ML20005D949
| ML20005D949 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 12/17/1989 |
| From: | Medford M TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9001020318 | |
| Download: ML20005D949 (5) | |
Text
................ -,...............
TENNESSEE VALLEY AUTHORITY 6N 38A I ookout Place Decedoer 17, 1989 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C.
20555 Gentlemen:
In the Matter of
)
Docket Nos. 50-327 Tennessee Valley Authority
)
50-328 SEQUOYAH NUCLEAR PLANT (SQN) - REQUEST FOR DISCRETIONARY ENFORCEMENT FOR LIMITING CONDITION FOR OPERATION (LCO) 3.3.2.1 This letter documents TVA's request for discretionary enforcement for both SQN units regarding LCO 3.3.2.1, Item 9.a. because of inoperability of more than one wide-range level indicator on the refueling water storage tank for each unit due to severe freezing conditions. Discretionary enforcement for a period of 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> was determined to have no significant impact on the safe operation of the SQN units. The severe freezing conditions also created a need for continued operation of SQN to meet the power demand. Consequently.
TVA requested discretionary enforcement to allow time for resolution of the equipment problems while meeting the power demand. The detailed justification for the discretionary enforcement is provided as an enclosure.
NRC's approval of the 48-hour discretionary enforcement for Unit I was provided to TVA by NRC at 0615 Eastern standard time (EST) on December 16, 1989. Unit 2 was subsequently discussed with NRC, and the 48-hour discretionary enforcement period to coincide with Unit I was granted at=1155 EST on December 16, 1989.
Please direct questions concerning this issue to B. S. Schofield at (615) 843-6172.
Very truly yours.
TENNESSEE VALLEY AUTHORITY
,b M. O. Medford, ice President, Nuclear Technology and Licensing Enclosure cc (Enclosure):
See page 2 f
\\ \\
B[
10 An Equal Opportunity Employer G
PNV
i U.S. Nuclear Regulatory Commiss. ion cct Ms. S. C. Black, Assistant Director for Projects TVA Projects Division U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. B. A. Wilson, Assistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379
v p
ENCLOSURE SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 JUSTIFICATION FOR DISCRETIONARY ENFORCEMENT FOR LIMITING CONDITION FOR OPERATION (LCO) 3.3.2.1 Description of Condition At 0357 Eastern standard time (EST) on December 16, 1989, the second of four wide-range level transmitters (LT) on the Unit i refueling water storage tank (RWST) was declared inoperable due to severe freezing conditions. A third LT was declared inoperable for the same reason at 0407 EST. At 0828 EST the second Unit 2 LT was affected by the freezing conditions. The wide-range RWST LTs provide control room indication for postaccident monitoring (LCO 3.3.3.7, Item 4) and also provide an input to the logic that controls automatic switchover to containment sump (LCO 3.3.2.1 Item 9.a).
LCO 3.3.2.1 requires that a total of four channels be operable with the units operating in Modes 1, 2, 3, and 4.
Action Statement 18 of that technical specification (TS) allows one of the channels to be out of service.
LCO 3.3.3.7 requires that two channels be operable with the units operating in Modes 1, 2, and 3.
The action statements for the TSs allow 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> to restore at least one inoperable channel when no channels are operable. As a result of the freezing conditions, Action Statement 18 was exceeded for both units.
Consequently, LCO 3.0.3 requires corrective action to be performed within one hour or that the unit be placed in at least HOT STANDBY within the following six hours.
Verification of RWST Levels The levels in the Unit 1 and Unit 2 RWSTs were verified to be within TSs allowable limits at approximately 0000 EST on December 16, 1989, using the four wide-range channels and the RWST narrow-range LTs (which are located inside the top of the RWST, well insulated, with no external sense lines).
The Unit 1 RWST level was again verified at 0500 EST by use of an installed mechanical float and the narrow-range LTs. The Unit 2 RWST level was also verified at 0500 EST using the narrow-range LTs. The Unit 2 mechanical float was not functional. These readings provided adequate assurance that the RWSTs contained the required volume of borated water. TVA will continue to monitor the RWST volumes once per shift by reading the narrow-range LTs and removing the manway on top of the tank to visually verify a level in the tank (i.e.,
the tank is full) while the discretionary enforcement remains in effect.
Evaluation of Automatic Switchover Function Automatic switchover is initiated when the level in the containment sump increases to greater than or equal to 11.25 percent and the RWST level decreases to less than 29 percent coincident with a safety injection signal.
The emergency instructions require verification that automatic switchover has occurred, and if not, they instruct the operator to initiate a manual transfer.
TVA has reviewed the emergency procedures that govern switchover from the RWST to the containment sump to determine if adequate guidance is provided in the event that automatic switchover does not occur because RWST level indication is not available. As a result of this review, TVA issued additional operator
4 guidance in the form of a night order.
The operators were notified that if automatic switchover did not occur or if RWST level was considered unreliable then the operator is to verify containment sump level is creater than or equal to 55 percent and complete the switchover to the sump manually.
Initially TVA considered placing the RWST level bistables associated with automatic sump switchover in the tripped condition to ensure completion of the automatic transfer function.
This approach would ensure automatic transfer when the containment sump water level reached approximately 30 inches.
However, this approach could also lead to switchover before the RWST was depleted.
Placing the RWST level bistables in the bypass condition, as required by Action Statement 18, was also considered. Placing the bistables in bypass would defeat input from the LTs to the solid-state protection system and, therefore, prevent automatic switchover regardless of sump water level.
Consequently, TVA decided that the most prudent action would be to make no adjustment to the bistables and to notify the operators that containment sump level should be used when taking any remedial actions to effect sump switchover.
This revised of approach provides adequate guidance for sump switchover while also ensuring sufficient RWST injection to satisfy postaccident sump chemistry and boration requirements.
Discussion of Specific Commitments When requesting this discretionary enforcement TVA committed to perform the following five actions.
1.
Verify that the plant emergency operating procedure (. provide sufficient guidance to ensure switchover to the containment sump will occur.
TVA reviewed the emergency procedures that govern switchover from the RWST to the containment sump to determine if adequate guidance is provided in the event that automatic switchover does not occur because RWST level indication is not available. As a result of this review, TVA issued additional operator guidance in the form of a night order. The operators were notified that if automatic switchover did not occur or if RWST level was considered unreliable then the operator is to verify containment sump level is greater than or equal to 55 percent and complete the switchover to the sump manually.
The 55 percent level in the containment sump will occur when the RWST level reaches approximately 29 percent, thereby ensuring adequate RWST depletion.
This night order is reviewed with each Operations crew during the shift turnover meeting prior to that crew assuming shift. Training will continue until the temporary RWST LT problem is resolved or until all Operations crews have been trained.
TVA considers this guidance as an enhancement to the SQN emergency procedures and will consider making a permanent revision through the normal procedure change process.
c.
.E-
- g. 2.
Ensure that adequate protective measures were established with regard to any compensatory actions taken.
In order to return the frozen lines to operable status, plastic tents were p
erected around the affected instruments and sense lines.
Once the enclosures were completed heating elements (electric heaters) were installed along with electric fans to circulate the heated air.
The heated air defrosted the frozen lines and maintained the temperature of the instruments within an operable range.
Good engineering practices were used when erecting the enclosures and installing the heaters to ensure adequate clearances existed between the heaters and any combustible materials. A fire watch was established at each tank to ensure protection of the equipment. The compensatory measures described above will remain in place until the heaters and tents are removed.
3.
During the time period of the discretionary enforcement, establish a method of physically verifying RWST level.
TVA committed to remove the manway located on top of the RWST and visually verify that the tank is essentially full once per shift to provide N
additional confidence in the operation of the narrow-range LTs.
TVA will continue this activity for the duration of the period that the discretionary enforcement remains in effect.
- 4. -- Address the reporting requirements of this event.
)
TVA is presently evaluating the events and evaluating the NRC questions regarding 10 CFR 50.72 and 10 CFR 50.73 reportability. TVA will provide a I
written follow-up to this evaluation by December 22, 1989.
5.
Provide NRC with a written follow-up to this discretionary enforcement action on Monday morning, December 18, 1989.
In a follow-up telephone call at approximately 1300 EST on Saturday, December 16, 1989, NRC project management requested that the written follow-up be provided by 1200 EST on December 17, 1989.
This submittal provides the requested written follow-up.
Summary RWST level for each unit was verified just prior to loss of the wide-range LTs due to severe freezing.
Following loss of the wide-range instruments, tank level was reverified using narrow-range instrumentation and will continue to be verified one per shift using narrow-range LTs and visual inspection.
Additional guidance to be followed to assure proper sump switchover is provided to each Operations crew. These actions, which will remain in effect for the discretionary enforcement period, ensure that the requirement for sump switchover are met.