ML20024G399
| ML20024G399 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 03/20/1978 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | |
| References | |
| A00L-780320-01, AL-780320-1, NUDOCS 9102110426 | |
| Download: ML20024G399 (21) | |
Text
{{#Wiki_filter:- _ _ _ _ _ _ _ _ _ _ . ___ 4 MSP NORTHERN STATES POWER COMPANY MIN N E A PO U S. MIN N E S OTA 55401 i .
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g\& March 20, 1978 r
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b Director of Nuclear Reactor Regulation si ' I' 22 U S Nuclear Regulatory Connission ci ~me- - Washington, DC 20555 ' uu. MONTICELLO NUCLEAR GENERATING PLANT Dochet No. 50-263 License No. DPR-22 Supplement No. 1 to License Amendment Request Dated September 2,1977 Un September 2, 1977, Northern Sta tes Power Company submitted a License Anen 6cn t Requert fcr the Monticelle Nuclear Generating Plant. His Request contained proposed changes to the Technical Specifications to cemit containment integrated leak rate tests to be teminated in less than 24 hours. The proposed test duration would be at least eight hours, be long enough to accumulate at least 20 sets of data at approximately equal time intervals, and have a duration long enough to accumulate and analyze enough data to verify that the measured leakage rate, at the 957. confidence level, it less than the test acceptance criterion. On November 2, 1977, the NRC Staff telecopied to us a Request for Additional In fo rma tion. This request consisted of 11 questions concerning our integrated leak rate test procedures at Monticello and our proposed test ccepletien criteria. The purpose of this supplement to our License Amend-ment Request is to provide ansvers to the Staff's questions. These answers are contained in Enclosure (1). Ue ask that you complete review of our September 2, 1977 License Amendment Request and issue the necessary Technical Specification changes ne later than October 1, 1978. This will permit us to incorporate the new test completion criteria in the integrated leak rate test scheduli.d for the autumn 1978 refueline outage. Please contact us if you have any additional questions on this matter or if we car assist in expediting its review.
, .h L 0 Mayer, FL Manager of Nuclear Support Se rvi ces 9102110426 780320 LCli/Dmi/deh DR ADOCK 050 3 g g
cc: J G Keppler p G Charncff / v aar . ,c - ittachme
. . _ _ . . _ . _ _ . _ _ . _ . _ _ _ . . . _ _ - _ _ _ . _ _ _ . _ . . _ _ . . . _ - __m - .. . _ _ _ __ __
1 l Enclosure (1) Letter dated March 20, 1978, L 0 Mayer, NSP, to Director, NRR, USNRC RESPONSE TO NOVDIBER 2,1977 REQUEST FOR ADDITIONAL INF01EATION MONTICELLO NUCLEAR GENERATING STATION CONTAINMENT LEAK TEST DURATION
- 1. Identify the computation procedures used to calculate the contain-ment leakage rate and the upper 95'/. confidence limit for the purpose of determining the acceptability of a specific contairnent integrated leakage rate test (CILRT).
l Response 1 1 1 The mass plot method is used. Containment mass, k'i, is computed l using the reference vessel method at approximately equal time J intervals. I or .the: first data point:
=
W1. 144 (P1 - l'y ,1 ) V - (1-1) R11 l'- for subsequent data points: ' Ut = W i.1 (1 - L i) (1-2) Where i . . L; = ( A Pi .1 - Py ,t.1) - (Tg .1/Tt ) (api - Py ,t) (1-3) (Pi .7 Pv,1,3)-
=
Leakage air mass as fraction of total contained air mass W= Weight of air in the containment V= free air volume of containment
- R= Gas constant for air P= Containment absolute pressure 6P - Reference-Chanber to containment differential pressure i
P= Containment weighted average vapor pressure [. T= Containment weighted average absolute tempe ra tu re l-i= 1 th data point, i = 1, 2, ..., n L
J l i The Icakage rate is determined from the above calculations of I the mass of air (Wi ) at each time point i by applying a linear regression analysis to the data. A linear regression analysis consists of minimizing the squares of the deviations of the data points from a straight line: , W = At + B (1-4) The slope (A) and the intercept (B) of the line are calculated l as follows (all summations are from i a 1 to n). l A = [tWii - ([ti[W)/n i (1-5) l [t,2 - ([tt)2 /n B = {Wi - A[t 1 -(1-6) n i khc re ! l
=
tice cf data peint i, houre (t1 = 0) The~icakage rate in weight percent per day is: L = - 2400 A l E (1 7)- The 95% upper confidence lirje for L, UCLL, is calculated using: ' UCLL E L + SA (2400) t 0.95,n-2 (1-5) b khere 5; = [ S
/n ([tt) 2 -
Qti)2 S = [(Wt - E )2 i i n-2 W = Att
- E 1
i> t 0.55,n-2
= 95th percentile of "t" distribution with n-2 degrees of freedom
We will judge a test acceptable if: a) tn } 8 hours b) n A 21 after rejection of spurious data points (see item 2) c) UCLL $ 0.75 La 2 Where le is the maximum permitted containment leakage rate at peak accident pressure, Pa.
- 2. Your September 2, 1977 submittal indicates that the point-to-point l calculational technique will be used to detect spurious data points. l Discuss and justify your proposed criteria for data rejection.
Response
The point-to-point method will be used to calculate-a leakage ra te , L;, for each data point using equation (1-3). Point-to-point leakage rates will be subjected to a statistical test. The widely used Chauvenet criterion will be used j (Rrference 1). A measurement in a set of n data points will be rejected if-it deviates from the mean value to the extent ) i that the probability of all .such deviations at least as great. I is less than 1/2n. A Gaussian distribution is assumed. i Analysis of data from the last four Type A tests indicates that none of the data points would have been rejected as spurious.
- 3. Discuss and justify the methods used to establish the weighting
' factors or volume assignments for the tanperature and dewcel sensors, p-;;ponse Rosemount Model 442A ALPHALINE Temperature Transnitters are placed throughout the containment to monitor temperature. The temperature sensing system consisted of twenty individual 2-wire temperature transmitters each connected to a platinum resistance temperature _ sensor and a regulated DC power supply.
Each resistance temperature detector is assigned a weighting factor proportional to the volume monitored for use in calcula-tine the average containment temperature. Tables 3-1 and 3-2 list the resistance temperature detector locations and assigned weighting factors. The RTD signals are transmitted to the plant process computer where a ten minute average of the temperature
- l. '
I at each locale is printed by the computer typer in degrees F. Foxboro Model 2701 RPG dewcels are used to monitor containment vapor pressure. Each dewcel is assigned a weighting factor proportional to the containment volume monitored for calcula-tion of average vapor pressure. Tables 3-1 and 3-2 list the dewcel locations and assigned weighting factors. The dewcel signals are transmitted to the plant process computer via resistance to current converters and a ten minute average of the vapor pressure is printed in inches of water by the computer typer. Reading of the deweci resistance and conversion to vapor pressure is accomplished by entering the required cali-bration curves into the computer memory. When instrument locations were originally specified, the dry-well was divided vertically into four levels and horizontally into four sectors. Sixteen volume assignments resulted. Because of the possibility of temperature stratification near the top of the drywell, smaller volumes were assigned at higher clevations than at the lower elevations to increase the number of temperature sensors in those regions. One temperature trant:Itter was located in each volume. One dewcel was located in each sector and at each elevation. The torus was divided horizontally into four sectors. Vertical division was not needcd. One temperator transmitter was located in each sector and one deweel was located in every other sector. As noted in Tables 3-1 and 3-2, generally higher weighting factors result for the torus than the drywell. There are no heat sources in the torus and conditions remain very stable thereby justifying the larger sensing volumes. A total of twenty temperature transmitters are used. The largest weighting factor is just over ten percent and is assigned to torus sensors. The largest temperature transmitter weighting factor assigned to a sensor in the drywell is just over five percent. The largest dewcel weighting factor is 227.. During the CILRT, one fan cooler unit is run throughout the tett and additional nortable fans are 1ccated in the torus and the drywell. This guarantees good air circulation and the reintenance of relatively stahlc temperatures and humidities throughout the containment vessel. Instrument error analysis indicates the number of sensors used exceeds the minimum number required by approximately 1007 in the case of both temperature and humidity sensors.
- 4. The ability of the CILRT instrumentation to detect a change in the containment a tmosphe rc nass is prtmarily a function of the number and location of temperature and dewcel sensors. Discuss I
1
and justify the criteria used to establish the number of tem-perature and deucel sensors, and the maximum volume fraction that may be assigned to any particular sensor.
Response
See response to question (3) above. As noted in the response to question (3), the number and location of temperature and humidity sensors was originally determined by attempting to locate a sensor in each major region of the contain=cnt. The containment was subdivided into twenty sensing volumes. One temperature sensor was located in each sensing volume. One humidity sensor uns located in every fourth sensing volume in the drywell and every other sensing volume in the torus (whcre vapor pressure is a more significant factor)._ This philosophy resulted in a total of twenty temperature sensors and six humidity sensors. Instrument error analysis confirms that this number is more than adequate. An = overall -figure of merit for the instrumentati on system, baced on the reference vessel method using a point-to-point leak rate calculation over an eight hour interval, has been computed to be less than one percent of tha allowable containment leakage rate. Refer to the response to question (6) for a discussion of the maximum volume fraction that may be assigned to any sensor in the event of instrument failure and reassignment of weighting fac tors .
- 5. Discuss the manner in which the mass plot technique is applied to certing with a reference vessel. .
Knsponse Refer to the response to question (1). While the mass plot technique is best used with the absolute method, it may also be used with the reference vessel method. Since the reference vessel method actually measures changes in the cer.tainment russ over c time interval, the initial containment air mass must be calculated for the first data point if the mass _ plot method is to be utilized. Equation (1-1) is used for this purpose. P, Py and T are determined using the CILRT instrumentation. V, the containment free air volume was measured during the 1974 Iype A test and was reported in reference (4). The measured volume was in exec 11ent agree-ment with the design value. There does not appear to be a statistical advantage in applying the mass plot method to the reference vessel technique. Other
. a , a 4 . e .a ._a-..a 44 m. .._ z..m..a _ . #
l
- l l
1 TABLE 3-1 DRWELL DEWCELS AND RTD's Sensor Type Location
- Volume Weib hting Sensor No. Elevation Azimuth , _ . Factor Dewcel 1 933 0 0.2158 2 951 90 0.2050 3 966 180 0.0787 4 994 270 0.C936 RID -1 933 0 0.0537 2 933 90 0.0537 3 933 180 0.0537 4 933 270 0.0537 5 951 0 0.0513 6 951 90 0.0513 7 951 180 0.0513 P 951 270 0.0513 9 966 0 0.0198 10 966 90 0.0198 11 966 180 0.0198 12 966 270 0.0198 13 994 0 0.0235 14 994 90 0.0235 15 994 180 0.0235 16 094 270 0.0235 i
TABLE 3-2 TORUS DEWCELS AND BJD's
~ 'C. Location
- Volurac Weighting Sensor Tyne Sensor No. j F.evation Azimuth
,_ Fac to r Deweel 5 915 0 0.2034 6 915 180 0.2034 RTD 17 915 0 0.1017 18 915 90 0.1017 19 915 180 0.1017 20 915 270 0.1017
- Referenced to the drywell floor at 5'0.5 ft, the torus center line at 912.5 ft, and the drywell airlock at 0 degrees.
computational-methods, such as the point-to-point method or the total- time method, cambined with least-squares data analysis,-are more directly applicable. The mass plot tech-nique is rapidly becoming the industry standard, however, and
-we have adopted it in the manner described to permit it to be-used with our reference vessel instrumentation. The absolute method may be used in the future.
- 6. Identify the criteria used to establish an instrument failure and the maximum number of instruments that may fail before a test is alarted. In addition, discuss the procedures for elimi-nating the data fram failed instruments from the leakage rate calculations, including the replacement of data and recalcula-
. tion of' weighting factors.
Response
Four Type A tests have been conducted at Monticello since the beginnitg of commercial operation. No test instrument failure has - curred in any of these tests. Special precautions have beer. taken to assure instrument reliability, both in the selection op quslity sensors and in their installation.
, instrumentation for those instruments located outside
-t:
Inment will be availabic during each Type A test (i.e., rec :nt manometer, pressure gauge, and flow meter). A rut.m a of one of these instruments is not serious. Instruments
;aca'ad inside containment, however, cannot be repaired or re-p .e4 during the course of the Type A test. In the event of a temperature or humidity sensor failure, provisions will be made to continue the test by reassigning instrument weighting factors. Because of the large number of sensors used at Monticello, multiple failures can be tolerated and a valid leak rate measurement can still be achieved.
The following-criteria will be used: Instrument Failure An instrument is considered to have failed if:
- a. Out of range high or Im.
- b. Intermittent indication
- c. Unexplained departure from trend of previous readings
- d. Analysis of a data point rejected using the criteria described in item (2) above indicates an unreasonabic sensor reading.
The output of all individual sensors will be scanned at each data print. e )*
... - _ _ . .. - . . _ _ . - ..- ~ . - _~.
Maximum Number of Instrument Failures Drywell - No more than four temperature sensors will
~
be permitted to fail. The failure of more usan two sensors'at any one elevation will not be permitted. No more than one humid-ity sensor will be pennitted to fail. Torus No more than two temperature sensors vill ' be permitted to fail. No more than one humidity sensor will be permitted to fail. 1 I In the event of instrument failures that exceed these numbers, the test will be suspended and repairs made. A new Type A test will be conducted when the minimum number of instruments are again made operable. Instrument error analysis indicates that the above permitted failures can be tolerated without significantly degrading the l figure of mc:rit for the' instrumentation system (the figure c f I merit remains better than 5% La - refer to question (4)). ne-cause of its relative insensitivity to terperature sensor error, the reference vessel method can be successfully used with far fewer. sensors than other methods. When an instrument failure occurs, instrument weighting factors will be reassigned and the faulty instrument will no longe r be used for computing average containment temperature or ve.por pressure. In the event that it is determined that past data may have been affected by an instrument failure, computations based on the faulty instrumcd; can be repeated using the re-assigned weighting factors and dropping the faulty instrument readings from the data set. Weighting factors will be reassigned as shown in Tables 6-1 and 6.2.
- 7. Discuss the effects of instrument bias as functions of time, temperature, and pressure on the CILRT results. Since the 0.25La acceptance criteria for the supplemental verification test was established based on a 24-hour test duration, discuss the adequacy of this acceptance critbria as it relates to the identification of systematic instrument errors for a test of shorter duration.
Response
Bias, or systematic error, can arise through faulty instrumen-tation, calibration procedures, or computational techniques, t
TABLE 6-1 RTD WEIG11 TING FACTORS TO BE USED AS A RESULT OF RTD FAILURES DURING Tile TEST ensors h her of I'eru i ning Weightin.; factor Mensor Group Pa ra')e rs) Sensor 1:ailures Sensors of remaining sensors lJi) l i,',3,1 1 of 4 3 0.0716 1 1,2,3,I 2 of 4 2 0.1074 lu'D 2 c,0,<,8 l 1 of 4 3 0.0681 2 5,6,7," ! 2 of 1 2 0.1026 i:i d ., 10,11,12 ' 1 of 4 3 0.0261 3
., 10,11,12 2 of 4 2 0,0396 l lii'u i 13,14 ,13,1 t . 1 of 4 3 0.0313 1 13,1 1, l 'i , l o 2 of 4 2 0.017 i; !'D "
'7,11,19,;a ! of 4 3 0.13 T,o ,
.1i ,1 S,Ii 2 i 2 of 4 2. 0.2034 l 9
I
^
m TABLE 6-2. DEWCEL WEIGHTING FACTORS TO BE USED AS A RESULT OF DEWCEL FAILURES DURING A TEST - l
.1 Failet! Sensor Romaining Sensors Weighting Factor J b,ensor (fit;nber) (tAunber) (Remaining Sensors)
Dehte 1 ] 2 0.4208 3 0.07S7 l 4 0.0936 ! 5 0.2034 0 0.2034 2 1 0.24975 3 0.21975' ' 4 0. 0!13b 5 0..?031 6- 0.2034
~
! 0.215S 2 0,18865 4 0.18 S'i5 5 0.2031 0 0.2031
- 1 0.215S 2 0.2050 3 0.1723 5 0.2031 0 0.2034 5 1 0..'15S 2 0;2059 3 0.0787 4 0.0036 6 0.406S o ) 0.215S
', 0.2050 a 0,07S~ ;
4 0.0936 5 0.4008 4
. .~ - , -- .- - . . - - - _ ,-
Because leak rate computations deal primarily with changes in containment parameters, errors in the measured leak rate due to systematic errors tend to be small. Before a CILRT is begun, all instrumentation is calibrated against standards traceable to the National Bureau of Standards. This guarantees that at the start of the test, systematic error will be held to within-very small 10mits. Following the completion of the CILRI, a verification test is conducted. This verification is a repeat of the CILRT for a short period of time with a known leak rate superim-posed on the containment overall leak rate. The CILRT results' are acceptable if the verification test confirms the overall containment leak rate measurement to within
- 0. 25 Lo . This places an upper limit on the effects of sys- I tematic error which is independent of the length of the CILRT.
To quantify the effects of instrument bias on CILRT results as a function of test duration, a number of calculations have been performed using the 1977 Monticello CILRT data. Using this ddta, worst case instrument error has been ' applied ac a bias and the effect on CILRT results noted. Using the case clot method, the leak rate and 95% upper confidence level leak rate were computed for the unbiased data (Table 7-1) and various combinations of biased data. The following cases were evaluated:
- a. Pressure instrument bias of 1.71 INWG high and low
- b. Temperature instrumentation bias of 0.1 F high and low
, c. Dew point instrumentation bias of 0.2 INWG high and' low
.d. Manometer bias of 0.01 INWG high and low Tnstrwment bian has the greatest impact for the case of Frccsurc instrument bias low Temperature instrument bias low Dew point instrumentation bias lov Manometer bias - na effect This case is shown in Table 7-2 for comparison with the un-biased case shoun in Table 7-1. The effect of worst case bias is seen to change the 95% upper confidence level leak-aga by C. M f a r e test duration of eight hourr.. ~he changc is C.5% for a test duration cf 24 hours. There is, there-fore, no advantage in extending the CILRT to 24 hours to 3
, - - --.,-----e- - , , - -
- - . ~ . .. ~ ~ . . . . _ ~ - . . ~. .x. - . - . . . .~ -
1 i l TABLE 7 1977 CILRT DATA I 1 l 1 1 T!PE PPEStINI TE**(R) VAP-(TN) OP (1N) .MAES LEAkAIE I teR3 . 95X L'O L L
#1NWOI (INWO) (INWO) 11NWO) (LEl WTydOAY. W T 'A /D A Y
_........ ........ ........ ............ ............ ............ q 0.0 1553 ?16 537.380 11.030 17.900 64 903'0E 04 0 000.155? eu 53?,360 11.000 I?.*eC 6.900?SE 06 1 1 1.000 !!53.195 537.310' 11.160 171580 6 '. 9 0 0 01 E 061 4.003E-01 '5 9-6E-01 l 1 500 1553 040. 537.300 11 1*C 17.*S0 6.9015eE 04 4.010E-01 4 5e5E 3 0.0C0 '15 E O . 7 8 3 537.0f0 11.180 17.360 6.90113E 06 3 995E-01 0.500 1550.7F3 4 30BE-C1 537.070 11.180 17 000 6.90064E C' '3.e*3E-01' *.1135-01
~3.0C0 1550.723- 537.070 :11.150 !?.100 6.9000EE 06 3 650E-01 3 939E-01 3 SCO 1550 03' 53'.060 11.15C 17.010 6.919'6E 06' 3.5SCE-01 3.764E-01 6 000-10504 100- 537.060 '11.130 16.900 e.9193ec 06 3e'6?E-01 3 6'3E-t!
6.500 1550 034 53?.06C 11.130 16.790 6.916e4E'06- 3 409E-01 3 599E-01 5.0C0 !r50c00- 537.070 11.130 16.490 6.916-3E C4 3.37BE-01 3 500E-01
- 0.fCC_15LO.i;0 537.0GO 111100 16.6CC- o.91607E 04 3.32tt-C1 3;6t9E-01 ;
6 0C0 15 51.. e G 7 53*.-090 11.110 16.5C0 6.91766E C6 3.076E-01 3 399E-01 6 500 1551.570 537.30C 11.110 16.60c 6.91701E C4 3.043E-01 3 353E*01
?.000 1551.-16 -5??.310 11.110 16,300 6.916?6E 04 3.019E-01 3 31EE-01 7.500 1551 416 537.310 11.100 16.000 6.91606E 04 3 000E-01 3 006E-01 8.CCC 1551 000 -E3?-340 .
11 100 le.110 6.915*-E D' 3.16-I-01 3,0-EE-01 0.ECO I E 51.1 - 5. fi'i3ec 11.C90 16.C30 e.91563E Ce 3.10SE-01 9.000 1551-1er 3 00eE-01 E7'~3(0 11.100 15.46C o.9150tE 04 3 0 SCI-01 3 leEE-01 4 0C: 1571.C' t
!sa .C't 15.;.* .t.41*c-E 04 3.0--;-01 10.0C0 '15El.CCi . 041-01
?!'.400- 11 04C 15 ?GC e.91'56E 06 3 00CE-01 10 5C0'1591.C0c 5?',410 3.CECE-CI 11.!?0 15.'OC e4 9139EE 0* 0.900E-01 0.06?E-01 11.000 15!-1s 005 :50' e30 11.11C 15.e0C e.513 TEE Ce 0.9c-E-t1 3.C'L;-C1 11 UC0 !E51.C04 33?.45C 11.110 15 5?0 6.9130?E 0' O.96eE-C1 3 . f.13 E - 01 4
10.000 1550.3r' 537.470 11.10C 15.630 6.910??E 04 0.930E-01 0 99+E-01
-1*<5t3 1550. 7' 5 3 ' . c !- 0 11.10C 15.300 6.9105-5 06 0.91CE-01 0 9705-01 13.000 1550.174 537.510 11.11C 15.300 6.91003E C6 0.893E-01
-13.500 1550.et? 0.953E-01 5*?wC00 11.100 15.030 6.91196E C6 0.674E-C1 0.933E-01 i
11 6 C(0.1E50 ec- 53?.550 11.l*0 It.1'c 6.91150E 0* 0.857E-01 0.915E-01 1 .50011000.3"O F3'.5t0 11-160 15-100 6.91110E 0* 0.821E-01 0.604E-01 15.CCC'1550.19t 537.E*C 11.I'0 15,030 6,91006E 06 0.610E-01 0.6*'t-01 15 5C0 15*+.900 53?.600 11.!!O 14.950. 6.91063E 04 0.796C-01 ' 0 -. 4 5 6 E - c i - 164000 1550.615 537.660 11.130 14.e60 6.910 3E 04- 0 ??6E-01 0.e31E-01 16.-500.1550.063 537.660 11,160 14 800 +.9098"E 06 - 0.764E-01 0 f"?E-01 17.000 1550.Sc5 537.7CC 11 1-0 14.740 6.*C95'E 0* 0.753E-01 0.E09E-C1 l' T00 1560 'ct E37.'30 11.130 !=.e90. 6.90936E 06 0.73CE-C1 0 76?E-01
- 19 . 7 0 0- 1 E 5 0 . 0 C 0 5:7 7'O- 11.110 14.+-0 6-*Cc1'E C=
16.5C0 1550;O09
~
0.7C9E-Cl 0.76'E-01 537.0 11.150 16 560 6.9Co?eE 06 0.690E-c1 0.769E-01 19 000 1550.004 5 3 7.' ? o c 11.150 16.500 6.90050E C6 0.673E-01 0 730E-01 19.ECO 155C.C73 53?.810 11.110 14.'00 e 90814E C4 0.656E-01 0 . 7 '1 E E - C 1
~~0.000 1550.t?3 537.e50 11.I'G 14.=30 6.9C413E C4 0.633E-01 0.69'I-01 00.500 1550.C?3 537e60 11 130 -14.350 6.90781E 04 0.611E-01 0.673E-01 01.000 1550.060 53?.910 11-140 16.000 6.90765E 06 0. 5 9 0 E-C l- 0.653E-01 i
01<500 1!'9 9?? C3'J9'O 11 1+! 14 000 6.90713E 04 0.5?lt-ci 0.t33E-01 00.000 15+4.9C- 53'.9ec 11.190 14 160 6.9066SE 0-0.SSOE-CA O.e19E-01 4 00.00C 1549.935 !?'.!'O 11,000 14 100 6,90637E 0' O.E*5!-!' O e0tt-01 03 C!. 15-4 ~~ 7 t".(5" 1. 1C; 1*.c4C 4.90o19E C4 U 2.50~I-c1 0.56'L-01 03 500<l5'9.741 537.99c. 11 190 13.960 6.90578E C4 0.515E-01 0.573E 06 00t 1549.7+G S38.C00 11.00C '13.90C- 6.9C566E 04 0.5c02-01 0;559E-C1 5 d
*Iid"
- .<- ..o.-.... _ . . . . . _
, , . ~ _ , -. - --. - . - . ~ . - . - ~ .. ~. - -- . . . ~ . -- ~
4. b TABLE 7-2 WORST-CASE BIASED 1977 CILRT DATA x 1N57RUMENT E!AS --~ P8Ef$USEtINdO) -r -1 71 TE** EPA *U*E(F1 = ' -0.10 VA70M PPES.t!WWC1 z -0.00 ONT-PEr gp g;gy;l = C '. 0 -
??"E PPI5f!N) '* E *
- 1 8 i VAP (14) CP ( !r). " A T E. LEAgar?
le 11 I '1 * .J O 3 - 9 5 ^# UC. t ! 'JW O ) (INWOI (!NwOf (Lb) WT X/C A V w?//0AY 0;0 1550.C 6: 53? 080 11 03C !?.900 6.-937940 Os 04 500 1E51,504 53?.060 11.000 I?.7't 6.91?reE C4 1.0C0 1551.6E5 537.01C 10.950 17.58C 6.91673E C4 6 0C(E-01 1 500 1551.350 =537.000 10.990 5.94*E-01 17.650 6.93609E 04 6 015E-01 4.569E-01 0h000 1551 C73 537.150 10.ceo 17.360 6.91564! C4 0.5CO 1551.073 537 170 3.940E-01 6.309E-01 IC.960 17 030 6 91515E'C4 3 861E-C1 3.000 1551.0?3 C3'.!?0 10.950 6 106E-01 '~ !? 10C e.916?9E C4 3 456E-01 3.9*5t.01 3 5CO lt30-50A 537ilec 10.&Lc !?l010 6.91*09E 04 4.000 1550.39C 3.55t!-01. 3.791E-C1
. 537 160 1C,930 le.9CC 6.913s9E C. 3.469E-01 e 500 1550.504l 537 le ? 10.93C 3 47tE-01 16 79C 6.91335! 04 3 431E-C1- 3.600E-01 5.CCC-1550 504- 537.170- 10.930 16.690 6.9109'E 0*
5 000 1350.390 537.160 3.36EE-ci 3.S10E-01 10.900 16.600 6.010SSE C4 3 309E-01 4.0a0'1549.9?? 537 100 10.910 3.66tE-01 16.50C 6.9101EE 06 3 074I-01 3.*00E-ci e . S to !! c.Se: E37.OO? IC.ela- le.cC0 e 911?3E c6 3 039;-01
?,C00 15 *.70e 53?.010 10.510 3.1&cE-e1 16.300 6.0110SE 06 3 01'C-C!
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reduce the effect of systematic error, i
- 8. Previous' testing experience has shown that there are a_ number !
of effects which become more ' pronounced as the CILRT duration _ I decreases. In many cases, these effects are not adequately
'l reflected in the confidence limits of the CILRT results. I Demonstrate that the proposed minimum test duration in con-junction with the proposed testing procedure will adequately reflect each of the following effects: 1 a) the containment volume change following 1 pressurization; I
b) outgassing and ingassing during and follow- l ing containment pressurization; I c) the variation of internal system heat loads; and d) diurnal effects relating to variations in the temperature of containment cooling water. Resronse a) Following pressurization and containment atmo-sphere stabilization, the containment volume will experience a very slight decrease as in- , ternal pressure decreases over the course of the CILRT. For the Monticello pressure sup-pression type containment, the volume can be shown to decrease less than 5ft3 for every reduction in pressdre of I psi. (ver the course of the CILRT, containment pressure may fall as much as 2 psia. - If the period of the CILRT is t hours, this pressure reductica is equivalent to the introduction of air into containment at the rate of 0.76/t scEm. For an eight hour test duration, the equivalent air addition rate is 0.09 scfm. This is less than one percent of La and is negligible, b) Ingassing and outgassing during and following containment pressurization has a small effect on the CILRT results at Monticello. Experience has shown that the effect of ingassing and outgassing on tests of BWR containments is slight because of the_ small internal surface area compared to a larger PWR type contain-ment. A BWR also has a larger specified value
-l I
of L abecause of its smaller containment volume l which tends to reduce the effects of ingassing l 1 and outgassing. (Reference 2). I
, The effect of ingassing'and outgassing is evi- !
dent in plots of containment leakage rate versus time. As shown in the plot for the 1977 Monticello CILRT, ingassing generally re- ; suits in a higher leak rate during the initial ; phases of the test and outgassing results in a lower leak rate during the final phases of the test. (Figure 8-1). Terminating the test following eight hours of data collection would result in a more conservative leakage rate measurement than the measurement obtained after 24 hours of testing. c) The variation of internal system heat loads is not a concern during conduct of the CILRT at Monticello. During early CILRI's, some difficulty was experienced in maintaining uniform stable tenperatures throughout the drywell. Since then a number of procedural and equipment changes have been made to peruit containment temperatures to stabilize rapidly following pres-surization and to remain essentially constant during the test. During the 1977 CILRT, over the 24 hour duration of the test, the temperature change amounted to less dhan 0.7 R. (Table 7-1). The only significant heat load inside contain-ment during the CILRT is the reactor sessel. Careful regulation of reactor water temperature by adjusting the RHR heat exchanger inlet valve p revent *. variations in this heat load. Strati-fication of water within the reactor vessel is prevented by running one recirculaticn pump at minimum speed throughout the test. d) Diurnal effects relating to variations in the temperature of containment cooling water are not a concern during the conduct of the CILRT a t Monticello. The worst case diurnal variation in river water temperature is 13 0F during a hot sunny day in July o r August. During the autumn, winter, and early spring months, daily temperature variation is less than i 1 F. CILRT's are conducted during refueling outages which are generally scheduled in late autumn and early spring. 1 I I plt. OF 1977 CILRT MEASURED LEAK RAL. ! TIGUI'I 6-1 VERSUS TUT g i W i , i
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'l Daily cooling water temperature variation is therefore small and generally has a negligibic effect on RHR heat removal rate or containment fan cooler heat removal rate. In each case, however, these temperatures are closely monitored during the CILRT to prevent significant varia-tion in average containment air temperature.
Since the Monticello containment vessel is entirely enclosed within the Reactor Building, the containment shell is not subjected to diurnal ambient temperature changes. Containment shell temperature remains essentially constant over the course of the test. 1 We have been unable to detect any diurnal varia- l tion in containment leak rate versus time. Refer, for example, to Figure 8-1 which shows no depen-dence on. time of day. Plots of all Monticello CILRT results may be found in References (3) through (7).
- 9. Discuss and justify the basis for the selection of an eight j hour. s tab 11iration period. '
l Re3ponse ' An eight hour stabilication period will not be used. Current procedures require a four hour stabilization period and ~this has generally been adequate during past CILRT's. Future tests will use a temperature stabilization criterion. Following containment pressurization to Pa Pl us one psi, con-tainment tempe ra ture sensors will be read every 10 minutes. The contaimacnt atmosphere will be considered stabilized when the change in weighted average air temperature averaged over an hour does not deviate by more than 0.50R/ hour from the average rate of change of temperature measured over the previous four hours. This is a videly used criterion for determining the ttme when stabilization is essentially complete.
- 10. The acceptance criteria proposed in your September 2,1977 submittal is based on a point-in-time measurement. Discuss the manner by which Icakage rate trends will be reflected in the acceptance criteria.
Desponec The mass plot method of computing CILP" leakage rate is rapidly becoming the standard in the industry. The method 1
4 ..aJ,h.. e k a-u4a4--wJ - has a number _ of advantages over older methods. -' The method generally.results in narrower confidence intervals for- leakage since maximum use is made of all measured data. L The mass plot method involves the assumption of a linear relationship between the containment air mass, W, and time, t. This is equivalent to assuming a constant rate of change of containment air mass. This rate of change is the contain-ment overall leak rate, L. L is, in fact, a function of the differential pressure across the containment shell and penetrations. It may also be in-fluenced to some extent by other factors such as temperature. In actual tests of a reactor containment vessel, however, 1 these effects were shown to be very_small. (Reference 8). During a CILRT, pressure will stay within 2% of Pa. Assuming a conservative laminar flow through leakage paths, this varia-tion in test pressure results in a 2% change in L. This ! change is within the statistical uncertainty of the mess plot l method. Temperature effects on the measured value of L are ! negligible since temperature remains constant within lo5 g th roughout the test. Because of the slight dependence of L ; l on test pressure, a larger value of L will be measured if the ' test duration is short, j To summarize, .the mass plot method assumes a constant contain-l- ment Icak rate, L. In actuality, there is a slight dependence of L on test pressure. This could be taken into account by fitting a higher order polynomial to the W versus t data at the expense of complicating the statistical analysis of the data. This is unnecessary, however, because of the very small departure of the W versus t relationship from a straight line. The linear assumption for the relationchip yields conservative values of L if the test is terminated-before test pressure falls below P a-
- 11. Identify the procedures that will be used when excessive leakage is encountered during the performance of a CILRT.
, Resnonse lhe Monticello Technical Specifications state: If lect repairs are necessary to meet the allow-able (CILRT) leak ra te, the integrated leak rate test need not be repeated provided local leak measurements are conducted and the Icak rate differences prior to and after repairs, when corrected to Pt and deducted from the integrated leak rate measurements, yield a leakage rate
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.1 value not in excess of the allowable operational leak rate Leo.
Appendix J to 10 CFR 50 currently requires a Type A test to be repeated in the event repairs are necessary to reduce leakage to an acceptable rate. Therefore, the current Tech-nical Specifications and Appendix J are in conflict on this - point. We believe that if, during the CILRT, excessive leakage is identified through a testable penetration, the leakage may be isolated and the CILRT continued. Type B or Type C tests made before and after repairs to the leakage path can be applied to the CILRT leak rate to determine the as-found and as-lef t overall containment leak rate. A request for exemption from this requirement of Appendix J will be submitted to permit the coarse of action described 'to be followed. This will be included in a supplement-to our submittal dated May 5, 1976, i- " Request for Exemption from Certain Requirenents of 10 CFR 50, Appendix J." T 4 RE FE RENCES
- 1. Wa ng La u , L. , " Data Analysis During Containment Leak Rate Test,"
Power Engineering, Februa ry, 1974, p. 46.
- 2. Fleshood, David L, Carolina Power & Light Co. , _" Containment Leak Rate Testing: Why the Mass-Plot Analysis Method is Preferred,"
Power Engineering, Februa ry, 1976, p. 56.
- 3. Reactor Containment Building Integrated Leak Test - May, 1973, submitted by NSP for NRC review August 5,1973.
- 4. Peactor Containment Building Integrated Leak Test - May. 1974, submitted by NSP for NRC review August 12, 1974.
- 5. Reactor Containment Building Integrated Leak Test - November, 1975, submitted by. NSP for NRC review January 23, 1976
- 6. Supplement No. I to Peport of Containment Building Integrated Leak Test -
November, 1976, submitted by NSP for NRC review March 16, 1976.
- 7. Reactor Containment Building Integrated Leak Test - November 1977, submitted by NSP for NRC review February 8, 1978
- 8. Binghan, G. E. , Final Results of the Carolinas Virginia Tube Reactor Containment Leakage Rate Tests, IN-1399, June, 19)q (TID-4500)
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