ML19247E432

Provides fracture-mechanics Parametric Analysis of Overcooling Accident at Facility,In Response to Request

ML19247E432
Person / Time
Site:	Rancho Seco
Issue date:	03/03/1981
From:	Cheverton R OAK RIDGE NATIONAL LABORATORY
To:	Vagins M NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
Shared Package
ML19247E428	List: ML19247E427 ML19247E430 ML19247E431 ML19247E432 ML19247E433 ML19248C222
References
TASK-2.K.2.13, TASK-TM TAC-45198, TAC-45202, NUDOCS 8105110223
Download: ML19247E432 (10)

Text

{{#Wiki_filter:REFk.ENCE4 c.a ) CAK RIDGE N ATIONAL LABORATCRY CPtmattD av UNION CARE!OE CORPOR ATION ~ n:::aAr :mir:n Pesi errice sex v cu at:ct. Tsuttst r :rco March' 3, IcB1 Mr. Milton Vagins Divisien of Reactor Safety Research U.S. Huclear Regulatory Commission Mail Station 1130 SS Vashington, D.C. 20555 t

Dear Milt:

m Subj ect : Para etric Analvsis of Rancho Sece Overcooline Acciden The fracture-mechanics parametric analysis that you requested fer the Rancho Seco everecoling accident (March 20,1978) has been completed, and the results and a discussion thereof fo11cw. t ' According to.information we received frc= NRC en December 5,1c o (1e::er from c FeSic to Serpan, Neve.mber 25, icBO), the F.ancho Seco transient condition started with a spike in primary-system pressure and,a rapid rise in cold-leg-coolan temperature as shown in Fig.1. By $1 min after the spike the pres-sure was decreasing gradually f rom s2150 psi, and the :emperature was rising slowly abcve 3E5'7. At c min into the transient both the pressure and tem-perature started drcpping ra:her rapidly. Up :o this point the transients would have had little effect on the vessel.. In a ia:er com: unique (le::er from 5:rcsnider to chever:en, January 30,1981), the informatica in Table 1 red Fig. 2 was made tvsilable to us. Time zero in these .<o sources of transient data is assumed to be censistent with a :Ime cf s3 min in Fig. 1. Figure 2 indicates that the initial majer drop in pre >- sure (: =c min, Fig. 11 : = 0, Fig. 2) extended devn to s1500 ;si in s1S ain. Feilewing this, there was an irregular series of ups and downs with a net increase to s2 00 psi within s35 min, and this in turn -as fc11ewed by a gradual decrease :o s1300 psi over a 50-min period. This is the end of a 100-min pericd that we were requested to analy:e. The pressure vs time curve that we used in our analysis is the smocth curve in Fig. 2, which was suggested and drawn through the pressure pesks by NRC. Pressure and temperature curves reproduced by us from the cata in Table 1 and Fig. 2 are shewn in Fig. 3, and corresponding tabulated da:a used at inpu: to CCA-1 is shewn in Table 2. W B/Of//020-3

Mr. Kiiton Vagins 2 ' March 3, 1951 1: shculd be peinted out that a: : = 100 min (Fig. 2' the wall tempera:ures are s:ill substantially higher than the cociant temperature and thus the aterial.:oughness will centinue to decrease for some tire, :he amount depend-ing upon the temperature of the coolant thereafter. Since the pressure is still high and eventually goes even higher (Fig. 2) a centinued decrease in wa.11 tempera, ure may be of ccncern. Ncaever, our analysis has cevered only that part of the transient reques:ed (at = 100 min). The analysis of Rancho Sece was performed using OCA-l with all of the built-in (default) input data (refer to CCA-1 draf: r e po rt, February 9,1c51), a hes:-transfer coefficient of 330 Etu/hr f:

• F and an initial wall temperature of 570*F.

Parameters varied in the analysis and specific values censidered are shown in Table 3 As indicated, the analysis included variations in cepper centent, initial RTNDT (ETHOT ) and Inner-surface fluence (F ). The g e analysis also included two variations' in :he ASME Section XI toughness curves other than RTNDT: ene variation cons:Ituted the use cf no upper shelf and the other censtituted the inclusion of an upper shelf of 100 ksi /in, for both K and K Ic la. Ce:ciled results of the analysis are presented'in tabular ferm (micrefiche) for both the hea:-tran_sfer and fracture-mechanics analyses. In addi:icn, results of the f racture-mechanics analysis are su=tari:ed in :he form of Kg V5 :Ime and a/w curves (Fig. L), critical-crack-depth curves fer the cases Involving Kg i Kge,(and two summary tables. As indicated by :he critical-crack depth curves Figs. 5 through'19), ccnditiens fer wa rm prestressing exist, and W75 mitigates the consequences of the transient. This comes about because during the 100-min pcrtion of the transient analy:ed b::5 the thermal and pressure leads first increase with tine and then decrease. This is indi-cated by the temperature and pressure transients in Fig. 3 and by the Kg vs . time and a/w curves in Fig. 4 1: should be nc:ed tha: the V?S curve is the same fer all cases calculated because the VPS curve is dependent cnly on the transient condition, ne en fracture toughness. Let us nes narrow our discuss sen to the case of ne upper shelf. An examina-tien of Figs. 5 through 19 and Table 4 indicates that if VFS is igncred, and if crack initiation skes place, which it does for the cases represented by the figures, then for seme but not all initiating crack dep:hs the crack will Jump more than 900 cf the way through the wall, and the cceresponding initial crack depths (a/w) range up.ard frcm so.03 (0.25 in.). Fu r t h e rme r e, the severe case (RTNOT, = LO*F threshold fluence for crack is so.75 *$fc= initiation for the mes 2 s6 years). l# VPS is included, the thfesheid and Cu = 0.35%) increasedtos17"E7:(=2 fluence is (s14 years). For some cases in Table ( the maxieum crack penetraticn [(a /w)33 is less :han c or equal to 0 9, indicating tha: :he vessel would r.c: f ail prior :c accumula:- Ing the corres:ending fluence. It must te remembe red, heweve r, : hat CC'-! dces not include a failure mode asscciated with sim;le rupture of :he uncracked ligamen: as a resul: ef excessive internal pressure. If the pressure is near normal crerating pressure, the threshold crack de;;h fcr ructure is O.7

.~, u e 4 Mr. Milten Vagins 3 Mar,ch 3, 1331 \\o 14

g Jith this in mind the results in Table 4 can be further cendensed to simply i

5 reveal the useful life of the vessel for :he particular accident analyzed. Rt ~ Such a su.~.ary is shown in Table 5 5 .ck:3 t Jf we assume that VPS is effec Ive, the cata.in Figs. 5 through 13 indicate v that the deepest crack that will initia:e will correspond to a/w 2 0.5 Vith 4-1 reference to'Fie. A we see that a/w = 0.5 corresponds to a maximum KI value 5 v-of s250 ksi /in., which is prehtSty below the upper shelf. This implies that c the analysis for flaw depths at leas: up to NO.5 is reasenably correct. he - Ji ever, Kg values for dee;cr flaws are greater and may exceed the upper sheif, dk ;, in which case an analysis that ignores the upper sheif would be in error. The ~ effective upper-shelf toughness for a large structure such as a pressure ves-sel is net knewn. However, an arbitrary value of 400 ksi (in. for Kje gnd Xg, was used fer a seccnd complete set of Rancho Seco-1 calculatiens in order to get a feel for the effect of an upper-shelf. Critical-crack-depth curves for these cases are presented in Figs. 20 through 55. As indicated in these fig-ures a.nd as reasoned abcve, the -in:reducticrl of the particular upper shelf af fects caly the very deep fizws (a/w > 0.3), ailewing them to initiate (tear). Ho-ever, VPS prevents shallow cracks f rom bcE6EIn? s~ufficiently deep for initi-ation a uccer-shelf teughness. Thus, the introduction of an upper shelf of 100 ksi /in. dces net substantially chance the results obtained without an ~ upper shelf. Sincerely, m2 R. D. Cheverten ROC:spf A::s chmen ts ec: S. K. Iskander R. V. Klecker, DOR-NRC F. R. Mynat: J. Stresnider, RSR-NRC # G. D. Whitman m k

3 TABLE 1. MARCH 20,1578, RANCHO SECO OVER-COOLING T?AN5 TENT TEy.PEPATURE Tts.E MISTORY TIME INTO T'AN51ENT TEr.PERATURE n (min) (* r) 0 Sco '~ 24 385 48 300 72 230 o6 310 TAELE 2. TEr.F EFATUF. AND PRESSURE TFANSIENTS USED IN OCA-1 FOR PANCHO SECO-l ANALYSIS TIME TEP.?ERATURE PRESSURE (min) ('F) (psi) .9.. 0 530 1500 10 L90 1710 20 412 1880 30 356 2020 ~ 40 318 2110 50 296 2130 60 232 2100 70 280 2050 ^ 80 284 2000 CO 293 1350 100 320 1c00 e o e mit e. 9 , en.

d ' = h 8 g e TABLE 3 PAP.A.".ETERS VARI E*) IN THE RANCHO SECO ANALYSIS AND THE VALUES CONSIDERED RTNDTo (*F) 20, 40 i Copper (%) 0.1, 0.25,.4 33 19 Fo (10 n/:M) 0.6, 0.8, 1.0, 2.0, 3 3, 4.0 e W e e e O em 9 9 9 e

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