ML20136F191

Proposed Tech Specs,Incorporating Requirements for Steam Line Rupture Detection/Isolation Sys.Significant Hazards Consideration & Analysis Value Discussion Encl

ML20136F191
Person / Time
Site:	Fort Saint Vrain
Issue date:	12/31/1985
From:	PUBLIC SERVICE CO. OF COLORADO
To:
Shared Package
ML20136F171	List: ML20136F166 ML20136F191 ML20136F210
References
TAC-60421, NUDOCS 8601070296
Download: ML20136F191 (23)

Text

j Fort St. Vrain el Technical Specifications

• Amendment

• Page 4.4-4 Specification LCO 4.4-1 Table 4. 4-2 INSTRUMENT OPERATING REQUIREMENTS FOR PLANT PROTECTIVE SYSTEM, LOOP SHUTOCwN MINIMUM DEGREE PERMIS-MINIMUM OF 'SIBLE TRIP CPERAELE REcuN- 8YPASS N1 FUNCTICNAL UNIT SETTING CHANNELS CANCY CCNDITICNS la. Deleted Ib. Deleted Ic. Deleteo Id. Coleted le. Deleted If. Deleted 2a. Deleted 2b. Deleted 2c. Celeted 2d. Deleted

34. Loop 1 Shutdcwn -----------

2 1 None Logic 3b. Loco 2 Shutdown -----------

2 1 None Logic

44. Circulator 1A and 19 Circulators 2 1 None Shutdown - Loop 1A and 19 Shutdown Logic Shutdown 4b. Cfeculator IC and 10 Circulators 2 1 None Shutdown - Loop IC and 10 Shutdown Logic Shutdown 8601070296 851231 PDR P ADOCK 05000267 PDR

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Fort St. Vrain 01

' Technical Specifications

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Page 4.4-6a Specification LCO 4.4.1 Table 4,4-3 (Continued)

PLANT PROTECTIVE SYSTEM. TRIP SETPOINTS - CIRCULATOR TRIP TRIP ALLOWABLE NO. FUNCTIONAL UNIT SETPOINT VALUE 10a. Steam Leak Detection s 202 degrees F s 205 degrees F Turbine Building 10b. Steam Leak Detection s 202 degrees F s 205 degrees F Reactor Building l'

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• Page 4.4 6b Specification LCO 4.4.1 Table 4.4-3 (Continued)

PLANT AROTECTIVE SYSTEM, OPERABILITY REQUIREMENTS - CIRCULATOR TRJ TOTAL CHANNELS MINIMUM FUNCTIONAL NO. OF TO NO. CHANNELS APPLICA8LE UNIT CHANNELS TRIP OPERA 8LE MODES ACTION 10a. Steam Leak 4 2 3

• Detection P' 1.2,3 Turbine Building 10 b. Steam Leak 4 2 Detection 3 P* 1.L3 Reactor Building

• Applicable only during POWER OPERATION above 8% RATED THERMAL POWER.

a Fort St. Vrain #1 Technical Specifications Amendment #

Page 4.4-6c Table 4.4-3 (Continued)

ACTION STATEMENTS (for 10a and 10b Only)

ACTION 1 - With the number of channels OPERABLE one less than the Total Number of Channels, POWER OPERATION above 8%

RATED THERMAL POWER may continue provided tne inoperable channel is placed in the bypassed or tripped condition within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. If the inoperable channel is bypassed, the desirability of maintaining this channel in the bypassed condition shall be reviewed in accordance with Specification 7.1.2. The channel shall be returned to OPERABLE status no later than during the next SHUTDOWN.

ACTION 2 -

With the number of channels OPERABLE one less than the Minimum Channels CPERABLE, POWER OPERATION above 8%

RATED THERMAL POWER may continue provided that one of the inoperable channels has been bypassed and the other inoperable channel is placed in the tripped condition within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.

POWER OPERATION above 8% RATED THERMAL POWER may continue until the performance of the next required CHANNEL FUNCTICNAL TEST. POWER OPERATION above 8%

RATED THERMAL POWER may a'so continue if One channel is restored to OPERABLE status and the orovisions of ACTION 1 are satisfied.

ACTION 3 - With inoperable channels other than as provided in ACTION 1 and 2 above, be below 8% RATED THERMAL POWER within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The circulator trip requirements provided in the introduction of Specification 4.4.1 do not apply.

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Fort St. Vrain #1 Technical Specifications Amendment #

Page 4.4-8 Specification LCO 4.4.1 NOTES FOR TABLES 4.4-1 THROUGH 4.4-4 (a) See Specification LSSS3.3 for trip setting.

(b) Two thermocouples from each loop, total of four, constitute one channel. For each channel, two thermocouples must be operable in at least one operr ing loop for that channel to be considered operable.

(c) With one primary coolant high level moisture monitor tripped, trips of either loop primary coolant moisture monitors will cause full scram. Hence, number of operable channels (1) minus minimum number required to cause scram (0) equals one, the minimum degree of redundancy.

(d)Both 480 volt buses IA and IC loss of voltage for no longer than 35 seconds.

(e) One channel consists of one undervoltage relay from each of the two 480 voit buses (two undervoltage relays per channel). These relays scram.

fail open which is the direction required to initiate a (f) The inoperable channel must be in the tripcad condition, unless the trip of the channel will cause the protective action to occur. Failure to trip the inoperable channel requires taking the appropriate corrective action as listed en Pages 4.4-1 and 4.4-2 within the specified time limit.

(g) RWP bypass permitted if the bypass also causes associated single channel scram. .

(h) Permissible Bypass Conditions:

I. Any circulator buffer seal malfunction.

II. Loop hot reheat header high activity.

III. As stated in LCO 4.9.2.

(j) Deleted.

(k) One operable helium circulator inlet thermocouple in an operable loop is required for the channel to be considered operable.

(m) Low Power RWP bistable resets at 4% after reactor power initially exceeds 5%.

(n) Power range RWP bistables automatically reset at 10% after reactor power is decreased from greater than 30%. The RWP may be manually reset between 10% and 30% power.

(p) Item 74, must be accompanied by item 7c for loop 1 shutdown.

Item 7b. must be accompanied by item 7c for loop 2 shutdown.

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• Tecnnical Scecifications Amendment

• Page 4.4-9 NOTES FOR TABLES 4.41 through 4.4-4 (Continued) r) Separate instrumentation is provided on eacn ctreulator for tnis functional untt. Only the affected nelium circulator shall be shut down within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> if the indicated requirements are not met, s) Deleted.

t) A primary coolant dew point moisture monttor shall not be considered operable unless the following conditions are met:

1) Reactor power Rance Mfnfmum Samola 81ew Startuo to 2% 1 sec/sec.

2% - 5% 5 s::/sec.

> 54 - 205 15 i::/sec.

> 20% - 35% 30 s::/sec.

> 35% -100% 50 5::/sec.

2) Minimum flow of item 1) is alarmed in the control room and the alarm is set in accordance with the power ranges speciff ed.

3) The asetent temperatures fact:atec ey both temporary the rmocouple s sounted on the flow sensors in penetrations B1 and 33 are less than 185'F.

4) Fixed alarms of I sec/sec and 75 sec.'see are operable.

r Fort St. Vrain #1 Technical Specifications Amendment #

Page 4.4-12 Plant Electrical System Power loss requires a scram to prevent any power-to-flow mismatches from occurring. A 30-second delay is provided following a power loss before the scram is initiated to allow the emergency diesel generator to start. If it does start, the scram is avoided.

Two-Loop Trouble. Operation on one loop at a maximum of about 50*. power may continue following the shutdown of the other loop (unless oreceded by scram as in the case of high moisture.)

Onset of trouble in the remaining loop (two-loop trouble) results in a scram. Trouble is defined as a signal which normally initiates a loop shutdown. Similarly, simultaneous shutdown signals to both loops result in shutdown of one of the two loops only and a reactor scram. However, the Steam Line Rupture Detection / Isolation System (SLRDIS), effectively overrides simultaneous two-loop shutdown :ecause it sends a simultaneous actuation logic signal to all four circulator trip logic channels. The consequences of a s'multaneous two-loop shutdown and subsequent loss of forced circulation have been analyzed and found to be acceptable. The consequences are bounded by an interruption of forced circulation cooling accident described in FSAR Section 14.4.2.2 Safe Shutdown Cooling.

Hioh Temperature in the pipe cavity would indicate the presence of an undetected steam leak. A steam leak or pipe rupture under the PCRV within the support ring would also be detectable in the pipe cavity, therefore only one set of sensors and logic is required to monitor both areas. The setpoint has been set above the temperature that would be expected to occur in the pipe cavity if the steam leak were detected.

w-Fort St. Vrain #1

,. Technical Specifications Amendment #

Page 4.4-12a b) Loop Shutdown Inputs l

Shutdown of Both Circulators is a loop snutdown input which is necessary to insure proper action of the reactor protective (scram) system (tarough the two-loop trouble scram) in the event of the loss of all circulators and low feedwater flow.

The remaining loop shutdown inputs are equipment protection items which are included because their malfunction could prevent a scram due to loss of the two-loop trouble scram input.

c) Circulator Shutdown inputs Circulator Shutdown Inouts (except circulator speed high on I

water turoines and steam leak detection) are equipment protection items wnich are tied to two loos trouble through the loop shutdown system. These items are included in Table 4.4-3 because a malfunction could prevent a scram due to loss of the two loop trouble scram input. Circulator speed high on water turbines is included to assure continued core cooling capability on loss of steam drive.

Steam Leak Detection in the Reactor Building is required for equipment qualification of Safe Shutdown Cooling Systems and personnel access in the event of a steam leak. The ALLOWABLE VALUE is set at s205 degrees F in order to :revent exceeding 210 degrees F, a temperature which if exceeced may prevent entry into the Reactor Building to make required system lineups for long term cooling of the reactor using tre PCRV Liner Cooling System. A setpoint calculation analysis performed per ISA Standard 57.04.and RG1.105 results in the stated ALLOWABLE VALUE and TRIP SETPOINT as specified in the LCO and this basis. The TRIP SETPOINT has been established with sufficient margin between the technical specification limit for the process variable and the nominal TRIP SETPOINT to allow for 1) inaccuracy of the instruments; 2) uncertainties in the calibration; 3) instrument drift that could occur during the interval between calibrations; and 4) inaccuracies due to ambient temperature changes, vibration and other environmental conditions. The TRIP SETPOINT is set at s202 degrees F until such time as the drift characteristics of the detection system are better understood from actual plant operating experience and the assumptions used in the setpoint analysis are verified.

• Fort St. Vrain #1 Technical Specifications i Amendment # '

Page 4.4-12b 4

The OPERABILITY requirements and their respective ACTIONS represent good operating practices' and judgement for a four channel detection system with a 2 of 4 coincidence trip logic.

The fourth channel mcy be placed in bypass for test and/or maintenance purposes while preserving a 2 of 3 coincidence logic OPERABLE. The Steam Line Rupture Detection / Isolation System as designed and installed has spare channels available for input.

Any of the available channels may be selected for input signal processing provided the surveillances are current on the channels used. The SLRDIS is required to be OPERABLE only during POWER OPERATION above 8' 'ATED THERMAL POWER. Analyses demonstrate that a Loss of Fort Circulation (LOFC) from 8%

RATED THERMAL POWER without liner cooling system loops in operation results in a maximum fuel temperature of 1030 degrees F after 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />. Thus, no fuel damage is ex:ected to occur.

Fort St. Vrain #1

Technical Specifications knendment #

Page 4.4-13 Steam Leak Detection in the Turbine Buf1 ding is required for equipment qualification of Safe Shutdown Cooling Systems and i

personnel access to assure long term cooling. Thus, the limits and basis are the same as discussed in the basis for steam leak detection in the reactor butiding.

d) Rod Withdraw Prohibit Inputs Startup Channel Countrate-Low is provided to prevent control rod -

withdrawal and reactor startup without adequate neutron flux indication. The trip logic is selected to be above the background noise leve!

Linear Channel (5% Pow =-) directs the operator's attention to either a downscale failure of a power range enannel or improper positioning of the I.S.S.

Linear Channel (30% Power) is provided to prevent control rod withdrawal if reactor power exceeds the I.S.S. limit for the

" Low Power" position.

1 Fort St. Vrain #1 Technical Specifications Amendment #

Page 5.4-2 Calibration frequency of the instrument channels listed in Tables 5.4.1, 5.4.2, 5.4.3, 5.4.4 are divided into three categories:

passive type indicating devices that can be compared with like units on a continuous basis; semiconductor devices and detectors that may drift or lose sensitivity; and on-off sensors which must be tripped by an external source to determine their setpoint. Orfft tests by GGA on transducers similar to the reactor pressure transducers (FSAR Section 7.3.3.2) indicate insignificant long term drift. Therefore a once per refueling cycle calibration was selected for passive devices (thermo-couples, pressure transducers, etc.). Devices incorporating semiconductors, particularly amplifiers, will be also calibrated on a once per refueling cycle basis, and any drift in response or bistable setpoint will be discovered from the test program. Orift of electronic apparatus is not the only consideration in determining a calibration frequency; for example, the change in power distribution and loss of detector chamber sensitivity require that the nuclear power range system be calibrated every month. On-off sensors are calibrated and tested on a once per refueling cycle basis.

The Surveillance Requirements , for the Steam Line Rupture Detection / Isolation System instrumentation in Table 5.4-3 include provisions for CHANN~L CALIBRATION, CHANNEL FUNCTICNAL TEST and an ACTUATION LOGIC TEST. The frequency of CHANNEL CALIBRATION is consistent with the interval for testing and calibrating similar detectors (heat sensitive cabling used for fire cetection). The manufacturer of the instrumentation recommends a 6 month interval for check / calibration of the electronics portion of the Steam Line Rupture Detection / Isolation System, thus, the CHANNEL FUNCTIONAL TEST is specified for that interval. The ACTUATION LOGIC TEST is specified for a REFUELING interval. The potential for an inadvertent LOFC during testing suggests that logic testing be performed only when the plant is in SHUT 00WN.

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• Tecnnical Specifications Amendment #

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MINIMUM FREQUENCIES FOR CHECMS. CAL 18 RATIONS AND TESTINC OF LOOP SHUT M SYSTEM Channei Descriotion Function Frecuency Methad I

3. Circulator 1A and a. Test M 18 tripped a. Pulse test and verify proper indications.

b. Test R b. Trip both circulators to test loop shutdown.

4. Circulator IC and a. Test M a. Pulse test and verify proper indications.

ID tripped

b. Test R b. Trip both circulators to test loop shutdown.

5. Steam Generator a. Test Penetration pressure M a. Pressure switches actuated by pressure applied.

b. Test M i be Pulse test each channel with another channel tripped and verify proper indications.

c. Ca l i b ra te R

c. Known pressure applied at sensor to adjust trip.

6. Reheat Header a. Check D

Activity a. Comparison of three separate indicators in each loop.

b. Test M

b. Pulse test each channel with another channel tripped and verify proper indications.

c. Calibrato R c. Expose sensor to known radiation source and adjust trips and indicators.

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O Fort St. Vrain #1 4

Technical Specifications

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Table 5.4g3 (Continued)

CIRCULATOP_ TRIP SYSTEM INSTRusPJTATION SURVEILLANCE RQUIREMENTS c

CHANNEL CHANNEL ACTUATION FUNCTIONAL CHANNEL CALIBRA- FUNCTIONAL LOGIC NO. UNIT APPLICABLE CHECK JTION TEST TEST MODES 8a. Steam Leak N/A R(a) SA(b) P*

Detection R(c)

Turbine Building 8b. Steam leak N/A R(a) SA(b) P*

Detection R(c) de'(ctor b ilding

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A (a) A L'nown resistance for a given temperature of the detector cable is verified over the range of temperatures expected for the detector.

(b) The clock in the SLRDIS CPU is checked against a known time standard. The potentiometer on each thermal detecticn board is compared to a 150K ohm, 1% tolerance, fixed resistcr.

(c) The logic shall be tested through the SLRDIS up to the existing PPS .

R - At least once per Refueling cycle.

SA - At least once per 184 days Applicable only during POWER OPERATION above 34 RATED THERMAL q POWER. s

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O ATTACHMENT 3 SIGNIFICANT HAZARDS CONSIDERATION

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a SIGNIFICANT HAZARDS CONSIDERATION I. EVALUATION ' '

Based upon PSC Safety Analysis Report (EE-EQ-0014), Steam Line Rupture Detection / Isolation System (SLRDIS), it is concluded that the SLRDIS is capable of performing its intended function to detect anc isolate major secondary coolant line ruptures of high energy steam pipe lines of the secondary cooling system without operator intervention. The resulting harsh environments from a SLDIS terminated leak are less severe than the harsh environment previously established on the basis of the operator manually -terminating the '

leak, at (4( minutes. These operator terminated leaks previously estaolished the harsh environments used for Fort (St. Vrain equipment qualification.

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The SLRDIS replaces the existing steam pipe rupture detection system.

SLRDIS is designed to detect steam leaks in either the reactor or turbine buildings and isolate those leaks to preserve or maintain an environment in which electrical equipment is qualified. This change f.n' steam leak detection and automatic action provides more inclusive coverage of' potential steam leaks and results in no change in the radiological consequences. For certain steam leaks, the.SLRDIS

' System has a slower response than the existing system, but analysis

' demonstrates that equipment qualification is maintained and access required for manual actions is assured. Thus, the existing steam pipe rupture detection system will no longer be required.

g/ ' , Manual operator intervention for isolating HELBs in the feedwater, condensate extraction steam systems and those line breaks not isolated by SLRDIS is adequate tn assure that the resulting temperature profiles are enveloped by that to which the equipment will be qualified, s 'l

1. ConsecteSce- of other accidents analyzed in the FSAR were exawir:s fc adverse impact as a result of the installation

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of .n. ,JRIS. Design Basis Accident ik) . 2, " Rapid Depressurization/ Blowdown Accident", was determined to have one assumption invalidated in that the SLRDIS could prevent '

initiation of forced circulation cooling at 5 minutes into 4

the accident. Reanalysis of the accident determined that forced circulation cooling could be delayed for at least 30 .

minutes without exceeding the conservative FSAR temperature for onset of fuel particle failure of 2900 degrees, a temperature well below that at which rapid fue{

deterioration is expected to occur. This is more than ample time for the operator to restore forced circulation cooling. 3 4

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2. The potential for the SLRDIS .to create new or different types of accidents not previously analyzed was examined.

The conclusion was that the SLRIS could result in interruption of forced circulation cooling through inadvertent trips. It was further concluded that sufficient information is currently available in conjunction with new information available from the SLRDIS for the operator to properly diagnose and recover from the event by re-establishing forced circulation cooling within 30 minutes, an accident previously analyzed in the FSAR.

3. A review was conducted to determined if any margins of safety defined in the basis for a Technical Specification or

.in the FSAR were significantly decreased. It was concluded that the SLRDIS isolating the secondary coolant system only causes a temporary interruption of forced circulation cooling in both loops. Recovery means exist to re establish circulation cooling in- ample time to mitigate the consequences of a pipe rupture. Thus, it is concluded that the margin of safety is not significantly reduced.

II. CONCLUSION Based on the above evaluation, it is concluded that operation of Fort St. Vrain in accordance with the proposed changes will not (1) involve a significant increasa in the probability or consequences of an accident previously evaluated, (2) create the possibility of a new <

or different kind of accident from any accident previously evaluated, 1

or (3) involve a significant reduction in any margin of safety.

Therefore, this change 'will not create an undue risk to the health and safety of the public nor does it involve any significant hazards consideration.

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ATTACHMENT 4 SLRDIS ANALYSIS VALUE DISCUSSION l

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1 ANALYSIS VALUE LFUNCTION: Circulator Trip r -FUNCTION UNIT: Steam Line Rupture Detection / Isolation System (SLRDIS)

ANALYSIS VALUE: < 210 Degrees Fahrenheit for Trip

-3160DegreesFahrenheitforAlarm PRESENT' TECH SPEC TRIP SETTING: Currently not contained in the

-Technical: Specifications. This is a new system for compliance with environmental qualification of electrical equipment as required by 10CFR50.49.

LICENSING ' BASIS: The original commitment for environmental

' qualification of electrical equipment at Fort St. Vrain was made in response to AEC question 6.1 in 1971. Initial approval of environmental qualification activities can be inferred from the issuance of an operating license'in 1973 and subsequent additional

- environmental qualification work performed and approved by the NRC in

. License Amendment ~ No. 18 dated 10-28-77. However, new requirements were issued by NRC ~for environmental qualification of electrical equipment starting in 1979. Specifically, these are IE Bulletin 79.01B, D0R Guidelines, NUREG-0588 and finally 10CFR50.49. These new

, requirements and their -interpretation have imposed requirements on the environmental qualification program not contained in the prior

. 1979 Fort St. Vrain environme '.al qualification program. These new requirements are (1) no operator intervention by the' performance of manual actions for at least the first 10 minutes, (2) consideration

' of. normal thermal aging prior to the accidental harsh environment, and (3) consideration of operability time over the total duration of

. the accident. SLRDIS-is being installed to assure compliance with

these new regulatory requirements plus assure personnel access to the building following a pipe rupture for the performance of local manual operations consistent with prior approved licensing commitments. The

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, alarm function assures the operators are informed of harsn

[ environments originating from pipe breaks of insufficient size to reach the SLRDIS trip setting.

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SAFETY LIMIT: None. The specific requirement is that the building bulk temperature-time histories- satisfy those temperature-time histories utilized' in the qualification test of equipment including

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consideration for aging and operability time. 'In addition, personnel access to either the Turbine or. Reactor Building must be possible one hour from.the onset of the pipe rupture. The latter requirement can be ' satisfied by the use' of thermal suits for required personnel protection.

' . LIMITING INITIATING EVENT: Full offset ruptures of either loop hot reheat steam piping in the Reactor Building or main hot reheat steam piping in the Turbine Building produce the highest air temperatures in these buildings. -These peak bulk building temperatures are 371 degrees' Fahrenheit for the Reactor Building and 360 degrees Fahrenheit for the Turbine Building (Ref. GA Document No. 908430 NC "FSV Buildin Response Analysis with Variable Heat Transfer Coefficients")g The above temperatures are based upon detection and isolation initiation by SLRDIS at 210 degrees Fahrenheit building temperature.

~ TRANSIENT ~0VERSHOOT: Transient overshoot will occur due to SLRDIS sensor time response, time for actuated isolation valves to close, subsequent blowdown of . steam inventories available to the leak following the closure of. the isolation valves, and- finally the i~ required assumption of a single active failure. The resultant maximum predicted transient building temperature overshoot based upon a 'SLRDIS trip at 210 ~ degrees Fahrenheit would' be '155 degrees Fahrenheit. See maximum building temperatures under " Limiting Initiating Event".

' TRANSIENT ' TIME RESPONSE: The temperature sensor portion of SLRDIS are thermistor cables-and.will sense ' actual temperature withir. 2 '

seconds of exposure -to that -temperature. A two-second sensor response was assumed in the analyses. Valve closure times for steam leak isolation are in addition to sensor response time and will vary dependent upon' postulated break location and the particular valves

that perform the isolation.

I PROCESS MEASUREMENT ACCURACY: Not applicable.

I DISCUSSION: The purpose of the Steam Line Rupture Detection / Isolation System is to detect and automatically isolate i

selected high energy line breaks in the secondary coolant system in

both the Reactor and Turbine Buildings. Leak detection results in alarms and automatic isolation of the high energy steam pipe lines of

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'the secondary coolant system, thereby limiting the steam release into

.the' . buildings. This -assures that resulting building harsh environments without any credit for operator action are much less severe than those harsh environments previously established and accepted based upon operator termination of the leak at 4 minutes. A

second : purpose is to assure that the subsequent building air temperature cooldown allows access within one hour from the onset of the steam leak by personnel wearing protective equipment. Human

. accessw= ill permit personnel to perform required manual safety actions. '

Detection of a high energy line break (HELB) is assured by continuous monitoring of area average temperatures' in both the Reactor and Turbine Buildings. The total area monitored is divided into two distinct zones, one in the Reactor Building and one in the Turbine Building. The zones selected provide coverage in the event of a I rupture in the high energy steam pipe lines (main steam, cold reheat, hot reheat,. auxiliary steam). SLRDIS is not designed to isolate feedwater, condensate, and extraction steam leaks since analyses demonstrate that these leaks. can be adequately isolated by the operators. . A two-out-of-four tripping scheme is established for each .

zone by routing 4 temperature sensing (termistor-type) cables in each zone'. The temperature sensors within each zone are located to sense the average temperature of~the building' volume.

Each thermistor cable independently acts as a zone temperature sensor

_and'provides a resistive signal that decreases exponentially with cincreasing temperature. The setpoint is based on a-resistive signal e

determined by the length of the sensor cable reaching high temperature. Both ends of each sensor cable are connected to the associated Temperature Monitor in a " loop" configuration. A break in a sensor cable will not negate the capability for a valid high temperature signal from being produced by the remaining ends. The sensor break itself actuates a Trouble Alarm.

The alarm contacts are connected to a control room annuciator window on control board I-05 that reads: " Steam Line Rupture Detection Panel - Acknowledge". Appropriate "reflash" provisions exist so that subsequent' valid alarms are presented to the control room operator while a -channel is disabled for maintenance or on test. The temperature from each sensor channel can be read out on the steam line rupture detection rack located in the control room.

l The automatic isolation -feature of the SLRDIS is provided by l redundant microprocessor-based logic. Each cable monitor, upon l- i 1

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actuation of the high level alarm / trip, transfers this information through optical isolators to the two redundant (Logic A and Logic B) microprocessors. Each microprocessor combines the four cable alarms from any single zone into a two-out-of-four logic trip signal. Upon actuation, the trip logic scheme provides isolated relay contacts to the existing secondary coolant isolation valve circuits.

The system employs " transmission logic" in that it takes power to cause an isolation signal. This is consistent with the use of

" transmission logic" in the existing PPS Loop Shutdown and Circulator Trip Logic.

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ATTACHMENT 5 SLRDIS SAFETY ANALYSIS REPORT