ML20009B235

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Accepts Util 780425 & 790829 Technical Repts on Two Loop Current Step Response Methods for Determining Resistance Temp Detector Response Time.Encl Safety Evaluation Documenting Methods Will Soon Be Released as NUREG
ML20009B235
Person / Time
Site: Calvert Cliffs  Constellation icon.png
Issue date: 06/30/1981
From: Clark R
Office of Nuclear Reactor Regulation
To: Lundvall A
BALTIMORE GAS & ELECTRIC CO.
References
NUDOCS 8107150128
Download: ML20009B235 (3)
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JUN 3 01981 Q\\M - M -O\\b Docket flos. 50-317 e"

ce and 50-318 g\\,0g\\M.a' t

Mr. A. E. Lundvall, Jr.

{11 Vice President - Supply g.

Baltimore Gas & Electric Company P. O. Box 1475 4

f:,

Baltimore, Itaryland 21203

Dear Mr. Lundvall:

Py letters dated April 25, 1978 end August 29, 1979, Florida Power and Light Company and !!ortheast fluclear Energy Company provided tech resistance tenperature detector (RTO) response time at St. Lucie, Unit No. I These nethods are similar in rest and itillstone, Unit flo. 2. respectively.

respects, but have a few differences which are discussed in the enclosed Based on our review of both reference reports, we Safety Evaluation (SE).

find the LCSR methods to determine RTO time response as described in each report and documented in the SE to be acceptable. We plan to issue the SE as a lluREG in the near future.

Extensive testing has shown the LCSR nethod to be extremely reliable and This compares very provide results with an accuracy of 10% (maximum error). favorabl Since the LCSR nethod offers a significant improvement high as a factor of 3.

in RTD response time testing, we recomend you consider its use at your It tppears to us that use of the LCSR method would also result facili ty.

in a reduction in personnel radiation exposure.

The extensive P.TO time response testing which has been etne in conjunction with the development of the LCSR method has revealed that the RTDs in operating Current Standard reactors suffer time response degradation as they age.

Technical Specifications (STS) require that one quarter of the safety system This corresponds to testing each RTD once RTDs be tested each 18 months.In view of the RTD time response degradation observed in every six years.

our study, it is clear that the present RTD surveillance testing schedule is We request that you nake application for TS changes to require the time response testing of ell safety system R10s within one month of operation not adequate.

This application for newly installed RTD and once every 10 months thereaf ter.

should be made before or as a part of your application for the next core If you plan to use the provisions of 10 CFR 50.59 for the next core reload.

reload, please submit the application for such a change at least 90 days chead 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 exarple) of determining the RT ) response tine.

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.2 If you have any questions on this subject, please contact your assigned NRC project manager.

Sincerely.

Original signed by Robert A. Clark Robert A. Clark, Chief Operating Reactors Branch #3 Division of Licensing Encicsure: As stated cc: See next page DISTRIBUTION:

Docket File PMKreutzer (3)

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9 Baltimore Gas ~and Electric Company cc:

James A. ~ Biddison, Jr.

Ms. Mary Harrison, President General Couns_el.

Calvert County Board of. County Commissioners Balt1more Gas and Electric Company Prince Frederick, MD 20768 P.: 0. Box 1475 Baltimore, MD 21203 U. S. Environmental Protection Agency Region III Office George F. Trowbridge, Esquire Attn:

EIS Coordinator

-Shaw, Pittman,' Potts and Trowbridge Curtis Building (Sixth Floor) 1800 M Street, N. W.-

Sixth and Walnut Streets Washington, D. C.

20036 Philadelphia, PA 19106 Mr. R. C. L. Olson, Principal Engineer Mr. Ralph E. Architzel Nuclear Licensing Analysis Unit Resident Reactor Inspector Baltimore Gas and Electric Company NRC Inspection and Enforcement-Room 922 - G8E Building P. O. Bos 437 P. O. Box 1475 Lusby, MD 20657 Baltimore, MD 21203 Mr. Charlps B. Brinkman Mr. Leon B. Russell Manager - Washington Nuclear Operations Plant Superintendent Combustion Engineering, Inc.

Calvert Cliffs Nucledar Power Plant 4853 Cordell Avenue, Suite A-1 Maryland Routes 2 & 4 Bethesda, MD 20014 Lusby, MD 20657 Mr. J. A. Tiennan, Manager Bechtel Power Corporation Nuclear Power Department Attn: Mr. J. C. Judd Calvert Cliffs Nuclear Power Plant ~

Chief Nuclear Engineer Maryland Routes 2 & 4 15740 Shady Grove Road Lusby, MD 20657 Gaitnersburg, MD' 20760 Director, Criteria and Standards Division i

Combustion Engineering, Inc.

Office of Radiation Programs ( ANR-460)

Attn: Mr. P. W. Kruse, Manager U. S. Environmental Protection Agency Engineering Services Washington, D. C.

20460 P. O. Box 500 Windsor, CT 06095 Mr. W. J. Lippold, Supervisor Nuclear Fuel' Management Public Document Room Baltimore Gas and Electric Company Calvert County Library Calvert Cliffs Nuclear Power Plant Prince Frederick, MD 20678 P. O. Box 1475 Baltimore, Maryland 21203 Director, Department of State Planning 301 West Preston Street Mr. R. E. Denton, General Supervisor Baltimore, MD 21201 Training & Technical Services Calvert Cliffs Nuclear Power Plant Mr. R. M. Douglass, Manager Maryland Routes 2 & 4 Quality Assurance Department Lusby, MD 20657 Fort Smallwood Road Complex -

P. O. Box 1475 Baltimore, MD 21203 Mr. T. L. _ Syndor, General Supervisor Administrator, Power Plant Siting Program

-Operations Ouality Assur ance Energy and Coastal Zone Administrition Calvert Cliffs Nuclear Power Plant Department of htural Resources Maryland Routes 2 & 4 Tawes State Of fice Building Annapolis, MD 21204 Lusby, MD 20657

REVIEW 02 RESISTANCE TEMPERATURE DETECTOR TIME CESPONSE CHARACTERISTICS SAFETY EVALUATION BY U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION DIVISION OF SYSTEMS INTEGRATICN INSTRuMENTATICN AND CONTROL SYSTEMS 3 RANCH NOVEMBER 1980 chcf<-Vf

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" Historically Resistance Temperature Detector (RTD) tine 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 developed two other in-situ methods which detect RTD degradation, but give no detailed inforaation on the RTD time response. These methods are the Self Heating Index (SHI) method and the Noise Analysis (NA) method. We have examineo the LCSR SHI, and NA methodologies and find all three to se viable methods for monitoring RTD time response, but we have not conducted a formal review of the SHI and NA methods. To date two vendor time respon:;e topical reports have been submitted 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.

The extensive RTD testing done in conjunction with the LCSR development has revealed RTD time response degradation with ageing. In view of this degradation we are recommending increased surveillance testing of RTD time response..

cs M

_TABIE Of CONIfNI'S a

SfCIION NUMBER MGE SECTION TITLE 4

. I N T RODUCT I ON, BAC KGROUND. AMD S uletAR Y ------------------------------------------------ 1.0 --------------

RTD TIME RESPONSE CilARACTERIZATION AND MEASUREMENT ------- --------------------------- 2.0 ------~-------- 11 RT D T I ME CONST ANT CONC E PT ---------------------------- ----- ------------------- --- 2.1 ------------- 11 LCSR METHOD FOR MEASURING RID TIME CONSTANT -------------------------------------- 2.2 ------------- 12 L CS R T E S T PROC E DUR E - -- - - ---- -- - - - -- - - - - - - - - - -- -- -- - - -- - - - -- - - - --- - - --- - - -- - 2. 2.1 --- -

THE LCS R TR ANS FORMAT I ON - ----- ----- -- ------------ ------ --- ------------- ------ 2.C. 2 ------------ 12 APPL I CAT I ON OF THE LCSR TRANS FORMAT I ON ---- ----- ----------------------------- 2.2. 3 ------------ 14 DEMONSTRATION OF CONSERVATISM OF THE LCSR TRANSFORMATION --------------------- 2.2.4 ------------ 14 EPRI (AMS) METil00 FOR CORRECTING FOR UNKNOWN tilGilER EIGENVALUES -------------- 2.2.5 ----------

N e

TEC METHOD FOR CORRECTING FOR UNKNOWN HIGiiER EIGENVALUES --------------------- 2.2.6 ------------ 17 RI D DE GR ADAT I ON T E ST S - - ---- - ------ - -- -- -- -- - - - - - - - - - - - - - -- - --- - - - - - - - - -- - --- ----- --- 3. 0 - ---- -- --- - - -- 18 RT D DEGRADATION TESTS USING LCSR METil0D ------------------------------------------ 3.1 -------------- 18 RTD DEGRADATION TESTS USING THE SELr' ilEATING INDEX (Sill ) ------------------------- 3.2 -------------- 22 RID DEGRADAT ION TESTS USING NOI SE ANALYSI S ( NA) -------------------- ------------- 3. 3 -------------- 25 POTENT I AL FOR RTD TIME R ESPONSE DEGRADAT ION ------------------------------------------ 4 5 -------------- 2 7 H0 DES OF RTD TIME RESPONSE DEGRADATION ----------------------------------------- e 4.1 -------------- 27 EVI DENCE OF RT D T IME RESPONS E DEGRADAT I ON ---------------------------------------- 4.2 -------------- 28 4

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1.0 INTRODUCTION

, BACKGROUND. AND

SUMMARY

sus mummmmmmmmmmmmme ammmmmmmmme== = summmmmmen 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, which is called the element. RTDs are used extensively for monito;ing 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 temper 0ture 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 This Safety Evaluation (SE) is a review of the current state of response.

the art of describing and measuring this time response.

Historically the 473 time response has been characterized by a single parameter

~ ~ ' ~

called the plunge time constant, or simply the Plunge :. The plunge : is defined as the time reouf red for the RTO to achieve 63.2% of its final response after a ste tenperature change is impressed on the surface of the RTD. Such a temperature change can be achieved by plunging the RTD into a heat sink, such as water, oil, sand, or molten metal. Whsa : 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 tcst'.;g posed an in-convenience in that the RTD 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 DEGF are difficult to reproduce in the laporatory, and hence all laboratory tests were performed at more benign condittons, and the laboratory results were then extrapolated to service conditions. The combination of manipulating the RTD and extrapolating the.

nrr:

' laboratory results to service conditions lead to significant errors in 'he nTD 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 EPRI launched a research project at the University of Tennessee (U of T) to investigate other possible methods for measuring an

- RTD's time response. Two requirements for any method being developed were:

. (1) that it could be perfomed 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 and 3, which will henceforth be referred to as the 1977, the 1978, and the 1980 EPRI topical reports.

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

1.

Loop Current Step Response (LCSR) Metnod.

In the LCSR Method the resistance element of the RTD is heated by an electric current, and the tanparature transient in the element is recorded.

From this transient the response of the RTD to changes in external temperature is inferred.

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 SH!. The SHI cannot be correlated with the Plunge r, but changes in the RTD 5HI can be used as a means of detecting RTD degradation.

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-3.

Noise Analysis (NA) Method.

In the NA method the srall fluctuations in RTD output under operating conditions are analyzed on line (or recorded for off'line analysis) using spectral density and/or auto regressive techniques. These fluctuations are the RTD response to fluctuations in the external temperature of the RTD.

If the pattern of fluctuations in the external temperature is known, then it is possible to deduce information about the tima response of the RTD. The NA method has been applied to obtain concistent results under optimum reactor conditions.for certain types of sensors; however, currently it has not been established in a statistically dependable manner that the NA method yields results comparable with deterministic methods. Thus, while in principle it should be possible to develop a viable deterministic method for measuring the Plunge t using NA, the realization of thts goat wtil still require a-substantial amount of investigative work. However, at the present state-of-the-art the NA method could be useful for detecting RTD time response degradation.

Charactertstics of these-three in-situ methods and the plunge test method are summarized in tables 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 developed somewhat different method' ologies. The AMS methodology is identical 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 1.1 Characteristics of Methods for Measuring RID Time Cesponse I "*'*55"IY Complex 1ty

]!

hD of Quality of Measurement Test l

easurement 2

of service a

PlungetestmeasuresPlunfeidirectly,butmeasurementhaspoor1) Hanipulating RTD Need to quality for two reasons:

Plunge response and (2) Service conditions are usually not reproduced in the F*""**

a Yes RID and Test lab. Lab results must be extrapolated to service conditions. (he s P to combined ef fect of these two factors can result in errors up to a 3

factor of 3.

Test simple.

LCSR provides an indirect measure of 3.

b Yes Special test N

LCSR Test egu ent Results are generally accurate to within 101.

g g

Test simple

  • Sill can be measured quite accurately.

Uses simple

=

s an ard from changes in the Sill, RID degrade. ton can be detected.

et Yes electronic

.5 test No good correlation between Plunge i and Sill exists.

equipment.

A good deal of sophisticated work has gone into NA. However, NA Test simple.

measurements of Plunge i conducted to date have been in error by up

=

to a factor of S.

A ntsaber of investigaf. ors are still endeavoring to NA SPecial develop a viable method for measuring the Plunge i using NA, and it is yo Test

'?

test hoped that future work will lead to much improved agreement between 3

e t

theory and experiment.

NA is still o useful tool for detecting RID degradation.

Table 1.?

Practical Aspects and Avollihility of RID Tfuie Rewnr.se Testing Methods Uttitty of N S[E AMS TEC 7,3g g

Test Procedure Provides Provides Provide Test for RTO Yes Yes None Degradation l

Plunge Test f

Measure Poor -- Errors to Service only Plunge x a factor of 3 (Lab Tests)

Yes Yes I

OK -- llowever if the utility buys equipnent for Equipment Equipment Test for RID degradation test they aluht and Training and Training egradation as well buy equipnent for LCSR Test measuring Plunge 1.

Service r Service or Measure Good Equipment Equipment Plunge 1 10% Accuracy and Training and Training Test for RTD Good -- No special test Training Training Degradation equipment needed.

3gg Test Heasure Poor -- No good Plunge i correlation with t exists.

Equipment Equipment Test for RTD Need Special e t Equipment.

Degradation /

RID need not be Tra n ng Tra n nq-f taken out of service.

Initial attempts to measure Plunge r produced j

NA Poor results with errors up to a factor of S.

Test 9"

Measure Over a period of 2 years a limited number of Plunge T careful NA measurements have produced results Training with 110% variation. No systematic correlation of these results with deterministic measurements has beensiiade.

8.

- g 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 NRC 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 electronic 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 SHI 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.

The current Standard Technical Specifications require that one quarttr of the safety channel RTDs be tested once every 18 months. The data on RTD degradation collected to date is rather scant, but does ap;*ar 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. Perform a surveillance test of all their safety channel RTDs at least once every 18 months, and verify that the time response of the slowest RTD is at least as fast as that assumed in the safety analysis.

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

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:

I'ongest time constant measured 'in last surveillance tesi 0"

1.2 *

[ including a 10% allowance for measurement uncertainty)_

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

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

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

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

o ggTg g CHARACTERIZtTION g MEASUREMENT 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 N

T(external)

(1 + ts)

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 temperature has reached 100%/c = 63.2% of its final response. For this reason the time required for the RTD output to attain 63.2% of its final response has been named the RTD plunge time constant.

In fact. RTJs 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 bet aen the Plunge r and the RDT is discussed, and it is shown that the Plunge r is always equal to or longer than the RDT, the saximum difference being about 2%. Thus the Plunge r can.

e

t.

be used as a conservative measure of the RDT. and in practice all Technical Specifications are written in terms of the Plunge t and hence all measurement techniques are directed toward evaluating the Plonge.r.

2.2 LCSR METHOD FOR MASURING LTD TIME CONSTANT 2.2.1 LCSR TEST PROCEDURE _

In the LC3R method a constant current is impressed on the RTD sensing element which heats the element and the whole of the RTD expedences a temperature transient. A time plot of eithar the heating of the element wnfle the current is impressed or tne cooling after the current is discontinued is recorded.

From this plot the RTD plunge time constant is inferred by means of the LCSR cransfor-nation, ahi;n is described in the next section.

The element temperature is inferred from its electrical resistance whicn 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 THE LCSR TRANSFORMATION The mathematical theory for analyzing heat transfer in an RTD is developed in the subject references. Two dif*erent approaches are described in detail:

(1) a nodal approach and (2) a continuum approach. In the 1980 EPRI Topical Report, paga 3-34 and Appendix 3, numerical 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..

It is shown that if:

(1) The RTD has cylindrical symetry and (2) There is neglegible heat capacity inside the sensing element then the transfer function which describes the RTD's response to an external temperature change is (AMS Tootcal page 23) 1 T(element)

(2.1)

T(external)

(its + 1)(T2s + 1)(:3s + 1 )..... (:n'

  • I )

n is finite if the nodal approach is used and infinite if the continuum approach is used. This difference is not significant in that the higher order factors contribute little to the solution.

The important feature of the above equation is that the transfer function contains poles, but no zeroes. As will soon become evident, this fact permits the inference of an RTD's response to an external tamperature change from the results of an LCSR :*ansient.

It is shown that the plunge time constant is given by (AMS Topical page 27) 3 t) - In(1 - :S/ t )..... J.

t[1 - In(1 - ::/T1) - In(1 -

/

(2.2) e

=

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

Ea exp(-t/:,)

(2.3)

T(element) - T,

=

n n

n (also defined in page 49 of the 1978 EPRI Topical) are functions of where the a the poles and zeroes of the transfer function..

Experimentally, the i can be detemined by breaking the temperature response n

into a series.of exponentials. Once the i are detamined they can be n

plugged into equation 2.2 to determine 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 APPLICATION OF THE 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 into a series of exponentials according to equation (2.3). This gives numerical values for the r9 (It is not necessary to evaluae the a ]

9 into equation (2.2) to obtain the Plunge :.

(3) Plug these values of t9 In practice step 2 is cerfomed either by -ax::enential stripping or a 13ast squares fit. Using either method it is usually possible to find ti and ::.

In exceptionally good cases it is possible to find it. T2 and :3. and in bad cases it is possible to only find rt.

If equation (2.2) is truncatec after the T2/T term the result can be nonconservative by as much as 20%, and if 1

equation (2.2) is truncated to r = tt the result can be nonconservative 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.

2.2.4 DEMONSTRATION OF CONSERVATISM OF THE LCSR TRANSFORMATION In reference 4 it is shown that if either the assumption of cylindrical synnetry is violated (say by a crack in the RTD) of the assumption of having no heat capacity within the element is violated then the transfer function i

(equation 2.1) would have zeroes as well as poles.

If this were the case.

j.

i then the Plunge r expression (equatica 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 (3) METHOD FOR CORRECTING FOR UNKNOWN HIGHER EIGENVALUES Af ter 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(:2/T1)

  • Ti(i - In(1 - T2 T1)3 =

/

(2.4)

Plunge t

=

where f(:2/T1) is given by the emperical relationship of figure 2.1.

Ff gure 2.1 was constructed by.nathematically computing the Plunge r (equation 2.2) and 2 :1)] for a number of different hypothetical RT3s and plotting rt(1 - In(1 - : /

the ratio of the two. The hypothetical RTDs had a variety of sized and geometries, which included both hollow core and central 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(t /T1) is, on the surface, rather amazing. With such a good correlation, 2

one would naturally be inclined to search for an underlying physical reason for all RTDs to display the same f(r2/T1). However, to date this underlying physical relationship has eluded us.

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.200 Figure 2.1 Plot of correction factor [f(2 /ti)] vs pole ratio [t /t i].

2 2

[ Reproduced frois Figure 5.3 of the 1980 EPRI Toph.a1 Report]

l 2/i t- This function is used in equation 2.4: (Plunge i) = f(t;/ g)*tg[1 - In(1 4 i I

2.2.6 TEC METHOD FOR CORRECTING FOR UNKNOWN HIGHER EIGHEVALUES The method used by TEC is the following: (1) Assume a continuum model for the RTD wt.ich geometrically consists of a the mowel1 (pipe which houses the RTD) and air gap, a steel sheath, a ceramic layer. a platinum element, and a ceramic cere. (2) Assume realistic values for the themal properties of the thermowell and the RTD steel sheath. (the element it w small that it can be ignored in the themal calculation) (3) The thermal resistance the film between the thermowell and water and [ that of the air gap between the thermowell and the sheath are not well known. These two thermal resistances are combined into a single resistance R(film + gap) wnich is left unknown. The thermal resistance of the ceramic R(ceramic) is also l' eft unknown. (a) The RTD continuum equations are solved for :t and :2 using various values of R(film + gap) and R(ceramic). This procedure is iterated until the values derived for :t and :, match those measured experimentally. (5) The now known values of R(film + gap) and R(ceramic) are used in the RTD continuum equation and the Plunge : is computed. 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 i accurate results, and thus frem a regulatory point of view must be cent sdered equally good. I 1 1..

3.0 RTO DEGRADATION TESTS suun _

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

3.1 RTD DEGRADATION TESTS USING LCSR METHOD For this test A simple application of the LCSR method is a degradation test. an LCSR transient is impressed on the RTD and the time required for the RTD to achieve 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 investigators attempted to correlate the Plunge : with the LCSR :. In making this correlation the time response of the RTO was varied by adding tape or rucoer insulation around the RTO and measuring both the ? lunge : and the LCSR :. Two such correlations are shown 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 RTO degrades, it is most likely due to increases in the thermal resistance of the RTD internals or the RTD-thermowell gap. Therefore one would expect to find a different correlation for normel degradation than that determined by adding insulation to the surface of the RTD. For this reason we do not, at present, consider the ccrrelations of figures 3.1 and 3.2 to be sufficiently well substantiated to be used in the determination of the Plurge :. i l l l I

While not providing an accurate means of computing the Plungo 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 approximcte increase in the Plunge t can be detenmined. If the Plunge e determined in this way is near the value asstmed in the safety analysis, this would indicate that it is necessr - to measure the Plunge 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 as described the degradation test equipment can be used to measure the Plunge : in section 2.2.1. l l l

s 1 l l 24-. 22-. 20 18 < - 16..] ? 14 12 t .e IO' Emperical Correlation c Curve S x, 5- / .c Emperical Data 2< - LCSR v (sec) 0 1 2 3 4 5 Figure 12 Emperical Carrelatien Curve for Plunge versus LCSR : f (Combusti2II. Enoineerino E g Rosanont g Fodel 104AFC. [ Reproduced from Figure 6.4 of the 1978 EPRI Topical Report] 20 - p. = ^

  • e 3.0 - -

f' 2.5 - a 'G 3 2.0 --l B 5 E a 1.5 - = J.=0erical..Carrelation Carya 1.0 - 4= 6::erical Ca:a / 0.5 LCSR t (sec) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 F1gure 3.2 Emoerical Correlation Curve for Plunge r versus LCSR r for Rosemont RTD Model 176KF. (Westinghouse RTD) [ Reproduced from Figure 6.5 of the 1918 EPRI Topical Report] f l - 2? - l

3;[ RTD DEGRADATION TESTS USING THE SELF HEATING INDEX (SHI) In the SHI test, a constant current is impressed through the RTD element ard 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 eleiment versus increase ir element resistance. Emperically this has always been found to be a straight line. and the slope of this ifne (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 : reasurement, the RTO time response was varied ey seding insulation to the surface of the RTD, and plots of Plunge r versus b SHI were constructed. T.vo such plo s are shown in firirts 3.3 and 3.4 These entrelations suffer tne same preolem as tne ? lunge : versus the LC3R : correlations, and thur we do not, at present, accept them as viable means for computing the Plungn T. However, like the Plunge r versus LCSR r correlation, the Plunge r versus SHI correlations would be useful in a degradation test. i

gg.> a. 20 < G is - ,] O 1s - 14 3 .3 E.mperical 12 c Correlation Curve in I Sperical Ca:a 8 pc s< 4 Extrapolated to Zero SHI (ohms / watt) o 3 s 7 5 I Fiqure M Empirical Correlation Curve f3 Plunge ; versus SHI g Rose ont 3 Model 10AAFC. (Combustion Encineerino B) [ Reproduced from Figure 6.7 of the 1978 EPRI Topical Report].

e .O l

3. 0- -
2. 5- -

Emoericai Data -+ o g ~

2. 0-e T

Y a 1 "5 - Emperical / Correlation 1 / Curve 0 1.0 / / 0.5 s/ SHI (ohms / watt) 0.C l 5-6 7 8 9 10 Figure M Emoerical_ Correlation Curve for Plunge e versus SHI for Rosemont RTD Model 176KF. (Westinghouse RTD)_ j (Reproduced from Figure 6.8 of the 1978 EPRI Topical Report] l l --e r g w-g-w

3.3 RTD DEGRADATION TESTS USins NOISE ANALYSIS (NA) NA tests are perfomed by carrying out statistical (spectral, correlation, zero crossing rate and/or auto regressive) analysis of nomal fluctuations of the RTD output signal during nomal steady state reactor operation. These fluctuations are the RTD's response to the fluctuations 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 methods. In the ap';11 cation of the NA method, assumptions must be made regarding the statistical properties of the coolant temperature fluctuations. If some minimum set of assumptions, such as stationarity and repeatability are met, the NA method is a talid degradation method since any change in the output fluctuations can be directly attributed to the RTD itse1f. If, in addition to stationarity and repeatability. the coolant temperature fluctuations are wnita" (having fluctuations whose ? curter representation displays constant energy per unit band width at every frequency in the range of interest). NA can be used to determine a Plunge t. The initial theoretical work in hA done by EPRI was directed toward developing a deterministic method for measuring the Plunge v. and this work produced some very sophisticated physical and mathematical developments. However, when the theory was applied to experiment. It was found that NA predictions of the Plunge r were seriously in error, sometimes by as much as a factor of 5. The EPRI researchers concluded that their principal problem was that the reactor coolant fluctuations were not white, as they has assumed. Having no other reasonable i rodel for reactor coolant fluctuations, EPRI has, at least for the time teing, abandoned efforts to perfom a deteministic measurement of the Plt le r using NA. 25 I I r

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 1,10% variation. However, it has been established that coolant temperature fluctuations do not meet the requirements for a Plunge i detennination under all reactor condt:.ons for all sensors. To date TEC has not succeeded in developing a systematic correlation between the measured statistical parameters and deterministic measurements of the Plunge r, bu: there are reasons to believe that such a correlation can be derived for certain senscrs under certain verifiable reactor conditions. As was just stated, the ccnditions for the cooTint temperature fluctuations for - an RTD degradation test are less restrictive than those for a deterministic Plunge r measurement. It has been established that the measured statistical

arameters which can be extracted from NA of RTDs under verifiable reactor conditions are highly reproducable and changes in these parameters can be used to infer changes in the RTD Plunge t.

Therefore NA methods can be used for RTD degradation measurements subject to the statistical accuracy of the measurement. l l.

g g g g g RESPONSE g 4.1 MODES OF RTD TIME RESPONSE DEGRADATION 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 modes 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 ine'sase the thermal conductivity between the thermowell and the RTD. Most of the deterioration in the PBX and NEVER-SEEZ is due to hign 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 frecuent tasting of the newer RTDs and less freqJent testing 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 insbletor in the RTD. While these are plausable modes of degradation, there 1 1 is ao evidence that either of these mechanisms is active in the observed time response degradations. l e

4.2 EVIDENCE OF RTO TIME RESPONSE DEGRADATION Records of measured RTD 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 most of the other data does not i show this consistent trend. A prudent ragulatory position for the present ) would be to increase the required surveillance at all plants until enough \\ data is collected to detemine if a consistent trend in RTO degradation does i exist. l l f l i

'1 l Table 4.1 Comparf son of In-Plant t.CSR g g Time Response Tests Conducted g g [Taken from Table 11.1 of the AMS Topical Report and Reference 4 3 Time Response Test Results & Rosamont Modal 104 RTDs al Millstone Unit J, For the Millstone tests. judging from either the Plunge i or the SHI test, almost all detsctors degraded and a few remained unaffer*ed by service. None improved. August Decanber August December 1977 1978 1977 1978 RTD Plunge t* Plunge

  • SHI SHI (sec)

(sec) (ohms / watt) (ohms /aatt) Number A7770 3.2 5.2 5.6 7.4 A7765 2.3 3.2 4.5 4.8 75313 4.7 5.6 5.2 6.5 A7774 3.8 4.3 5.3 6.2 75294 3.7 4.4 5.0 5.4 75299 5.5 ?.3 3.5 9.1 75310 4.5 4.9 5.2 5.5 75300 4.6 4.7 5.5 6.5 75297 3.6 3.6 4.7 4.9 80364 4.0 4.4 5.6 6.1 75309 4.0 4.7 5.5 5.8 A7769 3.1 3.6 4.8 5.0 l l ,7,1,mg Response T.253. Results for Rosemont Model 176 RTDs g Farley Unit 1 In these tests there was no evidence of time response degradation. October January October January i 1978-1980 1978 1980 RTO Plunge r PTunge r SHI SHI 1 (sec) (sec) (ohms / watt) (ohms / watt) Number 4123 0.10 0.11 7.5 7.4 412c 0.12 0.12 5.3 5.7

  • Since the correction factor had not been developed at the time of'the August

- 1977 measurements..all time constants shown here are uncorrected values.. m e

Table 4.2 Comoarison oh In-Plant LCSR Time Response Test Results Conducted jlf.3 on Rosimont Model 1g4 RTDs g Saint jgLgig Unit,1 [Taken from References 7 and 8] In these tests there is no evidence of time response degradation. January May October 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-lll 2HA 6.2 1 0.5 4.4 1 0.3 4.4 + 0.2 4.5 1 0.3 TE-1122CA 5.5 1 0.2 5.7 1 0.3 6.0 1 0.6 6.0 1 0.7 TE-1122HA 5.0 1 0.5 5.6 1 0.3 5.3 1 0.5 5.7 + 0.7/-0.5 5.0 1 0.5 4.8 + 0.6/-0.4 TE-1112C3 5.0 1 0.9 5.3 1 0.6 TE-lll2HB 5.9 + 0.3 5.4 + 3.2 TE-1122C8 5.3 1 0.3 5.5 1 0.4 TE-ll22HB

7--

4.5 1 0.7 4.3 + 0.8/-0.5 TE-lll2CC 5.4 1 0.4 5.4 + 0.7/-0.5 TE-lll2HC 5.4 1 0.3 5.7 1 0.5 TE-1122CC 5.4 1 0.4 5.0 + 0.7/-0.5 TE-1122HC 4.8 +; 0.3 4.9 1 0.5 TE-1112CD 4.9 1 0.5 5.7 + 1.0/-0.7 TE-1112HD 5.7 1 0.5 5.6 + 0.9/-0.7 TE-1122CD 4.3 j; 0.5 4.8 + 1.6/-0.9 TE-1122MD m w

MENNM E E M PARAMETERS THAT AFFECT 3TJ,T]g, RESPONSE The time response is not only a function of the RTD itself, but depends as well on the properties of the thermowell and the themal characteristics of the madium in which the thermowell or RTD is imersed. The themal properties of all these components change with temperature and the heat transfer prJperties of the medium (water) change with flow velocity. The match between the RTD and the themowell affects the time response, and even the slight change in match that occurs when an RTD is removed from a thermowell and placed back in the same well can significantly change the time response. Thus it is important to simulate-stryice undttions 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 DEGF are difficult to reproduce in the laboratory. For this reason, in the past most laboratory tests were performed 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 four:d that the historical plunge test procedure often produced results which were grossly l in error, sometimes by as much as a factor of 3. l

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. was soon demonstrated to be unsatisfactory. The reason is that the heat conduction properties of of f and sand are so different from water that a test in oil or sand gives no indication of what would happen in water. In nwnerical terms, the thermal match between the medium and the RTD is given by a quantity called the Biot modulus, which is defined as the ratio of the (f1m thermal conductance to the internal conductance of the RTD [More specifically, Biot modulus = hR/k, where h is the film coefficient, R is the RTD radius, and k is the thermal conductivity of the RTD]. When the Sfot modulus is less than about d.1 the thermal resistance is dominated by the film resistance, and wnen it is greater than about 10 the thermal resistance is dominated by the RTD internal resistance. The response of an RTO in one heat transfer regime indicates very little about how the RTD will respond in a different heat transfer regime. Values for the Biot modulus for several cases are given in table 5.1. i.

MM Variation g h Modulus h1q m Of fferent @ Coefficients Associated with Different Testing Conditions [Taken from Reference 93 4' Rosemont Rosemont RTD 104 176 Testing (Combustion (Westinghouse) Conditions Engineering) Reactor Service 300 3.8 Conditions 3 fthec 27 0.34 180 DEGF Water 1 ft/sec 115 1.2 500 DEGF Solder u2 = 500 CEGF 011 0.8 0.02 a $f 500 DEGF Sand 0.4 0.01 x 5 Internal No available resistance laboratory test dominates for both condition water and solder simulates service Consents tests. Good conditions well. service condition simulation is possible in laboratory tests. i l g i

ROOM TEMPERATURE M g TIME RESPONSE TESTING CONDITIONS USED IN PRACTICE: LABORATORY CONDITIONS While room temperature tests do not indicate much about the RTD's behavior at service conditi6ns, room temperature tests are a good way to compare various measurement methodologies. The main testing criteria for comparing methodologies 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 conditions. 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 seemed worthwhile to test the LCSR method versus the plunge method at simulated service conditions. The next two sections describe how this was ac:omplished. 5.3 RTO TIME RESPONSE TESTING CONDITIONS USjp p1 PRACTICE: 1E11 SERVICE CONDITION T_]l,S_TJ [FJE TIE}] S In order to test the LCSR method at service conditions, the U of T investigators in conjunction with Electricita de France (EDF), perfonned 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 simuldting a plunge test. The results of this test are shown in table 5.2. It can be seen that l the agreemant between the LCSR test and the plunge test is excellent..

Table 5.2 Results of LCSR and Plunge Testing done bl the V of T (Taken from Table 10.1 of 1978 EPRI Report and Tables 7-1 17-3 of 1980 EPRI Report] Room Teperature Tests aj U o,f1Themometry Laborattry Measured Plunge r Inferred from LCSR RM Plunge r Without Higher With Higher Error Model (sec) Mode correction Mode Correction Rosamont 176KF 0.38 0.39 0.41 +7.9 Rosamont 104ADA 3.1 2.9 3.1 0.0 (without thermowell) Rosraont 104ADA 7.1 5.9 7.2 +1.4 (with thermowell) Rosemont 104VC 2.3 1.7 2.1 -8.7 (without thermowell) Rosemont 104VC 5.3 4.5 5.5 +3.8 (with thermowell) Rosemont 177GY 5.8 5.1 6.2 +6.9 Rosemont 177GY 5.1 5.2 5.3 +3.3 Sost: nan 8606 7.0 1.7 2.1 +5.0 5.2 -1. 9 Rosemont 104AFC 5.3 (air in well) 3.9 0.0 Rosemont 104AFC 3.9 (NEVER-SEEZ in well) 12.3 +5.1 Rosemont 177HW 11.7 0.41 -2.4 Rosamont 176KF 0.42 Service Condition Tests al gF Test loop Measured Plunge t Inferred RTD Plunge e from LCSR Test Percent Model (sec) (sec) Error Rosamont 104AFC 6.2 5.9 -4.8 (Air in well) Rosamont 104AFC 4.1 3.7 -9.8 (NEVER-SEEI in well) Rosamont 177HW 8.8 8.4 -4.5 Rosamont 176KF 0.14 0.13 -7.1

  • eD.

Id 379 EE RESPONSE TESTING CONDITIONS USED Il PRACTTCE: T_[C, SERVICE CONDITION R E}, ((Qg(( Tig)) TEC has gotten arouno the problem of gett*ng service condition temperatures by using molten solder, rather than pressurizW water, as was done in the EPRI-EDF tests. As can be seen in table 5.1, for the Rosanont TC4..T0 the mosten solder provides a very good simulation of service conditions. For the Rosemont 176 RTD the simulation is rather poor. The TEC ccmparison of plunge tests and LCSR tests is shown in table 5.3. As with the EPRI tests, the agreement is excellent. J 6 l 1 36 - e w.

Table M Results of LCSR and Plunge Testing done by TEC on Rossnont Model 104 RTOs (Taken from Tables 3.1 and 3.2 of Reference 11] h Temperature Tests Measurd Pl uge r Infe d Percent Themo RTD Plunge t* fr m LCSR Tests" Error g,;j .tumber (sec) (sec) 60 57161 5.910.2 5.610.3 -5.1 60 57165 5.910.2 6.010.3 +1.7 60 A8994 6.810.5 6.73 3 -1.5 60 B5642 8.310.7 7.29 6 -13.3 ,5 fag,DEGF Solder M Measured Plunge r Inferred Percent Themo RTO Plunge " from LCSR Tests" Erior .g,;) gg,7 (sec) (sec) 60 57147 5.910.2 6.010.4 +1. 7 50 57151 6.09 2 6.0$.4 0.0 60 57161 5.010.2 4.810.3 -4.0 60 57165 6.910.2 6.510.4 -5.8 60 57170 5.410.2 5.29 2 -3.7 l l 60 A8994 6.710.2 7.010.4 +4.5 I 60 B5630 5.610.2 5.810.4 +3.6 l l 60 S5642 6.89 2 6.910.4 +1.E 66 57161 5.410.2 6.010.2 +11.1 66 57165 S.9 10.2 5.310.5 -10.2 66 A8994 6.29 2 7.010.5 +12.9 66 B5642 5.910.2 5.7$.3 -3.4

  • Uncertainty = la based on histrerical uncertainty in reproducibility of plunge tssts.
    • Uncertainty = upper and lower bounds of all variables with uncertainty in them. Uncertainties combined additively. _

i 6.0 AMS Attu TEC FIELD EXPERIENCE

=== su s u ma = = saamma a mmmm m mmmes 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 i979 Farley Unit 1 ---------- Oct 1978, Jan 1980 Farley Unit 2 --------- May 1980 AMS has sold testing equipment to North Anna, Farley, V.C.Sunner, San Cnofre, LCFT, and ORNL. In addition Millstone plans to purchase AMS test equipment in the near future. TEC has cer'ormed LCSR measurements at the following plants: Saint L;cie " nit 1 ----- Jan 1973,."ay 1978, Oct 1978,. var 1979 LO FT ------------------- Ma r 1979 Sequoya ---------------- b;ay 197 9 Zion ------------------- Aug 1979 TEC has sold LCSR testing equipment to Saint Lucie.

q N EMEME Most of the reser$ations 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 r versus the LCSR r correlation to infer the Plunge i from a measurement of the LCSR r (Section 3.1). (2) Using the Plunge r versus SHI correlation to infer the Plunge r fran a i measurement of the SHI (3ection 3.2). (3) Using the NA method for measaring the Plunge r (Section 3.3). 4 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 EPRI Topical Report. It is demonstrated to be a poor approximation on page 42 of the same report.] (5) On page 46 of the 1978 EPRI Topical Report it is stated that if only one eigenvalue, rt, can be found, then an upper ifmit for the Plunge r is 1.4

  • tt. This should be 1.47
  • tt, which for practical purposes can be rounded to 1.5
  • tt.

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 l 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 I Report and page 140 of the 1978 EPRI Topical Report..

e D g REGULATORY g (1) The LCSR method has been demonstrated to be the only reliable method for measuring the 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 has been demonstrated to be inadequate for measuring the time response of RTDs in nuclear plaats. We should cease putting credance in RTD time constants which have been measured by a plunge test. (3) doth tite AMS and TEC LCSR measurement procedures have been demonstrated to consistently predict the Plunge r to within 10t. The number of ccmparisons done to date is inadequate to form a basis for any sophisticated statistical model, and the best procedure to account for uncertainties wulo be to simply add 10t to the measured Plunge ; and use this as the measured upper bound. [in some cases (e.g. the EDF data on table 5.2) the errors appear to be composed of a substantial bias plus a random fluctuation. In this case simply adding a 10% uncertainty to the best estimate Plunge r is a reasonable procedure.] (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 employ degradation tests. Degradation tests should*not be permitteo as a substitute for LCSR tests until such a proposal has been submitted, reviewed, and approved by us. Once degradation tasts are approved they may be used by utilities instead of LCSR tests to detect RTD degradation, and then only those RTDs which show degradation would need to be tested via the LCSR procedure.._ a --n-,. -yw-_-,-

O (S) The extensive RTD time response testing done recently has revealed that the RTDs in operating reactors are suffering time response degradation as they Current Technical Specification surveillance schedules permit such age. deficiencies in RTDs to go undetected fue several years. Consequently the i RTD time lags assumed by utilities in their RPS setpoint computation may in some instances be unrealistically short. In these cases the coaputed 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 *.ime lags in their safety analyses", we recomend that they" comply withTne ofTheTollosiiig options:

a. Perform a surveilltace test of all their safety channel RTDs at least once every 16 months, and verify that the time response of the slowest RTD is at least as fast as that assumed in the safety analysis.

In addition perform a test of each newly installed RTD at operating conditions as.soon as practical after its installation. If this 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:

41 - i e l -e e

l ? l I'ongest time constant measured in last surveillance test C" 1.2 * (including a 10% allowance for measurement uncertainty); ~ i CE ----- Rosemont Model 104 RTD ------ 12 sec. M ------ Rosemont McJet 176 RTD ----- 0.8 sec. l 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 thought that an occasional spot check would be adequate to assure that no degracation was taking place. However, with the testing done recently, it has become apparent that RTD degradation is widespread, and we must take steps to assure that in every instance it occurs it is soon detected, and corrective measures taken. For utilities which have procured LC5R test equipment, option (a) is decidedly 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 time lags of their RTDs. without any extra conservatism factors being added, would be direct input data ta their safety analysis. This would give them the most relaxed RPS setpoints possible, which would add to their operating flexibility.. w w T

In most instances utilities without LCSR equipment remove the RTDs from 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 reconnending 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 response for an RTD which has not been tested in several While we do not anticipate measuring time constants greater than years. 12 seconds and 0.8 seconds, if this should occur, then the longest sesured time constant, with an appropriate conservatism factor added snould be used as the RTD time constant input into the safety analysis..

,s.. ggg REFERENCES _ 1. EPRI NP-459. IN SITU RESPONSE TIME TESTING OF PLATINUM RESISTANCE THERMOMETERS, Karlin, Miller, Mott, Upadhyaya. Hashemian, Arendt, January 1977.[Herein called the 1977 EPRI Topical Report] 2. EPRI NO-834, IN SITU RESPONSE TIME TESTING OF PLATINUM RESISTANCE THERMOMETERS, Xerlin, Miller Hashemian, Poore, July 1978. [Herein called the 1978 EPRI Topical Report] 3. EPRI Report (To be Published), TEMPERATURE SENSOR RESPONSE CHARACTERIZATION, Karlin, Miller. Hashemian, Poore, Skorska, Cormault, Upadhyaya, Jacquet. [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. Karlin, '1ril 22,1980 5. RESPONSE TIME QUALIFICATION OF RESISTANCE THERMGMETERS IN NUCLEAR POWER PLANT SAFETY SYSTEMS, Northeast Utilities Topical Report prepared by Dr.T.W.Xerlin of Analysis and Measurement Services Corporation (AMS), November 1979. [Herein called the AMS Topical Report] Sv-RESPONSE TIME OF PLATINUM RESISTNACE THERMOMETERS USING THE LOOP CURRENT STEP RESPONSE TECHNIQUE, Mott, Robinson, Jones, Mathis, Fisher, Technology for Energy Corporation (TEC) April 1978. [HereincalledtheTECTcpica? Report] 7. RTD (IME CONSTANT SURVEILLANCE REPORT, Latter from Robert E. Uhrig (FPL) to Robert W. Reid (NRC), January 3,1979. 8. RTD TIMi 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 CURRENT STEP RESPONSE TECHNIQUE, Ackermann,& Mott, August 16, 1978.

10. Letter. T.W. Karlin (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),

l December 4,1979. l ' o w --}}

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