ML20246B535
| ML20246B535 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 08/18/1989 |
| From: | Michael Ray TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TASK-2.B.1, TASK-TM TAC-49759, TAC-54415, TAC-54416, TAC-54569, NUDOCS 8908230387 | |
| Download: ML20246B535 (9) | |
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TENNESSEE VALLEY AUTHORITY
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10 CFR 50.90 X
'U.S. Nuclear Regulatory Commission ATTN:. Document Control Desk.
Washington, D.C.
20555 Gentlemen:
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'In the Matter of
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' Docket'Nos. 50-327
. Tennessee Valley Authority _
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50-328 1
SEQUOYAH NUCLEAR PLANT (SQN)'-' REQUEST FOR ADDITIONAL INFORMATION FOR
~ TECHNICAL SPECIFICATION.(TS) 52 (TMI ITEM II.B.1, REACTOR COOLANT SYSTEM VENTS)'
Reference:
.NRC letter to TVA dated June 1, 1989, " Reactor Coolant System High Point Vents.(TMI Item II.B.1, MPA F-10, MPA B-83).(TAC 54415/54416/
54569/49759)-(TS -52) - Sequoyah Nuclear Plant, Units 1 and 2" As requested in the referenced letter, TVA is submitting additional information for SQN's TS change 52 regarding the reactor coolant head vent system (RCHVS). Also included is the RCHVS design analysis for postulated missile characteristics from RCHVS component failures and potential fluid spray effects from such failures..contains the justification'for three minor differences between SQN's RCHVS TS and the guidance provided in NRC's Generic Letter 83-37 and s 6 dard TSs for Westinghouse Electric Corporation (W) pressurized water reactors. Enclosure 2'contains the requested system design analysis information. 'TVA is in agreement with the W conclusions that there are no postulated missiles associated with the RCHVS and that there is no possibility for steam or fluid spray from the RCHVS valves as a result of mechanical failures. contains TVA's commitment for revising SQN's RCHVS TSs to include revised action requirements.
Please direct questions concerning this issue to D. V. Goodin at
-(615) 843-7734.
Very truly yours.
TENNESSEE VALLEY AUTHORITY
'l Manager, Nucleefr Licensing and Regulatory Affairs Enclosures cc:
See page 2 g
8908230387 890818 I I PDR ADOCK 05000327 i
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. An Equal Opportunity Employer
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U8 l8 Ebb U.S. Nuclear Regulatory Commission cc (Enclosures):
.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. 8. A. Wilson, Assistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory. Commission Regien II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Mr. Michael H. Mobley, Director (w/o enclosures)
Division of Radiological Health
.T.E.R.R.A. Building 150 9th Avenue, N Nashville,-Tennessee 37203 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379 American Nuclear Insurers Attention:
Librarian The Exchange, Suite 245 270 Farmington Avenue Farmington, Connecticut 06032
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ENCLOSURE 1 By letter dated June 1,1989, NRC issued ' Amendment No.116 to Facility Operating License DPR-77 and Amendment No. 106 to Facility Operating License DPR-79 for Sequoyah Nuclear-Plant (SQN) Units 1 and 2 respectively.
These amendments were in response to TVA's letter dated January 25, 1984 (SQN' Technical Specification {TS] Change 52). NRC's June 1989 letter requested that TVA provide justification to address three minor differences between SQN's reactor coolant vent system (RCVS) TS and the guidance provided in NRC Generic Letter 83-37 and the standard TS for Westinghouse Electric Corporation's pressurized water reactor. The following provides TVA's justification for these minor differences.
Difference No. 1 TVA's RCVS TS does not require RCVS paths to be operable in Mode 4.
TVA should pravids justification for this difference.
TVA's Justification SQN's RCVS is required to vent noncondensible gas or steam voids that would
. obstruct natural circulation heat removal. The introduction of noncondensible gas or steam into the reactor coolant system (RCS) can be caused by two events or conditions:
1.
A rapid RCS cooldown/depressurization under natural circulation conditions resulting in the formation of a steam void in the upper head region.
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Inadequate core cooling resulting in the production of hydrogen gas.
For Condition 1, the TS requirement for maintaining the reactor head vent system operable while in Modes 1, 2 and 3 is appropriate because high cooldown rates and associated RCS depressurization under natural circulation conditions would only be expected in Mode 3 following operation in Modes 1 and 2.
A plant cooldown below Mode 3 (350 degrees F) requires placing the residual heat removal (RHR) system in service. This mode of operation cannot lead to void formation in the upper head because RCS pressure is controlled by the RHR system..It is not coupled to the RCS cooldown rate. Consequently, formation of a steam void is not expected to occur below Mode 3 as a result of a rapid cooldown/depressurization.
l The second condition that could result in formation of a void in the RCS would be an accident condition where inadequate core cooling exists and the production of hydrogen.is being caused by the high temperature reaction of Zircaloy and water.
For these temperatures to be reached, forced convective heat transfer would not be available, and natural circulation within the RCS would have become ineffective.
Protection against such an accident is provided in the emergency core cooling system (ECCS) design requirements under 10 CFR 50.46.
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. TS applicability for full ECCS operability is required in Modes 1, 2, and 3.
(SQN specification 3.5.3 does require certain ECCS equipment to be operable while in Mode 4; however, this equipment is not required to meet single failure criteria on the basis that reactivity conditions in the reactor are stable and core cooling requirements are limited.) TS compliance for ECCS equipment in Modes 1, 2, and 3 ensures that the ECCS 10 CFR 50.46 criteria can be met for limiting hydrogen generacion in the NCS. The RCHVS TS applicability'is consistent with the full ECCS operability specification.
The Westinghouse Owners Group developed procedural guidelines for vent i
operation trat rely on the reactor vessel level indication system (RVLIS).as the primary means of determining if voids exist in the RCS. The venting operation is linked to RVLIS through SQN's Functional-Restoration Guideline FR-I.3, Response to Voids in Reactor Vessel. Venting proceeds only with a reliable means of determining the location of noncondensibles (e.3., reactor i
vessel head) and when to terminate the venting. The venting operation is controlled and monitored to ensure no resultant or additional core damage j
occurs because of loss of'RCS inventory.
The Westinghouse Owners Group has concluded that'a direct reliable indication of vessel level is needed to conduct the venting operation.
RVLIS requirements are contained in SQN's
'I accident monitor instrumentation TS 3.3.3.7, which specifies applicability in Modes 1, 2, and 3.
Since operation of SQN's RCVS requires that RVLIS is available for determining if voids exist in the upper head regions of the reactor' vessel, consistent mode applicability is provided in the ISs for both the RCVS and RVLIS.
SQN's venting operation is also closely linked to SQN's combustible gas control systems (i.e., hydrogen analyzers, hydrogen recombiners, and hydrogen ignitors). These systems are required for detection and control of hydrogen gas inside containment. Prior.to venting, these hydrogen mitigation systems q
aid the operator in determining if containment hydrogen concentration is below 3 percent. These systems also provide information in determining the maximum allowable venting time. TS applicability for these hydrogen mitigation systems encompasses Modes 1 and 2 (see SQN's specifications 3.6.4.1, 3.6.4.2, and 3.6.4.3).
These requirements are less restrictive than the mode 4
applicability for the RCVS technical specification.
RCVS IS 3.4.11 also contains requirements for having two vent paths operable in Modes'1, 2 and.3.
SQN's pressurizer power-operated relief valves (PCRVs) serve to provide a' vent path that satisfies a portion of the RCVS specification (see footnote provided with 3.4.11).
PORV operability is required by TS 3.4.3.2, Relief Valves--Operating, and is applicable in Modes 1, 2, and 3.
This provides consistency between RCVS specification 3.4.11 and PORV specification 3.4.3.2 for mode applicability.
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. l Difference No. 2 i
TVA's action statement for both paths being inoperable (action [b]) does not require the inoperable vent paths be maintained closed with power removed from the' valve's actuators as proposed for action statement (a) for one path being inoperable. TVA should provide justification for this difference.
IVA's Justification TVA inadvertently omitted the action for closing and removing power from the valve actuators for the case when both RCVS paths are inoperable.
TVA is currently evaluating SQN's entire RCVS TS for general improvements that would provide consistent action requirements for both the reactor vessel head vent path and the pressurizer PORV vent path. TVA will submit these improvements to NRC as a proposed TS change by November 15, 1989. Enclosure 3 centains TVA's commitment for submitting this TS change.
Difference No. 3
~ The action statements (a) and (b) for SQN's RCVS specification do not require the plant to eventually enter cold shutdown (Mode 5).
TVA should provide justification for this dif a
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TVA's Justification Based on the evaluation of mode applicability for the RCVS TS as discussed above, the action requirements (a) and (b) for entering hot standby (Mode 4),
rather.than cold shutdown (Mode 5), are considered to be appropriate.
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ENCLOSURE 2 WESTINGHOUSE ELECTRIC CORPORATION LETTER DATED JULY 31, 1989
" TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANTS UNITS 1 (, 2 REACTOR VESSEL HEAD VENT SYSTEM OUESTIONS"
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Electric Corporation Pittsburgh Pennsylvania 15230 0355 l
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Mr. P. G. Trudel i
Sequoyah Project Engineer TVA-89-810 Tennessee Valley Authority July 31, 1989 Sequoyah Nuclear Plant. DSC-A
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PO Box 2000 i
Soddy - Daisy, TN 37379 i
Tennessee Valley Authority Sequoyah Nuclear Plants Units 1 & 2 Reactor vessel Head Vent System Ouestions
Dear Mr. Trudel:
As part of their approval of a technical specification change to Section 3/4.4, the NRC has asked TVA to provide information on postulated missile characteristics from Reactor Vessel Head Vent System (RVHVS) component failures and potential fluid spray effects from such failures.
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t' The following information is being provided to assist you in your response to the NRC.
The RVHVS is designed to remove noncondensable gases or steam from the reactor vessel via remote manual operations from the control room.
The system consists of two parallel flow paths with redundant isolation valves I
in each flow path.
The venting operation uses only one flow path at e time.
The active portion of the RVHVS consists of four one-inch
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open/close solenoid operated isolation valves.
j Components within the reactor coolant accident boundary have been examined to identify and classify potential missiles. Those components within the missiles are: reactor coolant accident boundary whose failure may result in postulate 1
Instrument wells and thimbles Huts and bolts Control Rod Drivt,Chaft and/or housing Pressurizer heV ers Valves installed in tb NSSS have integral stem backstops which rules out the possibility of efecting valve stems.
Valves are not considered credible missiles.
i Relative to the above it formation and the fact that valves are the only active component in the RVhi'S, there are no postulated missiles associated with the RVHVS.
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There is no possibility for steam or fluid spray from the RVHVS valves as result of mechanical failure. The analysis concerning the effects of fluid sprays on~ safety-related systems is the responsibility of the AE and should be addressed in their jet spray and environmental effects analysis.
Please let me know if you require additional' information.
Very truly yours.
WESTINGHOUSE ELECTRIC CORP 0 RATION N&
T. A. Lordi, Manager TVA sequoyah Project Customer Projects Department I
cc:.
D. M. Lafever W. R. Manglante R. G. Davis R. E. Daniels J. A. Vogel C. C. Mason J. T. LaPoint i
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l-ENCLOSURE 3 TVA Commitment TVA.will submit a-TS change to SQN's RCVS Specification 3.4.11 by November-15, 1989.
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