ML19340E400
| ML19340E400 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 12/31/1980 |
| From: | CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | |
| Shared Package | |
| ML18046A301 | List: |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.F.2, TASK-TM NUDOCS 8101140344 | |
| Download: ML19340E400 (38) | |
Text
0 f
O INADEQUATE CORE COOLING DETECTION SYSTEM
SUMMARY
STATUS REPORT 1
December, 1930
.- * *'uo 39H
TABLE OF CONTENTS Section Title Page
1.0 INTRODUCTION
1-1 1.1 Summary of Activities 1-1 1.2 Definition of ICC 17 1.3 Description of Event Progression 1-3 1.4 Summary of Sensor Evaluations 1-3 2.0 SYSTEM FUNCTIONAL DESCRIPTION 2-1 2.1 Subcooling and Saturation 2-1 2.2 Coolant Level Measurement in Reactor Vessel 2-1 2.3 Fuel Cladding Heatup 2-2 3.0 SYSTEM CONCEPTUAL DESIGN DESCRIPTION 3-1 3.1 Sensors Design 3-1 3.2 Signal Processing Equipment Design 3-4 3.3 Display Design 3-7 4.0 SYSTEM VERIFICATION TESTING 4-1 4.1 RTD and Press 0rizer Pressure Sensors 4-1 4.2 HJTC System Sensors and Processing 4-1 4.3 Core Exit Thermocouples 4-4 4.4 Processing and Displays 4-4 5.0 SYSTEM QUALIFICATION 5-1 6.0 OPERATING INSTRUCTIONS 6-1
o
1.0 INTRODUCTION
1.1 Sul+1ARY OF ACTIVITIES This rem.rt responds to the requirements in Section II.F.2 of NUREG-0737 (Ref.1).
The report describes the status of desier and development activities being conducted by the C-E Owners Group to define a system of instrumentation to be used to de-tect inadequate core cooling (ICC). The report also provides information specific to the Palisades Plant in order to demonstrate the applicability of the generic activity to the Palisades Plant.
Results of initial studies by the C-E Owners Group are documented in reports CEN-ll7 (Ref. 2) and CEN-125 (Ref. 3). These results were referenced in a letter from Consumers Power Company dated 12/27/79. All studies have been based on the require-ment to indicate the approach to, the existence of and the recovery from ICC.
A three step process is being used to define the ICC Detection System.
Fi rs t,
a definition for the state of ICC has been selected. Second, typical accident events which progress toward the defined state of ICC have been analyzed. Third, instruments which indicate the progression of these events have been selected and evaluated.
Based on initial evaluations of a variety of instruments, an ICC Detection System has been defined. This system is judged to be technically sufficient for ICC detection. However, this system is not uniquely necessary, and functions of its various ccmponents may be perfonned by alternative components. This system is described in Section 3.
Further developments are necessary before the system can be implemented and these are planned as described throughout this report.
1.2 DEFINITION OF ICC l
The definition of ICC and the functional requirements for the ICC Detection System have been established within the bounds of the following core conditions:
1-1
i 1.
The reactor is tripped so only decay power is considered.
2.
The coolant level falls below the top of the core, which can occur only with a loss of coolant mass from the Reactor Coolant System (RCS).
3.
The event proceeds slowly enough so that the operator has time to observe and to make use of the instrument displays.
These conditions provide the boundaries for a range of sizes of small break loss of coolant accident (LOCA) caused by either RCS ruptures or primary co.lant expansion.
The following definitions of ICC have been considered:
1.
First occurrence of saturation.
2.
Core uncovery.
3.
Fuel clad temperature of 9000F (below which return to normal operation may be permissible).
4.
Fuel clad temperature of 11000F (below t?.i h clad rupture in not expected t
to occur).
5.
Fuel clad temperature of 22000F (which is the licensing limit for design basis events using approved analytical models).
It has been concluced that the events can progress too rapidly for the instrumen-tation to reliably display the approach of ICC if one of the first four defini-tions is used. Therefore, it is concluded that definition 5, a fuel clad 0
temperature of 2200 F, should be selected as the criterion for existence of ICC.
1-2
1.3 DESCRIPTION
OF EVENT PROGRESSION A typical small break LOCA illusf. rates the progression of an event which causes the approach to ICC.
Figure 1-1 shows a representative behavior for the two phase mixture level and the RCS pressure vs. time for the event. The event progression is divided into four intervals which are shown in Figure 1-1 and are defined in Table 1-1.
1.4
SUMMARY
OF SENSOR EVALUATIONS Several sensors have been evaluated for use in an ICC Detection System. The instruments considered are listed in Table 1-2, where their capabilities are sunnarized. Significant conclusions about each instrument are given below.
1.4.1 Subcooled Margin Monitor The Subcooled Margin Monitor (SMM), using input from existing Resistance Temperature Detectors (RTO) in the hot and cold legs and from.the press"rizer pressure sensors, is adequate to detect the initial occurrence of saturation during LOCA events and Juring loss of heat sink events.
The usefulness of the SMM can be significantly increased by also feeding into it the signals from the fluid temperature measurements from the Reactor Vessel Level Monitoring System (RVLMS) and the signals from selected core exit thermo-couples and by modifying the SMM to calculate and display degrees superheat (up to about 18000F) in addition to degrees subcooling. The signals from the l.
RVLMS temperature measurements provide information about possible local differences in temperature between the reactor vessel upper head / upper plenum (location of the RVLMS) and the hot or cold legs (location of the RTDs).
The core erit thermocouples respond to the coolant temperature at I
the core exit and their signal indicates superheat af ter the coolant level drops below the top of the core and, thus, provide un approximate indication of the depth of core uncovery.
i 1-3
t With these modifications, che SMM can be used for detection. of the approach to ICC, namely Interval *. (loss of subcooling), Interval 3 (core uncove y) and Interval 4 (core recovery).
Even with the modifications, the SMM will not be capable of indicating the existence of Interval 2 when tne coolant is at saturation conditions and the level is between the top of the vessel dnd the top of the Core.
The recovery interval may occur at low system pressure and temperature.
Since the errors in the existing SMM calculations increase with lower temperature and pressure, required subcooling margins need to be revised for this situation.
l 4.2 Resistance Temcerature Dete'ctors (RTD)
The RTD are adequate for sensing the initial occurrence of.s_aturation. The hot leg RTD range is sufficient to sense saturation for events initiated at power.
The cold leg RTD, which have a wider' range, are sufficient to sense saturation for events initiated from zero power or shutdown conditions.
The, RTD range is not adequate for ICC indications during core uncovery.
For cepressurization LOCA events, the core may uncover at low pressure, when the
~
saturation temperature is below the lower limit of the hot leg RTD.
Ini tial superheat of the steam will therefore not be detected'by the hot leg RTD. As the uncovery proceeds, the superheated steam temperature aay quickly exceed the upper limit of the RTD range.
In order to be useful during the core uncovery interval, the range of RTD would need to be increased to cover a U
U temperature range from 100 F to 1800 F.
1.4.3 Reactor Vessel Level Monitoring. System The Reactor Vessel Level Monitoring System (RVLMS) is being designed to show the liquid inventory of the mixture of liquid and vapor coolant above the core.
It is an instrument which shows the approach to ICC and is the only one which functirns in Intervai 2, namely the period from the initial occurrence of saturation conditions until the start of core uncovery.
1-4
(
a f
1.4.4 Core Exit Thermoccuoles The core exit thermocouples are adequate to show the approach to ICC after core uncovery for the events analyzed provided that the signal processing and display does not add substantial time delay to the thermal delay at the thermocouple junction. As mentioned above, the core exit thermocouples respond to the coolant temperature at the core exit and indicate superneat after the core is no longer completely covered by coolant. Except for a time delay of about 200 to 400 sec, depending on event, the trend of the change in superheat correspcnds to the trend of ctre uncovery as well as to the accompanying trend of the change in cladding temperature, 1.4.5 Self Powered Neutron Detectors (SPND)
The SPND yield a signal caused by high temperature as the two-phase level falls below the elevation of 'he SPND. However, testing is required to identify the phenomena responsible for the anomalous behavior of the SPND at TMI-2. At the present, their use is limited to low temperature events (less than 1000*F clad temperature) or to only the initial uncovery portion of an event.
1.4.6 Ex-Core Neutron Detectors Existing source range neutron detectors are sensitive enough to respond to the formation of coolant voids within the vessel during the events analyzed.
However, the signal magnitude is ambiguous because of the effects of varying boron concentration and deuterium concentration in the reactor coolant.
A stack of ex-core detectors gives less ambiguous information on voids and level in the vessel. The relative shape of the axial distribution of signals from a stack of five detectors shows promise as an ICC indicator, but additional development would be needed.
1-5
1.4.7 in-Core Thermccoucles It appears in general feasible that in-core thermoco_ les could be added to or sub-stituted for some SPND in the in-core instrument string. They would respond more quickiy to gore uncovery than the core-exit thermocouples. Also, due to thermal radiation from the fuel rods they see temperatures closer to the cladding tem-peratures than to the steam temperature seen by the core exit thermocouples.
For top mounted in-core instrumentation, the core exit thermocouples may survive longer for deep uncovery events because the thermocouples and their leads see only core exit steam temperature which is less than the fuel clad temperature.
For bottem mounted in-core instrumentation, those in-core thermocouples which 1e located below the two-phase level will survive longer than the core exit r.hermoccupies because the core exit thermocouple leads pastdown through the high temperature region during core uncovery.
Using a synthesis approach, sim.ilar to the one described for core exit thermo-l couples, it is expected that the in-core thermocouple temperature can be related more directly to the adjatant fuel clad temperature than is possible with a syn-thesis which uses core-exit thermocouples.
However, additional work would be
(
required to study the temperature response of in-core thermocouples as well as to develop the mechanical design for incorporating the thermocouples into the in-core instrument string and to develop a synthesis method for calculating fuel cladding temperatures.
l l
l-6
~ _.,
Table 1-1 Definition of Intecvals in ICC Event progression Interval No.
ICC phase Bounding parameter Description 1
1 Approach to Reduction in RCS subcooling Depressurization of RCS to satura-untii saturation occurs.
tion pressure at hot leg temperature or heatup to saturation temperature j
at safety valve pressure.
l 2
Approach to Falling two phase mixture level in Net loss of coolant mass from RCS upper plenum, down to top of active accompanied by boiling from continued fuel.
depressurization and/or decay power.
1 3
Approach to Two phase level falls from top Two phase level drops in core causing and/or of active fuel until mininom clad heatup and producing superheated Existence of level during event progression steam at core exit.
occurs or until 2200"F clad tanperature occurs.
4 4
Recovery from Two phase level rises above top Coolant addition by ECCS raises level of core.
and quenches fuel.
ICC progression is defined to tenninate when vessel is full or when stable, controllable conditions exist.
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FIGURE l-1 DEFINITION OF INTERVALS IN EVENT PROGRESSION
l l
2.0 SYSTEM FUNCTIONAL DESCRIpTICN In the following sections a functional description of the instruments of the ICC Detection Sys. tem is given and the function of the instruments is related to the ICC intervals which were described in Section 1.0.
2.1 SUSC00 LING AND SATURATION The parameters measured to detect subcooling and saturation are the RCS coolant temperature and the pressurizer pressure. Temperature is measured in the hot legs for typical LOCA type events and is measured in the vessel upper head region for cooldown events. The measurement range extends from the shutdown cooling conditions up to saturation conditions at the pressurizer safety valve setpoint.
The response time needs to be such that the operator obtains adequate information during those events which proceed slowly enough for him to observe and to act upon the information from the instrument display.
Plant specific analyses for Palisades may need to be performed for a selection of small break LOCA events in order to establish the required response times. Generic analyses done to date show that existing or planned instruments have adequate range and response.
The information whicn is derived from the reactor vessel temperature and pressure measurements is the amount of subccoling during the initial approach to saturation conditions and the occurrence of saturation during Interval 1.
During Interval 4, the reestablishment of subcooled conditions is obtained.
2.2 COOLANT LEVEL MEASUREMENT IN REACTOR VESSEL The Reactor Coolant System is at saturation conditions until sufficient coolant is lost to lower the two-phase level to the top of the active core.
During tnis interval there are no existing instruments which would measure A Reactor Vessel Le' el Monitc.ing System provides a directly the coolant inventory loss.
v direct measurement during this period. The parameter which is measured is the collapsed liquid level above the fuel alignment plate.
The collapsed level represents the amount of liquid mass which is in the reactor vessel above the core. Measurement of the collapsed water level was selected in pr eference to 2-1
measuring two-phase level, because it is a direct indication of the water inventory wnile the two/ phase level is determined by water inventory and void fraction.
The collapsed level is obtained over the t'me temperature and pretsure range as the saturation measurements, thereby encompassing all operating and accident conditions where it must function.
Also, it is intended to function during Interval 4, the recovery interval. Therefore it must survive the high steam temperature which may occur during the preceeding core uncovery interval.
The level range extends frem the top of the vessel down to the top of the fuel alignment plate.
The response time is short enough to track the level during small break LOCA event 3.
The resolution is sufficient to show the initial' level drop, the key locations near the hot leg elevation and the lowest levels just above the alignment plate.
This provides the operator with adequate indication to track the progression during Intervals 2 and 4 and to detect the consequences of his mitigating actions or the functionability of autcmatic equipment.
2.3 FUEL CLADDING HEATUP The overall intent of ICC detection is understood to be the detection of the potential for fission product release from the reactor fuel.
The parameter wnich is most directly related to the potential for fission product release is the cladding temperature rather than the uncovery of the core by coolant.
Since clad temperature is not directly measured, a parameter to which cladding temperature may be related is measured. This parameter is the fluid temperature at the core exit. After the core becomes uncovered; the fluid leaving the core is superheated steam and the amount of superheat is related to the fuel length exposed and to the cladding temperature.
The amount of superheat of the steam leaving the core will be measured by the l
core exit thermocouples. The time behavior of the superheat temperature is, with the exception of an acceptably small time delay, similar to the time -
l 2-2
~
- _ _. - - - -. _., _ _ -., _ - - _-. ~. - - _ - _ - _..,
behavior of the cladding temperature.
Thus, from the observaticn of the steam superheat, the behavior of the cladding temperature can be inferred. Observation of the cladding temperature trends during an accident is considered to be of more value to the operator than information en the absolute value of the cladding temperature.
The core exit steam temperature is measured with the thereccouples included in the In-Core Instrument (ICI) string.
They are located inside the ICI support tube, at an elevation a few inches above the fuel alignment plate.
Generic calculations of a similar installation for representative uncovery events show
-hat the thermocouples respond sufficiently fast to the increasing steam tem-perature.
Plant specific calculations on the Palisades configuration may need to be made to verify this response.
The required temperature range of the thermocouples extends from the lowest satura-tion temperature:at which uncovery may occur up 'to the maximum core average exit _
temperature which occurs when the peak clad temperature reaches 2200 F.
The required thermocouple range is therefore 200 F to about 1800 F, which is the l
approximate upper service temperature limit.
Thermocouples are expected to function with reduced accuracy at even higher temperatures, 7 the range for 0
processing the thermocouple output extends to about 2300 F.
l l
1 l
l 2-3
3.0 SYSTEM CONCEPTUAL DESIGN DESCRIPTION The following sensors have been selected as the basic instruments to meet the functional requirements described in Section 2. '
1.
the Subcooled Margin Monitor (Sit) (Ref.1),
2.
the Heated Junction Thermocouple (HJTC) System (Ref. 3), and 3.
the Core Exit Thermocouple (CET) System.
The conceptual design of each ICC instrument is described in this section which addresses:
1.
sensors design 2.
signal processing desige 3.
display design.
Figure 3-1 is a functional block diagram for the ICC instrument systems. Each instrument system consists of two safety grade channels from sensors through signal processing equipment. The outputs of processing equipment systems feeding the primary display are isolated to separate safety grade and non-safety grade systems. Channelized safety grade backup displays are included for each instrument system. The following sections present details of the conceptual design.
3.1.
SENSORS DESIGN 3.1.1 Subcooled Margin Monitoring System The subcooled margin monitor requires reactor coolant system temperature and pressure inputs to determine saturation margin. Each of the two SMM channels are expected to use the following sensors:
1.
two cold leg resistance temperature detectors (RTDs) l 2.
one hot let RTD 3.
one pressurizer instrument l
3-1 l
i 4.
one HJTC System thermocouple (maximun HJTC System unheated jur:ction temperature from one channel) 5.
one core exit thermocouple (maximum CET temperature of one channel)
The RTDs are the wide range element of a dual RTD design. The RTDs are located within wells which protrude through the pipe wall into the coolant flow.
The RTD output is connected to a transmitter located outside containment. The 0
RTD temperature range is from 100 F to 7000F.
The pressurizer pressure sensors are of a force balance design obtaining the pres;ure input from taps on the pressurizer in the steam volume. The sensor and transmitter functions are perfomed in one piece of squipment located inside containment. The pressure range is from 0 psia to 2500 psia. These sensors also provide the process inputs for the Reactor Protection System low pressurizer pressure trip.
3.1.2 Heated Junction Therinocouole (HJTC) System The HJTC System measures reactor coolant liquid inventory with discrete HJTC
~
sensors located at differcat levels within a separator tube ranging from the top of the core to the reactor vessel head. The basic principle of system operation is the detection of a temperature difference between adjacent heated and unheated thermocouples.
l As pictured in Figure 3-2, the HJTC sensor consists of a Chromel-Alumel thermoccuple ne.ar a heater (or heated junction) and another Chromel-Alumel thermocouple positioned away from the heater' (or unheated junction).
In a fluid with relatively g000 imat transfer properties, the temperature difference between the adjacent thermocouples is very small.
In a fluid with relatively poor heat transfer properti.es, the temperature difference between the themocouples is large.
Two design features ensure proper operation under all themal-hydraulic conditions.
First, each HJTC is shielded to avoid overcooling due to direct water contact during two phase fluid conditions. The HJTC with the splash shield is referred 3-2
to as the HJTC sensor (See Figure 3-2).
Second, a string of HJTC sensors is enclosed in a tube that separates the liquid and gas phases that surround it.
The separator tube creates a collapsed liquid level that the HJTC sensors measure. This collapsed liquid level is directly i
related to the average liquid fraction of the fluid in the reactor head volume above the fuel alignment plate. This mode of direct in-vessel sensing reduces spurious effects due to pressure, fluid properties, and non-homogeneities of the fluid medium. The string of HJTC sensors' and the separator tube is referred to as the HJTC instrument.
The HJTC System is composed of two channels of HJTC instru-ments. Each HJTC instrument is manufactured into a probe assembly. The probe assembly includes eight (8)-NJTC sensors, a seal plug, and electrical connectors (Figure 3-3). The eight (8) HJTC sensors are electrically independent and located at eight levels from the reactor vessel head to the fuel alignment plate.
The probe assembly is housed in a stainless steel structure that protects the sensors from flow loads and serves as the guide path for the sensors. Installation arrangements have been developed for each C-E reactor vessel including Palisades.
Installation details will be provided in future documentation if Consumers Power Company decides to install the HJTC System.
3.1.3 Core Exit Thermocouples (CET) System
~
The Palisades Plant reactor contains 45 thermocouples that are top mounted and placed above the fuel assemblies above the fuel alignment plate. Figure 3-4 shows the CET locations. The thermocouples are Type K (Chromel-Alumel) and are connected in the same Incore Instrumentation (ICI) cabling as the fixed incore neutron detectors. The thermocouples monitor the temperature 3-3
of the reactor coolant as it exits the fuel assemblies.
The junction of each themocouple is located above the fuel assembly inside a structure which supports and shields the instrument string from flow forces in the outlet plenum region.
The basic design of the CETs will not change for the ICC Detection System. However, design modifications must be made to meet the qualification requirements (See Section 5.0).
The CETs have a maximum usable temperature range from 0
1000F to approximately 1800 F (Reference 6).
3.2 SIGNAL PROCESSING EQUIPMENT DESIGN The processing equipment of the ICC instruments is presently being developed. The processing equipment portion will be composed of a combination of new and existing equipment. The design objective for the equipment is to address ~the NUREG-0737 criteria, including the criteria of Attachment 1 to II.F.2 and Appendix A.
The following description present functional and general hardware design criteria in terms of the three instrument systems described in Section 3.1.
Tlie processing hardware will be confioured to orovide information to the displays described in Section 3.3.
The processing equipment includes operator interfaces for equipment testing, setup, and maintenance. The descriptions are for each l
of the two separate channels.
l All three ICC instrument systems will have similar sensor input processing. The outputs of the sensors will be transmitted to the processor, all of which is outside of containment, using l
qualified cable systems.
3-4
o The processing for the ICC instrumentation will he<e' surveillance testing and diagnostic capabilities. Automatic on-line surveil-I lance tests will continuously check for specified hardware and software malfunctions.
The on-line automatic surveillance tests as a minimum will indicate inputs that are out of range and computer hardware malfunctions. The malfunctions will be indicated through the operator interface. A manual on-line diagnostic i
capability will be incorporated to aid the operator in locating the source of these malfunctions.
'. 3. 2.1 Subcooled Margin Monitoring System The SMM processing equipment will perform the following I
functions:
1.
Calculate the subcooled margin.
The saturation temperature is calculated from the minimum pressure input and the saturation pressure is calculated from the maximum temperature input (fc3 Section3.1). The temperature subcooled margh? 14 the difference between saturation temperatgrt tab the maximum temperature input. The pressure subcooled margin is the difference between t?5:rvdon pressure and the minimum pressure input.
ing 9.MM will indicate superheated conditions.
2.
Process all out;p+.t fdf r.itplay.
3.
Provide an alarm output when subi;ooled margin reaches a preselected salpoint.
The EMN ;J?! A;r.c' the temperature and pressure inputs over 0
0 the input range of the sensors -- CET from 100 F to 1800 F, ths glTr from 100*F to 1800*F, the RTDs from 0*F to 710*F.
3-5
and the precrure from 0 psia to 3200 psia. The saturation temperature and pressure are calculated from a saturation curve derived from the 1967 ASME steam tables and an inter-polation routine.
3.2.2 HJTC System The processing equipment for the HJTC performs the following functions :
1.
Determine if liquid inventory exists at'the HJTC positions.
I The heated and unheated themocouples in the HJTC are connected in such a way that absolute and differential temperature signals are available. This is shown in
~
Figure 3-5.
When water surrounds the thennocouples, their temperature and voltage output are approximately equal. \\(A-C) n Figure 3-5 is, therefore, approximately zero.
In the absence of liquid, the thermocouple temperatures and output voltages become unequal, causing V(A-C) to rise. When V(A-C) of the individual HJTC rises above a predetermined setpoint, liquid inventory does not exist at this HJTC position.
2.
Determine the maximum upper plenu.n/ head fluid temperature from the unheated thermocouples for use as an input to the SMM.
(The temperature processing range is from 100*F to 1800*F.)
l 3.
Process all inputs and calculated outputs for display.
i 4.
Provide an alarm output to the plant annunciator system when any of the HJTC detects the absence of liquid level.
l f
(
3-6
5.
provide control of heater power for proper.HJTC output signal level. Figure 3-6 shows a single channel conceptual design which includes the heater power controller.
3.2.3 Core Exit Thermocouple System The processing equipment for the CET will perform the following functions:
1.
Process all core exit thermocouple inputs for display.
Half of the available CET inputs will be processed in each channel.
2.
provide an alarm output to the plant annunciator system when the temperature from any of the CET's exceeds a preselected setpoint.
3.
Detennine the maximum CET temperature to be supplied to the Stei.
The processed temperature range will be from 100*F to 2300*F.
These functions are intended to meet the design requirements of NUREG-0737, II.F.2 Attacnment 1.
The display section will describe the display design for the CET system.
i 3.3 DISPLAY DESIGN I
The ICC instrument outputs will be displayed through a human engineered cathode ray tube (CRT) based primary disolav and separate backup displays. The ' Critical Function Monitor (CFM) System (Ref. 7) is being considered as the primary display for the ICC l
instrument outputs. As shown in Figure 3-1, each channel of the l
ICC Instrument system will also have safety grade backup displays.
l Both primary and backup displays are intended to be designed consistent with the criteria in NUREG-0737 Action Item II.F.2, II.F.2 Attachment 1, and Appendix A.
The following description presents the conceptual I
design for display.
3-7
(.
The CFM System is a dedicated, computer based display system that monitors s, f tical olant functions:
1.
Core reactivity control 2.
Core heat removal control 3.
RCS inventory control 4.
RCS pressure control 5.
RCS heat removal control 6.
Containment pressure / temperature control 7.
Containment isolation If any of the critical functions are violated, (by exceeding logic setpoints) a Critical Function Alarm (CFA) is initiated.
The ICC instruments outputs will be incorporated in this critical function alarm logic.
The CFM displays data on four cathode ray tubes. The data has three levels of information:
i Level 1 Critical functions status (very general)
Level 2 System overview (general, on system)
Level 3 System detail (specific information)
This hierarchy allows the operator to progress from an overall l
system view to a detailed diagnostic view. The ICC instrument i
outputs will be incorporated in all three levels of disolay. The l
l detailed ICC information is anticipated to be displayed on the l
Level 3 display. Trending displays are also available with the l
CFM.
l l
3-8 i
~~
Each channel of backup display will present the most reliable basic information for each of the ICC instrument systems.
These displays will be human engineered to give the operator clear unambiguous indications. The backup displays are designed:
1.
to give primary instrument indications in the remote chance that the primary display becomes inoperable.
2.
to provide confirmatory indications to the primary display.
3.
to aid in surveillance tests and diagnostics.
The following sections present details on the display for each of the instrument systems as presently conceived.
3.3.1 Subcooled Margin Monitor Display The following information is anticipated to be presented on the primary display:
1.
Pressure margin to saturation.
2.
Temperature margin to saturation.
3.
Maximum temperature and source (i.e., HJTC, RTD, or CET) 4.
Minimum pressure The following information is anticipated to be presented on the backup displays:
1.
Pressure margin to saturation 2.
Temperature margin to saturation 3.
Temperature inputs 4.
Pressure inputs 3-9
)
3.3.2 Heated Junction Thermocouple System Display The following information is anticipated to be displayed on the primary display:
1.
Two channels of 8 discrete HJTC positions indicating liquid inventory above the fuel alignment plate.
2.
Maximum unheated junction temperature of each of the two channels which is provided to the SMM.
The following information is anticipated to be displayed an the backup displays:
1.
Liquid inventory level above the fuel alignment plate derived from the 8 discrete HJTC positions 2.
Unheated junction temperature at the 8 positions 3.
Heated junction temperature 6t the 8 positions 3:3.3 Core Exit Thermocouple System Display The following information is anticipated to be displayed on the primary display:
1.
A spatially oriented core map indicating the temperature at each of the CET locations.
2.
A selective reading of CET temperature At least the maximum CET temperature of each of the two channels which is provided to the SMM will be presented.
The backup displays are anticipated to display at least four CET from each quadrant with an identification number for each CET temperature.
3-10
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3-14
COPPER INCONEL i
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3-15
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o.
4.0 SYSTEM VERIFICATION TESTING This section describes tests and operational expurience with ICC system instruments.
l 4.1 RTD AND PRESSURIZER PRESSURE SENSORS The hot and cold leg RTD temperature sensors and the pressurizer pressure sensors are standard NSSS instruments which have well known responses. No special verification tests have been per-formed nor are planned for the future. These sensors provide basic, reliable temperature and pressure inputs which are con-sidered adequate for use in the SMM and other additioTial display functions.
4.2 HJTC SYSTEM SENSORS AND PROCESSING The HJTC System is a new system developed to indicate liquid inventory above the core. Since it is a new system, extensive testing has been perfonned and further tests are planned to assure that the HJTC System will operate to unambiguously indicate liquid l
inventory above the core.
The testing is divided into three phases:
l Phase 1 - Proof of Principle Testing l
Phase 2 - Design Developmer.t Testing Phase 3 - Prototype Testing The first phase consisted of a series of five tests, which have been completed. The testing demonstrated the capability of the 4
4-1
.o HJTC instrument design to measure liquid level in simulated reactor vessel thermal-hydraulic conditions (including accident conditions).
Test 1 Autoclave test to show HJTC (themocouples only) response to water or steam.
In April 1980, a conceptual test was performed with two themocouples in one sheath with one thermocouple as a heater and the other thermocouple as the inventory senser. This configuration was placed in an autoclave (pressure vessel with the capabilities to adjust temperature and pressure). The thermocouples were exposed to water and then steam environments. The results demonstrated a significant output difference between steam and water conditions for a given heater power level.
Test 2 Two phase flow test to show bare HJTC sensitivity to voids.
In June 1980, a HJTC (of the present differential themocouple design) was placed into the Advanced Instrumentation for Reflood Studies (AIRS) test facility, a low pressure two phase flow test facility at Oak Ridge National Laboratory (ORNL). The HJTC was exposed to void fractions at various heater power levels. The l
results demonstrated that the bare HJTC output was virtually the l
same in two phase liquid as in subcooled liquid. The HJTC did l
generate a significant output in 100% quality steam.
l Test 3 Atmospheric air-water test to show the effect of a splash shield A splash shield was designed to increase the sensitivity to voids. The splash shield prevents direct contact with the liquid in the two phase fluid. The HJTC output changed at intermediate l
4-2
void' fraction two phase fluid. The results demonstrated that the HJTC sensor (heated junction thermocouple with the splash shield) sensed intermediate void fraction fluid _ conditions.
Test 4 High pressure boil-off test to show HJTC sensor response to reactor thermal-hydraulic conditiins.
In September 1980, a C-E HJTC sensor (HJTC with splash shield) was installed and tested at the ORNL Therm'al-Hydraulics Test Facility (THTF). The device is still installed and available for further tests at ORNL. The HJTC sensor was subjected to various two phase fluid conditions at reactor temperatures and pressures.
The results verified that the HJTC sensor is a device that can sense liquid inventory under norm'al'and accident reactor vessel high pressure and temperature two phase conditions.
Test 5_ Atmospheric air-water test to show the effect of a l
separator tube l
A separator tube was added to the HJTC design to form a collapsed liquid level so that tnc HJTC sensor directly measures liquid inventory under all simulated two phase conditions.
In October, 1980, atmospheric air-water tests were performed with HJTC sensor and the separator tube. The results demonstrated that the separator tube did form a collapsed liquid level;and the HJTC output did accurately indicate liquid inventory. This test verified that the HJTC instrument, which includes the HJTC, the splash shield, and the separator tube, is a viable measuring device for liquid inventory.
The Phase 2 test program will consist of high pressure and tempera-ture tests on the HJTC instrument. These tests will provide input for the C-E HJTC instrument design and manufacturing effort. The Phase 2 test program is expected to be completed in early 1981.
4-3
The Phase 3 test program will consist of high temperature and pressure testing of the manufactured prototype system HJTC probe assembly and processing electronics. Verification of the HJTC system prototype will be the goal of this test program. The 4
Phase 3 test program is expected to be completed by the end of 1981.
4.3 CORE EXIT THERMOCOUPLES No verification testing of the CETs is planned. A study at ORF.
was performed to test the response of CETs under simulated acci-dent conditions (Reference 6). This te'st showed that the instru-ments remained functional up to 2300 F.
This test along with previous reactor operating experience verify the response df CETs.
4.4 PROCESSING AND DISPLAYS The final processing and display design for the ICC detection system has not been completed. As the design effort proceeds, design evaluations will be performed prior to installation.
Correct implementation of the sof tware and hardware will be included and documented as part of the design effort.
h _h
5.0 SYSTEM QUA!.IFICATION The qualification program for the ICC Detection System instrumentation has not been completely defined. However, plans are being developed based on the following three categories of ICC instrumentation:
1.
Jensor instrumentation within the pressure vessel.
2.
Instrumentation components and systems which extend from the primary pressure boundary up to and including the primary display isolator and including the backup displays.
3.
Instrumentation systems which comprise the primary display equipment.
A preliminary outline of a qualification program for each classification is given below.
The in-vessel sensors will meet the NUREG-0737, Appendix A guide to install the best equipment available consistent with qualification and schedular requirements.
Design of the equipment will be consistent with the guidelines of Appendix A as well as the clarification and Attachment 1 to Item II.F.2 in NUREG-0737. Specifically, instrumentation will be designed such that they meet appropriate stress criteria when subjected to normal and design basis accident loadings.
Verification testing will be conducted to confinn operation at DBA (as defined by C-E) pressure and temperature conditions. Seismic testing to safe shutdown conditions will verify function after being subjected to the seismic loadings.
The cut-of-vessel instrumentation system, up to and including the primary display isolator, and the backup displays will be environmentally qualified in accordance with IEEE-323-1974 as interpreted by Combustion Engineering Document, CENPD-255, " Qualification of Combustion Engineering Class 1E Instruments." This document describes the method which will be used to qualify out-of-vessel Class lE equipment.
5-1
e Plant-specific containment temperature and pressure design profiles will be utilized where appropriate in these tests. This equipment will also be seismically qualified according to IEEE-STD-344-1975.
CENPD-182, " Seismic Qualification of C-E Instrumentation Equipment,"
describes the methods used to meet the criteria of this document.
The primary display will not be designed as a Class lE system, but will be designed for high reliability; thus it will not be qualified environmentally or seismically to Class lE requirements nor will it meet the single failure criteria of Appendix A, Item 2.
Post-accident maintenance accessibility will be included in the design. The quality assurance provisions of Appendix A, Item 5 do not apply to the primary display according to NUREG-0737. However, the computer driven primary display system will be separated from the Class lE sensors, processing and backup display equipment by means of an isolation device which will be qualified to Class lE criteria.
l l
l l
l 5-2
6.0 OPERATING INSTRUCTIONS Guidelines for reactor operators to use to detect ICC and take corrective action has been developed by the C-E Owners Group and submitted to NRC for review (Ref. 8). These guidelines have been used to review and revise the plant emergency procedures for (Plan Neme).
In addition, the C-E Owners Group has developed reactor operator training materials concerning ICC.
The C-E Owners Group is defining a program for development of further emergency procedure guidelines and operator training materials associated with the ICC Detection System described in Section 3.
This program is expected to provide these guidelines and training materials during 1981. A more specific schedule is subject to finalization of the ICC Detection System design, specifically the instrument displays.
6
.., o REFERENCES 1.
NUREG-0737, " Clarification of TMI Action Plan Requirements,"
U. S. Nuclear Regulatory Commission, November,1980.
2.
CEN-ll7, " Inadequate Core Cooling - A Response to NRC I E Bulletin 79-06C, Item 5 for Combustion Engineering Nuclear Steam Supply Systems," Combustion Engineering, October,1979.
3.
CEN-125, " Input for Response to NRC Lessons Learned Requirements for Combustion Engineering Nuclear Steam Supply Systems," Combustion Engineering, December,1979.
4.
C-E Proposal No.1579 SP, "C-E PWR Subcooled Margin Monitor," September, 1979.
5.
C-E Proposal No. 2580 SP, " Heated Junction Thermocouple System,"
September,1980.
i i
6.
Anderson, R. L., Banda, L. A., Cain, D. G., "Incore Thermocouple Performance Under Simulated Accident Conditions", presented at IEEE Symposium, November,1980.
7.
C-E Paper TIS-6649, " Operational Aids to Improve the Man-Machine Interaction in a Nuclear Power Plant," Presented at American Nuclear Society Annual Meeting, Las Vegas, Nevada, June 8-12, 1980.
8.
Letter C-E Owners Group to NRC, "C-E Generic Emergency Procedure Guidelines," December 10, 1980.
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