ML20004E826
| ML20004E826 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 06/08/1981 |
| From: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.F.2, TASK-TM NUDOCS 8106150344 | |
| Download: ML20004E826 (14) | |
Text
SOUTH CAROLINA ELECTRIC a gas CcMPANY 4
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CotumelA. SOUTH CAROUNA 29218 f
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Mr. Harold R. Denton, Director t
Office of Nuc. lear Reactor Regulation 7
U. S. Nuclear Regulatory Commission Washington, D. C.
20555
Subject:
Virgil C. Summer Nuclear Station Docket No. 50/395 Inadequate Core Cooling-NUREG 0737 Item II.F.2.
SER Open Item 1.6.16
Dear Mr. Denton:
In three previous submittals in response to NUREG 0737 item II.F.2 South Carolina Electric and Gas Company (SCE&G) provided information regarding inadequate core cooling instruments. These letters were dated December 4, 1980, December 15, 1980; and December 30, 1980.
In discussing these submittals with Mr. Tai Huang, the staff reviewer, it was indicated that some information was missing that was required by NUREG 0737. He also requested that in sub-mitting the new information that we provide a point by point comparison of the NUREG 0737 requirements and our response for each. This letter provides the requested information.
As discussed in this letter, the core subcooled monito:: was purchased prior to the issuance of NUREC 0737. New requirements regarding qualification of equipment were issued by NUREG 0737. SCE&G is in the process of providing the required qualification upgrade; however, it will not be completed until June, 1983. Since the 1.nplementation date listed in NUREG 0737 is January 1, 1982, we request your approval of our schedule.
If you have any questions, please let us know.
Very truly yours, T. C. Nichols, Jr.
RBC:lkb Attachment cc: Page 2 8106150 %
6 i
i
e Mr. H. R. Denton June 6, 1981 Page 2 cc:
H.
R.' Denton V. C. Sunumer G. H. Fischer H. N. Cyrus T..C. Nichols, Jr.
1 D. A. Nauman W. A. Williams,-Jr.
R. B. Clary
- 0. S. Bradham A. R. Koon M. N. Browne
,B. A. Bursey y
J. B. Cookinham J. L. Skolds t
4 J. B. Knotts,-Jr.
i H. E. Yocom NPCF l
File i
i i
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L._:
NUREG 0737 II. F.2 INSTRUMENTATION FOR DETECTION OF INADEQUATE CORE COOLING DOCUMENTATION REQUIRED (1) Description of Final System The final instrumentation systems to be used by SCE6G at the Virgil C.
Summer Nuclear Station for detection of inadequate core cooling will consist of the Reactor Vessel Level Instrumentation System, the core subcooling monitor, and the incore thermocouple temperature displays provided by the plant process computer and the core subcooling monitor.
The Reactor Vessel Level Instrumentation System has been described in the document entitled "
SUMMARY
REPORT WESTINGHOUSE REACTOR VESSEL IN-STRUMENTATION SYSTEM FOR MONITORING INADEQUATE CORE COOLING" Dec. 19CO.
This document was previously transmitted under a letter dated Dec. 30, 1980, to Mr. Harold R. Denton.
(Hereafter Referred to as Reference 1.)
The core subcooling monitor is a two channel microprocessor based system which calculates and displays the subcooling margin based on reactor coolant system temperatures and pressures.
Df. splays and alarms are provided on the main control board for operator use in detection of inadequate core cooling. The monitor, which is located in the control room, also provides a digital readout of input signals, including incore thermocouple temperatures. This provides a backup system for monitoring incora thermocouple temperatures as described below.
The following incore thermocouple displays are available to the operator:
- Primary System The primary means of monitoring thermocouple temperatures is the plant's process computer. The computer constantly monitors all 51 incore thermocouple temperature values over a range of 70 F to 2200 F.
Computer displays and alarms available to the operator are described in section II. F.2. Attachment 1.
Backup System The second means of monitoring incore thermocouple temperature is the core subcooling monitor. Each channel of the subcooling monitor re-ceives inputs from 8 thermocouples (2 per core quadrant per channel, for a total of 16 thermocouples). A digital readout of any of the 16 single thermocouple temperatures may be obtained at the subcooling monitor panel located in the control room. The range of the readings is 0 F to 2300 F.
These systems are described in greater detail in section of (1-b) of this report.
(1-a) Additional Instrumentation The additional instrumentation to be added to the present system to
attain the above configuration is described as follows:
a) No additional instrumentation required for RVLIC.
b) No additional displays are required.
c) Incore thermocouple system.
1.
Reference junction boxes which couple the output of the thermocouples to the input of the process computer and sub-cooled monitor to be qualified to Reg. Guides 1.89 and-1.100.
2.
Electrical isolators and data links (computer and TSC inter-faces).
(1-b) Detailed Description of the Existing Instrumentation CORE SUBC00 LING MONITOR a)
Introduction The Westinghouse core subcooling monitor provides improved infor-mation presentation and display to the plant operators on the status of core heat removal capability. This system was designed to address NUREG-0578, Item 2.1.3b and consists of redundant channels of surveillance grade instrumentation with redundant control board meters to indicate the margin to saturation.
b) -Technical Description The core subcooling monitor utilizes inputs from the existing hot leg RTDs, reactor coolant system pressures, and 16 selected incore thermocouples. A microprocessor is employed to calculate the saturation temperature for the existing reactor coolant system pressure and determine the margin t4 saturation based on the various temperature inputs. The margin to saturation is then displayed on dual indicators located on the main control board. Each dual indicator displays margin to saturation based on incore thermo-cougle inputs and on hot leg RIDS.
Each scale indicates from 300 F subcooling to 2262 F superheat.
The supplied system utilizes redundant inputs, microprocessor units, and indicators which satisfy the requirements for redundant safety grade equipment. The system is divided into two redundant channels, each accepting inputs from two hot leg RTDs, 8 thermocouples, and three reactor coolant system pressures.
The auctioneered low reactor coolant system pressure is utilized by the microprocessor to calculate the saturation temperature for the reactor coolant system. By subtracting the auctioneered high inccre thermocouple temperature or the auctioneered high hot leg i
RTD temperature from the calculated saturation temperature, the margin to saturation is determined. This information is then ;
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I displayed on two vertical indicating scales on the main control board and on the core subcooling monitor located in main control room.
Two levels of alarm are provided; the first to indicate the development of abnormal conditions; the second to indicate the loss of core subcooling. These alarms are integrated into the main control board annunciator system and are currently set at:
Caution - 25 F subcooled for RTD input; 15 F subcooled for T/C input.
Alarm - 0 F subcooled for both RTD and T/C inputs.
Expanded information is displayed on the front of the monitor to enable plant personnel to determine core cooling conditions during all plant operating conditions. Each of the redundant microprocessors will utilize the computed saturation temperature for comparison with the following plant parameters.
Individual loop wide range T hot
- Auctioneered high wide range Thot Average incore thermocouple Auctioneered high incore thermocouple.
Also, available for display on the monitor are the following:
4
- The difference between the average incore thermocouple temperature and individual loop T temperaturas.
g A graphic, color, 15 lamp display of the incore temperatures.
The core is divided into five regions, four peripheral and one central, with inputs from two thermocouples used to generate the display for each region. Each region has three lamps, green, yellow, and red. Two sets of three lamps are also provided for the hot leg RTDs input into each drawer.
If all temperatures are sufficiently below saturation, the lamps will be green.
If any individual temperature reaches an off-normal condition, the lamp display changes to yellow and alarms on the control board annun-clator. Should conditions continue to degrade to the preset margin to saturation, the lamp display changes to red and alarms on the control board annunciator.
(1-c) Planned Modifications The planned modifications are described in (1-a) above.
(2) Design Analysis / Evaluation The evaluation of the instrumentation to provide reactor vessel
- vel indication is included in Reference 1.
The evaluation of the Core Subcooling Monitor is included in Point (1-b) above.
(3) Additional Test Programs In order to establish anc upgrade qualification of the equipment to comply with NUREG 0737, the following additional test programs are required.
3.1 Qualification tests or analysis of incore thermocouples.
3.2 Qualification tests of incore thermocouple reference junction boxes and connectors.
(For additional information on points 3.1 and 3.2 refer to point 5 of Attachment #1.)
3.3 Environmental and seismic qualification tests of electrori.cs to oe added to the system to provide isolation and data links between the subcooled monitor and the plant computer or TSC computer.
(4) Conformance to Attachment I and Appendix B.
4.1 Evaluation of conformance of the reactor vessel level indication system is included in Reference 1.
4.2. Refer to separate sections addressing Attachment 1 and Appendix B for this evaluation of the subcooled monitor and incore charmocouple systems.
(5) Description of Computer Functions The subcooled monitor and process computer functions associated with I.C.C.
are derxribed in previous sections of this report. There are no computer functions associated with the RVLIS.
(6) Current Schedule EQUIPMENT INSTALLATION CALIBRATION QUALIFICATION TESTING 1.
RVLIS 2.
Core Subcooling Aug. 1981 Aug. 1981 In Progress Sept. 1981 Monitors 3.
Incore Thermo-Installed Installed In Progress Completed couples 4.
Cabling for 16 qualified TC's June, 1983 NA June, 1983 June 1983 5.
Qualified refer-NA In Progress June
- 1983 June, 1983 ence junction boxe s and connectors EQUIPMENT
' INSTALLATION CALIBRATION QUALIFICATION TESTING 6.- Qualified isola-June, 1983 NA June, 1983 June, 1983 tors from output of subcooled monitor to process computer
-(7) Guidelines for Use of ICC Instrumentation Based on the analysis defined in the summary report on Westinghouse Reactor Vessel Level Instrumentation dated December, 1980, Westinghouse and the Westinghouse Owners Group have developed a Reference Emergency Operating Instruction to address recovery from ICC conditions caused by a small break L.O.C.A. without high head safety injection.
SCE&G is currently _ working with the Westinghouse Owners Group to include the
- use of the new ICC instrumentation in this procedure.
(8) Summary of Emergency Procedures for ICC Operator Actions in Current ICC' Procedure
'A Symptoms of ICC (1) Main and emergency feedwater is not operable or sufficient to maintain a heat sink and adequate _ core cooling.
(2) Steam generator levels are off scale.
(3) Secondary steam releaae is not sufficient to provide adequate core cooling.
(4) Any five (5) incore thermocouples indicating 211200 F and increasing as measured on:
- 1) Plant computer, 2)
Subcooling monitor, or 3)
Incore Thermocouple indicator.
(5) Wide range Tc indicating;7 700 F, with no reactor coolant pumps
. running.
(6) Abnormal. containment conditions (pressure, radiation, sump level) exist.
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Immediate Actions (1)
Initiate or continue steam dump to the condenser or to atmosphere.
(2)
Initiate safety injection and verify flow.
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(3) If during the procedure a refueling water storage tank low / low alarm is received establish cold leg re. circulation.
(4) When steam generators are empty secure all operating reactor coolant pumps to reduce heat load.
(5) Open one pressurizer power operated relief valve (P.O.R.V.)
(6) Open an additional P.O.R.V. to maintain reactor coolant pressure less than 2400 psig.
(7) If pressure stabilizes near 2400 psig:
(a) Reset Safety Injection Train A & B.
(b) Open MVG-8109A, B, and C and MVG-8106 to establish charging pump minimum flow.
(c) Close MVG-8109A, B, and C and MVG-8106 whe.ever pressurizer pressure drops to 1550 psig.
(8) Continue monitoring incore thermocouples on the core subcooling monitor or plant computer.
(a)
If thermocouple readings exceed the computer range, have a millivolt meter attached to the core exit thermocouple indicator for reading higher temperatures.
.(b)
If incore thermocouple indication is lost, monitor wide range Tc indicators (9)
If the above does not result in. decreasing core exit thermocouple temperatures, star t one (1) Reactor Coolant Pump to establish
' forced flow through the core.
Note: Precautions and limitations for RCS status are waived for this procedure.
(a) Run the Reactor Coolant Pump for 5 to 10 minutes and then stop.
(b) Alternating the reactor coolant pump in use, start and stop another reactor coolant pump at 30 minute intervals as long as they are available.
C.
Final Conditions (1) Reactor cooling has been achieved via the pressurizer relief valves.
(2) Reactor cooling via the secondary steam dumps has been achieved.
SCE&G is currently working with Westinghouse to improve this procedure and to revise the loss of core coolant procedures to include ICC instru-mentation. _
(9) Additional Submittals SCE6G will submit the revised inadequate core cooling and loss of coolant procedures for NRC review in the future, if required.
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NUREG 0737 ITEM II. F.2
-Evaluation of Conformance of the Core Subcooling Monitor to Appendia B Criteria.
I Applicability 1
The core subcooled monitor was designed and purchased prior to the issuance of NUREG 0737 and Regulatory Guide 1.97, Rev. 2.
In order to meet the qualification requirements of these new documents some equipment must
.be qualified and/or replaced. The equipment as originally designed will
~be installed by September, 1981. The equipment qualification will be complete by June, 1983 in accordance with Reg. Guide 1.97, Rev. 2, Implementat'on Requirements.
l.
The Core Subcooling Monitor system (cabinet, microprocessors and displays) is qualified to Reg. Guide 1.100.
The system is located 4.n the control room which is temperature and humidity controlled by a Class IE air conditioning system. The cabinet also contains the aucoustic leak monitor electronics which is also qualified to comply with the same requirements as the subcooling monitor.
The aging of the electronic components will be addreesed in the Westing-house component aging program. Representative samples of similar components will be included in Subprogram C of Appendix B to WCAP 8587. (A) 2&3. The core subcooling monitor contains'two independent channels which are powered from independent class IE battery backed power supplies The power supplies are physically separated in accordance with Reg.
Guide 1.75.
Each channel has a separate, independent dual indicating scale located on the main control boerd.
The purpose of qualification of the core subcooling monitor system is to generate evidence that the equipment will maintain and perform its functions during a Design Basis Event.
It is of special concern during the qualification effort to uncover common mode failures.
In the event of a failure of one channel of the subcooling monitor, diverse instruments such as the RVLIS and RCS temperatures and pressures are available to allow the operator to deduce actual plant conditions.
4 The subcooled monitor contains two channels. The procedures used to test the subcooled monitor during power operations will be written such that only one channel will be tested at a time.
The subcooled monitor contains no automatic protection features which could be defeated during testing.
5.
a) Reference junction boxes, electrical isolators and data links will be constructed and installed using a Quality Ass..ance program as recom-mended by NUREG 0737.
b) A Quality Assurance program was not required for the subcooled monitor prior to the issuance of NUREG 0737.
SCE6G is participating in the Westinghouse program to verify the quality of the components used in the subcooled monitor.
6.
Continuo 2s indication of subcooled margin is provided by two meters on
~ the mair - control board.
7.-
Reactor coolant system temperatures and pressures are recorded on strip chart recorders in the control room and can be used for trend or transient intarmation.
8.
The core subcooling meters have been functionally located on the reactor coolant system section of the control board. After qualification is complete unique labelling will identify the meters as qualified post accident monitoring instruments.
9.
The inputs to the subcooled monitor from the hot leg RTD's and reactor coolant system pressures are isolated.
Isolation between the subcooled monitor and the process computer and TSC are provided by a data link.
10.
The operational availability of each monitoring channel will be verified during reactor opet 1 tion by cross-checking between each channel and comparing tha channels with installed loop pressure and temperature indications.
11&l8. Procedures for calibration, testing and servicing the subcooling monitor are currently being written.
Since it is only a monitoring instrument and performs no protection function, a channel can be removed for test or calibration during power operation.
12&l3. The subcooled monitor is located in the control room. This permits easy access for reading incore thermocouple temperatures, removing channels from service and also for administrative 1y controlling access to the monitoc.
14&l5. The system is designed _to meet this requirement.
- 16. The core subcooling monitor system receives its input for incore temperatures directly from sensors.
Inputs for loop T and reactor H
coolant system pressures are received from the reactor protection system via isolators.
- 17. The core subcooling monitor.is used for monitoring both normal and post accident plant conditions.
Note (A) Westinghouse letter to the NRC NS TMA-2229 dated May 5, 1980. l.
NUREG 0737 II. F.2 Attachment 1 Design and Qualification Criteria for Pressurized Water Reactor Incore Thermocouples 1.
The 51 incore thermocouples installed at V. C. Summer are the same type as those-that Westinghouse is using to establish qualification to comply with Reg Guides 1.89.and 1.100.
The incore thermocouples are located at the core exit;in an arrangement such that radial distribution of coolant temperature exiting the core is easily obtained.
2.
The primary display is the plant process computer which is a display and calculation system using a total of 51 thermocouple inputs. Thirty-five thermocouples are directly input to the computer.
Sixteen thermocouple inputs (4 per core quadrant) come from the core subcooled monitor via a qualified isolator, a) A spatially oriented core map can be printed on operator demand
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giving the temperature at each core exit thermocouple location.
This process takes less than 10 minutes.
b) The computer is capable of determining and displaying the highest thermocouple value and the average of all thermocouple values on the CRT. _Also, up to 30 thermocouples may be selected for continuous display on either control room CRT.
c).The computer constantly mqnitors all 51 incore thermocouple temperature values over a range of 70'F to 2200 F.
A printed list of all incore temperatures can be provided in less than five minutes.
')
Up to 51 thermocouples can be trended by the ccmputer with the output on the trend typewriter. Four of the fifty-one incore thermocouples may be selected for trending on the computer trend recorders located on the main control board, e) When any value exceeds preset alarm limits (700 F hi and 1200 F hi hi) the computer prints an alarm message on the alarm typewriter and on the control board CRTs.
f) The Operator-Plant Computer Interfaces have been evaluated to identify any human factors concerns. The man machine interface was found to be acceptable subject to a few improvements which are being made.
These improvements include replacing the alarm and trend typewriters with high speed printers thus minimizing the delay in receiving printed information and improving the labelling of computer push-button controls to enhance readability and minimize substitution errors.
The computer CRT displays are located on the main control board in the center section with the reactor and feedwater controls. The plant computer console with the printers is located in the center of the control room for easy access by all operators. --
[
3.
Back up system.
The second means of monitoring incore thermocouple temperature is the
' core subcooling monitor' system.- Each channel of the subcooling monitor receives input from the 8 thermocouples (2 per core quadrant per channel),
for a total of 16 thermocouples. A digital readout of any of the 16
. single thermocouple: temperatures may be obtained at the subcooling monitor panel located-in the control room. The time span between readings is one per second. The range of the display is 0 F to 2300 F.
4.- The alarms for this system have been included with the annunciaturs on the name area of the main control board as the indications. These alarms have been prioritized along with the rest of the annunciators on the control boards to draw attention to the more critical alarms during an emergency.
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-The proper use of these new instruments will be included in normal and emergency procedures and operator training. The procedures are being revised to reflect' changes to the main control board to correct human factors discrepancies.
5.. From the 51 incore thermocouples available, 16 (8 per channel) were selected for input to the subcooling monitor. These 16 thermocouples will be supplied with qualified connectors, cable, reference junction boxes, i
penetrators and isolators.- They will be electrically separated from where 4
they leave the reactor vessel head to the two redundant subcooling monitor jchannels.- The two channels including the isolators and main control l.
board 1 indicators are electrically in.lependant and are energized from idenpendent class IE battery backed power sources. The subcooled monitor provides a reliable, redundant Class IE back up display for the 16 selected incore thermocouples. The attached Appendix B evaluation discusses the
-qualiffcation:of the_subcooled monitor.
4-LThe plant process computer provides the primary display for incore ther-
^'
_mocouple temperatures. This Non Class IE computer is electrically in-dependent from the two channels of the subcooling monitor and is supplied
. rom an independant battery backed kdghly reliable power source.
It receives inputs from all 51 incore thermocouples; 35 from the incore instrument. panel, 16 from insolated outputs of the subcooling monitor.
Conformance to the Appendix B criteria for the 16 incore thermocouple inputs to the subcooling monitor is as follows:
- (l) Qualification of the thermocouples to comply with Reg Guides 1.89 and
)
1.100 will be attained by a qualification program using test thermo-couples identical to the ones used at the Virgil C. Summer Nuclear Station. The program includes environmental and seismic tests and will comply with the test sequence requirements of IEEE 323-1974.
j Aging and margin will also be addressed. Connectors and cables will be qualified to comply with Reg Guides 1.89 and'l.100.
The reference junction boxes, part of the existing equipment, will be replaced qualified junction boxes which will be supplied by Westinghouse.
These new boxes will be qualified to comply also with Reg Guides 1.89 and 1.100. - - -
- o (2&3) See the above discussion and attached Appendix B evaluation of the core subcooling monitor.
(4) This requirement is_not applicable for the-incore thermocouples.
connectors, and junction boxes.
Refer to Appendix B(4) for conformance of the core subcooling monitor to.this requirement.
(5) A Quality Assurance program for the. incore thermocouples reference junction boxes and connectors was not required prior to the issuance of NUREG 0737.
SCE6G is participating in the Westinghouse generic program to verify quality of the incore thermocouples. The replacement reference junction boxes and connections will be procured under a quality assurance program.
(6) The subcooling monitor can continuously display selected incore thermocouple temperatures. The plant process computer can con-tinuously display and record any of the incore thermocouples.
(7) Refer to Point-(6) above and the attached Appendix B evaluation of core subcooling monitor.
(8) The back up display is in the core subcooling monitor cabinet which is in the control room.
~(9) The transmission of the sixteen thermocouple signals from the sub-cooled monitor to the process computer is through qualified isolators.
The transmission of signals to the subcooled monitor is discussed in the attached Appendix B.
(10) The incore thermocouple inputs are cross-checked during operation by comparison with each other and with loop temperatures.
.(11-18) The 16 incore thermocouple inputs to the subcooled monitor meet criteria 11-18 of Appendix B as applicable. -