ML18152B769
| ML18152B769 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 07/14/1998 |
| From: | Ohanlon J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 98-396, NUDOCS 9807210324 | |
| Download: ML18152B769 (5) | |
Text
VIRGINIA ELECTRIC AND PowER COMPANY RICHMOND, VIRGINIA 23261 July 14, 1998 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC. 20555 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 Serial No.
NS&L/BCB:
Docket Nos.
License Nos.
CLARIFICATION OF PROPOSED LICENSE CONDITION AND TECHNICAL SPECIFICATIONS CHANGE TEMPORARY SERVICE WATER SUPPLY LINE TO THE CCHXS98-396 R1 50-280 50-281 DPR-32 DPR-37 Virginia Electric and Power Company (Virginia Power) submitted a request for a License Condition and Technical Specifications amendment in a letter dated November 5, 1997 (Serial No.97-496).
The proposed license condition and Technical Specifications change establish the requirements for the use of a temporary supply line Uumper) to provide service water (SW) to the component cooling heat exchangers (CCHXs). The temporary SW supply jumper is necessary to facilitate repairs on the existing single, concrete-encased, SW supply piping to the CCHXs and/or integral components (e.g., pipe recoating, weld repair, replacement of expansion joints or SW isolation valves).
The November 5, 1997 submittal was subsequently revised in response to NRC review comments and resubmitted for NRC review on June 19, 1998 (Serial No.98-327). One of the NRC comments addressed by the revision was an explanation of the contingency actions for a loss of the temporary SW supply jumper at the most limiting unit condition.
The revised submittal indicated that a loss of decay heat removal has been previously considered and addressed by existing station procedures.
The revision also summarized the contingency actions directed by these procedures and indicated that they would also be applicable to a loss of the temporary SW supply jumper.
During a conference call on June 25, 1998 between the NRC and Virginia Power personnel, the NRC requested further clarification of the contingency actions for a loss of the temporary SW supply jumper. In that regard, a more detailed explanation of these actions and the governing procedures is provided in Attachment 1.
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9807210324 980714 PDR ADOCK 05000280 P
- No additional commitments are contained in this letter. Should you have any questions or require 'additional information, please contact us.
Very truly yours,
~-~H~E~--L Senior Vice President - Nuclear Attachments
- 1.
Clarification of Contingency Actions for a Loss of the Temporary Service Water Supply Jumper cc:
U. S. Nuclear Regulatory Commission Region II Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303 Mr. R. A. Musser NRC Senior Resident Inspector Surry Power Station Commissioner Bureau of Radiological Health Room 104A 1500 East Main Street Richmond, Virginia 23219
Clarification of Contingency Actions for a Loss of the Temporary Service Water Supply Jumper NRC Question Describe the worst case scenario for a loss of decay heat removal when the temporary service water (SW) supply line Uumper) is in service. In addition, provide a discussion of the contingency actions and equipment/systems that are available to mitigate such a scenario.
Virginia Power Response The concern for a loss of decay heat removal is not unique with respect to the use of a temporary SW jumper. A loss of decay heat removal, including that resulting from a loss of the normal SW supply line, has been previously considered and addressed by existing station procedures. The implementation of those same procedures, in the event of a loss of the temporary SW jumper, will ensure that core cooling can be maintained until the normal SW supply line can be returned to service. The specific procedures and contingency actions for a loss of the temporary SW jumper at the most limiting plant condition are discussed below.
The Unit 1 refueling schedule includes three general Reactor Coolant System (RCS) conditions of concern which will exist concurrent with the use of the temporary SW jumper as the sole source of SW to the component cooling heat exchangers (CCHXs).
Condition 1 The refueling cavity will be flooded with refueling operations under way. During this period, the entire core will be offloaded to the fuel building where inserts are shuffled, etc. The new core, which consists of approximately one-third new and two-thirds previously used fuel assemblies, will then be loaded.
Condition 2 At a minimum of 360 hours0.00417 days <br />0.1 hours <br />5.952381e-4 weeks <br />1.3698e-4 months <br /> after shutdown, the RCS inventory will be decreased to approximately reactor flange level once the new core has been loaded. The purpose for decreasing the inventory is to facilitate the installation of the reactor vessel head. The RCS loops are scheduled to be unisolated before the cavity level is decreased-to-this -point;-however,-the-loops may -still be-isolated due to emerging changes during the outage.
Condition 3 The RCS inventory will be increased to a level in the pressurizer following the installation of the reactor vessel head. The RCS loops will also be unisolated and filled.
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Of these three general RCS conditions, Condition 2 has been determined to be the r-nost limitihg. Although there will be a decrease in RCS inventory during Condition 2, the system will not be at mid-loop level (i.e., "reduced inventory") while the temporary SW jumper is in service. The scheduled duration of Condition 2 is approximately 3.5 days.
Contingency actions for a loss of decay heat removal are addressed by Operations Surveillance Procedure 1-0SP-ZZ-004, "Unit 1 Safety Systems Status List for Cold Shutdown/Refueling Conditions," and Abnormal Procedure 1-AP-27.00, "Loss of Decay Heat Removal Capability." These procedures have been in place for some time and are included in routine Operator training as well as "just in time" training for Operators, which is conducted prior to refueling outages.
1-0SP-ZZ-004 provides instructions for determining the required equipment during Cold Shutdown and Refueling Shutdown conditions, including that equipment required to provide backup core cooling in the event of a loss of the Residual Heat Removal (RHR) system.
The procedure also provides guidance on selecting the most appropriate backup core cooling method for the prevailing plant conditions, equipment availability, etc.
An Operator will perform 1-0SP-ZZ-004 at the beginning of each shift (when fuel is in the vessel). For the three conditions described above, the procedure will guide the Operator to select a "feed and bleed" backup core cooling method (described below).
In addition, the procedure will define the equipment that must be available, given the unit conditions, to implement the selected contingency method.
In the event of an RHR failure, 1-AP-27.00 will be initiated. This procedure provides guidance on how to use the selected backup core cooling method, as well as restoration of the RHR system.
While in Condition 1, the flooded cavity provides sufficient heat sink to mitigate a loss of SW. However, the decrease in RCS inventory while at Conditions 2 and 3 will require "feed and bleed" core cooling.
The "feed and bleed" method requires an available source of water (refueling water storage tank), a motive force (safety injection pump or gravity), a sufficient "feed" or flowpath to the core, and an adequate "bleed" or discharge path (pressurizer safety valve removed, pressurizer PORVs opened or removed, or open reactor vessel). This method has been analyzed and found to be an adequate means of preventing core bo~ling and uncovery, thereby precluding fuel damage.
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Based on the contingency actions described above, a complete loss of decay heat 11em'oval is unlikely. However, if the temporary SW jumper failed at the limiting RCS condition (Condition 2) and the backup contingency actions were not implemented, core boiling and uncovery could occur, resulting in fuel damage. With a loss of decay heat removal while at Condition 2 (loop stop valves closed), core boiling has been calculated to begin at 0.6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, core uncovery (collapsed level at the top of the fuel) at 1.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and fuel clad damage at 2.0 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />. It is important to note that these durations are very conservative in that they are based on a total loss of the RHR system. As such, the calculations do not include any credit for the heat capacity of the RHR or component cooling (CC) systems. Assuming only a loss of SW, the RHR and CC pumps would continue to operate, which would significantly increase the duration to core boiling, core uncovery, and fuel clad damage.
A loss of the temporary SW jumper would be immediately recognized since the line will be continuously monitored while in service. To mitigate the consequences of such an event, the contingency actions prescribed by 1-0SP-ZZ-004 and 1-AP-27.00 (i.e., "feed and bleed") would be implemented as needed. A simulation of this event has been performed, which demonstrated that control room operators can initiate this alternate core cooling method within 15 minutes.
This backup method would preclude core boiling and provide sufficient core cooling until the normal SW supply line could be placed in service (within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />).
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