ML20059L138
| ML20059L138 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 08/31/1990 |
| From: | Battelle Memorial Institute, PACIFIC NORTHWEST NATION |
| To: | |
| Shared Package | |
| ML20059L088 | List: |
| References | |
| NUDOCS 9009260155 | |
| Download: ML20059L138 (28) | |
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SYSTEM' OPERABILITY REPORT, C0lH0NWEALTH EDIS0N ZION NUCLEAR STATION'S
' COMPONENT COOLING WATER SYSTEM 1
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CONTENTS
SUMMARY
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1.0 BACKGROUND
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1.1 Diagnostic Evaluation ~ Team 2
1.2 NRC Region III 2:
1.3 Objective of.the Operability inspection........:...
2 1.4_
Inspection Plan........................
3 1.5
' Pacific Northwest Laboratory Assignment...........
4 2.0 SYSTEM DESCRIPTION'.........................
5 3.0 SYSTEM CONFIGURATION.........................
6-3.1 Common Header Configuration.,................
6 3.2 Split System Configuration
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3.3 Operating Configuration.........._
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'9J 3.3.1 FSAR...................... <.
3.3.2 Pre-Operational Testing................
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3.3 Configuration Analysis - 1988...-.........-
10-3.4
- Configuration Analysis - 1990...-.............
11 3.5 -Operating Procedures 11
.3.5.1 Normal Operating Procedures................
11 3.5.2 Abnormal Operating Procedure 12 4.0 SYSTEM CONDITION............................
.13 "4.1 General.-.......................-....
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4.2 Maintenance.........................
'13' 4.2.1 Pumps..............-.............
13 4.2.2 Heat Exchangers.....................
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Surveillance
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4' 3.1, AC 'and: DC Power Supplies 16
!4;3.2 Pumps.....................-.....-
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7 4.3.3 Heat Exchangers............
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- 4.3.4-Surge Tanks...........
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'4.4' Modifications..........................
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4.4.1 Completed Modifications..........,......
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4.4.2 In-progress Modifications......
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4.5-Chemistry................-..........
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Ea 4.6, Operating Procedures
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4.7 Trending..........................-..
19-7 5.0 THERMAL HYDRAULICS'.........................
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k 5.1 CCW~ Flow Requirements.....................=...
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H L-5.2-Thermal Requirements 21-1 1
5.3 CCW Heat Exchanger Tube Side 22 L
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6.0 SYSTEM OPERABILITY.........................
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4 6.1
. Normal Plant at Full Power.
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6.3 Reactor Pressure Boundary LOCA
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7.0 CONCLUSION
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24 1B.0 REFERENCES-........'...................
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SUMMARY
The component cooling water (CCW) system is capable of meeting the normal startup, operating and shutdown heat removal needs of the Zion Station nuclear reactors.
In iLJ avent of a single pipe break in the CCW system (CCW system loss of coola t accident) the entire system can be disabled. This vulnerability n
exists due to the current operating configurttion which does not appear consistent with original CCW system design bases. Because of this operating configuration, responding to the single postulated failure will require challenging the safety systems for both nuclear reactor units.
Procedures and operator act;ons are in place to mitigate a CCW system ioss of coolant accident, but do not limit the effects to a single unit.
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for postulated reactor pressure boundary loss of coolant accidents, the CCW system is capable of meeting the heat removal requirements to assure safe
. shutdown of the reactor units although some CCW component degradation can be expected.
Lack of planned maintenance, marginal surveillance and no trending a
program for 'he CCW system reduces the confidence of the system's continued
. availability and operability.
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1.0 BACKGROUND
1.1 Diaonostic Evaluation Team A review of Commonwealth Edison's Zion Station service water system was rt.cently aerformed by a NRC Diagnostic Evaluation Team (DET). The DET found the opera)ility of the service water system to be suspect. The findings dealt with the adequacy of the system flow balance, the adequacy of testing to demonstrate system operability, the maintenance of the system, and the comparison of the system to its design bases.
1.2 NRC Region 111 On July 25, 1990 the licensee (Commonwealth Edison) met with Region !!!
and Head uarters staff to 3 resent information to assist in understanding the DET find ngs.
Following tie meeting, further clarification was determined necessary, and the licensee was infomed that a Region 111 operability inspection team would be at the licensee's facility on July 30, 1990.
Further evaluation of the DET findings resulted in concerns that the findings are not limited to the service water system but may be applicable to the component cooling water system. The intent of the Region !!! inspection was expanded to include an operability inspection of both the service water system and component cooling water system.
1.3 Objective of the Operability inspection Tt.e objective of the operability inspection team was to assess the operational readiness of the service water system in light of the DET findings. To gain insight into the pervasiveness of the DET findings, the operability of a similar system, the component cooling water system, was also assessed. The team's objective was accomplished by determining whether the systems are capable of performing the safety functions required e
by their design bases testing is adequate to demonstrate that the systems would perform all a
of the safety functions required by their design bases management controls including procedures are adequate to ensure that e
the safety systems will fulfill the safety functions required by their design bases.
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1.4 Inspection Plan l
The inspection plan, developed by a Region 111 team member, delineates the requirements for the review and verificatire of each system to determine its o>erability.
The ins i
opera)ility review areas;pection plan requirements consist of three perform a review of each system's design bases i
requirements, perform a review of each system's function and test data, and perform a system verification.
j The first operability review area ir 24 pc
're a review of the FSAR design bases requirements as applicab!e f r eact ystem and determine its emergency operating conditions.
The revh 4,vd determine if the design 1
bases are met by the installed components, 1
if the design bases have i
changed since licensing and the reasons for i. nose changes.
Applicable design inputs to be considered ares basic function of each component I
performance requirements such as capacity, head, NPSH, allowable fluid j
e velocities, etc.
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design conditions such as pressure, temperature, fluid chemistry, and system operating characteristics operational requirements under plant emergency operation.
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Thc second operability review area is to perform a review of the J
functional and flow test data of active pumps and valves to determine if the testing demonstrates functional operability of individual components and systems.
These tests as appropriate should demonstrate the following:
system pressure drops under emergency conditions i
validity of throttle valve settings e
adequacy of test instrumentation and calibration status.
e The third operability review area is to perform a walkdown of the service water system and component cooling water system with emphasis on:
verifying that major valves are in the correct position and locked if 1
required for the existing plant conditions
-1 verifying that all valves used for throttling are positioned in accordance with the last valid flow balance test or its equivalent 1
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observing the material conditions of the system components for cracked e
or broken parts, corrosion, leaks, missing handles and bolts, indications of misalignment, excessive vibration, evidence-of excessive movement as a result of water hammer, and bearing over-heating.
1.5 Pacific Northwest Laboratory Assignment The operability inspection team leader assigned the component cooling wate
' stem operability inspection to the Pacific Northwest Laboratory team member.
Since the DET inspection was limited to the service water system, the DET findings were reviewed for applicability to the component cooling water system and the objective of this operational assessment.
The DET's findings, which apply to the operability inspection of the component cooling water system, included; operability issues, maintenance, and engineering design and technical support. TheDET'sfindingsconcerningmotoroperatedvalves(MOVs) are assigned to a special MOV investigation team and therefore, as applicable to the component cooling water system, required only a limited operability inspection.
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l 2.0 SYSTEM DESCRIPTION I
'The component cooling water (CCW) system supplies cooling water to various plant components during normal operations, removes residual heat from the reactor coolant system during the second phase of plant cooldown, and supplies cooling to safeguard equipment loads during and after a postulated accident..
i Interface of the heat source and the ultimate heat sink is achieved by using component cooling water as an intermediate heat transfer medium.
The heat absorbed by the CCW system, which will vary with the mode of reactor j
operation, is transferred to the service water system at the component cooling water heat exchangers.
Each heat exchanger is designed to remove the normal heat load of each reactor (or unit) with an additional heat exchanger required when the residual heat removal system is in operation.
Component cooling water flow through any of the three parallel heat exchangers'and,the CCW system is provided by five component cooling water pumps.
The pumps are arranged in parallel and may be operated as needed to sup)1y sufficient cooling water for the combined heat loads of either unit or bot 1 units. A suction head for the component cooling water pumps is provided by two surge tanks (one for each unit).
The surge tanks allow for expansion and contraction of the component cooling water due to system temperature changes and provide a point in the system where chemical corrosion inhibitor' may be added.
The component cooling water system piping is fabricated from i
carbon steel and hence, potassium chromate, KpCr2 7, is added to the system
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water to minimize general corrosion and to prevent stress corrosion of the i
stainless steel components cooled by the component cooling water system.
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i 3.0' SYSTEM CONFIGURATION l
The Zion Station component cooling water (CCW) system is a conventional Westinghouse Electric Corporation pressure water reactor design.
The system
. description section of this technical letter report describes the CCW system as it is currently configured, that is, in a " common header" configuration.
An alternate operating configuration is the " split system" configuration where j
the CCW system is operated as two separate parallel systems (as shown in the UFSARP&lD).
The original operating configuration of the CCW system design as intended by the Westinghouse designers is unclear.
Based on information provided by the licensee, a compelling argument exists that the CCW system is j
not being operated in its original design bases configuration.
3.1 Common Header Confiouration In the common header configuration, any single active er passive failure
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in the CCW system can render the system incapable of performing its design function.
i Figure 1, adapted from the Zion Station trair,ing manual, shows the CCW '
j system in the common header configuration. With oae exception, this fi represents the normal operating mode of the CCW system at Zion Station.gure o
The exception is that the unlabelled isolation valve shown closed (leadirg to the 0-heat exchanger) was found open during the plant walkdown. Maintaiaing this valve open is typical for the common header configuration and is mar. dated for most plant operating modes by Technical Specification.
i 3.2 Split System Confiouration In the split system configuration, any single active or )assive failure l
in one side of the system will not prevent the other side of tie system from performing its design function.
To change the CCW system show in Figure 1 to the split system L
configuration requires closing four valves; 100-9459B, 100-94588, 100-9467D l
and 100-94678.
Figure 2 shows the CCW system in the split system i
configuration.
The same effect can be obtained by closing the equivalent Unit-2 valves instead.
Closing all eight valves establishes the split header configuration with the Unit-0 pump and heat exchanger in standby and an i
isolated condition.
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3.3 Operatino Configuration Several documents are available at Zion Station to assist in making a reasonable determination of the intended operating configuration from which the original design basis accidents were evaluated. Among the documents are the Zion Station Final Safety Analysis Report (FSAR), Pre-operational testing documents,' configuration analyses and operating procedures. 3.3.1 FSAR The FSAR (Ref.1) provides both text and drawings to describe the component cooling water system. Included in the FSAR text are the General Desian Description (Section 9.3.1.1) and the Design and Operation (Section water system (FSAR Figures 9.31(1&2) grams (PITDs) of the component cooling 9.3.2). The drawings include the dia ). The FSAR with its text and drawings is the fundamental document on which the utility's license for operation is based. The FSAR General Design Description provides two somewhat conflicting perspectives on the operation of the CCW system:
- 1) isolation valves are provided so that the Component Cooling System con be divided into two subloops if desired, one for each unit.
- 2) Any single active or passive failure in the system will not prevent the system from performing its design function.
The cor.flict is; in meeting the second statement, the first statement is no longer an option, i.e., the component cooling system must be divided into two subloops. The FSAR dia0 rams of the component cooling water system make the distinction between. valves intended to be o)en (drawn in outline) and valves. intendedtobeclosed(shadedinsolid). Tie valves that when open or closed make the determination between common header and spli. system configuration are shown closed. Therefore, according to the FSAR component system diagrams, the design intent is to operate the CCW system in the split system configuration. 3.3.2 Pre-Operational Testino System pre-operational testing occurred mostly in 1972 followed by station startup in 1973. A review of pre-operational testing documents was performed to determined the initial CCW system valve lineup, pre-operational testing configuration, and startup test results. Initial testing of the CCW system was in a split header configuration, that is, all necessary valves were closed to establish isolation. Later, an exception to a completely split system was established by opening all suction 9
I 4 q i i valves. This was deemed necessary since the water inventory in one half of i the split system was increasing to the point of overflowing the surge tank due l to flow imbalance. Another early change made during pre-operational testing was to maintain i one surge tank isolated from the remainder of the CCW system. A hand written note in the pre-op notebook describes the change in testing configuration made [ from the initial two surge tank configuration testing to single surge tank ~ testing with the other surge tank isolated. The problem encountered, which precipitated the configuration change, was surge tank overflow in one tank l commensurate with a loss of coolant in the other tank. j t The final CCW system valve lineup established for pre-opsetional testing was the common header configuration. At some unidentified time in the pre-operational test program, the valve lineup was changed by lirin i original valve position and writing in the opposite valve position.g out the This i revised handwritten valve lineup changed the CCW system from a split header to a common header configuration. In the " Evaluation of Test Results" for the CCW system it is stated: Unit 1 surge tank "only" was used; it is difficult to operate the system split, as crosstie volves leak through and unbalance the surge tanks if both are volved in simultoneously. Further more, in a letter describing the " Component Cooling Pre-Operational Testing" it is stated: Currently, this system cannot be operated as per the FSAR. The volves on the ring (common) header leak through, therefore, if the system is split on both suction and discharge,- water inventory changes between units. 3.3 Configuration Analysis - 1988 On December 19, 1988, Westinghouse Electric Corporation Energy Systems provided Commonwealth Edison Company an engineering evaluation of the Zion Station Component Cooling Water System (Ref. 2) for the necessity of separating the system between unit-1 and unit-2. Of particular concern was that Byron, Braidwood, and Zion all use a component cooling water system of a vintage that features five component cooling water pumps, and three component cooling heat exchangers shared between two identical nuclear units. The specific area of concern revolves around the operating differences between the plants. Byron and Braidwood operate the CCW system in a split s configuration whereas Zion operates the CCW system in a shared (ystemcommonheade configuration. Westinghouse evaluated the CCW system supply temperatures and determined ^ the effects these temperatures would have on equipment and on the ability to shutdown the non accident reactor unit. Westinghouse determined that there 10
1 I will not be any significant impacts on the equipment or on the ability to i shutdown the non-accident unit if the reactor unit's CCW system is not i separated when the other reactor unit sustains an accident. l l i 3.4 Confiouration Analysis - 1990 l Westinghouse Electric Corporation recently submitted a Component Cooling Water System Design Bases document (Ref. 3) to Commonwealth Edison Company. The document is in draft form and, at the time the o)erability inspection team ( was on site, it had not been approved by Comonwealti Edison Company. The draft document was provided to the operability inspection team with the understanding the document is a draft and only provided for review. l accident (LOCA) ping this document, Westinghouse analyzed loss-of-coolart In develo I scenarios for differing operating conditions. Westinghouse recognizes in the draft document tF t during normal operation the two trains are cross connected, that is, in a comon header configuration. In assessing i the component cooling water system's capabilities, Westinghouse determined the CCW system's heat transfer capability is adequate given the minimum of three-pumps and two heat exchangers with a full spent fuel pit heat load. Additionally, Westinghouse calculates that failure (active failure) of any one of the minimum complement of components in use will increase the. time required for plant shutdown but will act affect safe operation of the plant. Since the component cooling water system is required for post-accident removal of decay heat from the reactor, the draft Westinghouse design bases document recognizes the CCW system as an engineered safeguard system. As an engineered safeguard system, the CCW system design is to meet the single failure (passive failure) criteria, which the system cannot meet in a cross connected or comon header configuration. To resolve the contradiction between the current o)erating condition and the single failure criteria Westinghousestatest1attheequipmentwillbesharedbetweenunitsdurIngall l phases of plant operation except normal cooldown, and the recirculation _ phase of operation subsequent to a LOCA. During these operations the equipment servingtheoff-normalunitmustbeisolatedfromtheunitInnormal
- operation.
In other words, a split-header configuration. t 3.5 Operatino Procedures Operating procedures currently used at Zion Station support the comon header configuration. Procedures reviewed included both normal operating and abnormal operating procedures. 1 3.5.1 Normal Operatino Procedures The CCW system normal operating procedure, S01-6 Component Cooling", valve lineup positions the system in a common header configuration. 501-6 >provides only for continuous operation of the CCW system regardless of the reactor plant conditions. Isolation and retur. to service of individual 11
i components are expressly not part of this procedure and, when required, are covered by maintenance work procedures. 3.5.2 Abnormal Operatina procedure The procedure established to mitigate most failures in the CCW system it. Abnormal Operating Procedure A0P-4.1 " Loss of Component Cooliig". This AOP assumes the operating configuration of the CCW system is comman header. Operating the CCW system in the common header configuration leaves both reactor units vulnerable in the event of a catastrophic failure of the CCW system. Catastrophic failure of the piping or a major component in the CCW. system could result in rapid loss of component cooling water subsequently rendering the CCW system inoperable. The first evidence of a loss of component cooling is usually a loss of level indication in the CCW surge tank. Procedurally, the only course of action is to attempt to restore surge tank level. Changing the system configuration to split header, or isolating a pipe break or a failed component .is not a procedural option. Inability to isolate the point of component cooling water loss will eventually result in cavitation of the CCW pumps. When cavitation of the CCW pumps is evident, A0P-4.1 directs reactor operators to " Trip BOTH reactors." Reactor operation is now governed by the Emergency Operating Procedures (EOPs). 12 i
e t 4.0 SYSTEM CONDITION The component cooling water (CCW) system was examined to determine its physical condition. A general assessment was made by performing a walkdown of the system to determine its superficial condition. Maintenance, surveillance and chemistry information were reviewed to determine the extent of upkeep the system has received during its operating life. A review of the CCW system modification history was performed to determine if changes are consistent with licensing design bases. CCW system operating procedures were examined tr verify the system is operated within design constraints. A search was made for a trending or similar program that would provide indicators of the future health needs of the CCW system. 4.1 General r A system walkdown was performed to determine, superfidally, the general condition of the CCW system. Due to the plant's current ope"ating condition, high radiation fields existed at some of the load side components of the CCW system. In su) port of the ALARA program, thes9 components were observed from i a oistance or )y reviewing recent photographs. General housekeeping of the CCW system was wry good. Nonradiological contamination was almost nonexistent. A2 appropriate, component and piping surfaces were painted, insulated or exposed. Out-of service ta clearly visible and legible. Pump-oil (from a failed oil seal)gging was and potassium chromate found outside of their intended environment were adequately controlled. A water leak on the service water side of a CCW heat exchanger i was sufficiently contained to prevent a safety hazard. No debris or unnecessary equipment was present that would compromise the CCW system's equipment qualification requirements in the event of a seismic event. 4.2 Maintenance Maintenance records were reviewed for all major com)onents of the component cooling water system and for minor components w1ose function is critical to the safety function of the CCW system. 4.2.1 Pumps The CCW pumps are not part of any preventive maintenance program. The pumps have been running almost continuously for 17 years with only obligatory corrective maintenance. Without any historical maintenance information and superficial surveillances, the health of these pumps is unknown. -Two pumps were torn down and repaired due to mechanical seal failure. Both'of the pumps had the same symptoms, a leaking outboard mechanical seal. The first pump was serviced during March 1988. Although only new bearings, mechanical seal and miscellaneous small parts were required to correct the identified problem, the pump impeller was replaced. The reason for the 13
impeller replacement wasn't documented. Impeller damage due to excessive end play is possible but so is excessive wear due to erosion. The second pump was serviced during' January 1990. This pump received repair in a manner similar to the first except without the impeller replacement. When disassembled, neither pump received a documented maintenance inspection report describing the internal condition of the pump. The remaining three pumps have not received any form of maintenar inspection or preventive maintenance since originally put into service n 1973. The " Post Maintenance Test / Verification Forms" for CCW pumps requires performing PT-8A " Component Cooling Pumps Operability Test". PT-8A is an operability and acceptance test procedure and is discussed further in this report under Section 4.3, Surveillance. 4.2.2 Heat Exchangers On June 2, 1990 the_ Unit-1 CCW heat exchanger was opened on the tube (service water) side. The purpose was to inspect and repair suspected tube leakage,identifiedbydecreasing)surgetanklevel.of a heat exchanger inspection and impact In contrast to pump repairs, a sunnary report (Ref. 4 on heat exchanger operability was written. The findings of the summary report are paraphrased below. the inspection estimated that the heat exchanger had an as-found performance factor of approximately 60% - 70% of design tube cleaning reduced the fouling of the heat exchanger to a minimum pressure testing revealed 15 tubes leaking eddy current testing identified an additional 48 tubes with indications of reduced wall thickness greater than 40% all (63) tubes leaking and with excessive thinning were plugged e bore scope examination of tubes showed concentrated cell corrosion a pitting of an undetermined chemistry inside of the tubes based on cleaning, examination and inspection testing, Zion Technical Staff believes the heat exchanger is capable of performing acceptably for both normal operation and acciducit loads. All of the inspection findings paraphrased'above refer only to tube side (service water) side of the CCW heat exchanger. No inspection was performed on the shell (CCW) side of the heat exchanger. A recommendation was made in the report to inspect the Uriit-0 and Unit-2 CCW heat exchangers but, to be-scheduled in accordance with the planned heat exchanger preventive maintenance program and in response to Generic Letter 89-13. 14 g
l i Silting was identified by Zion staff as the main cause of the reduced performance factor stated in the summary inspection report. Photographs taken of the Unit-1 CCW heat exchanger clearly show a silt or sediment accumulation j at the bottrr of the inlet water box. Silting is generally regarded as a. self-limitin equilibrium phenomena and as such, slit accumulation is small and therefore has a minor impact on heat exchanger performance. The accumulation visible in the photographs is significant and, although silting i . maybe present, dense mineral particles are accumulating in the heat exchanger i inlet water box in the form of sediment. The sediment collection is cumulative rather than equilibratory and therefore could lead to significant i flow obstruction through the heat exchanger. 1 Another contributor to reduced heat exchanger performance is tube i fouling due to corrosion. Accordin Analysis Department (SMAD) report (g to a Zion Station System MaterialsRef 5), corro Unit-1 heat exchanger tubes in the form of wall thinning, pits and nodule j formation. Although SMAD did not determine the exact corrosion mechanism it did acknowledged future corrosion is likely to occur. l L During a meeting with Zion Station management and separately from two individuals, each with over ten years of service at Zion Station, the claim was made that the Unit-0 heat exchanger was opened for inspection or maintenance service, in either 1980 or 1985. No documentation was found to authenticate this alleged inspection or maintenance effort. -Inspection documentation on the Unit-1 CCW heat exchanger provides a single data point to indicate the heat exchanger's operability. Without additional historical information, the value of this single data point for the 'l Unit-1 heat exchanger is limited. This single data point does provide reason l to suspect the performance capability of the Unit-0 and the Unit-2 heat exchangers. From the Unit-1 heat exchanger experience, there is every reason . to believe Zion Station will soon experience tube leaks in the other two heat exchangers and during the inspection and repair identify sediment accumulation, tube wall thinning, and corrosion. 4.3 Surveillance Surveillance and testing of component cooling water system components j are required to meet Technical Specifications established for specific plant cperating conditions. The purpose of the surveillance and testing is to demonstrate the operability of equipment considered available. For all CCW system Limiting Conditions for Operation (LCOs), only three types of surveillance tests are required; associated standby AC and DC power supplies, CCW pumps and CCW heat exchangers. One of the two surge tanks is always isolated but assumed available without the benefit of a surveillance procedure. 15 s ~ ~ a.
4.3.1 AC and DC Power Supplies The first requirement is to demonstrate the availability of the standby AC and DC power su) plies associated with the pumps and instrumentation relied on as operable. T1e demonstration of availability of the AC and DC standby power supplies is accomplished by performing the AC & DC Power Supply surveillance tests. The adequacy of the AC & DC Power Supply test was not evaluated as part of the CCW investigation. 4.3.2 Pumps The second surveillance requirement to demonstrate the operability of theCCWpumps,isidentifiedintheTechnlcalSpecificationsby: The component cooling pumps shalI be operated each month. Performance will be acceptable if the pump starts upon actuotton, operates for at least four hours, and satisfies the cooling requirements necessary for the routine operation of the component cooling system. .The procedure used to demonstrate operability is PT-8A " Component Cooling Pumps Operability Test". This procedure vaguely meets tiie Technical Specification statement but doesn't demonstrate operability of any one particular pump. The Technical Specification statement contains three performance requirements to demonstrate operability of a CCW aump;he pump starts and tha so does the acceptance criteria in PT-8A. The first two requirements, t1at t the pump operates for at lest four hours, are easily determined by performing i PT-8A. I The third performance requirement, that the pum) satisfies the cooling l requirements necessary for the routine operation of tle component cooling i system, cannot-be determined by performing PY-8A. For example, assume one of the five CCW pumps has a defective im)eller; possibly from erosion. Technical Specifications require a minimum of t1ree pumps running at all times. PT-8A tests individual ) ump operability with the CCW system in the common header configuration. T1e defective pump will pass the PT-8A performance test since l it will start, operate for four hours and appear to satisfy the cooling requirements of the CCW system loads. The other pumps required by Technical ' Specifications will carry the cooling load for the defective pump. Operating in the common header configuration results in adequate header pressure developed by operating pumps masking inadequate pressure by the defective pump. ) Operability Test PT-8A does not include flow measurement for individual purps even though the capability to determine pump flow was installed as a modification to the CCW system, i i 16 ) i i . +,
.:o included in the PT-8A acceptance criteria is a requirement to meet specific pump and pump motor vibration velocities. Inability of a pum) or-pump motor to meet the vibration reading criteria requires declaring tie pump inoperable. 4.3.3 Heat Exchanoers The third surveillance requirement, to demonstrate the operability of the CCW heat exchangers, is identified in the Technical Specifications by: The status of the heat exchangers shalI be checked imediately and dally thereafter. There is no unique surveillance test to demonstrate the operability of.CCW heat exchangers. For conditions where equipment operability must be demonstrated and there is no unique procedure Zion Station's PT-14, "InoperableEquipmentSurveillanceTests" applies. Implementation of PT-14 is by the Station Control Room Engineer (SCRE). The SCRE determines the specific surveillance test activity according to his or her interpretation of the Technical Specification compliance requirements. Generally this testing, to establish the status of the heat exchangers, is limited to verification of the heat exchanger's presence. Primarily due to insufficient installed instrumentation, no attempt is made to verify individual heat exchanger flows, inlet and outlet pressures, or heat transfei. capability. 4.3.4 Surce Tanks In the current common header operating configuration useri at Zion-Station, one of the two CCW system surge tanks is isolated. 0)erating with one surge tank on line assumes the second surge tank is availa)1e in the event of an accident condition or failure of the on-line surge tank. No surveillance or operability test for the surge tanks, including its instrumentation and manual valves, exists. PT-14 is used to demonstrate operability of the CCW heat exchangers in the absence of a dedicated procedure but is not considered ap)11 cable to the surge tanks. The closest procedure that demonstrates availa)ility/ operability of the standby surge tank is GeneralOperatingProcedure-4(GOP-4),PlantShutdownandCooldown. GOP-4 requires changing from one surge tank to the other depending on the operating or hot shutdown status of the plant. At a maximum then, the longest that a surge tank could go without demonstration of operability is once every refueling outage or about eighteen months. 17
l 4.4 Modifications The component cooling system has had few modifications since its initial startup. The limited number of modifications is not unexpected since this system's design was based on previously well proven designs and that the system is built O th a substantial design margin. 4.4.1 Completed Modi,fications Eighteen modifications to the com)onent cooling water system have been completed since the 1973 startup. Of t1ese, six have direct application to the current evaluation by the operability inspection team. Only-four of the six modifications are unique since two modifications are duplicated, i.e., one modification for Unit-1 and a second modification for Unit 2. Component cooling water system solenoid operated valves were replaced in 1984 in response to NRC IE Bulletin 79-01. This effort replaced environmentally unqualified solenoid valves with environmentally qualified solenoid valves. An environmental qualification effort similar to the solenoid operated valves was performed on the component cooling water system valve actuators. Qualification of the CCW system valve actuators was completed in 1984. A modification was performed in 1985 to add discharge flow meters to the component cooling system pumps. The addition of this modification provided built-in capability to directly measure pump flow. In 1986, a modification installed pressure gauges on the component cooling water pump discharge piping. The addition of this modification .provided limited additional capability because of the current comon header operating configuration. Operating in the comon header configuration results in the installed pressure gauges reading the comon header pressure, not individual pump discharge pressure. Although, with the_ existing isolation valves the capability does exist to establish a testing configuration where pumpdIschargepressureisindicativeofindividualpumpdischargehead. 4.4.2 In-proaress Modifications Two modifications to the CCW system are in-progress. No other modifications have been initiated beyond conceptual discussions. One modification provides additional pressure indication in the control room. The additional indication sensor reads the pressure at the pump comon header. The second modification removes the Boron Recycle System (BRS). The CCW system provides cooling water to several components in the BRS when it's operating. The BRS has not been used for several years and because of its 18 l
pending removal, its interface with the CCW system was not included in the-operability inspection. Since the BRS is isolated from the CCW system during accident conditions, the-removal of the BRS does not provide any additional cooling capability to the CCW system. 4.5 Chemistry Chemistry testing of the CCW system is limited to two measurements; chromate and pH. Each are tested on a weekly basis. No additional laboratory testing is performed to determine the status of the system. No testing is performed to monitor for changes in system chemistry or ways to extend system design life and operability. No examination of the CCW system's coolant is performed to monitor for particulate matter, which would indicate system fouling or internal breakdown. 4.6 Op_eratina Procedures CCW system operating procedures were reviewed for applicability to current system status, approval for use and consistency with design operating conditions and heat loads. The procedures obtained for review were current, approved for use and where operating limits were specified, they were consistent with the design bases document. l 4.7 Trendina Zion Station does not have a trending program for the CCW system or its individual-components. Until 1988, procedure TSGP-32 " Primary Heat Exchanger Performance" was l >erformed routinely. The purpose of the procedure was to produce values of 1 eat exchanger effectiveness and heat transfer to be used to trend heat l exchanger performance. l l- ) 5 19 ,-~.
If I 5.0 THERMAL HYDRAULICS As an.intennediate loop cooling system, the component cooling water (CCW) system must be capable of removing the thermal energy from the plant components it supports and transferring the energy to the service water system. Significant degradation in flow or heat transfer will prevent the CCW system from meeting its intended function. To determine if system degradation is severe enough to impair the CCW system's safety function, three parameters were inspected for operability degradation; CCW system flow, CCW system heat transfer and CCW heat exchanger tube (service water system) flow. 5.1 CCW Flow Requirements Tabulated flow data from the FSAR Table 9.3.2-1 gives nominal flow requirements for three plant o The maximum CCW system flow requirement (14,316 gpm) perating conditions.is during an accident where one a LOCA and the other unit is in cooldown. This maximum flow was the value used to establish the Technical Specification operating limits for pumps and heat exchangers when in two plant operation. The CCW system is not tested to demonstrate its ability to meet the worst' case flow requirement and system demand curves were not available. To assess the system's flow capacity, actual component cooling pump data sheets were used to establish a known reference or data point. The conditions during the test were as follows: three pumps running and three CCW heat exchangers operating. The calculated system flow requirement for this configuration would bei Residual Heat Removal 4500 gpm Reactor Coolant Pum)s 800 gpm Seal Water Heat Exc1 anger 420 gpm Sample Heat Exchangers 196 gpm i Letdown Heat Exchangers 1000 gpm Spent Fuel Heat Exchangers 1500 gpm Remaining Heat Exchangers 670 gpm Total Maximum Load 9086 gpm During the test, any three pumps operating delivered about 9400 gpm. l This single t<!st provides some assurance that the present CCW system flow capacity is rhout the same as the original design bases flow requirements. That is, given the design bases accident flow demand and operating with a fourth pump as required t,y Technical Specifications, the CCW L system could prc ide well in excess of the 14,316 gpm requirement. The above aest configuration is only one data point along the CCW system demand / flow curve. Also, this data point represents the collective l performance of three pumps rather than the sum of the performance of three individual pumps. Collectively, three pumps were supplying sufficient flow to 20
meet the calculated system load demand. Assuming the three pumps are r performing similarly and assuming an average net positive suction head, the three pumps are operating near their performance curve. 5.2 Thermal Reauirements The original design specifications required each heat exchanger to have the capacity of transfeiring 53 million BTV/ hour. Zion Station no longer has a heat exchanger test program to determine thermal performance. At one time heat exchanger surveillance testing was performed but was discontinued in 1988. Results of a surveillance test completed in October of 1984 were obtained for review by the operability inspection team. Actual )lant operating conditions at the time of the test were not recorded, only t1e minimum temperature and flow data necessary to determine heat exchanger performance were recorded. During that particular test ar.d plant operating condition, the CCW heat exchangers were transferring 20 million, 51 million and 46 million BTV/ hour for the Unit-0, Unit-1 and Unit-2 heat exchangers respectively. All three CCW heat exchangers have a similar operating history and.it is reasonable to assume they have developed similar fouling over time. Since. in 1984, at least one heat exchanger demonstrated the ability to transfer at least 51 million BTV/ hour, the other two most likely can perfom similarly. To obtain a different perspective on the CCW system's thermal capability,in closed cooling loops was consulted.a Pacific Northwest t.aboratory subject matte experience From examinations of closed cooling loops found in the Department of Energy's nuclear reactors with similar operating histories and environments, the expert's judgement is that CCW fouling would not exceed 25% of the original design. Based on original design data, the design heat transfer coefficient for the CCW-heat exchanger is U 199.6 BTV/(hr-deg F-sqft) with a fouling factor of 0.0005. Referring to Hicks (Ref. 6), the heat transfer coefficient for the heat exchanger when fouled is about U 135. Thus, to compensate for fouling, the required CCW heat exchanger heat transfer surface areas were increased by 50% to compensate for the reduction in heat transfer anticipated from fouling. Since the subject matter expert's judgement is CCW fouling would not exceed 25% and CCW heat exchangers are compensated to 50%, it is the subject matter expert's opinion that adequate heat transfer capability exists at the CCW heat exchangers. The detailed specifications for the load heat exchangers supported by the CCW system were not reviewed. Given the design conservatism of the CCW heat exchangers, it is reasonable that the same conservatism was applied to the remainder of the components associated with the CCW system and therefore adequate heat transfer capability exists. 21
4 i S.3 CCW Heat Exchancer Tube Side i L The CCW system interfaces with the service water system at the CCW beat j exchangers. The CCW heat exchangers are a typical tube in shell design with the CCW system on the shell side and the service water system on the tube side l of the interface. Insufficient flow through the tube (service water) side of i the CCW heat exchanger will result in the system's inability to meet design l bases accident heat transfer requirements. ] Durin the month of June 1990, the Unit-1 CCW system heat exchanger was taken out o tervice, opened and ins)ected because of a leak identified by 1 decreasing surge tank level. Only t1e tube side was ins)ected as shell side inspection capability is not built into the CCW heat exc1 anger. Zion Station j staff performed a visual ins)ection of the condition of the heat exchanger and i determined that the heat exc1 anger had an "as found" performance factor of ] approximately 60% to 70%. Although the report isn't explicit, it implies that fouling was the )rimary cause of the reduced performance factor of 60% to 70%. Isased on the 1 eat exchanger's designed service heat transfer rate (U=459) and its fouling factor (0.00233), the tube side of the heat exchanger can have a performance j factor as low as 44% and still meet design bases accident requirements. L Pictures taken of the disassembled CCW heat exchanger attest to the i presenceoflargeamountsofsilt(sediment)intheinletwaterbox. Another l interpretation of the Zion Station inspection report is that the heat l exchanger reduced performance of 60% to 70% is due to plugging from silt i accumulation. Assuming silt plugging is the cause of the reduced performance, j the consequence of the silt accumulation is predominately a combination of reduced flow through the tubes and an increase in flow velocity. J Reduced flow through the CCW heat exchanger tubes will result in an I increase in heat exchanger outlet temperature. The heat exchanger maximum I design load outlet temperature is 90 degree F. Reducing tube flow by 40% i while maintaining a constant transfer of heat will raise the outlet temperature to about 97 degree F, which is well within the structural design l of the. service water system. J Increasing flow velocity through the heat exchanger tubes to maintain a constant mass flow of coolant can lead to accelerated degradation of the heat exchanger due to erosion. The heat exchanger design flow velocity at accident conditions is 4 feet per second. Increasing the flow velocity to compensate for a 60% reduction in performance will increase the flow velocity to about J 6.7 feet per second. Since good engineering design practices recommend limiting piping system flows to under 7 feet per second to minimize erosion. Thus, at 6.7 feet per second, accelerated erosion isn't likely. 1The operability assessment of the service water system is included in a separate report. 22 l i
6.0 SYSTEM OPERABillTY 6.1 Normal Plant at Full Power The component cooling water (CCW) system is capable of meeting the-normal startup, operating and shutdown heat removal needs of the Zion Station nuclear reactors. This capability is primarily due to a substantial design safety margin and the use of a corrosion inhibitor. Single point checks of the CCW system's operational status indicate system degradation during the last seventeen years of operation has not exceeded the original design margins. The CCW system is normally operated in a common header configuration. This configuration appears different than the original design bases. Documentation from Westinghouse professes this configuration as safe, at least in the safety realm for which the NRC has responsibility. Zion Station staff could not demonstrate that this independent documentation has been submitted to the Nuclear Regulatory Commission for its review and concurrence, and eve-+9 ally its inclusion into the Technical Specifications. 6.2 CCW LOCA Operating the CCW system in the common header configuration lends itself to common-mode failure. A single pipe break can result in a loss of coolant accident for th6 entire CCW system with subsequent impact on both nuclear reactor units, that is, challenging the safety systems for both nuclear entering emergency operating prciedures (quires tripping both reactors andTrip procedures a reactor units. Loosing the CCW system re EOPs). actions are in place in the event of this type of failure although they do not require action to be taken that would limit the CCW LOCA to a single unit. 6.3 Reactor Pressure Boundary LOCA Reactor pressure boundary loss of coolant accidents are analyzed with the assumption the integrity of the CCW system remains intact (single failure criteria). Based on t.nofficial analyses by Westinghouse, the CCW system when v erated in the common header configuration is capable of handling the thermal loads, as delineated in Technical Specifications, to the extent required to meet the health and safety of the public. The consequence of operating in the common header configuration during the worst case reactor pressure boundary LOCA is that CCW system component degradation may result. Any degradation will result in reduced CCW system component life but will not impair the system's ability to function throughout the duration of the accident. 23 I
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7.0 CONCLUSION
S Safe plant operation is not compromised by the outstanding question concerning the operating configurations of the CCW system, in the unlikely event of a catastrophic loss of the CCW system, procedures are in place to safely shut down both reactor units. Zion Station has not formally documented its bases for operating the CCW system in the open header configuration. A revised CCW system design bases document by Westinghouse exists in draft form and is currently in review by Zion Station staff. Approval by Zion Station staff and the Nuclear Regulatory Commission will formally sanction the open header configuration. An alternative to approving the draft Westinghouse design bases document is to realign the CCW system into the split header configuration. Implementing the split header configuration requires procedure modifications, revised training and CCW system maintenance, primarily to isolation valves that leak through, Lack of any planned maintenance program on the CCW system reduces the confidence of the systems availability and continued operability. Until Generic Letter 89-13 is implemented by Zion Station management, any maintenance program will be of proven benefit to both licensee and regulator alike. An adequate CCW system heat exchanger and pump surveillance program is needed. The CCW heat exchanger surveillance program is nonexistent. The procedure used to verify CCW pump performance requires revid on..This procedure is not in accordance with ASME code section XI, ing this procedure, the pumps are tested in groups rather than indi,idually and new reference values are not establisu;d following pump repair. 24 -_ a
8.0 REFERENCES
f Reference 1. Updated Final Safety Analysis Report Zion Station, 2. Toth, GP (Westinghouse Electric Corporation) Letter.to Moerke, CA (ConsolidatedEdisonCompany),CCWInterunitSharina", December 19, 1988. 3. Desian Bases, Commonwealth Edison Company Zion sistion Units 1 & 2 Component Cooling Water System, Revision 0 Draft, Westinghouse Electric Corporation, 1990. T'Nieml,AMandStoddard,MC,ZionStationInternalLetterto Padleckas 4. WD Summary of "1" CC Heat Exchanaer Inspections and Impact on Heat Exchanger Operability, June 28, 1990. 5. System Materials Analysis Department Report on the Inspection of the Zion Unit i Component Coolina Heat Exchanaer, Zion Station Report M-3083-90, July 2, 1990. 6. Hicks, TG, Standard handbook of Engineerina Calculations, New York - McGraw-Hill, 1972. f 25 4}}