ML20009B619

Requests That Util Make Application for Tech Spec Changes to Require Time Response Testing of All Safety Sys Resistance Temp Detectors within One Month of Operation for Newly Installed Resistance Temp Detectors

ML20009B619
Person / Time
Site:	Arkansas Nuclear
Issue date:	06/30/1981
From:	Clark R Office of Nuclear Reactor Regulation
To:	Cavanaugh W ARKANSAS POWER & LIGHT CO.
References
TAC-7545, NUDOCS 8107160448
Download: ML20009B619 (50)

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JUN 3 01981 DOD N ~ CJN '

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2 $(b gof Q Docket Ho. 50-368 Mr. William Cavanaugh, III p

Senior Vice President, Energy

'b Supply Arkansas Power & Light Company P. O. box 551 Little Rock, Arkansas 72203

Dear fir. Cavanaugh:

By letters dated April 25, 1978 and August 29, 1979, Florida Power and Light Company and flortheast Nuclear Energy Company provided technical reports on two different Loop Current Step Response (LCSR) methods for determining the resistance temperature detector (RTD) response time at St. Lucie, Unit No.1 and Millstone, Unit No. 2, respectively. These methods are similar in most respects, but have a few differences which are discussed in the enclosed Safety Evaluation (SE). Based on our review of both reference reports, we find the LCSR methods to determine RTD time response ar, described in each report and documented in the SE to be acceptable. We plan to issue the SE as a HUREG in the near future.

Extensive testing has shown the t.CSR method to be extremely reliable and provide results with an accuo w of 10% (maximum error). This compares very favorably with the older c?w wt method, which often has inaccuracies as high as a factor of 3.

Re. a LCSR method offers a significant improvement in RTD response time b v W recommend you consider its use at your facility.

It appears t;p us tnt use of the LCSR method would also -esult in a reduction in personnel radiation exposure.

The extensive RTD time response testing which has been done in conjunction with the development of the LCSR method has revealed that the RTDs in operating reactors suffer time response degradation as t ry age. Current Standard l

Technical Specifications (STS) require that on : 49arter of the safety system RTDs be tested each 18 nonths. This corresponds to testing each PsTD once every six~ years. In view of the RTD time response degradation observed in l

our study, it is clear tht' the present RTD surveillance testing schedule is not adequate.. We request that you nake application for TS changes to require the time response testing of all safety system RTDs within one month of operation for newly installed RTD and once every 18 months thereafter. This application should be made before or as a part of your application for the next core reload.

If you plan to use the provisions of 10 CFR 50.59 for the next core reload, please submit the application for such a change at last 90 days ahead of the next planned reactor shutdown. This request is independent of i

whether you plan to use the LCSR or some other method (plunge test for example) of determining the RTD response time.

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If you have any qLestions on this subject, please contact your assigr.ed

.NRC project manager.

Sincerely,

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Original signed by Robert A. Clark Robert A. Clark, Chief Operating P,eactors Branch #3 Division of Licensing

Enclosure:

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NUCLEAR REGULATORY COMMISSION -

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- JUN 3 01981.

Docket' No~'. 50-368 -

' Mr. William Cavanaugh, III Senior Vice President Energy S pply Arkansas Power & Light Company P. O. Box 551.

Little Rock, Arkansas 72203

Dear Mr. Cavanaugh:

By letters dated April 25,.1978 and August 29, 1979, Florida Power and Light Company and Northeast Nuclear Energy Company p%vided technical reports on two different Loop Current Step Response (LCSR) methods for determining the resistance temperature detector (RTD) response time at St. Lucie, Unit No.1 and Millstone,- Unit No. 2, respectively. These methods are similar in most

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respects, but have a few differences which are discussed in the enclosed Safety Evaluation (SE).. Based on ocr review of both reference reports, we find the LCSR. methods to determine RTD time response as described in each report and documented in'the SE to-be acceptable. We plan to issue the SE as a NUREG in.the near future.

Extensive testing has shown the LCSR method to be extremely reliable and provide results with an accuracy of 10% (maximum error). This compares very favorably with the older plunge test method, which often has inaccuracies as high as a factor of 3.

Since the LCSR method offers a significant improvement in RTD response time testing, we recommend you consider its use at your facili ty.

It. appears to us that use-of the LCSR method would also result in a reduction in personnel radiation exposure.

The extensive RTD time response testing which has been done in conjunction with the development of the LCSR method has revealed that the RTDs -in operating' reac' ors suffer' time response degradation as they age. Current Standard Technical Specifications (STS) require that one quarter of the safety system RTDs be: tested each 18 months. This corresponds to testing each RTD once l.

every six years.

In view of the RTD time response degradation observed in

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our study, it is clear that the present RTD surveillance testing schedule is not adequate.- We request that you make application for TS changes to require I

the time response t1 sting of all safety system RTDs within one month of operation for newly' installed RTD and once every 18 months thereafter. This application should be made before or as a part of your application for the next core reload.11f'you plan to use the provisions of 10 CFR 50.59 for the next core reload, please submit the application for such-a change at least 90 days ahead of the next planned reactor shutdown. This request is independent of

~ whether you plan to use the LCSR or some other method (plunge test for example)

.of determining the RTD response time.

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2-If you have any questions on this subject, pleate centact your assigned NRC project manager.

Sincerely, f ',<

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obert s_.. Clark, Chief Operating Reactors Branch #3 Division of Licensing

Enclosure:

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Arkansas Power & Light Company cc:

Mr. David C. Trimble Director Criteria and Standards Division Manager, Licensing-Office of Radiation Programs (ANR-460)

Arkansas Power & Light Company U.S. Environmental Protection Agency P. O. Box 551 Washington, D. C.

20460 Little Rock, Arkansas 72203 U.S. Environmental Protection Agency Mr. James P. O'Hanlon Region VI Office General Manager ATTN:

EIS COORDINATOR Arkansas Nuclear One 1201 Elm Street P. O. Box 608 First International Building Russellville, Arkansas 72801 Dallas, Texas 75270 Mr. Robert B. Borsum Babcock & Wilcox Nuclear Power Generation Division Suite 420 7735 Old Georgetown Rcad Director, Bureau of Environmental Bethesda, Maryland 20014 Health Services 4815 West Markham Street Nick Reynolds Little Rock, Arkansas 72201 c/o DeBevoise & Liberman 1200 Seventeenth 3treet, N.W.

Washington, D. C.

20036 Arkansas Polytechnic College Russellville, Arkansas 72801 Honorable Ermil Grant Acting County Judge of Pope County Pope County Courthouse Russellville, Arkansas 72801 Mr. Charles B. Brinkman Manager - Washington Nuclear Operations l

C-E Power Systems 4853 Cordell Avenue, Suite A-1 Bethesda, Maryland 20014

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REVIE'el02 RESTSTANCE TEMPERATURE DETECTOR g RESPONSE CHARACTERISTICS SAFETY EVALUATION BY U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION DIVISION OF SYSTEMS INTEGRAT!CN ItiSTRUMENTATION AND CONTROL SYSTEMS 3aANcs NOVEMBER 1980

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A8STRACT Historically Resistance Temperature Detector (RTD) time responses have been measured by the plunge test technique. For RTDs installed in nuclear plants the plunge test is inconvenient and very inaccurate, sometimes leading to errors as large as a factor of 3.

Recently EPRI has developed an in-situ

. method for measuring the RTD time response called the Loop Current Step Response (LCSR) method. The LCSR method is convenient to perform and it produces results that are accurate to within about 10%. In addition, EpRI has d,eveloped two other in-situ methods which detect RTD degradation, but give no detailed information on the RTD time response. These metteds are the Self Heating Index (SHI) method and the Noise Analysis (NA) method. We have examined the LCSR, SHI, and NA methodolcgies and find all.three to be viable methods for monitoring RTD time response, but we nave not concucted a formal review of the SHI and NA metnads. To date two vendor time response topical reports have been submit:ed to the NRC, one from Analysis and Measurement Services Corporation (AMS) and the other from Technology for Energy Corporation (TEC). Both vendor topicals propose only the use of the LCSR method. We have reviewed both the AMS and TEC LCSR topicals and find their methodologies acceptable for RTD time response measurement.

l The extensive RTO testing done in conjunctics with the LCSR development has revealed RTD time response degradation with ageing. In view of this degradation l

l we are recanmending increased surveillance testing of RTD time response.

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SECTION D.GE.

SECTION TITLE NUMBER

. I N T RODUCT I ON. ' BAC KGR OUND. AND S UMMAR Y - -- -- ----- ---- ------ ------ ----------- --------- 1.0 -'-------------- - 4 s

RID T I ME RESPONSE - CHARACTERI ZAT I ON AND MEASUH EHLHI ----------------------------------- 7.0 -------------- 11 RI D T I ME C ONST ANT C ONCE PT ------ ------- -- - - --- --- -- - - -- ----- - - - - - - ---- - ----- - -- --- 2.1 -------- ----- 1 1 -

LCSR ME THOD FOR MEAsuRI NG RTD T IME CONSTANT -------------------------------------- 2. 2 ------------- 12 L C SR T E S T PR OC E DUR E - -- - - - --- -- - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - ----- - - - - - - -- - 2. 2.1 -- ------ - ~- 12 T HE L C S R T RAN S FORMAT I ON -- -- - - - - - - -- - - -- - -- - - -- - - - -- - - - -- - - -- - - - - - - - -- --- -- -- - 2. 2. 2 ' ---------- -- 12 APPL I CAT ION OF Tile LCSR TRANS FORMAT I ON --------------------------------------- 2.2. 3 ------------ 14 DE. MONSTRATION OF E DNSERVATI SM OF Tile LCSR 1RA ISl eidtAl!0N --------------------- 2.2.4 ------------ 14 y

4 EPRI (AMS) METil00 FOR CORRECTING FOR UNKliUWN 111011LH E I GEllV ALUE S. --- ----------- 2.2. 5 ------------' 15 ~

i TEC NETii00 FOR CORRECTING FOR UNKNOWN ll!GillR EIGI NV/l UES --------------------- 2.2.6 ------------ 17 R I D DE GR ADAT I DH T E ST S - - - - - - -- - - -- - - - - -- - - -- -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - -- - - - - 3. 0 - --- - -- -- - - - - - 18 RTD DE GRADAT 10N T EST S US ING L CS R HETil0D ---------------------------------- -------- 3.1 -------------- 18 RID DEGRADATION TESTS USING IllE SELF llEAIING 11101 X (Sill ) ------------------------- 3.2 -------------- 22 RI D DEGRADAT I ON TE STS US ING NO I SE ANALYS I S. (IIA) ---------------------------------- 3. 3 -------------- 25 l

POTENTIAL FOR RID TIME HESPONSE DLGRADATION -----

---

4.0--------------27 MODES OF RID TIME RESPONSE DECRADAll0N ------------------------------------------- 4.1 -------------- 27 i

E V I DE NCE O F RID T IME RES PONS E DE GRADA Il0N -- - --- - --- ------------------------------ 4.2 -------------- 28 i

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1.0 INTRODUCTION

, BACMGROUND, AND

SUMMARY

same ammmmmmmmmmma sums -mem-ma A Resistance Temperature Detector (RTD) is a type of thermometer in which the temperature in inferred from the electrical resistance of a piece of wire,

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which.is called the element. RTDs are used extensively for monitoring water

. temperatures in nuclear reactor plants. The RTD element does not respond instantaneously to changes in water temperature, but rather there is a time delay before the elenent senses the temperature change, and in nuclear reactors this delay must be factored into the computation of safety setpoints. For this reason it is necessary to have an accurate description of the RTD time response. This Safety Evaluation (SE) is a review of the current state of the art of describing and measuring this time response.

Historically the 970 tire response has been characterized by a single parameter

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called the plunge time constant, or simply tne Plunge

. The Plunge - is tefined as the -ime recuired for the RTO to acnieve 53.2". of its final response afte-a step tsncerature cnange is impressed on the surf ace of the RTJ, Sucn a temoerature change can be acnieved by clunging the RTD into a heat sink, such as water, oil, sand, or molten metal. When : is measured by this means the technique is called the plunge test method.

Until 1977 all testing of RTD time response was performed by means of the plunge test technique.

In nuclear reactors, surveillance testing posed an in-convenience in that the RTU had to be removed from the reactor coolant piping and shipped to a laboratory for testing. Nuclear reactor service conditions of 2235 psig and 540 CEGF are difficult to reproduce in the laceratory, and hence all laboratory tests were perfonned at more benign condittons, and the laboratory results were then extrapolated to service conditions. The canbination of manipulating the RTD and extrapolating the e

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1aboratory results to service conditions lead to significant errors in the RTD time response, sometimes.as high as a factor of 3, Thus there was considerable incentive to find a better way to measure an RTD's time response.

With this impetus. in 1976 CFRI launched a research project at the University of Tennessee (U of T) to investigate'other possible methods fee measuring an RTD's time response. Two requirements for any method being developed were:

(1) that it could be performed in-situ, and (2) that it produce reasonably accurate results. The products of this investigation are described in 'three EPRI topical reposts, which are references 1, 2 ano 3, wnich will henceforth be referred to as the 1977, the 1978, and the,1980 EPRI copical reports.

This investigation produced three in-situ methods for testing the time response of RTDs, which are as follows:

1.

Loop Current Step Resconse (LCSR) Method.

In the LCSR Method the resistance et ement of the RTO is neated by an electric current, and tite temperature transient in the element is recorded.

From this transiert the response of the RTD to changes in external temperature is inferred, t

2.

Self Heating Index (SHI) Method.

In the SHI method a constant current is impressed through the element i

and the equilibrium change in resistance is recorded. The ratio of the element resistance change to the power dissipated is called the SH1. The

- SHI cannot be correlated with the Plunge :. but changes in the RTD SHI can be used as a means of detecting RTD degradation.

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s 3.

NoiseAnalysis(NA) Method.-

In the NA. method the small fluctuations -In RTD output under operating conditions are analyzed on line (or retorded for off'line analysis) using spectral densicy and/or auto regressive technicues, These fluctuations are the RTD response to fluctuations in the external temperttece of_ the RTD.

If the pattern of fluctuations in the external temperar.are is known, then it The is possible to deduct information about the time respon:e 0f the RTD.

NA method has been applied to obtain consistent results under optimum rea: tor conditions.for certain types of sensors; however, currently it has not bee.t established in a statistically depondable manner that the NA method yields results comparable with deterministic methods. Thus, while in principle it should be possible to develop a viable detarministic method for measuring the Plunge i using NA, the realization of tMts goal will still require a-substantial s ount of investigative worx. However, at the cresent s ate-of-the-art the NA method could be useful for detecting R7D time response degradation.

Characteristic: of these three in-situ methods and the plunge test method are summarized in cables 1.1,1.2 and 1.3.

All these methods have their However, for determining the RTD Plunge r, the only currently purpose.

viable method is the LCSR method.

Currently in-situ LCSR RTD measurement services and test equipment are available from two vendors, Analysis and Measurement Services Corporation (AMS) and Technology for Energy. corporation (TEC). Both these vendors began operations before the final phases of the EPRI study were complete, and as a result l

developed somewhat different methodologies. The AMS methodology is identical l

to that described in the EPRI topicals. We have reviewed both the AMS and TEC LCSR methodologies and find them both to be reliable and adequate to measure the RTD time constant to within 10%.

6-

Table

• 1 Characteristics of Methods for Heasuring RID pme, Response l

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.'lecessary Complea;ty I!

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• I 4"*IILY "I "**S"'""*"'

Test I

Measurement 2

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a Plunge test measures Plun e i directly, but measurement has poor Need to quality for two reasons: 1) Hantpslating RTD may change its time Plunge S

response and (2) Service conditions, are usually not reproduced in the Ves RID and Test lab. Lab results must be extrapolat ed to service conditions. The a

5 sh p to combined effect of these two factors can result in errors up to a factor of 3.

Test simple.

"SN P## ** '" I" # "Cl **d5"#" *I **

LCSR Ves Special test Test eg" P "'

Results are generally accurate to within 101.

ed Test simple.

Sill can be measured quite accurately.

Uses simple a

standard from changes in the Sill. RID degradation can be detected.

T Ves electronic

.5 test No good correlation between Plunge r and SHI exists.

equipment.

f A good deal of sophisticated work has gone into NA. Ho=aever NA Test simple.

measurements of Plunge t conducted to date have been in arror by up a

to a factor of S.

A nisaber of Investigators are still endeavoring to NA Y

SPecial l

No develop a viable method for measuring the Plunge t using NA, and it is Test

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test hoped that future work will lead to m.:ch improved agreement between 5

equipment thm 'y and experiment.

needed, NA is still a useful tool for detecting RID degradation.

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Tal>1e M Practical Asp

• cts d Avallitillity of RTD Ti~e Response Testing Methods N

Utility of AMS TEC 9,7 g3 Test Procedure Provides Provides Provide Test for RTD Yes Yes Hone Degradation Plunge Test Measure Poor -- Errors to Service Only Plunge 1 a factor of 3 (Lab Tests)

Ye5 Y'S OK -- However if the utt ity buys equipuent for Equipment Equipment Test for RID degradation test they might and Training and Training Degradation LCSR as eell buy equipme a for.

Test seasu Ing Plunge t.

Se.vice or Service or Measure Good Equipaent Equipment Plunge 10% Accuiacy and Training and Training oo Test for RID Good -- No special test N

WM Degradation ecluipnent needei Sill Test Measure Poor -- No good i

Plunge t correlation with r exists.

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Test for RTD Need Special t Equipment.

gegradation /

RTO need not he Training Tnaining

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taken out of service.

Initial attempts to measure Plunge r produced HA poor results with errors up to a factor of S.

Measure Over a period of 2 years a limited number of Plunge T careful NA measurements have produced results Tra ilng with 110% verlation. No systematic correlation of these results with l

deterininistic acasurements has been made.

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.A Table 1.3 Modes of RTD Surveillance Testing 1.

Historical Method: Plunge Test.

Because of the inconvenience of removing the RTD for testing and the inaccuracy of the test results this method is being abandoned by a number of utilities. The NFC should take steps to encourage all utilities to abandon this method in a timely fashion.

2.

LCSR Method: Maximum Utility Involvement.

The utility can purchase their own eitctronic equipment and have their own trained personnel perform the LCSR tests.

3.

LCSR Method: Moderate Utility Involvement.

The utility personnel can do regular degradation tests using either the 5HI or NA methods. If evidence of RTD degradation is found then a consultant can be brought in to measure the RTD time constant using the LCSR method.

4.

LCSR Method: Minimum Utility Involvement.

The utility can have the consultants measure the RTD time constants on their regular surveillance schedule.

7ei l

1

The currant Standard Technical Specifications require that one quarter of the safety channel RTDs be tested once every la months.

The data on RTO degradation collected to date is rather scant, but does appear to give positive evidence of RTD time constant degradation with service. A prudent interim regulatory position would be to require the utilities to either:

a. Pe-form a surveillance test of all their safety. channel RTDs at least once every 18 months, and verify that the time response of the slowest RTO is at least as fast as that assumed in the safety analysis.

In addition perfonn a test of each newly installed RTD at operating conditions as soon as practical after its installation.

b. Continue with the present RTD surveillance requirenents and schedules in the Technical Scecifications, but in the safety analysis assume an RTD time constant ecual to the greater of:

I'ongest time constant measured in last surveillance tes'E 1.2 *

[includinga10%allowanceformeasurementuncertainty),_

CE ----- Rosemont Model 104 RTD ------ 12 sec.

W ------ Rosemont Model 176 RTO ----- 0.8 sec.

B&W ---- Rosemont Model 177 RID ------ 12 sec.

The rationale for options (a) and (b) above are discussed in section 8.0 of this report.

,_ ~

2.0 RTD TIME RESPONSE CHARACTERIZATION AND MEASUREMENT man ama mems

=

2.1 RTD TIME CONSTANT CONCEPT If an RTD were a first order system, the Laplace Transform of the sensing element's response to an external temperature change would be:

T(element) 1 T(external)

(1 + :s)

The response [T(element)] to a step function change in T(external) is T(ext. final) - [T(ext. final) - T(ext. initial)]

• exp(-t/ )

T(element)

=

At time t=;

the element tamcerature has reacned ICC%/c = 53.2% of its final respcnse. For this reason the time required for the RT3 cutput to attain 53.2% of its final response has been namec :ne RTO plunge time constant.

In fact, RTDs are not first order systems, but the historical definition of RTD time constant is still used and is still a useful concept.

In applications in nuclear plants the external temperature changes to an RTD are typically ramp functions, and the parameter of importance is the time by.which the sensing element temperature lags the external RTD temperature.

This time is called the Ramp Delay Time (RDT). In the AMS Topical Report (Reference 5) pages 105-109 the relationship between the Plunge : and the RDT I

l is discussed, and it is shown that the Plunge : is always equal to or longer than the' ROT, the maximum difference being about 2%. Thus the Plunge ; can

be used as 'a conservative measure of the ROT, and in practice all Technical Ipecifications are written in terms of the Plunge t and hence all measurement techniques are directed toward evaluating the Plunge r.

2.2 LCSR HETH00 jpR MEASURING RTO TIME CONSTANT 2.2.1 LCSRTEST1ROCEDURE_

In the LCSR method a constant current is impressed on the RTD sensing el,ement which heats the elenent and the whole of the RTD experiences a temperature transient. A time plot of either the heating of the element while the current is impressed or the cooling after the current is discontinued is recorded.

From this plot the RTD plunge time constant is inferred by means of the LCSR transformation, which is described in the next section.

The element temperature is inferred from its electrical resistance wnich is measures by a bridge circuit. The required electronic test equipment is discussed-in detail in the subject references, and this discussion will not be reiterated in this SE.

2.2.2 g LCSR TRANSFORMATION The mathematical theory for analyzing heat transfer in an RTD is developed in the subject references. Two different approaches are described in detail:

(1) a nodal approach and (2) a continuum approach.

In the 1980 EPRI Topical Report, page 3-34 and Appendix B, nwnerical results of the two approaches are compared, and for the two cases cited the differencer are 1.5% and 1.1%

respectively. Thus for practical purposes the two approaches can be considered to be identical..

t

.I It'is shown that if:

(1) The RTD has cylindrical symmetry and (2) There is neglegiole heat capacity inside the sensing element

- then the transfer function which describes the RTD's response to an external tunperature change is (AMS Topical page 23) 1 T(element)

(2.1 )

T(external)

(: s + 1)( 2s + 1)(:3s + 1 )..... (:ns + 1) n is finite if the nodal approach is used and infinite if the continuum This difference is not significant in that the higher order aporoach is used.

factors cor.6tibute little to the solution.

The important feature of the above equation is tnat the transfer function As will soon become evident, this fact permits contains poles, but no zeroes.

the inference of an RTD's resconse to an external temcerature enange from tne results of an LCSR transient.

It is shown that the plunge time constant is given by (AMS Tcpical page 27) 3 t) - In(1 a/:t)..... ].

g(1 - in(1 - ::/ 3) - in(1 -

/

(2.2)

=

It is shown that the response of an RTD to a step change in el'ement currenc (LCSR transient) is given by (1978 EPRI Topical page 49)

[a

• • E(~*/In)

(2.3)

T(elenent) - i

=

n n

n where the an (als defined in page 49 of the 1978 EPRI Topical) are functions of the poles and :eroes of the transfer function.

- I L

Experimentally, the e can be determined by breaking the temperature response n

into a series of exponentials. Once the e are determined they can be n

plugged into equation 2.2 to determinf, the plunge time constant. Thus all A

~ the information required to evaluate the plunge time constant is contained in the LCSR transient.

2.2.3 ApPt.ICATION g TJH LCSR TRANSFORMATION In an ideal world the LCSR transfomation could be used as follows:

(1) Conduct an LCSR test to obtain a plot of T(element).

(2) Resolve this plot in.to a series of exponentials according to equation (2.3). This gives numerical values for the :q.

[It is not necessary to evaluate the a ]

g (3) Plug these values of r, into eauation (2.2) to obtain tne Plunge t.

In practice step 2 is performed either by exponential stripoing er a least squares fit. Using either method it is usually possible to find :t and ::.

In exceptionally good cases it is possible to find it : and :3, and in bad cases it is possible to only find :1 If equation (2.2) is truncated after tem the result can be nonconservative by as much as 20%, and if the rz/tt equation (2.2) is truncated to r = tt the result can be nonconservative J

by as much as 47%. AMS and TEC correct for this problem in different ways, which will be discussed in sections 2.2.5 and 2.2.6.

2.2.1 OEMONSTRATION g CONSERVATISM Of TJH LCSR TRANSFORMATION i

In reference 4 f t is shown that if either the assumption of cylindrical l

symetry is violated (say by a crack in the RTD) of the assumption of having k

no heat capacity within the element is violated, then the transfer function (equation 2.1) would have zeroes as well as poles.

If this were the case, i:

-, ~ - - =

w

i, l

i then the Plunge r expression (equation 2.2) would contain terms with these poles.- It.is shown in reference 10 that these terms would decrease the computed value of r, and hence applying the LCSR method when the two assumptions for the LCSR mathematical development are violated leads to a conservative computed value of the Plunge t.

2.2.5 EPRI (AMS) METHOD FOR CORRECTING FOR UNXNOWN HIGHER EIGENVALUES After trying a number of correlation schemes, the U of T investigators found that a very good approximation for the Plunge r is given by f(T2 ti)

• t (i - In(1 - rz/ri)],

/

(2.4)

Plunge r

=

i where f(t /tt) is given by the enperical relationship of figure 2.1.

Figure 2.1 2

was constructed by mathematically computing the Plunge r (equation 2.2) and it[1 - In(1 - r:/rt)] for a numoer of different hypothetical RTDs and plotting the ratio of :he two. The hypothetical RTDs had a variety of si:ed and geometries, which included both holicw core and centrai element RTDs. Thus the curve of figure 2.1 applies to any RTD which fulfills the two requirements of section 2.2.2.

The fact that this large variety of RTDs all enjoy the same f(r2/ti) is, on the surface, rather amazing. With such a good correlation, one would naturally be inclined to search for an underlying physical reason for all RTDs to display the same f(r2/tt). However, to date this underlying-physical relationship has eluded us.

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.200 Fl9ure 2.1 Plot of correction factor [f(iy/i ll vs pole' ratio [i2/t i].

i f

[ Reproduced from figure 5.3 of the 1980 EPit! Topical Report]

I This function is used in equation 2.4:

(Plunse i) " f(2:/ai)*t i[1 - In('2/t ill-1 I

i

2.2.6 E METH00 g CORRECTING g UNKNOWN HIGHER EIGHEVAt.UES The method used by TEC is the following:

(1) Assuma a continuum model for the RTD which geometrically consists of a thernowell (pipe which houses the RTD), and air gap, a steel sheath, a

~--

- - ~

ceramic layer, a platinum element, and a ceramic core.

(2) Assume realistic values for the thermal properties of the thermowell and the RTD steel sheath. (the element is so small that it can be ignored in the thermal calculation) e (3) The thermal resistance ff) the film between the thermowell and wate

)ds that of the air gap between the thermowell and the sheath are not well known. These two thermal resistances are canbined into a single resistance R(film + gap) which is left unknown. The thermal resistance of the c.eramic R(ceramic) is also left unknown.

(4) The RTD continuum equations are solved for :1 and :2 using various values of R(ffim + gap) and R(ceramic). This procedure is iterated until the values derived for :t and :: match those measured experimentally.

(5) The ncw knevn values of R(film + gas) and R(ceramic) are used in the RT3 continuum equation and the Plunge : is ccmputed.

The TEC method has the advantage over the EPRI (AMS) method that it uses a recognizable line of physical reasoning to attain its result, whereas the EPRI method is emperical. The TEC method has the disadvantage that it requires a detailed knowledge of the geometry of the RTD, which is not needed for the EPRI method. However both the EPRI and the TEC method produce about equally accurate results, and thus from a regulatory point of view must be considerec equally gcod.

e-

.D.

-4 i

3.0 - Jt_Tjl OEGRADATION TESTS' I

ENER ---

Although neither AMS or TEC have presented proposals to do degradation tests, the subject of degradation tests is discussed in the EPRI reports, and it seems worthwhile to summarize the status of these degradation tests here.

3.1 RTO DEGRADATION TESTS USING LCSR METHOD A sin.ple application of the LCSR method is a degradation test. For this test an LCSR transient is impressed on the RTD and the time required for the RTD to schieve 62.3% of its final response is measured. This time is called the LCSR :. An increase in the LCSR : is a sign of RTD degradation.

The U of T ' '.-tf jetors attenoted to correlate the Plunge : with the LCSR :.

In maki! g this cat. alation the time response of the RTD was varied ' y aeding a

tape or rucber insulation around the RT3 and measuring botn ne Plunge : ant ene LCSR :. Two such correlations are shcwn in figures 3.1 and 3.2.

An obvious difficulty with this method is the following: This correlation was formed by altering the thermal resistance on the surface of the RTD. When an RTD degrades, it is most likely due to *ncreases in the thermal resistance of the RTD internals or the RTD-thermowell gap. Therefore one would expect to find a different correlation for normal degradation than that determined by adding insulation to the surface of the RTD. For this reason we do not, at present, consider the correlations of figures 3.1 and 3.2 to be sufficiently

-well substantiated to be used in the determination of the Plunge :.

~

While not.providing an accurate means of computing the Plunge T, these correlations are useful for the degradation test. If in a degradation test the LCSA t is found to increase, then from the correlation the approximate increase in the Plunge t can be determined. If the Plunge r determined in this way is near the value assumed in the safety analysis, this would indicate.

that it is necessary to measure the Plunge t via the usual LCSR procedure.

Using the LCSR technique to detect detector degradation is a rather wasteful use of'the LCSR electronic equipment. With the addition of one microprocessor the degradation test equipment can be used to measure the Plunge t as described in section 2.2.1.

==w,

1 24- -

22- -

20 - -

13 - -

16.}e

14..,

s 12 g

2 73 IO

=

Emperical Correlation Curve 3

'l+

5-f s

TA 4.

/

ft c Em;:erical Ca a 2

LCSR : (sac) 0.

1 2

3 4

5 Figure 3.1 Emcerica. Correlation Curve for Plunge : versus LCSR :

for Rosemont RTO Model 104AFC.

(Combustion Encineerina 3,JJ,)

(Reproduced from Ff gure 6.4 of the 1978 EPRI Topical Report]

t l

I l

l e -

i

O 3.0 --

'2.5--

8 7*

2.0 - !

o 5

E o

o

1. 5 - -

.imperic.1LCarrelAt.1on Carva-_

c.

l.0 - -

Emcerical Cata o =

0.5

/.

LCSR - (sec) 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Figure 3.2 Emoerical Correlation Curve for Plunge e versus LCSR :

for Rosemont RTD Model 176KF.

(Westinghouse RTO)

(Reproduced from Figure 6.5 of the 1978 EPRI Topic;' Report]

l l

21 -

~

O s

o 3.2 RTD DEGRADATION TESTS USING THE SELF HEATING INDEX (SHI)

In the SHI test, a constant current is impressed through the RTD element and the steady state change in element resistance is measured. This test is performed at several different currents, and a plot is made of power dissipated by the element versus increase in element resistance. Emperically this has always been found to be a straight line, and the slope cf this line (ohms / watt) is called the SHI.

An increase in SHI is a positive indication of RTD degradation.

As with the LCSR :. the.U of T investigators attempted to correlate the SHI with the Plunge :.

Again, as with the LCSR weasurement, the RTD time response was v'aici by adding insulation to the surface of the RTD, and plots of Flunge : versus SHI were constructed. Two such plots are shown in figures 3.3 and 3.a.

These correlations suffer the same problem as the ? lunge : versus the LCSR :

correlations, and thus we do not, at present, accept then as viable means for computing the Plunge :. However, like the Plunge versus LCSR : correlation, the Plunge : versus SHI correlations would be useful in a degradation test.

l i

l

-e '

- le '

tr.

10 <

g 13 is. O 3

14,

[f3

,,,, [

Sperical m

Correlation f

Curve to

/

8 2 + E:cer k31 Cats s

4 g Extrapolated to Zero SHI (ches/ watt) s s

r s

Flourt M Empirical Correlation Curve fg Plunge t versus SHI fjr Rosemont G Mg 104FC. (Combustion Encineerine B)

(Reproduced from Figure 6.7 of the 1978 EPRI Topical Report].

' ese-

n s

3.0- -

2. 5- -

g Emperical Data -o i

2.0. ' '

e?

d5 1*- -

Emperical

/

~

Correlation

/

Curve 0

1.G.

,/*

/

0.5 -

af SHI (ohms / watt) 0.C l

5 6

7 8

9 10 Figure 3.4 Emcerical Correlation Curve for Plunge versus SHI for Rosemont RTD Model 176KF. ('destinghouse 170)

(Reproduced from Figure 6.8 of the 1978 EPRI Toof cal Report]

'l

y 30EGRADATION TESTS USING NOISE ANALYSIS (M)

NA tests are performed by carrying cut statistical (spectral, correlation, zero crossing rate and/or auto regressive) analysis of normal fluctuations of the RTD output signal during normal steady state reactor operation. These fluctuations are the RTD's response to the fluctuatier.2 in the reactor coolant temperature.

The statistical methods referred to above will not be discussed here, and the reader is referred to the three EPRI topical reports for a discussion of these me thods.

In the application' cf the NA method, assumptions must be made regarding the statistical properties of the coolant temper 1ture fluctuations.

If fome minimum set of assumptions, such as stationarity and repeatability are met, the NA aethod is a valio degradation method since any change in the output fluctuations can be

~

dirtetly attributed to the.lTD itsel f.

If, in addition to stationarity and repeat 30flity, the coolant temperature fluctuations are "4nita" (naving fluctuations whose Fourier representation displays constant energy per unit band width at every frequency in the range of interest). NA can be used to determine a Plunge v.

The initial theoretical work in NA done by EPRI was directed toward developing a deterministic method for measuring the Plunge t, and this work produced some very sophisticated physical and mathevtical developments. However, when the theory was applied to experiment, it was found that NA predictions of the Plunge t were seriou',1y in error, sometimes by as such as a factor of 5.

The EPRI researchers concluded that their principal problem was that the reactor coolant fluctuatiord were not white, as they has assumed. Having no other reasonable model for reactor coolant fluctuations, EPRI has, at least for the time being, abandoned efforts to perform a deterministic s.&.surement of the Plunge t using NA.

j e

Researchers at TEC are still pursuing a deterministic method for measuring the Plunge r using NA. Over a period of 2 years TEC has demonstrated that for certain types of sensors and certain reproducable reactor coolant conditions.

careful NA measurements of the.various statistical parameters have produced results with +10% variation. However, it ha; been established that coolant temperature fluctuations do not meet the reouirements for a Plunge r determination under all reactor conditions for all sensors. To date TEC has not succeeded in developing a systematic correlation between the measured statistical parameters and deterministic measarements of the Plunge t, but there are reasons to believe that such a correlation can be derived for certain sensors under certain verifiable reactor cenditions.

As was just stated, the conditions for the coofant Temperature fluctuations for ~

sn RTO degradation test -sre less restrictive than those for a detarministic Plunge ; measurement.

It has been established that the measured statistical parameters which can be extracted from itA of RTDs under verifiable reactor conditions are highly reproducable and changes in these parameters can be used to infer changes in the RTD Plunge :. Therefore NA methods can be used for RTD degradation measurements subject to the statistical accuracy of the measurement.

f -

N LMNNM 4.1 MODES OF RTD TIME RESPONSE CEGRADATION The U of T investigators have evaluated various modes of RTD degradation in section 2.5.3.1 of the 1978 EPRI report and part II, chapter 7 and part V of the 1980 EPRI report. Their conclusion is that the main medes of RTD degradation are due to deterioration of the PBX Cement used to hold the RTD element in place and deterioration of NEVER-SEEZ, a substance used to increase the thermal conductivity between the thermowell and the RTD.

Most of the deterioration in the PBX and NEVER-SEEZ is due to high temperatures and takes place fairly soon after the elevated temperature is reached. Thus the RTDs are expected to show a marked degradation shortly after they are put in service, and afterward degrade more gradually. If future data bears out this-trend, then a reasonable surveillance schedule would require frequent testin; of the newer RTDs and less frequent tasting of the older ones. However, with the data currently available, this point is inconclusive.

In the TEC topical report it is suggested that RTD time response degradation may be caused by fouling of the thermowell by crud and cracking of the ceramic insulator in the RTD. While these are plausable modes of degradation, there is no evidence that either of these mechanisms is active in the observed time response degradations.

4.2 E'/IDCNCE OF RTD TIME RESPONSE DEGRADATION Records of measured AfD time constants for various reactors are presented in tables 4.1 and 4,2.

The AMS data from Millstone 2 indicates a systematic degradation of RTDs with service. However teost of the other data does not show this consistent trend. A prudent regulatory position for the present would be to increase tha required surveillance at all plants until enough data is collected to detemine if a consistent trend in RTD degradation does exist.

i l

l

j o

Table 4.1 Comparison of In-Plarit LCSR and E

]

Time Resoonse Tests Conducted g M

[Taken from Table 11.1 of the AMS Topical Report and Reference 4 3 Time Response Tg Results fg Rosement Model E R3 a,t M111stong, Unit,1,.

t For the Millstone tests, judging from either the Plunge r or the SHI s

test, almost all detectors degraded and a few remained unaffected by service. None improved.

August Decenber August December

'9l

'9l8

'9Il

'9l8 Plunga r*

Plunge r*

SHI SHI RTD (sec)

(sec)

(ohms / watt)

(ohms / watt)

Number A7770 3.2 5.2 5.6 7.4 A7765 2.8 3.2 4.5 4.8 75313 4.7 5.6 6.2 6.5 A7774 3.8 4.3 5.8 6.2 75294 3.7 4.4 5.3 6.4 75299 5.5 9.3 8.6 9.1 75310 4.6 4.9 6.2 5.5 75300 4.6 4.7 6.5 6.5 75297 3.6 3.6 4.7 4.9 80364 4.0 4.4 5.5 75309 4.0 4.7 5.5 5.8 A7769 3.1 3.6 4.8 5.0 Time 4esconse Test Results for Rosemont Model 176 RTDs at Farley Unit 1 In these tests there was no evidence of time response degradation.

October January October January 1978 1980 1978 1980 RTO

)

Plunge e PTunge r SHI SHI (sec)

(sec)

(ches/ watt)

(ohms / watt)

M '"

l 4123 0.10 0.11 7.5 7.4

~

i l

412C 0.12 0.12 5.8 5.7

]

• Since the correction factor had not been developed at the time of the August 1977 measurements..all time constants shown here ara uncorrected values. ~

e Table 4.2' Comparison of In-Plant LCSR Time Response Test Results Conducted,gy,,TJG on Rosimont Model 104 RTDs g h M Unit,1,

-(Taken from References 7 and 8]

_ In these tests there is no evidence of time response degradation.

January May Octobec March 1978 1978 1978 1979 Plunge r Plunge r Plunge r Plunge r (sec)

(sec)

(sec)

(sec)

TE-1112CA 4.0 1 0.2 4.2 + 0.4 4.0 + 0.4 4.1 + 1.2/-0.7 TE-1112HA 6.2 1 0.5 4.4 1 0.3 4.4 1 0.2 4.5 1 0.3 TE-Il22CA 5.5 1 0.2 5.7 1 0.3 6.0 1 0.6 5.0 1 0.7 TE-ll22HA 5.0 1 0.5 5.6 + 0.3 5.3 1 0.5 5.7 + 0.7/-0.5 5.0 1 0.5 4.3 + 0.5/-0.4 7E-1112C3 5.0 + 0.9 5.3 1 0.6 TE-1112HB 5.3 + 0.3 5.4 + 0.2 TE-1122C3 5.3 1 0 3 5.5 3 0.4 TE-1122HS 4.5 1 0.7 4.3 + 0.3/-0.5 TE-1112CC 5.4 1 0.4 5.4 + 0.7/-0.5 TE-1112HC 5.4 1 0.3 5.7 1 0.5 TE-1122CC 5.4 1 0.4 5.0 + 0.7/-0.5 TE-Il22HC 4.8 1 0.3 4.9 1 0.5 TE-lll2CD 4.9 1 0.5 5.7 + 1.0/-0.7 l

TE-1112HD i

5.7 1 0.5 5.6 + 0.9/-0.7 TE-1122CD 4.3 1 0.5 4.8 + 1.6/-0.9 TE-1122MO I

I

a MEERM E M M PARAMETERS THAT AFFECT RI2,IL.1 Resp 0NSE The time response is not only a

• function of the RTD itself, but depends as well on the properties of the themwell and the themal characteristics of the medium in which the thernowell or RTD is imersed. The ther nal properties of all these components change with temperature and the heat transfer properties of the medium (water) change with flow velocity. The match between

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the RTD and the thermowell affects the time response, and even tne slight change in match that occurs when an RTD is removed fecm a thermowell and placed back in the same well can significantly change the time response. Thus' it is important to simulste stryice unditions as closely as possible when testing the RTD time response.

As stated earlier, historically the time response of RTDs has been measured by a plunge test in the laboratory. Normal service conditions of 2235 psig and 540 OEGF are difficult to reproduce in the laboratory.

For this reason, in the past most laboratory tests were perfomed at more benign conditions and the results extrapolated to service conditions. With the advent of the LCSR method, the plunge test methodology has been re-examined, and it was found that the historical plunge test procedure often produced results which were grossly in error, sometimes by as much as a factor of 3. -

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One of 'the first suggestions for achieving 540 DEGF without elaborate laboratory This

- equipment was to use hot of f or sand as the medium, rather than water.

The reason is that the heat was soon demonstrated to be unsatisfactory.

conduction properties of oil and sand are so different from water that a test In numerical in oil or sand gives no indication of what would happen in water.

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terms, the thermal match between the medium and the RTD is given by a quan called the Stot modulus, which is defined as the ratio of the film thermal i

conductance to the internal conductance of the RTD [More specifically. Sfot modulus = hR/k. where h is the film coefficient. R is the RTD radius, and k When the Biot modulus is less than is the thermal conductivity of the RTD].

about 0.1 the thermal resistance is dominated by the film resistance, and when it is greater than about 10 the thermal resistance is dcminated by the RTD The response of an RTD in one heat transfer regime internal resistance.

indicates very little about how the RTO will respond in 3 different heat Values for the 31ot modulus for several cases are given transfer regime.

in table 5.1.

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MM Variation gf M Modulus M 3 h Of fferent Film Coefficients Associated with Of fferent Testing Conditions

[Taken from Reference 9]

Rosemont Rosemont RTD 104 176 Testing (Combustion (Westinghouse)

Conditions Engineering)

Reactor Service 300 3.8 Conditions 3 ft/sec 27 0.34 180 DEGF Water 1 ft/sec 115

1. s.

500 OEGF Solder a

5 500 DEGF Oil 0.3 0.02 500 DEGF Sand 0.4 0.01 x

5 Internal No available resistance laboratory test dominates for both condition water and solder simulates service Connents tests. Good conditions well.

service conditicn simulation is possible in laboratory tes+a.

er,

M g M RESPONSE TESTING CON 0!TIONS USED g PRACTICE: ROOM 'f PERATURE LABORATORY CONDITIONS While rooo tesperature tests do not indicate much about the RTO's behavior at service conditions, room temperature tests are a good way to compare various measurement methodologies. The main testing criteria for comparing methodologiss is that all methodologies are compared under identical conditions, whether these be service conditions or room temperature laboratory conditions.

In fact, all of the development work for the LCSR methodology was done under room temperature laboratory conditiora. Results of the room temperature tests are given in tables 5.2 and 5.3.

With the development work on the LCSR methodology complete, it seened worthwhile to test the LCSR method versus the plunge method at simulated service conditions. The next two sections describe how this was accomplished.

M RTO M RESPONSE TESTING CONOTTTONS QSQ 1,N, PRACTICE: IER1 SERVICE S

CONDIT~ 1 T E [FJf ILE}]

In order to test the LCSR method at service conditions, the U of T investigators in conjunction with Electricita de France (EDF). performed tests on a simulated reactor coolant test loop constructed by EDF. This loop operates at reactor service conditions of temperature, pressure and flow, and has special valves to induce a step change in temperature for the purposes of simulating a plunge j

test. The results of this test are shown in table 5.2.

It can be seen that the agreement between the LCSR test and the plunge test is excellent.

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Table 5.2 Results of LCSR and Plunge Testing done bg the U of T i

[Taken from Table 10.1 of 1978 EPRI Report and Tables 7-1 17-3 of 1980 EFRI Report]

Room Temperature Tests at U of,f Thermometry Laboratory i

Measured P1'ange r Inferred from LCSR ercent RTO Plunge t Without Higher.

With Higher Model (sec)

Mode Correction Mode Correction Rosemont 176KF 0.38 0.39 0.41

+7.9 Rosenont 104ADA 3.1 2.9 3.1 0.0 (without thermowell)

Rosemont 104ADA 7.1 5.9 7.2

+1.4 (witt thermowell)

Rosemont 104VC 2.3 1.7 2.1

-8.7 (without thermowell)

Rosenont 104VC 5.3 4.:

55

+3.8 (with thermowell)

Rosemont 177GY 5.8 5.1 5.2

+6.9 Ros emont.177GY 6.1 5.2 6.3

+3.3 Sostman 3606 2.0 1.7 2.1

'5.0 5.2

-1.3 Rosemont 104AFC 5.3 (air in vell) 3.3 0.0 Rosemont 104AFC 3.9 (NEVER-SEEZ in well) 12.3

+5.1 Rosemont 177HW 11.7 0. 41

-2.4 Rosemont 176KF 0.42 Service Condition _ Tests at EDF Test loop easure unge r In erred RfD Plunge e from LCSR Test Percent Model (sec)

(sec)

Error Rosemont 104AFC 6.2 5.9

-4.8 (Air in well)

Rosemont 104AFC 4.1 3.7

-9.8 (NEVER-SEEI in well)

Rosemont 177HW 8.8 8.4

-4.5

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t Rosemont 176KF 0.14 0.13

-7.T 35

.jid 3In ng, RESPONSE TESTIN3 CONDITIONS USED IN pRACTTCE: TE SERVICE CONDITION HEI. (19M2 IEEJ3 TEC has gotten around the proble of getting service condition temperatures by using molten solder, rather than pressurized water, as was done in the EPRI-EDF tests. As can be seen in table 5.1 for the Rosemont 104 RTD the

nolten solder provides a very good simulation of service conditions For the Rosemont 176 RTD the simulation is rather poor.

The TEC comparison of plunge tests and LCSR tests is shown in table 5.3.

As with the EPRI tests, the agrement is excellent.

e 36 -

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,.g.

MM Results of t.CSR and plunge Testing done g g g Roseont Model 13 RTOs

[Taken from Tables 3.1 and 3.2 of Reference 11]

Room T eoerature T,. tug, Measured Plunge r InferrM Percent Thermo RTD Plunge t*

from LCSR Tests" Error Well

.Mer (sec)

(see) 60 57161 5.910.2 5.610.3

-5.1 60 57'65 5.9_+0.2 6.010.2

+1. 7 60 A8994 6.810.5 6.710.3

-1.5 60 85642 8.310.7 7. 2_+0. 6

-13.3

$}Q,2,q[SolderT,gg1 Measured Plunge e Inferred p, peg,g ATO Tu., r90 Plunge :*

from LCSR Tests "

Error

.j, ;

, W er (sec)

(sec) i]

57127 5.3+0.2 5.09 2

+1.7 SC 57151 5.09 2 5.39.s 0.0 50 57161 5.0$.2 4.89 3

-4.0 60 57165 6.910.2 6.59 4

-5.8 50 57170 5.49 2 5. 2_+0. 2

-3.7 60 A8994 6.7_+0.2 7.010.4

+4.5 60 B5630 5.610.2 5.89 4

+3.6 60 85642 6.810.2 6.9+0.4

+1.5 66 57161 5.410.2 6.010.2

+11.1 66 57165 5.910.2 5.39 5

-10.2 66 A8994 6.2$.2 7.09 5

+12.9 63 85642 5.93 2 5.79 3

-3.4

• Uncertainty = la based on historical uncertainty in reproducibility of plunge tests.

" Uncertainty a upper and lower bounds of all variables with uncertainty in them. Uncertainttes combined additively. _

e-r

6.0 AMS AND TEC FIELO EXPERIENCE ness name - aus - -

AMS has perfonned LCSR measurements at the following plants:

Millstone Unit 2 ------- Aug 1977, Dec 1978 June 1979, July 1980 AN01 Unit 2 ------------ Nov 1978 North Anna Unit 1 ------ Aug 1979 Farley Unit 1 ---------- Oct 1978, Jan 1980 Farley Unit 2 ---------- May 1980 AMS has sold testing equipment to North Anna, Farley, V.C.Sumer, San Onofre, LOFT, and ORNL. In addition Millstone plans to purchase AMS test equipment in the near future.

TEC has perfonned LCSR measurements at the following plants:

Saint Lucie Unit 1 ----- Jan 1973 May 1978, Cet 1978, Mar 1979 LOFT ------------------- Mar 1979 Sequoya ---------------- May 1979 Zion ------------------- Aug 1979 TEC has sold LCSR testing equipment to Saint Lucie 38 -

9 9

r-l

=

M f.5 E!.EE.2! 2A !.t.!L1 HF!

Most of the reservations we have with in-situ tests have been iterated in other sections of this SE. We are listing them here in order to have a compact list for reference. These are:

(1) Using the Plunge t versus the LCSR r correlation to infer the Plunge :

from a measurement of the LCSR r (Section 3.1).

(2) Using the Plunge r versus SHI correlation to infer the Plunge from a measurement of the SHI (Section 3.2).

(3) Using the NA method for measuring the Plunge t (Section 3.3).

P)[1 + (1 - 1)]2 to estimate the higher (4) Using the expression P

=

9 poles of the transfer function. [This appears on page 29 of the 1977 I?RI Topical Report. It is demonstrited to be a poor scoroximation an page 42 of the same recort.]

(5) On page 46 of the 1978 EPRI Topical Repert it is stated that if only one eigenvalue, :t, can be found, then an upper limit for the Plunge r is 1.4

• 2 This should be 1.47 * :1. whic'. for practical purposes can be rounded to 1.5 *rt.

The first four of these techniques were originally described in the EPRI Topical Reports at a time when they were still in the experimental stage, and there was hope that these techniques would be proved viable. Since then the U of T investigators have conceded that these are not viable techniques. The disclaimers for these techniques appear on page 42 of the 1977 EPRI Topical Report and page 140 of the 1978 EPRI Topical Report.

f g REGULATORY M (1) The LCSR method has been demonstrated to be the only reliable method for measuring, he time response of RTDs in nuclear plants. We should take a position that would favor the universal adoption of the LCSR method in a timely fashion.

(2) The historical plunge test nas been demonstrated to be inadequate for measuring the time response of R70s in nuclear plants. We should cease putting credance in RTD time constants which have been measured by a plunge test.

(3) Both the kMS and TEC LCSR measurement procedures have been demonstrated to consistently predict the plunge r to within 10%. The number of comparisons done to date is inadequate to form a basis for any scphisticated statistical model, and the best procedure to acc:unt for uncertainties would be to simply add 10% to the measured plunge r and use this as the measured upper bound. (in sene cases (e.g. the EDF data on table 5.2) tne errors appear to be composed of a substantial bias plus a randon; fluctuation.

In this case simply adding a 10% uncertainty to the best estimate plunge r isareasonableprocedure.]

(4) While the RTD degradation tests are discussed in some detail both here and in the EPRI Topical Reports, neither AMS nor TEC nor any other vendor /

consultant / utility has submitted a proposal to amploy degradation tests.

Degradation tests should not be permitted as a substitute for LCSR tests until such a proposal has been submitted, reviewed, and approved by us.

Once degradation rosts are approved they may be used by utilities instead of LCSR tests to detect RTD degradation, and then only tnose RTDs which show degradation would need to be tested via the LCSR procedure.

e

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(5) The extensive RTD time response test ng done recently has revealed that the i

RTDs in operating reactors are suffering time response degradation as they Current Technical Specification surveillance schedules pemit such age.

deficiencies in RTDs to go undetected for several years. Consequently the RTD time lags assumed by utilities in their RPS setpoint computation may in some instances be unrealistically short.

In these cases the computed RPS setpoints will be nonconservative, and this situation should be corrected.

Fortunately, the transients against which RTDs provide protection are all rather slow. Assuming a slightly slower RTD time response in the safety analysis would change the RPS setpoints only a very small amount, and would not present severe restrictions on reactor operations.

In order to guarantee that all utilities are using conservative RTD time lags in their safe *y analyses, we recomend that tney" comply 7ith one of theTollowing options:

~

a. Perfom a surveillance test of all their safety channel RTOs at least once every 18 months, and verify nat the time response of the sicwest RTD is at least as fast as that esumed in the safety analysis.

In addition perfom a test of each newly installed RTD at operating conditions as soon as practical after its installation.

If chis option is chosen the Technical Specifications must be modified to match the new surveillance schedule. (As mentioned previously, most current Technical Specifications require that a quarter of the RTDs be tested every 18 months.)

b. Continue with the present RTD surveillance requirements and schedules in the Technical Specifications, but in the safety analysis assume an RTD time constant equal to the greater of:

e

e e,

Iongesttimeconstantmeasuredinlastsurveillancetesi Of

1. 2 *

(including a 10% allowance for measurement uncertainty),

CE ----- Rosemont Model 104 RTD ------ 12 sec.

l W ----- Rosemont Model 176 RTD ---- 0.8 sec.

j B&W ---- Rosemont Model 177 RTD ------ 12 sec.

A few words are in order to explain the rationale for options (a) and (b) above.

The present Technical Specification RTD surveillance schedule was formulated before any evidence of RTD time response degradation appeared, and it was thougnt that an occasional spot check would be adequate to assure that no degradation was taking place. However, with the testing done recently, it nas tecome apoarent that RTD degradation is widespread, and we must take steps to assure that in every instance it oct.ars it is soon detected, and corrs:tive measures taken.

or utilities wnica have procured LCSR test equipment, cotion (a) is decicedly

~

preferable both from NRC's and the utilities point of view. From the NRC point of view the frequent and thorough surveillance testing would assure us that conservative values for RTD lags were being used in the safety analyses.

From the utilities point of view, the accurately measured titne lags of their RTDs, without any extra conservatism factors being added, would be direct inout data to their safety analysis. This would give them the most relaxed RPS setpoints possible, which *;ould add to their operating flexibility.

w In most instances utilities without LCSR equipment remove the RTDs frem their reactors and send them to the Rosemont laboratories for surveillance testing. For these utilities having option (a) imposed upon them in a short time frame would represent a severe and unnecessary hardship. For

~

this reason we are recornending option (b) for those utilities which cannot easily comply with option (a). The time constants of 12 seconds and 0.8 seconds in option (b) are the longest time constants observed to date for the RTDs in question.

It would not be prudent to assume any faster resconse for an RTD which has not been tested in several While we do not anticipate measuring time constants greater than years.

12 seconds and 0.3 seconds, if this should occur, then the longest measured time constant, with an appropriate conservatism factor added should be used as the RTD time constant input into the safety analysis.

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. UM 1.

EPRI NP-459. IN SITU RESPONSE TIME TESTING OF PLATINUM RESISTANCE THERM 0 METERS Karlin, Miller, Mott, Upadhyaya Hashemian, Arendt, January 1977.[Herein called the 1977 EPRI Topical Report]

2.

EPRI NO-834, IN SITU RESPONSE TIME TESTING 0F PLATINUM RESISTANCE THERM 0 METERS, Karlin, Miller Hashemian, Poore, Jely 1978.

[Herein called the 1978 EPRI Topical Report]

3.

EPRI Report (To be Published). TEMPERATURE SENSOR RESPONSE CHARACTERIZATION, Xerlin, Miller. Hashemian, Poore. 5korska, Cormault. Upadhyaya, Jaccuet.

[Herein cassed the 1980 EPRI Report]

'4.

Material extracted from a paper in preparation entitled ACCURACY OF LOOP CURRENT STEP RESPONSE TEST RESULTS T.W.Xerlin April 22,1980 5.

RESPONSE TIME QUALIFICATION OF RESISTANCE THERMCMETERS IN NUCLEAR POWER

~ PLANT SAFETY SYSTEMS, Northeast Utilities Topical Report prepared by 0.'.T.W.Xerlin of Analysis and Measurement _ Services Ccrporation (AMS),

November 1979. [Herein called the AMS Topical Report]

6,-RESPONSE TIME OF PLATINUM RESISTNACE THERMCMETERS USING THE LOOP CURRENT m--

STEP RESPCNSE TECHNIQUE, Mott, Robinson, Jones, Mathis Fisner, Tecnnology for Ener3y Corcoration (TEC), April 1978.

[Herein called the TEC Topical Report]

7.

RTD TIME CONSTANT SURVEILLANCE REPORT, Latter frca Re:ert E. Uhri 3 (?:L) to Robert W. Reid (NRC), Ja:.9sry 3,1979.

8.

RTD TIME CONSTANT SURVEILLANCE REPORT, Letter from Robert E. Uhrig (FPL) to Robert W. Reid (NRC), May 1,1979.

9.

TEC handout at NRC meeting entitled REVIEW OF TEMPERATURE SENSOR RESPONSE

~ TIME USING LOOP CURRCNT STEP RESPONSE TECHNIQUE, Ackermann,& Mott, August 16, 1978.

10. Letter. T.W.Kerlin (AMS) to P.S.Kapo (NRC). April 28, 1980

11. TEC LCSR METHOD TEST RESULTS, Letter from R.E.Uhrig (FPL) to R.W.Reid (NRC),

Cactaber 4, 1979.

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