primary Dow path. In addition, a skimmeris installed to clean the SFP surface. The skimmer takes suction from the SFP surface, discharges the water
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DISTRICT RESPONSE TO NRC BULLETIN 94-01 Requestod Action #1:(Continued) through the filter and ion exchanger in the purification loop, and returns the water through a set of nozzles back into the SFP. The nozzles are arranged to cause the water to move in the SFP and facilitate cleaning. To maintain optimum SFP water conditions, the SFC pump and SFP demineralizer pump are normally operating.
Rancho Seco operates the SFC in accordance with Operations Procedure A.21, " Spent Fuel Cooling System." The actions required to address a loss of SFC are addressed in Casualty Procedure OP-C.38, " Loss of Spent Fuel Pool Cooling or Level." Rancho Seco semi-annually functionally tests SFC to verify that it continues to provide design flow in accordance with the Surveillance Program, using Surveillance Procedure 64 (SP.64), "Special Frequency Spent Fuel Cooling System Surveillance Test."
Rancho Seco's licensing basis requires a back-up SFP cooling system. This system is the Radwaste and Fuel Storage Area HVAC system. This system nonnally runs continuously to maintain good atmospheric conditions in the FSB. Procedure A.14B,
" Auxiliary Building HVAC System," addresses operation of this system. The main components in this system are exhaust fans A 542A & B and supply fan A-541.
Exhaust fans A-542A & B are part of the Rancho Seco In-service Confirmation Program. As part of this program, Rancho Seco personnel implement procedure SP,625A & B," Permanently Defueled Auxiliary & Spent Fuel Building Filter System Testing," to demonstrate their operability every 18 months or after any work that could alter this system's HEPA filter integrity.
LEVEL MONITORING Rancho Seco meets or exceeds the Permanently Defueled Technical SpeciGcation (PDTS) D3/4.1 surveillance requirements and performs SFP level checks every operator shift (two shifts per day) and SFP level alann switch calibrations at least every 18 months. These surveillance requirements are implemented through procedures SP.2, " Daily Instrument Checks and Systems Verification," and SP.512, "Special Frequency Spent Fuel Pool Level Instrumentation Calibration," respectively.
Rancho Seco recently performed the SFP levelinstrumentation calibration within the time requirements in accordance with SP.512. The SFP level instrumentation passed this surveillance.
The minimum SFP levels specified in PDTS D3/4.1 ensure a minimum of nine feet of water is maintained over the top of fuel assemblies while the fuel is being stored or i
moved in the SFP. This ensures adequate shielding is maintained to protect operators and other personnel in the FSB during both fuel storage and fuel handling operations.
The Control Room, which is continuously manned has a TV monitor that is continuously tuned to the FSB and specifically directed at a numeric SFP level indicator 'This monitor provides a visual means by which the Control Room operators monitor the SFP level. I
DISTRICT RESPONSE TO NRC BULLETIN 94-01 j
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Requested Action #1:(Continued)'
1 M AKE-UP WATER Make-up water to the spent fuel pool may be provided by any of the following methods:
A.
Pumping water from the Miscellaneous Water Holdup Tank directly to the spent fuel pool through a valve and pipe.
B.
Pumping water from the Demineralized Water Header, which gets its water from the Condensate Storage Tank, to the spent fuel pool through a hose that must be attached.
C.
Pumping water from the Folsom South Canal or Rancho Seco reservoir to the spent fuel pool via the diesel or electric fire pump and a Dre hose station. (Emergency Supply Only)
D.
Supplying water from the pressurized Service Water system to the spent fuel pool through a hose. (Emergency Supply Only)
These SFP water addition methods are addressed in procedure OP-C.38. Currently, approximately 250,000 gallons of demineralized water is available for addition to the SFP, with millions of gallons availsble from the non demineralized make-up water sources.
CHEMISTRY CONTROLS Rancho Seco implements a chemistry control program for the SFP in accordance with the Permanently Defueled Technical Specification (PDTS) D3/4.5 and other prudent chemistry control practices. The PDTS Chloride and Fluoride chemistry limits basis is derived from the B & W Water Chemistry Manual - Dual Type Plants, BAW-1385, April 24,1974 The Chloride and Fluoride PDTS limits ensure the potential for degradation of fuel assemblies, fuel transfer equipment, storage racks, and the SFP liner is minimized during long-term storage of spent fuel.
Rancho Seco monitors and maintains the SFP water quality in accordance with the PDTS D3/4.5, " Spent Fuel Pool Water Chemistry," and Chemistry procedure CAP.0006,"Chmistry Frequencies, Ranges, and Limits." The PDTS SFP water quality monitoring requirements are satisfied through implementation of SP.949,
" Monthly Spent Fuel Pool Water Chemistry Doct. mentation." Rancho Seco continues to maintain the SFP within the PDTS D3/4.5 chemistry limits. In addition to the PDTS SFP chemistry control program, Rancho Seco administratively controls SFP water quality and make-up water systems through implementation of Chemistry procedure CAP-0006. Parameters routinely monitored on a monthly basis include pH, Boron, sulfates, and radioactivity Implementation of CAP-0006 provides 3-
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i DJSTRICT RESPONSE TO NRC BULLETIN 94 01 Requested Action #1:(Continued) important SFP water quality data at regular intervals. This administrative SFP chemistry control program ensures (1) Rancho Seco will continue to maintain i
excellent SFP water quality, (2) plant management is informed if a SFP water quality limit is exceeded, and (3) corrective actions are promptly initiated to restore SFP water quality to within its limits.
The following additional monitoring and administrative programs provide additional assurance of continued safe operation and maintenance of Rancho Seco during the permanently shutdown condition.
As part of the operator plant status tour required in Operations Procedure OAP-0060,
" Control of System Status and Tours," an operator is required to enter the FSB every shift to observe the condition of the FSB and SFP from inside the building and check the SFP temperature.
Annunciator Procedure Il2X directs operators to implement the appropriate response and recovery actions needed to mitigate the consequences of the following fuel storage related Control Room alarms:
1.
Low SFC Pump Discharge Pressure 2.
High SFP Temperature 3.
High-Low SFP Level 4.
Low-Low SFP Level 5.
High SFC Filter Differential Pressure 6.
High-Low SFC lon Exchanger DilTerential Pressure Rancho Seco implements a calibration program for SFP monitoring equipment as follows:
1.
Calibrate SFP Temperature Instruments (Annually) and Indicators (Triennially) 2.
Flush SFP Leak Chase Flow Measuring System with Warm Water (Quarterly) 3.
Verify SFP Level Alarms (Quarterly)
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DISTRICT RESPONSE TG NRC BULLETIN 94-01 Requested Action ill:(Continued) 4.
Calibrate the SFC Mechanical Filter Pressure DilTerential and Flow Indicator Devices (Annually) 5.
Clean, Insped, and Calibrate the SFC Pump Pressure Switch and SFC Pump i
and Ion Exchanger Pump Pressure Indicator Devices (Annually) i I
6.
Calibrate the SFC lon Exchanger Differential Pressure Indicator Device I
(Annually) 7.
Test and Adjust Exhaust Fan A-542A Switchgear Breaker 3C39 (Triennially) 8.
Test and Adjust Exhaust Fan A-542B Switchgear Breaker 3D38 (Triennially)
Requested Action ft2: Ensure that systems for essential area heating and ventilation i
are adequate and appropriately maintained so that potential freezing failures that could cause loss of SFP water inventory are precluded.
District ResponSc.
Due to the historically moderate climate in the Sacramento Valley, Rancho Seco does
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not require and was not designed with heating systems for the purpose of freeze protecting SFC or the SFP inventory.
The climate in the Sacramento area lends itself to only moderately low temperatures during the winter months. Generally, temperatures rarely drop below 25 "F or even stay below freezing (32 "F) during a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period. The record low temperature recorded in the Sacramento area is 17 "F This occurred in December 1990, while the 1
plant was in the same shutdown condition it is today. This record low temperature did not result in the loss of SFP boundary integrity and did not result in a loss of any -
SFP water inventory. No freeze damage occurred to any SFC or SFP lines, and no SFP drainage or siphoning resulted from this record freeze.
Two fuel transfer tubes connect the FSB to the Reactor Building. The fuel transfer tubes are horizontal tubes that are attached to the SFP liner to ensure SFP leak integrity. These tubes have gate valves on the FSB side and bolted and gasketed Hanges on the Reactor Building side. The fuel transfer tubes are not susceptible to freezing failures due to (1) their large diameter (approximately 30 inches), (2) the relatively moderate winter weather experienced in the Sacramento area, and (3) the.
insulation provided by the concrete vault the fuel transfer tubes are housed in that nms between the FSB and Reactor Building. Therefore, a loss of SFP inventory due to a fuel transfer tube freezing is not a credible event.
5-
DISTRICT RESPONSE TO NRC BU.LLETIN 94-Q1 -
Requested Action #2:(Continued)
In response to the record cold temperatures Sacramento experienced in December 1990, Rancho Seco reviewed and upgraded operating procedure OP-C.33 " Freeze Protection." Procedure OP-C.33 identifies corrective actions necessary to avoid potential operational problems that may result from sub-freezing temperatures.
The SFC and its demineralizer sub-system are normally continuously operating.
These systems are mostly underground or in the Auxiliary Building. Because these systems are normally operating, they are not a freeze concern.
The NRC approved the Rancho Seco PDTS based on the fact that there are no safety hazards associated with a minimum SFP level of 23 feet 3 inches (Reference the Bases for PDTS D3/4.1). This minimum, allowed SFP level is based on the design and licensing basis of the SFP. The lowest piping penetration in the SFP, excluding the fuel transfer tubes (which are not a freeze concern as explained above), isjust above the 23 foot 3 inch level. So, even if the piping associated with this penetration froze and broke, a SFP inventory loss to below the design basis for plant operations during the PDM could not occur. (Note: This particular penetration and piping is part of the SFC and normally has SFP water circulating through it.) Therefore, based on the design of the Rancho Seco SFP, a frozen pipe that breaks can not result in a loss of SFP inventory below the SFP's licensing design basis.
In spite of the above freeze evaluation and based on the freeze concerns raised in NRC Bulletin 94-01, the District decided to enhance procedure OP-C.33 to include a provision to ensure the SFC and the SFC demineralizer sub-system are either running or isolated from the SFP any time the ambient air temperature drops to s25 "F.
The HVAC system that services the FSB is the Radwaste and Fuel Storage Area HVAC system. This system is a ventilation system only, provides no heating, and normally runs continuously. Procedure A.14B," Auxiliary Building HVAC System,"
addresses operation of this system. The main ventilation components in this system are exhaust fans A-542A & B. See the response to Requested Action #2 for additional information on this system. This system is not required for freeze protection. No HVAC or other heating systems are necessary to ensure the SFP will not drain down below its design basis level.
i Requested 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.
District Resnonse:
As addressed in the response to Requested Action #2, the fuel transfer tubes connect the FSB to the Reactor Building, are attached to the SFP liner to ensure SFP leak i
DISTRICT RESPONSE TO NRC BULilTIN 94-01 Requested Action ft3:(Continued) integrity, and are not susceptible to freezing. The fuel transfer tubes have valve and blind flange ends that isolate the fuel transfer tubes. Administrative controls contained in procedure OAP.0099, " Operations Locked Valve List," ensure the fuel transfer tube gate valves remain closed. No credible fuel transfer tube failure modes exist due to the static condition of the transfer tubes and their closures. Therefore, the fuel transfer tubes are not a credible SFP drain down pathway.
Also, all first-off valves on the SFC, which is the only system that penetrates the SFP besides the fuel transfer tubes, are locked closed and administratively controlled in accordance with OAP.0099. This measure provides an additional administrative control designed to prevent inadvertent SFP draining or siphoning.
The most serious type of failure associated with the SFP would be a complete loss of SFP water. To protect against the possibility of a severe loss of SFP water inventory due to a breach in connected piping, all SFP piping penetrations, except the fuel transfer tubes, penetrate the SFP no lower than approximately the 24 foot level.
As discussed in the response to Requested Action #2, the minimum, allowed SFP level (23 feet 3 inches) isjust below the lowest piping penetration in the SFP that can lead to a major SFP inventory loss. So, even if the pipe associated with this lowest SFP penetration broke or began siphoning the SFP,it could not result in draining down the SFP below the normal licensing design basis operating level. At this lowest, allowed SFP water operating level, a minimum of nine feet of water would remain above the top of stored spent fuel assemblies.
Finally, Rancho Seco has no hoses in or directly attached to the SFP and does not normally use hoses to put water into or remove water from the SFP. In order to siphon the SFP using hoses, an individual would have to hold open a FSB door and run a hose from the SFP to outside the FSB. Access to the FSB is controlled by Security. The FSB doors are alarmed and are maintained locked closed in accordance with the Rancho Seco Security Plan. Based on the FSB door design and administrative controls associated with FSB access, hoses do not represent a concern at Rancho Seco regarding SFP siphoning or draining. But, based on the hose concerns raised in NRC Bulletin 94-01, the District decided to enhance the operator plant status tour procedure (OAP.0060, " Control of System Status and Tours") to include a shiftly check for hoses running from the FSB.
5 Requested Action 1/4: 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.
F DISTRICT RESPONSE TO NRC BULLETJN 94-01
$lequested Action #4:(Continued)
District Response:
The response to Requested Action #1 addresses the issues raised in Requested Action
- 4, except for SFP leak detection systems. The evaluation below addresses the SFP leak dettetion program at Rancho Seco.
The SFP is designed with a leak-chase system that collects and conveys SFP liner leakage to radioactive waste collection and treatment systems in the Auxiliary Building. The leak collection part of the leak-chase system monitors the leakage from the SFP liner. Procedure RT-SFC-001, " Spent Fuel Pool Leak Detection Trending,"
l requires monthly collection, tabulation, and trending of the SFP liner leakage data.
SFP liner leakage is monitored by a device that is capable of measuring very small flows and larger flows up to 1.75 liters / minute. This SFP liner leakage monitoring device is flushed with warm water quarterly as part of the Rancho Seco calibration program.
Procedure A.21, " Spent Fuel Cooling System," provides the operators with instructions on how to operate the SFP liner leak-chase system. Also, Operators collect SFP liner leak data daily in accordance with the Shift Routines log, which is controlled by OAP.0050, " Shift Routine." The SFP liner leakage monitoring device has an input into the plant computer and provides SFP liner leakage data and trends in the Control Room and locally at panel H4CDAR4. High SFP liner leak flow (>3 gallons per hour) alarms in the Control Room. Annunciator procedure IDADS addresses the response to a high SFP liner leak rate alarm. Procedure OP-C.38 addresses the prescribed response options for SFP inventory losses.
In conclusion, the District believes that the structures and systems currently in operation, coupled with routine implementation of the PDTS and administrative requirements cited above, is consistent with Rancho Seco's licensing basis during the PDM and provides more than adequate assurance that Rancho Seco will continue to:
1.
Preclude high levels of radionuclides in the SFP and adverse effects on stored fuel, the SFP, fuel transfer components, and related equipment; 2.
Preclude freezing failures that could cause loss of SFP water inventory to below the minimum allowed level; 3.
I revent piping or hoses attached to the SFP causing the SFP to drain or siphon down to below the minimum allowed level; and 4.
Provide operating procedures that address conditions and observations that could indicate changes in SFP level and address appropriate maintenance, calibration, and surveillance of available monitoring equipment, including leak detection system.
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