ML17339A478
| ML17339A478 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 12/17/1979 |
| From: | EG&G, INC. |
| To: | |
| Shared Package | |
| ML17339A476 | List: |
| References | |
| NUDOCS 8001240240 | |
| Download: ML17339A478 (14) | |
Text
TECHNICAL EVALUATION OF THE ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE OVERPRESSURE MITIGATING SYSTEM FOR TURKEY POINT, UNITS 3 AND 4 (Docket Nos.
50-250,
-251)
EGLG
- Idaho, Inc.
l8 0 0 1 2 4 0 2. jo
1.0 INTRODUCTION
2.0 EVALUATION.
CONTENTS
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1 2.1 System Electrical and Control Description........
2 2.1.1 Channel Separability 2.1.2 Isolation Valve and Setpoint Alarms 2.1.3 Operator Action 2.1.4 IEEE 279 Criteria 2.1.5 Testabi1 ity 2.2 Pressure Transient Reporting and Recording Requirements 2.3 Disabling of Components During Cold Shutdown 2.4 Technical Specificati'ons
3.0 CONCLUSION
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4.0 REFERENCES
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TECHNICAL EVALUATION OF THE ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE OVERPRESSURE MITIGATING SYSTEM FOR TURKEY POINT, UNITS 3 AND 4 1'DocketNos.
50-250,
-251)
- 1. 0 INTRODUCTION 8y letter dated October 18, 1977 (Reference
- 1) Florida Power E
Light Company (FPL) submitted to the NRC a plant specific analysis in support of'the proposed reactor vessel overpressure mitigating system (OMS) for Turkey Point Nuclear Power Station, Units 3 and 4.
This information supplements other documentation submitted by FPL durin l lng 1976 and 1977 (References 2 through 7).
The electrical, instrumenta-
- tion, and control system aspects of the proposed design have been reviewed for this, Technical Evaluation Report.
The proposed OMS includes
- sensors, actuating mechanisms,
- alarms, and valves to prevent a reactor coolant system transient from exceeding the pressure/temperature limits included in the Turkey Point, Units 3
and 4 Technical Specifications as required by Appendix G to Chapter 10, Code of Federal Regulations, Part.50 (30 CFR 50).
2.0 EVALUATION The proposed overall approach to eliminating overpressure events incorporates administrative, procedural, and hardware controls with reliahce upon the plant operator for the principal line of defense.
Preventive administrative/procedural measures include (a) procedural precautions, (b) deenergization of essential components not required during the cold shutdown mode of operation, and (3 ) maintaining a
nonwater-solid reactor coolant system condition whenever possib'...
The basic design criteria that were applied in determining the adequacy of the electrical, instrumentation, and control aspects of the low temperature overpressure protection system are:
operator action until ten minutes after the oper-ator is aware, through an action alarm, that a
pressure transient is in progress.
(2)
Sin le Fai lure Criterion the pressure protec-tion system shall be designed to protect the reac-tor vessel given a single failure in addition to the failure that initiated the pressure transient.
provisions for testing on a schedule consistent with the frequency that the system is relied upon for pressure protection.
(4)
Seismic and IEEE 279 Criteri a ideally, the system should meet seismic Category I and IEEE 279 criteria.
The basic objective is that the system should not be vulnerable to a
common failure that would both initiate a pressure transient and dis-able the OMS.
Such events as loss of instrument air and loss of offsite power must be considered.
In addition to complying with these criteria, the licensee has agreed to provide a variety of alarms to alert the operator to.( a) manu-ally enable the p'ressure protection system during cooldown,
( b) indi-II cate the occurrence of a pressure transient, and (c) indicate closure of either power operated relief valve (PORV) isolation valve which ensures a complete pathway from the pressurizer to the pressurizer relief tank.
2.1 S stem Electrical and Control Oescri tion The OMS.design for Turkey Point, Units 3 and 4 uses pressurizer PORVs with a variable low pressure setpoint as the pressure relief mechanism (Reference I).
The variable low setpoint is energized and
deenergized by two switches, one for each
- PORV, on the main control board.
The variable low pressure setpoint is derived from reactor coolant system (RCS) wide range temperature using redu'ndant transmit-ters.
The reactor coolant pressure signal is obtained from redundant wide range pressure transmitters.
Below an RCS temperature of 300 F, the setpoint is a constant 415 psig.
Above 300 F, the setpoint in-creases linearly from 415 psig at 300 F to 2335 psig at 462 F.
Various alarms are included in the OMS.. On decreasing
- pressure, an alarm and annunciator will activate at 390 psig.
This a'iarm alerts the operator to energize the OMS.
The alarm will not clear unless (a) the low pressure setpoint is energized, (b) the PORY mode selector switch is in AUTO, and (c) the motor operated valves (MOVs) upstream of the PORVs are indicated open.
This assures proper alignment of the OMS.
On increasing pressure an alarm and annunciator will actuate at 400 psig.
This alarm will inform the operator that RCS pressure is approaching the PORY low setpoint.
Action can then be taken to remedy the cause of increasing
- pressure, or, if part of a normal heatup, to deenergize the OMS by placing the two NDTT control switches to the "Normal" position..
Should pressure continue to increase to the PORV
- setpoint, an alarm and annunciator wi 11 inform the operator that the PORVs have received a signal to open from the OMS.
The PORVs are spring-loaded closed and require air to open.
The air js presently supplied by instrument air.
A redundant supply of air to the valves is included in the OMS.
Redundant accumulators, one dedicated to each PORV, will be added to the present air source.
Each accumulator will be sized to ensure a minimum of ten minutes operation of the ONS.
Redundant check valves will be provided for each accumu-lator to prohibit backfeeding the instrument air system.
Existing alarms in the control room will alert the operator to a loss of instru-ment air to the PORVs and associated accumulators.
- 2. 1.1 Channel Se arabi lit.
The OMS has two channels, one to control each PORV, that provide complete redundancy and are independent except for the use of cocoon alarms and annunciators
( as established by
the single failure analysis reported in Reference
- 6) which are isolated,'o that a failure in the circuitry will not incapacitate either chan-'el.
Either one of the two PORVs provides the relief capacity needed to protect the vessel against a low-temperature overpressurization event; the other PORV provides redundant capacity.
The OMS setpoints and RCS pressure signals are derived from redundant temperature and pressure transmitters.
Each ch'annel has its own ENABLE/DISABLE switch installed on the main control board.
The installation of the OMS is in accordance with the separation criteria used in the design.of the Turkey Point Plant.
Each of the two channels uses an independent power supply from the transmitters to the solenoid valves controlling the air to the PORVs.
As discussed in the system description, the OMS has separ ate backup air supplies for each PORV.
These design features are in compliance with the single failure design criterion.
2.1.2 Isolation Valve and Set oint Alarms.
As described in Para-graph 2.1, various alarms are included in the OMS.
Clearing of these alarms ensures proper alignment of the OMS.
The alarms provided meet the OMS design criterion.
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"'ended function for at least ten minutes without operator action.
The most restrictive condition is the continued operation of a safety injec-tion pump with an assumed loss of instrument air.
The redundant sources of air to the PORVs are sized to ensure a minimum of ten I,
minutes of operation after the'oss of instrument air, and existing alarms alert the operator to this loss.
The system meets the design criterion for operator action.
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2.1.4 IEEE 279 Criteria.
The OMS meets the intent of IEEE 279, is designed against single failure, and has two channels that are electrically separate and meet the physical separation requirements used in the design of the electrical system for the Turkey Point Plant.
In addition, periodic testing of the OMS prior to the need for
its operation is. included to enhance system reliability.
The compli-ance of the design with the IEEE 279 design criteria is adequate.
.I.
cooldown procedures include verification of OMS operability prior to soli d-system, low-temperature operation.
Testing will be accomplished by (a) closing the PORC isolation valves, (b) enabling the OMS, 'and (c) inputting a signal below 300 f (test done with RCS pressure above 415 psig).
In this manner, OMS circuits as well as.PORV operability will be verified.
In addition, the associated instrumentation'will be surveilled for calibration and proper operation using the same methods followed for safety-related instrumentation.
These provisions and procedures for testability are adequate.
2;2 Pressure Transient Re ortin and Recordin Re uirements The staff position on a pressure transient which causes the overpressure protection system to function, thereby indicating the occurrence of a serious pressure transient, is that it is a 30-day reportable event.
In addition, pressure and temperature instrument-ation are required to provide a permanent record of the pressure tran-sient.
The response times of the temperature/pressure recorders shall be compatible with a pressure transient increasing at a rate of approxi-mately 100 psi per second.
This instrumentation shall be operable whenever the OMS is enabled.
2.3 Disablin of Com onents Not Re uired Ourin Cold Shutdown Except as required for brief intervals by operating procedures or Technical Specifications, the staff position requires that essential components not required during cold shutdown that could produce an overpressurization event be disabled or isolated from the RCS during cold shutdown, and that the controls to disable or isolate these com-ponents be incorporated in the Technical Specifications.
In particu-lar, the safety injection accumulators and the high pressure safety injection pumps are included in the components to be disabled or
isolated.
Valves and breakers used to disable essential equ'ipment during cold shutdown must be tagged or locked to prevent inadvertent changes of state.
2.4 Technical S ecifications To ensure operation of the OMS, the licensee is to sub'mit for staff review Technical Specifications to be incorporated into the license for Turkey Point, Units' and 4; These specifications are to be consistent with the intent of the statements listed below.
The licensee should ensure that the Technical Specifications proposed are compatible with other licensee requirements.
(I)
Whenever the RCS temperature is less than the mini-mum pressurization temperature, the OMS shall be
, enabled with both PORVs operable, except one PORV may be inoperable for seven days.
If these condi-tions are not met, the primary system must be de-pressurized and vented to the atmosphere or to the pressurizer relief tank within eight hours.
(2 )
Enablement of the OMS requires that the low pres-sure setpoint will be selected, the upstream iso-lation valves
- open, and the backup air supply charged.
(3)
No more than one high head SI pump injection valve may be energized at RCS temperatures below 380 F
unless the vessel head is removed.
(4)
'A reactor coolant pump may be started (or jogged) only if there is a steam bubble in the pressurizer, or the SG/RCS temperature difference is less than SooF.
(5)
The OMS must be tested on a periodic basis consis-tent with the need for its use.
(6}
When the plant is in a cold shutdown condition the safety injection accumulators shall be isolated from the RCS by verifying that the accumulator'solation valves are in the closed position and power to the valve operators is removed.
3.0 CONCLUSION
S The electrical,, instrumentation, and control aspects of the Turkey Point, Units 3 and 4
OMS design are adequate on the basis that (a) the proposed control circuitry meets the intent of IEEE 279, (b} the system is redundant and meets the single failure criterion, (c) the design requires no operator action for ten minutes after the operator receives an overpressure action alarm, (d) the system is testable on a periodic
- basis, and (e) the proposed changes to the Technical Specifications reduce the probabi-lity of an overpressurization event to an acceptable level.
However, it is recomnended that final acceptance be contingent upon the licensee incorporating Technical Specifications that comply with the list in Section 2.4.
4.0 REFERENCES
1.
FPL letter (Uhrig) to NRC (Lear) dated October 18, 1976.
2.
FPL letter (Uhrig) to NRC (Lear) dated October'5, 1976.
3.
FPL letter (Uhrig) to NRC (Lear) dated December 10, 1976.
4.
FPL letter (Uhrig). to NRC (Lear) dated March 1, 1977.
5.
FPL letter (Uhrig) to NRC (Lear) dated March 16, 1977.
6.
FPL letter (Uhrig) to NRC (Lear} dated March 31, 1977.
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7.
FPL letter (Ukrig) to NRC (Lear) dated April 21, 1977.
8.
Memorandum R.
B
. Baer to K. Goller, Oecember 29, 1977 Safet ation of the Over r
e ver pressure Mitigating System Designed for Turkey Point, Units 3 and 4.