ML20205K334
| ML20205K334 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 02/19/1986 |
| From: | Leblond P COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.F.2, TASK-TM 1303K, NUDOCS 8602270301 | |
| Download: ML20205K334 (38) | |
Text
_ _
- . ./^2N Commonwe
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) One First N1tional Plaza.Edison Chicago. Ilknois kO s
Address Reply to. Post Office Box 767
. Chicago. Illinois 60690 February 19, 1986 Mr. Harold R. Denton, Director office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Comission Washington, DC 20535
Subject:
Zion Nuclear Power Station Units 1 and 2 NUREG-0737. Item II.F.2 WRC Docket Nos. 50-295 and 50-304 References (a): May 30, 1984 letter from S. A. Varga to D. L. Farrar.
(b): August 24, 1984 letter from R. N. Cascarano to H. R. Denton.
(c): March 5, 1985 letter from R. N. Cascarano to H. R. Denton.
(d): April 25, 1985 letter from P. C. LeBlond to H. R. Denton.
(e): October 17, 1985 letter from S. A. Varga-to D. L. Farrar.
Dear Mr. Denton:
Reference (a) requested additional information concerning Comonwealth Edison Company's Inadequate Core Cooling Instrumentation System at Zion Station. References (b), (c) and (d) supplied the requested information. After additional review, the NRC issued reference (e) which discussed the remaining issues and requested additional information.
A meeting was held on January 21, 1986 in Bethesda between Comonwealth Edison Company and members of the NRC Staff. This letter serves to document material that was presented at the January 21, 1986 meeting, provide information requested at that meeting, and to respond to reference (e).
Attachment 1 to this letter contains information that was presented by Comonwealth Edison at the January 21, 1986 meeting. Included it, this material is a description of the use of the Reactor Vessel Level Instrumenta-tion System (RVLIS) in Zion's Emergency Operating Procedures (EOP). This 8602270301 860219 PDR ADOCK 05000295 I b-P PDR
O H. R. Denton February 19, 1986 description also proposed changes to the EOPs to account for the maxiaum potential RVLIS uncertainty. Attachment 1 also contains Commonwealth Edison's assessment of the financial considerations and provisional implementation schedules. These schedules are based upon receiving NRC approval by June 1, 1986.
Attachment 2 provides the actual proposed changes to the Zion E0Ps.
It should be noted that in some instances a caution statement has been added in lieu of simple removal of a reference to RVLIS. This option was discussed at the January 21 meeting and it has been incorporated into the proposed changes.
Attachment 3 provides a short description of the proposed changes.
It also highlights where increased reliance has been placed on the thermocouple (T/C) and subcooling margin monitor (SNM) systems.
Attachment 4 provides a description of Zion's proposed thermocouple and subcooling margin systems and compares them to the criteria contained in NUREG-0737, Appendix B. In addition, a block diagram of the final T/C and SMM systems is included. This material is in response to Requests 2, 3 and 4 of reference (e), as well as verbal requests made at the meeting.
Attachment 5 transmits documentation on the basis for Commonwealth Edison Company's RVLIS uncertainty estimate of 115.5%. This uncertainty assumes the existence of extremely adverse environmental conditions. Thus, the actual error would be less than 15.5% in all but the most unusual of circumstances.
If any further questions arise concerning this matter, please direct them to this office.
Sincerely, h
P. C. LeBlond Nuclear Licensing Administrator 1
1m Attachments cc: NRC Resident Inspector - Zion J. Norris - NRR 1303K
ATTACHNENT 1 MATERIAL PRESENTED BY Ceco at January 21. 1986 Meeting Contents;
- 1. Meeting Agenda
- 2. Purpose of Meeting
- 3. Sunnary of RVLIS Correspondence
- 4. RVLIS Financial Summary
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NRC/ CECO RVLIS MFFTING JANUARY 21, 1986 I. INTRODUCTION AND HISTORY OF ZION'S RVLIS - P. C. LEBLOND II. FINANCIAL CONSIDERATIONS - F. G. LENTINE III. USAGE OF RVLIS IN ZION'S ERGS - M. S. ESTES 1
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PURPOSE OF THE MEETING
- 1. RESPOND TO 10/17/85 R.A.I. - ITEM 1.
- 2. DEMONSTRATE COMPLIANCE WITH GUIDANCE OF NUREG-0737 - II.F.2.
- 3. OBTAIN NRC APPROVAL 0F CURRENT ZION RVLIS DESIGN (MODIFIED TO YIELD 115.5% ACCURACY).
- 4. DISCUSS IMPLEMENTATION SCHEDULES.
SIGNIFICANT RVLIS DATES 9/13/79 - D. G. Eisenhut to all Operating Nuclear Power Plants
- Submit within 30 days a commitment to install a RVLIS by 1/01/81 per NUREG-0578.
10/18/79 - Cordell Reed to D. G. Eisenhut - Response to 9/13/79
- WOG to develop generic RVLIS with a submittal by 1/01/80.
1/01/80 - D. L. Peoples to H. R. Denton
- RVLIS is the most promising means of detecting ICC. Provided a system description and a sketch. Ceco will install by 1/01/81.
4/29/80 - Modification approval letter for Unit 2 issued. ,
- Design and drawings are complete. Parts have been ordered.
Station is given approval to proceed with installation.
7/02/80 - Unit 2 RVLIS installed.
8/07/80 - Modification approval letter for Unit 1 issued
- (see above).
10/31/80 - D. G. Eisenhut to All Licensaes
- Transmitted NUREG-0737. Item II.F.2 restated earlier requirements of NUREG-0578, Item 2.1.3.b. Implementation date was changed to 1/01/82. New requirements for the consideration of environmental effects were provided.
4/08/81 - Unit 1 RVLIS installed.
7/30/81 - L. O. De1 George to D. G. Eisenhut
- Provided W RVLIS system description and discussed the differences from Zion's design.
3/01/82 - U. D. Swartz to D. G. Eisenhut
- Provided additional technical information from W. This included a determination of potential instrument uncertainties.
12/10/82 - Generic Letter 82-28
- Review RVLIS against II.F.2 and send in design plus review results. Do not turn on until NRC approval is obtained.
3/10/83 - F. G. Lentine to H. R. Denton - Response tn G.L. 82-28
- Described history and gave status.
5/30/84 - S. A. Varga to D. L. Farrar
- Proposed RVLIS approach is acceptable, but requests information on environmental effects.
8/24/84, 5/05/85 - R. N. Cascarano to H. R. Denton
- Submitted information on RVLIS errors and ERG usage.
10/17/85 - S. A. Varga to D. L. Farrar
- Request for additional information on RVLIS
SUMMARY
9/13/79 - Original NRC requirement.
1/01/80 - CECO commitment to install RVLIS.
7/2 /80, 4/08/81 - RVLIS installed on both units.
10/31/80 - NRC issues additional requirements on RVLIS.
7/30/81 to Present - Discussion of technical adequacy of RVLIS relative to NUREG-0737.
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R7LIS FINANCIAL SIMIARY I. RVLIS Expenditures to Date; For both Units - $2,970,000.00
- II. RVLIS Upgrade with Transmitters Remaining Inside of Containment; Each Unit - $110,000.00 Both Units - $220,000.00 III. RVLIS Upgrade with Transmitters Relocated outside of Containment; Each Unit - $650,000.00 Both Units - $1,300,000.00
- Desired Option 1329K l
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PROPOSED IMPLEMENTATION SCHEDULES RVLIS The RVLIS system installation will be completed during the following refueling outages; Unit 1 - October, 1987 Unit 2 - February, 1987 These dates are based upon receiving NRC approval by June 1, 1986 and subsequently requiring six months to complete;
- 1. Design drawing preparation.
- 2. Purchase modified transmitters or contract for the modification of the existing transmitters.
- 3. Contract for capillary fill services.
- 4. Incorporate into outage schedule.
The only scheduled refueling outage in 1986 is for Unit 1 in June.
THERMOCOUPLE /SUBCOOLING MARGIN MONITOR The following activities must be performed to complete the proposed modification;
- 1. Prepare design drawings.
- 3. Procure components and construct microprocessor.
- 4. Seismically qualify the microprocessor through testing.
- 5. Develop the required software.
- 6. Perform a human factors review.
- 7. Implement training and any new procedures.
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Assuming that NRC approval is received by June 1, 1986, the installation will be completed during the following outages:
Unit 1 - October, 1987 Unit 2 - The outage-related hardware will be installed in the February,1987 outage. Items 3, 4, 5, 6 and 7 may not be completed until 7/01/87.
Items 4 and 6 are anticipated to require a substantial time period to complete. Thus, the microprocessor may not be available for installation during the February,1987 Unit 2 outage. In any event, it is expected that the microprocessor will be operational by the 7/01/87 date discussed above.
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RVLIS USAGE IN ZION EOPS Problem With Level Of Procedure _ Max. Error Interest Resolution i ES-0.3 Natural Cire. Cooldown No Adverse Error Since No a.) Top Of Core N/A With Steam Void In Vessel Accident Is In Progress b.) Top Of Hot Leg l ,
(With RVLIS) Nozzle
! c.) Top Of Core ECA-1.1 Loss of Emergency Coolant Additional Loss ofInventory Top of Core Remove RVLIS From
) Recirculation Temperatures And Curve For Flow Are ll -
Adequate Indicators Of Core Cooling
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ECA-3.2 SGTR With Loss Of Reactor Possible ECCS Pump Restart Top of Hot Leg No Change, Small j
Coolant-Saturated Recovery After SI Flow Reduction Nozzle Problem If Slight Increase Of Mass Loss i ECA-3.3 SGTR Without Pressurizer None,If Rx Level Has Top of Core No Change, Large
! Pressure Control Decreased,Then Multiple RVLIS Error Produces j Events Have Occurred. .
More Conservative This WillCause An Early Results Transfer To ECA-3.1. (No 1 Rapid Cooldown Required)
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RVLIS USAGE IN ZIO'N EOPS (Cont.1 Problem With Level Of Max. Error Interest Resolution Procedure a.) None,TransitionTo a.) 1/3 Core a.) No Change, RVLIS Is F-0.2 Status Tree For Core Cooling FR-C.1 Requires > 700*F , Used As Confirmation AND Low RVLIS Indication Of Core Heat-Up b.) None, Transition To b.) 50% Void b.) No Change, Large FR-C.2 Will Not Result Fraction RVLIS Error Produces :
In Rapid Cooldown More Conservative Results Status Tree For Inventory Could Allow A Bubble Rx Vessel full No Change, This Is A F-0.6 -
To Exist Above'Ihe 86% Yellow Priority Level With 100% Indicated Procedure a.) None, Low RVLIS AND a.) 1/3 Core a.) No Change, RVLIS Is FR-C.1 Response To Inadequate Core Cooling > 700*F Required For Rapid Used For, Confirmation Cooldown OfICC b.) Could Stay In Loop b.) Top Of Core b.) Change To Make In FR-C.1 .
EOP More Efficient, Qualify RVLIS Actions
RVLIS USAGE IN ZION EOPS (Cont.)
Problem With Level Of Max. Error Interest Resolution Procedure Response To Degraded Core a.) Transition To Degraded a.) 50% Voids a.) No Change, FR-C.2 Cooling Core Cooling Could Occur .
100*/hr Cooldown Early Required By FR-C.2 Is Not Severe Transient b.) Transition To Degraded b.) 1/3 Core b.) No Change, Core Cooling Could Occur 100*/hr Cooldown Early Required By FR-C.2 Is Not Severe Transient c.) Could StayIn Loop In c.) Top Of Core c.) Make EOP More FR-C.2 Efficient, Qualify RVLIS Actions
. FR-P.1 Response To Imminent Could ResultInNot Top Of Core Remove RVLIS From Pressurized Thermal Shock Terminating SI, Prolongs EOP, Subcooling Condition PTS Threat RequirementIs Adequate For SI Termination ,
Response To Voids In Reactor May Try To Vent With No Rx VesselFull No Change, Yellow FR-I.3 Vessel Voids Priority Procedure D o
l ATTACHMENT 2 PROPOSED REVISIONS TO ZION's EOPs 1303K
ECA-1.1 LOSS OF EMERGENCY COOLANT RECIRCULATION CAUTION RVLIS uncertainties may not allow INDICATED RVLIS to be maintained above the top of the core (60% for normal,70% .
for adverse containment). Core exit thermocouples are used as an additional parameter to determine if ECCS flow should be increased.
- 10. Verify Adequate ECCS Flow:
- a. Check RVLIS narrow range - a. Go to Step 10.c.
AVAILABLE
- b. RVLIS Narrow range - b. Monitor RVLIS GREATER THAN 60% (70% level for indication of FOR ADVERSE CONTAINMENT) adequate ECCS flow and proceed to step 10.c. to determine if ECCS flow should be increased.
- STABLE OR DECREASING flow as necessary i
ECA-1.1 LOSS OF EMERGENCY COOLANT RECIRCULATION CAUTION RVLIS uncertanties may not allow INDICATED RVLIS to be maintained above the top of the core (60% for normal,70%
for adverse containment). Core exit thermocouples are used as additional parameter to determine if intact SGs
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- 16. Depressurize All Intact SGs To inject Accumulators As Necessary:
- a. Check RVLIS Narrow range - a. Monitor RVLIS GREATER THAN 60% (70% FOR level for indications ADVERSE CONTAINMENT) of adequate ECCS flow and proceed to step 16.b. to determine if SGs should be depressurized.
- b. Check Core exit TCs b. Dump steam from
- STABLE OR intact SG(s) AS DECREASING NECESSARY by one of the following in preferred order:
- 1) Steam dumps.
- 2) SG atmospheric relief valves.
- 3) SG blowdown.
- 4) Turbine-driven AFW pump.
- 5) Other.
- c. Check SG pressures - LESS THAN c. Return to step 16.a.
160 PSIG
- d. Stop SG depressurization
FR-C.1 RESPONSE TO INADEQUATE CORE COOLING
- 17. Check Core Cooling:
- a. Core exit TCs - LESS THAN 1200*F , a. Go to step 19.
OBSERVE NOTE PRECEDING STEP 19.
- b. At least two RCS hot leg b. Return to step 15.
temperatures - LESS THAN 350*F
- c. Check RVLIS narrow range - c. Go to step 18.
AVAILABLE
- d. RVLIS narrow range - GREATER d. Ecore exit THAN 60% (70% FOR ADVERSE thermocouples are CONTAINMENT) stable or decreasing, THEN go to step 18.
Ecore exit thermocouples are increasing, THEN return to step 15, 1
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FR C.1 RESPONSE TO INADEQUATE CORE COOLING
- 24. Check Core Cooling:
- a. Check RVLIS narrow range - a. Go to step 24.c.
AVAILABLE
- b. RVLIS narrow range - b. IEcore exit GREAT THAN 60% thermocouples are (70% FOR ADVERSE stable or CONTAINMENT) decreasing, THEN go to step 24.c.
IEcore exit thermocouples are increasing, THEN return to step 19.
- c. At least two RCS hot c. Return to step 19.
leg temperatures - OBSERVE NOTE LESS THAN 350*F PRECEDING step 19.
FR-C.2 RESPONSE TO DEGRADED CORE COOLING
- 20. Check Core Cooling:
- a. Check RVLIS narrow range a. Go to step 20.c.
- AVAILABLE
- b. RVLIS narrow range - b. Ecore exit GREATER THAN 60% thermocouples are (70% FOR ADVERSE CONTAINMENT) stable or decreasing; THEN go to step 20.c.
Ecore exit thermocouples are increasing,ItiEN. return to step 16.
- c. At least two RCS hot leg c. Retum to step 16.
temperatures - LESS THAN 350*F 1
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FR-P.1 RESPONSE TO IMMINENT PRESSURIZED THERMAL SHOCK CONDITION CAUTION
- maintained above the top of the core (60% for normal,70%
- for adverse containment). Subcooling is used as an *
'. additional parameter to determine if additional actions *
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- 4. Check If SI Can Be Terminated:
- a. Check RVLIS narrow range - a. Go to step 4.c.
AVAILABLE
- b. RVLIS narrow range b. Monitor RVLIS level for indication - GREATER THAN 60% indication of adequate ECCS flow and proceed (70% FOR ADVERSE CONTAINMENT) to step 4.c. to determine if additional actions are required.
- c. RCS subccoling - GREATER THAN c. IF NO RCP is running, THEN attempt to start 80*F (RCS PRESSURE - HOT LEG at least one RCP per TEMPERATURE ABOVE50*E SUBCOOLING CURVE PER FIGURE Appendix A on page 15..
1 ON PAGE 11 FOR ADVERSE Go to step 20.
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l ATTACHMENT 3 DESCRIPTION OF PROPOSED EOP REVISIONS 1303K
e ECA-1.1 - Sten 10 A caution statement has been added to alert the operator that the required RVLIS indication may not be attainable under some' circumstances.
The caution statement also states that the core exit thermocouples can 3
provide additional information concerning the adequacy of ECCS flow.
The only change to the procedure itself is in the right-hand column of step 10.b. This change reduces the reliance on the RVLIS indications in the procedural decision process and directs the operator to observe the trend of the core exit thermocouples. Thus, there is increased reliance on the thermocouple system in step 10 of ECA 1.1. A low RVLIS indication is no longer sufficient criteria to increase ECCS flow.
ECA-1.1 - Sten 16 A caution statement has been added to alert the operator that the required RVLIS indication may not be attainable under some circumstances.
The caution statement also states that the core exit thermocouples can provide additional information concerning the need for S/G depressurization.
The only change to the procedure itself is in the right-hand column of step 16.a. This change reduces the reliance on the RVLIS indications in
- the procedural decision process and directs the operator to observe the trend
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of the core exit thermocouples. Thus, there is increased reliance on the j thermocouple system in step 16 of ECA 1.1.
1 FR-C.1 - Steps 17 and 24 Changes have been made to the right-hand column of steps 17.c and 24.b. In both instances the operator is directed to observe the trend of the core exit thermocouples. If the thermocouples are stable or decreasing, then the operator may exit FR-C.1, assuming that the other required conditions are satisfied.
Thus, a low RVLIS indication is no longer sufficient criteria for remaining in FR-C.1. If adequate core cooling is indicated by the thermocouples, an exit from FR-C.1 may be allowed. These changes have placed increased reliance on the core exit thermocouple system.
i FR-C.2 - Step 20 4
A change has been made to the right-hand column of step 20.b. This
- change is similar to the changes discussed under FR-C.1. If there is a low RVLIS indication, the operator is directed to observe the trend of the core exit thermocouples. If the trend is stable or decreasing, then the operator may exit FR-C.2, assuming that the other required conditions are satisfied.
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I FR-C.2 - Step 20 (cont'd)
Thus, a low RVLIS indication is no longer sufficient criteria for remaining in FR-C.2. If adequate core cooling is indicated by the thermocouples, an exit from FR-C.2 may be allowed. These changes have placed increased reliance on the core exit thermocouple system.
FR-P.1 - Step 4 A caution statement has been added to alert the operator that the required RVLIS indication may not be attainable under some circumstances.
The caution statement also states that the subcooling monitor can provide additional information.
The right-hand column of step 4.b states that RVLIS should be monitored and that the subcooling monitor is to be consulted. The subcooling monitor is now the sole instrument used to determine the need for starting an RCP. A low RVLIS indication is no longer sufficient criteria for restarting an RCP. This change has increased the reliance on the subcooling margin monitor.
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ATTACHIENT 4 DESCRIPTION OF PROPOSED T/C AND SMM SYSTEMS CONTENTS;
- 1. Evaluation of proposed SMM and CET (core exit T/C) System's Conformance with Appendix B of NUREG-0737.
- 2. Review of Zion Station's proposed T/C System against NUREC-0737 Item II.F.2, Attachment 1.
- 4. Figures 1, 2, 3 describing the T/C and SMM Systems.
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Evaluation of Proposed SMM and CET System's Conformance with Appendix B of NUREG-0737
- 1. The intent of the design changes to the Subcooling Margin Monitor SMM and Core Exit Thermocouple (CET) Systems is to make them safety grade and qualified. In the Subcooling Margin Monitor (SMN) and Core Exit Thermocouple (CET) systems we will be using some existing plant equipment with certain components replaced to upgrade its accident survival capability and qualification. The major components in the system are:
a) Core exit thermocouples b) W.R. RCS pressure transmitters c) Containment penetration d) Cables e) Reference junction boxes f) M.C.B. indication g) Process computer h) 68000 based microcomputers For items b,c, and d CECO has reviewed environmental qualification test reports on similar or identical components and previously have stated that the components in question are fully qualified to all environmental conditions expected at Zion Station. These components currently fall I within the scope of 10CFR50.49 at Zion Station.
The instrumentation, items f, g, & h located in Computer Room.
Electrical Equipment Room and Main Control Room are in mild environment (not in the scope of 50.49). Therefore, normal surveillance and maintenance practices in effect at Zion Station will be sufficient to guarantee operability.
The proposed new redundant microcomputers item h, and the redundant back-up displays would be constructed by CECO. using standard commercially available components. The hardware & software will be analyzed to qualify them to meet lE requirements using Commonwealth Edison Corporate Quality Assurance Program. The hardware will be seismically qualified and mounted.
Reference junction boxes will contain qualified components.
(See description of proposed upgrade)
The seismic qualification of existing components meets the criteria in effect at the time of plant licensing. The replacement equipment will be designed and/or tested to meet new seismic requirements.
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- 2. The complete SMM and CET Systems were not designed to be redundant or single failure proof. It is difficult to maintain sufficient separation in restricted areas of reactor head for example.
The existing copper t/c extension wires outside of containment are in two trains with t/c leads 1-33 in one train and t/c leads 34-65 in the other train. Even though the thermocouple cables are routed with "non-safety related" instrumentation cables, the cable trays have been seismically mounted.
The new redundant microcomputers will be powered from independent and class 1E power sources.
- 3. Plant process computers are fed from Class IE Motor Control Centers (U-1-MCC 139-1, U2-MCC 239-1). The microcomputers will be powered from redundant class IE power sources.
- 4. No comment.
- 5. The equipment at Zion is installed in accordance with CECO. Corporate Quality Assurance Manual in effect at the time of installation.
- 6. Continuous indication is provided on Main Control Board.
- 7. Recording is provided by Process Computer. Historical information is available from Prime Computer.
- 8. No comment. Instruments are properly identified on control panels.
- 9. The isolation of safety related signals is currently in for all safety-related inputs to the computer, and will be provided for the microprocessor's inputs.
- 10. On line testing capabilities are incorporated into the design of microprocessors.
11 & 18 The testing and calibrations at Zion for systems that are not governed by Tech. Spec. requirements are usually performed on refueling outage basis. See also item 10 above 12 - 17 No comment. The intent of the requirements are incorporated into the design of SMM and CET systems.
1303K
r Review of Zion Station T.C. System Against NUREG-0737 Item II.F.2. ATTACHMENT 1
- 1) The incore instrumentation at Zion consists of thermocouples, positioned to measure fuel assembly coolant outlet temperature at preselected locations, and flux thimbles, which run the length of selected fuel assemblies to measure the neutron flux distribution within the reactor core. The design have 65 thermocouples and 58 flux thimbles. (Not all t/c's are required to be operational).
The in-core instrumentation provides information which may be used to calculate the coolant enthalpy distribution, the fuel burnup distribution, and to estimate the coolant flow distribution. Both radial and azimuthal symmetry of power distributions may be evaluated by comparing the detector and thenmocouple information from one quadrant with similar data obtained from the other three quadrants.
- 2) The primary displays for the ICC instrumentation are generated by the plant process computer using isolated outputs from the CET processor cabinets and NSSS protection system cabinets (for the reactor coolant system pressures). The exist 1ng CET processors will be replaced by new, redundant, safety grade microcomputers.
- a. A process computer generated core map display is available on the "Ramtec" CRT in the Control Room.
- b. plant main computer can provide the reading of the highest, average of the 10 highest and individual temperatures.
- c. All thermocouple readings are monitored and recorded by a computer and hard copy printout is available. The range is from 00F to 2500*F.
- d. Capability exists in the computer to obtain temperature time history trend.
- e. There are no tharmocouple alarms on main control board. E0p's instruct operators on the the acceptable t/c values. Input validation and open t/c detection is done by computer.
- f. The thermocouple display was reviewed by human-factor engineers.
- 3) As stated above the computer is the primary monitor of t/c temperatures, with backup readout provided by a precision indicator with manual point selection. The range of the t/c readout is 0-2500*F. When installed, the microcomputer driven displays will become the back-up displays. The precision indicator will be removed at that time.
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- 4) A human-factors analysis and a detailed control room design review was just performed at Zion Station. The new microcomputer driven displays will undergo similar human factors review before implementation. The results of the study will be reviewed and incorporated into the design, emergency procedures, and operator training.
- 5) For the evaluation of conformance of T.C. system to Appendix B see the review of SNM and CET Systems in this response.
- 6) The primary and backup display channels will be electrically independent, powered from Class lE power sources, and physically separated. The primary display is powered from a high reliability power source. The design's intent is to have the backup displays as Class lE.
- 7) The environmental qualification and seismic qualification of the instrumentation is addressed in item 1 of SMM and CET Systems review to Appendix B of NUREG 0737.
- 8. The intent of the design is to provide 99% availability of T.C.
display. The Incore T.C. system is mentioned in Zion Station Tech Specs, Section 3.2.2.c.2, as a backup to excore detectors, (4 per each quadrant).
- 9. The equipment at Zion is installed in accordance with CECO Corporate Quality Assurance Manual in effect at the time of installation.
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Proposed Upgrade to CET and SMM Systems at Zion Station I. In Containment Upgrade Option Part of the CET System has been upgraded recently for both Units 1 & 2, and will not require changing. This upgrade consisted of replacing the existing thermocouple (TC) yellow connectors at the TC ports with qualified stainless steel (SS) connectors. New SS mineral insulated (MI) cable was installed between the connectors at the t/c's to qualified ERI connectors at a bulkhead on top of the steam generator shield wall at the end of the cable bridge. From the bulkhead connector to the electrical penetrations, changes are required.
At the bulkhead connectors, CONAX environmentally qualified seal assemblies will be installed. These seal assemblies would consist of chromel-alumel t/c wires with a mating ERI connector to interface with the bulkhead ERI connector of the MI cable. Each seal assembly would also have pigtail leads at the other end to enable a qualified splice to be made with organic LOCA qualified single pair chromel-alumel t/c extension wire. The splices would be physically prctected by a cover or pull box and the seal assemblies would be seismic 211y supported.
The chromel-alumel t/c extension wires will be divided into two (2) trains and routed physically separated to a new reference junction box for each train. The new junction boxes will replace the existig heated reference junction boxes and will be installed in a horizontal position to minimize any vertical temperature gradient errors.
In the new reference junction boxes the chromel-alumel t/c extension wires will be joined to the existing copper cables going to the existing electrical penetrations.
Inside the reference junction box a copper block will be installed.
This block will be grooved to accommodate cables and thermocouple / copper reference junctions. Each t/c ref. junction will be insulated with qualified heat shrink tubing and installed in grooved copper block in a single horizontal plane. A second copper block, similarly grooved, will be installed on the top of first block, serving as a clamp and also providing thermal sink to minimize temperature gradients at the reference junction. The cable shields will be carried through the copper block and will be insulated from ground. Redundant and environmentally qualified platinum RTD's, with a range that includes temperatures expected in containment during the accident, will be installed between the two halves of copper blo:k and insulated similarly to t/c reference junctions. It is anticipated that the thermal gradient across reference junctions will not exceed 0.10 F. Reference junction boxes will not be environmentally sealed since all the included components and connections inside the box are environmentally qualified and provided with hermetic seal. Reference junction boxes will be seismically installed. (See Figure 2)
' l II. Out of Containment Upgrade Option The upgrade out of containment will use the existing copper t/c ext 2nsion wires between the containment penetrations and main control room.
These safety grade cables are routed in different trains with other nonsafety related in-trumentation cables.
The upgrade in main control room would add two microprocessor based microcomputer systems and associated displays, one system per train. The new microcomputers will be constructed as Class lE by Commonwealth Edison Company using standard commercially available components. The hardware and software will be analyzed to qualify it for Class lE service using CECO Corporate Quality Assurance program. The heart of the system will be Motorola 68000, 32 bit microprocessor. The use of an industry-standard VMEbus in the design allows us to take advantage of readily available, high quality, and compatible microcomputer cards. This assures that replacement parts will be available for many years. The VMEbus chassis will contain the field termination blocks with signal conditioning and A/D cards with signal conditioning and isolation.
The microprocessor program itself will be " burned in", permanently written into programable read only memory chips (EpROMs). This feature allows the system to function immediately after power-up, without the need to reload the program. The EPROM software is modularized to ease software development, verification, testing, troubleshooting and replacement. The program scans the inputs, verifies the values, compensates for the reference junction temperature, performs engineering unit conversions, and quality checks on measurements. All inputs are normally scanned, processed, and transmitted once every two seconds. The displays are updated every five seconds.
Functionally, each microcomputer will provide thermocouple monitoring, compensation, and indication and in addition the subcooled margin calculations, monitoring and display. The intent of the design is for each train to process up to 32 thermocouples, 4 RTD's, and 4 pressure signals. Each input will be electrically isolation from every other input and can withstand up to 250 VAC rms common mode potential with no degradation. Figure 3 provides a simplified diagram of the proposed CET/SMM system. It is the intent of the design that each microcomputer will use all working t/c's (after proper isolation) in calculating the margin to saturation. Each microcomputer has capability of having four RS232 optically isolated outputs. One port will be used for the display, one for communication with plant computer, with the remaining two for future use.
The microcomputer displays (backup displays) will be multiline, digital and controlled by a keyboard. The operator entry can call up temperature of individual thermocouples, the hotest, average of the ten highest, reference junction temperature, subcooling margin, etc.
Extensive diagnostics have been built into the system to detect failures (EpROM Checksum, parity Checksum, Watchdog Time, Open T/C Check, Limit Check, etc.). The software will undergo extensive Verification and Validation review. The complete system will undergo a human factors review. The microcomputer and the displays will be seismically tested and mounted.
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-O T T O T - Thermocouple Upper Head Penetration for Thermocouples (5)
Figure #1
s EXISTING 33 TWISTED 4
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REFERENCE JUNCTION -
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" REACTOR VESSEL 4 NARROW RANGE PRESSURE TRANSMITTERS CONTAINMEN T WALL INCORE T/C AND SU B COOLING MARGIN MONITOR
( INSIDE OF CONTAINMENT PORTION )
Figure #2
i IE NONlE BACK UP DISPLAY
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I OUTSIDE CONTAINMENT UPGRADE Figure #3 i
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ATTACHMENT 5 TECIMICAL BASIS FOR i15.5 UNCERTAINTY 1303K
e.
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ZION REACTOR VESSEL LEVEL INSTRUMENTATION SYSTEM The overall Reactor Vessel Level Instrumentation System (RVLIS) accuracy of il5.5% was determined based on the uncertainties introduced by each component in the instrument system and includes the uncertainties resulting from the severe environment imposed on the instrumentation located inside the containment. The individual uncertainties that are unaffected by the environmental effects and that are a result of random effects were combined statistically and then added to the uncertainties resulting from the environmental effects to obtain the overall RVLIS accuracy during an accident.
In determining the uncertainties resulting from the severe environment, the design base accident for the Zion station was used for the temperature (271*F), humidity (100%), and pressure (47 psig). For the radiation effects a total integrated dose (TID) of 50 megarads gamma was used from the ITT Barton Qualification Report and is more severe than the design basis accident at Zion. Since the active components inside containment are totally enclosed within their own metallic housing, the effects of BETA radiation are not applicable and have not been included.
As some of the individual uncertainties vary with conditions, such as system pressure and vessel level, the uncertainties were determined based upon a system pressure of 1200 psia and a full reactor vessel. This results in the most conservative maximum expected level error.
The following table identifies the random individual uncertainties for the full range measurement (0-40.7 f t.) based upon the existing in containment RVLIS design configuration and with the assumption th::.t the transmitters will be upgraded to meet ITT Barton environmental quolification specifications. It also assumes that the vapor density compensation modifi-cation recommended by Westinghouse will be made to the 7300 electronics.
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ZION REACTOR VESSEL LEVEL INSTRUMENTATION SYSTEM Component and Uncertainty Uncertainty Definition % Level a) Differential pressure transmitter calibration and drift allowance 1.69 (i,1.52% of span) corrected to 110%
indicated level.
b) Differential pressure transmitter allowance for change in calibration due to ambient temperature change ( 0.5% of 10.56 span for 500F) corrected to 110% indicated level.
c) Differential pressure transmitter allowance for change in calibration due to change in system pressure ( 0.2% of span i,0.23 per 1000 psi change) at 1200 psia, corrected to 110% indicated level.
d) Differential pressure transmitter allowance for change in calibration due to exposure to long-term overrange N/A. Proper calibration procedures will null out any effects after calibration.
e) Reference leg temperature instrument (RTD) uncertainty of 12oF and an allowance of iSoF applied to each vertical section of the reference leg where a measurement is made. Stated uncertainty 10.82 is based on a maximum containment temperature of +271oF and the Zion reference leg installation. This uncertainty includes associated electronic system calibration uncertainties.
f) Reactor coolant density based on auctioneering for highest water density and the lowest vapor density obtained from the hot leg temperature uncertainty (1180F) or system pressure uncertainty (166 psi). Magnitude of uncertainty varies with system pressure and level. This uncertainty is based upon 12.88 maximum expected error occurring at 1200 psia Temperature with reactor vessel full. This value includes ( 1.44 function generator mismatch with ASME Steam Pressure)
Tables and associated electronic system calibration uncertainties for these measurements.
i 7- -
e )
+ ,
i Component and Uncertainty Uncertainty Definition % Level ,
I g) Maximum expected error due to differences in capillary line volume and local temperatures 1.32 is conservatively estimated to be equivalent to about 5 inches.
h) Process measurement accuracy. This uncertainty accounts for effects of changing 1.0 fluid density in the reactor vessel under normal circulation.
i) Electronic system calibration for the differential pressure transmitters, il.12 j) Control board indicator resolution.
This value includes the uncertainty for the indicator accuracy (11.0%) i1.5 and an allowance for readability
( 0.5%)
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ZION RVLIS The statistical combination (square root of the sum of the squares) of the individual uncertainties described above results in an overall system instrumentation uncertainty of 4.3% of the level span, before accounting for containment environmental effects. Since the transmitters are located inside containment the following uncertainties must also be considered and are evaluated at a system pressure of 1200 psia:
Component and Uncertainty Uncertainty Definition % Level k) Differential pressure transmitter 7.5 allowance for long-term temperature, radiation and aging effects.
- 1) Reactor coolant density based i3.6 on wide range pressure transducer allowance for long-term temperature, radiation and aging effects.
These level uncertainties are added directly to determine the total uncertainty including the environmental effects. The total uncertainty for the Zion RVLIS installation is 115.5%.
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