ML20029E522
| ML20029E522 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 05/13/1994 |
| From: | Thayer J YANKEE ATOMIC ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| BYR-94-030, BYR-94-30, IEB-94-001, IEB-94-1, NUDOCS 9405190019 | |
| Download: ML20029E522 (6) | |
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May 13,1994 BYR 94-030 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555
References:
(a)
License No. DPR-3 (Docket No. 50-29)
(b)
NRC Bulletin 94-01, dated April 14,1994 (c)
Letter M. B. Fairtile, Nuclear Regulatory Commission to G.
Papanic, Yankee Atomic Electric Company, dated July 16,1987 (d)
L.etter, J. K. Thayer, Yankee Atomic Electric Company to T. E.
Murley, Nuclear Regulatory Commission, dated December 20,1993.
Subject:
RESPONSE 'IO NRC BULLETIN 94 POTENTIAL FUEL POOL DRAINDOWN CAUSED BY INADEQUATE MAINTENANCE PRACTICES AT DRESDEN UNIT 1
Dear Madame or Sir:
Yankee Atomic Electric Company (YAEC) has reviewed NRC Bulletin 94-01 (Reference (b)) and provides the following response for the Yankee Nuclear Power Station (YNPS).
The response addresses the requested actions: namely to ensure 1) that the quality of the Spent Fuel Pool (SFP) coolant is maintained; 2) that the cooling and shielding for the fuel or equipment stored in the SFP is not compromised; and 3) that all necessary structures and support systems are maintained. Descriptions of the SFP Cooling and Purification System, Fuel Transfer Chute, Spent Fuel Pit, and Spent Fuel Pit Building are contained in Sections 2.2.22,2.2.43, and 2.2.47 of the YNPS Decommissioning Plan (Reference (d)).
L Action: Verify that the structures and systems required for containing, cooling, cleaning, level monitoring and makeup of water 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.
YAEC Response:
The SFP and adjacent structures were analyzed as part of the NRC's Systematic Evaluation Program (Reference (c)). The SFP was determined to be structurally DO
Nuclear llegulatog Commission Page 2 adequate to resist forces imposed by the weight of the stored spent fuel, the racks, and the pool water, in combination with an earthquake equivalent to the NRC Spectrum event. The Spent Fuel Chute and the SFP Building were also determined to be structurally adequate to withstand the NRC Spectrum earthquake.
1 The YNPS has been permanently shutdown and defueled since February 1992.
Ilowever, the Spent Fuel Pit (SFP) and associated support systems are being operated and maintained in a manner similar to when the plant was operating, with two exceptions. One difference is that due to the low decay heat load of the spent fuel, the SFP Cooling and Component Cooling pumps are run intermittently to maintain SFP temperature between 75 F and 100 F. The pumps are currently operated about 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> every 21/2 days. Another difference is that a smaller auxiliary Service Water pump has been installed to conserve energy since overall plant heat load for the Service Water system is significantly reduced. The normal Senice Water pumps, currently are maintained operable.
During SFP cooling operation, a portion of the SFP water is circulated through an ion exchanger capsule for purification. Periodic sampling of the SFP ensures that water chemistg is maintained within plant administrative limits. Sampling is conducted by procedure for the following parameters:
Test Frequency Typical Limits p1i Weekly 4.8-5.2 4.0-9.0 Conductivity Weekly 4 mhos 150 ppb Chloride 2 / Month
< 50 ppb Fluoride 2 / Month
< 50 ppb
< 150 ppb Tritium 2 / Month 3x10 4x10'3 Ci/ml 4
d Gamma Isotopic 2 / Month 2x10 - 6x10 Ci/ml Baron Monthly 1100 ppm The SFP water level is maintained within a normal operating range of -8 to -16 inches (measured from the top of the SFP) which is in compliance with Defueled Technical Specification 3/4.1 and consistent with accident analysis assumptions.
The Component Cooling and Service Water pumps are included in the Predictive Maintenance Testing Program and are tested in'a manner consistent with the former Inservice Testing Program. The SFP Cooling pumps are being added to 4
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Nuclear Regulatory Commission Page 3 this quarterly testing program pending completion of the installation of flow instrumentation.
The following SFP-related instrumentation and controls are available in the Control Room:
o SFP level indication and alarm o
SFP temperature indication and alarm o
SFP manipulator crane area radiation monitor indication and alarm
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SFP Cooling pump discharge pressure indication and alarm o
SFP Cooling pump start /stop control switches o
SFP Cooling pump flow indication and alarm (installation pending) o Each of the above indications is recorded on the Equipment Operator logsheet once per 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> shift. The Equipment Operator also enters the SFP building to inspect the area once per 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> shift. TV cameras are installed and can be used by operators to immediately survey the area within the SFP building to assess any problem should the need arise.
The inventory of potential makeup water for the SFP from several on-site tanks is monitored and recorded on the Equipment Operator logsheet once per 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> shift. Additionally, Fire Water pumps taking suction from Sherman Reservoir are available as a method of SFP makeup. Plant procedures related to SFP operations have all been revised to reflect the permanently shutdown and defueled condition of the plant. These revisions included the creation of a procedure to address the numerous SFP makeup options.
2.
Action: 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.
YAEC Response:
The SFP building and associated buildings which contain SFP support systems are heated and ventilated using the same systems and procedures that were used when the plant was operating. Portions of the SFP Cooling piping which are -
located outside of buildings are heat traced and insulated. This heat trace is tested using an established procedure every Fall by the Maintenance Department
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Nuclear Regulatory Commission Page 4 and checked once per 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> shift by the Equipment Operator during cold weather months.
The Fuel Transfer Chute, which connects the SFP to the Shield Tank Cavity in the Vapor Container, is contained within a reinforced concrete enclosure. The Fuel Transfer Chute contains water up to an elevation even with the SFP water level, and an isolation valve at the base of the transfer chute isolates the SFP from the Fuel Transfer Chute. The Fuel Transfer Chute is not heat traced and the concrete enclosure is not heated. This design is unchanged from plant operations. There have been no freezing problems with the Fuel Transfer Chute in over thirty years of operation..
This past winter, a freezing incident occurred involving a line which is joined to the Fuel Transfer Chute at an elevation above the SFP water level. This line, which is normally empty except during transfer operations between the Vapor Container and the SFP, was in use to support reactor internals segmentation activities in the Shield Tank Cavity. A failure of the heat trace combined with an unusually cold winter resulted in rupture of the line at a point outside of the concrete enclosure for the Fuel Transfer Chute. The resulting leak was isolated and did not threaten the SFP since this line elevation was above the SFP water level. A check of the Fuel Transfer Chute showed no problems within the concrete enclosure. Thermocouples have been installed on the Fuel Transfer Chute pipe to monitor temperature.
The YNPS Decommissioning Plan requires that the Fuel Transfer Chute be isolated by capping the chute inside the Spent Fuel Pit and filling the chute with structurally stable material between the cap and the lower lock valve. This must be completed before initiating activities that could adversely interact with the Spent Fuel Pit.
3.
Action: 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.
YAEC Response:
Defueled Technical Specification 5.2.2 requires that the SFP be designed and maintained to prevent inadvertent draining of the pit. The Fuel Transfer Chute (described in item 2 above) is the only line which joins the SFP at an elevation below the top of the stored spent fuel. The integrity of the Fuel Transfer Chute and the SFP Building was evaluated during the Systematic Evaluation Program (Reference (c)) and determined to be structurally adequate to withstand the NRC Spectrum earthquake.
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Nuclear Regulatory Commission Page 5 The SFP Cooling suction and return lines enter the SFP from above and do not extend below the top of stored spent fuel. These lines are approximately four feet above the top of stored spent fuel. The Equipment Operator logsheet contains a listing of four valves off the SFP Cooling system which are verified once per 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> shift to be closed and locked. This valve positioning precludes inadvertent siphoning or draining of SFP water.
Loss of SFP Cooling System integrity could result in a rapid reduction of the SFP inventory. If the break is isolated within 30 minutes of the annunciation of the SFP low level alarm, SFP water level would be reduced to about 10 feet above the fuel. The fuel in the SFP remains covered by about 4 ft of water even if the break is not isolated and the level is allowed to decrease to the SFP Cooling System suction elevation. After the break is isolated SFP inventory can be re-established using one of several proceduralized alternatives.
4.
Action: 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.
YAEC Response:
As stated in item 1 above, all SFP-related procedures have been reviewed and revised to reflect the permanently shutdown and defueled condition of the plant.
Training for the Certified Fuel llandlers and Equipment Operators reinforces the importance of the SFP and supporting systems. The instrumentation listed in item I is maintained, calibrated and surveillance tested similar to when the plant was operating.
k We trust that you will find this response satisfactory; however, if you have any questions or desire additional information, please contact us.
Sincerely, YANKEE ATOMIC ELECTRIC COMPANY h
L bay K. Thayer Vice President and Manager of Operations 1
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Nuclear Regulatory Commission Page 6 COMMONWEAUl'Il OF MASSACIIUSETTS)
)ss WORCESTER COUNTY
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Then personally appeared before me, J. R. Thayer, who, being duly sworn, did state that he is a Vice President and Manager of Operations of Yankee Atomic E!ectric Company, that he is duly authorized to execute and file the foregoing document in the name and on behalf of Yankee Atomic Electric Company and that the statements therein are true to the best of his knowledge and belief.
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Kathryn Gatef blotary Public My Commission Expires January 24,1997 c:
M. Fairtile, NRC, NRR NRC Region 1 j
Vermont Yankee Resident inspector
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