ML20003A555
| ML20003A555 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 10/05/1977 |
| From: | Bixel D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Desiree Davis Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8102040275 | |
| Download: ML20003A555 (5) | |
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Att: Mr Don K Davis, Acting Branch Chief 3perating Peacters Branch No 2 US Huclear Regulatory Commission Washington, DC 20555 DOCKE" 50-155, LICEUSE DPR BIG ROCK POIUT PLANT - REDU7 DANT CORE SPRAY: 70F E7TRY STEAM 19, 1977, Consumers Power Company submitted an evalua-Ey letter dated September tien of the adequacy of the redundant core spray systen at Big Rock Point based on actual bundle spray flows and bundle evaporation rates. This evaluation used neasured spray flow data for botton only and top and botten combined steam entry.
The tcp only stes: entry mode was excluded because the proportion of top entry steam to total steam flow that existed for the combined steem entry tests was It thought to conservatively bound that which would be expected in a LOCA.
should be noted that between 365 and kl% of all steam supplied in the combined steam entry tests entered at the top of the test facility vessel. To justify the exclusien of top only entry steam, all breaks considered in the 10 CFR 50, Appendix K, analysis as sub=ltted by letter dated July 25, 1975, have been evalu-ated ccrrelating the results of the reference analysis with the SAFE code to de-termine whether or not the propcrtion of top entry steen vould exceed that which actually existed for the combined steen entry tests.
Based on this evaluation, it is concluded that in the event of a LOCA the frac-tion of top entry steam would not exceed that which actually existed in the top and botton combined steam entry tests.
Table 1 provides a tabulation of time of rated spray, water levels at ti=e of rated spray and drum e=ptying times for the range of breaks censidered in the App g dix K analysis. Based on this tabulatien, it is possible to place each of he breaks into one of three categories. The first category is composed of thesFbreaks in which the pressure vessel, the drum and the recirculaticn piping are essentially empty at the time of rated spray. The second category is cat-posed of those breaks in which there is some water in vessel and the devncocers i
at the time of rated spray. The third category is co= posed of those breaks in which there is water in the drum at the time of rated spray.
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Catecory 1 For breaks in this category, the primary system is essentially empty at the tihe of rated spray and, hence, the only source of steam is from the core through the evaporation of spray water.
Since the core is the only source o{7 steam,itisnecessarytodeterminetheamountofsteamrisingthroughthe core as compared to that which flows backward through the pumps, up the down-co'mers, through the steam drum and down the risers.
During normal operation, the pressure drop through the core is less than one quarter of that around the remainder of the primary loop. With the recirculation pumps stopped as was assumed in the Appendix K analysis, and without two-phase flow (ie, only steam would be flowing through the system), the pressure drop through the core vould be even snaller in comparison to the pressure drop throu5h the primary piping.
Hence, for this break category, it can be concluded that at least two times as much stea= vould rise through the core as would flov backward through the primary piping and enter via the risers, and thus no more than 335 of the total amount of steam generated would be top entry.
Caterary 2 For breaks in this category (ie, steam line, feed-vater line, ring spray line, and snall pump suction line breaks), the lover plenum and the downcomers are partially filled at the time of rated spray.
In this case, all steam generated in the core as a result of evaporation of spray water would flow upward through the core and none would be available for top entry.
However, as the system de-pressurizes, the water. lying in the downcomers would flash and thus provide a source of top entry steam.
The SAFE runs indicate that for all breaks in this category some water in the lower plenum and downcomers vill be saturated at all times during the transient.
Following the time of rated spray and until very late in the transient (past the time of PCT), the rate of energy addition to the saturated downcomer fluid from the hot piping is generally 2 to 10 times lower than the rate of energy addition to the saturated lover plenum fluid from the vessel lower head and internals.
Therefore, the flashing rate in the lower plenum would be at least 2 times thst in the downccmers, thus no more than 33% of total stems generated would be top entry. Late in the transient, the rate of energy addition to the saturated lover plenum fluid continues to exceed that to the saturated downcomer fluid but by a lesser amount.
However, at this point in the transient, the flashing rate in the downcomers is approximately the same as the rate of evaporation of spray sster in the core; hence, the amount of top entry steam would continue to be no more than 337'of the total amount of steam being generated in the system.
Caf4cory 3 (Riser P=eak)
In the case of the riser break, the steam dru= is not empty at the time of rated spray; therefore, significant amounts of steam would be generated in the drum by flashing. Hevever, due to the location of this break, as long as the primary system is depressurizing, most of the steam generated in the drum vill flow out of the break instead of into the reactor vessel.
In fact, the primary system continues to depressurice well past 67 seconds, at which time the drum empties.
In addition, because the break is above the core, the direction of steam flow muot.be upwards through the core.
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TABLE 1
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~ Drum /Downconer Spray (Tgp,)
Level at T at T spray Drm: E pties
-Break (Seconds)'
(Feet)
(Feet).
(Seconds)
DBA 20.h
<1.0
<1.0 1.0
+
0.8 x DBA 21.79
<1.0
<1.0~
1.2 0.6 x DBA 2h.26
<1.0
<1.0 1.5 2
-1.0 Ft 36.87-
<1.0
<1.0 30
- rs 2
0.5 Ft 55 07
<1.0
<1.0 50 2
1.0
<1.0 8.0 0.25 Pt 93,17 2
0.10 Ft 155 90
<1.0
<1.0
~12.0 0.05 Ft 209.83 3.5 15 15 0 0.025 Ft
.306.35 21.0
$15 0 19.0 2
0.008 Ft 649 70 24.5 s16.0 22.0 Downcomer 24.06 35
' <1.0 1.2 Riser 30.08 25.3 69.0 67.0 Feedvater 112.23 24.5
%15 0 36.0 Recire Discharge 21.33
<1.0
<1.0 1.3 S ray 3h7. 08 24.0 16.5 21 2.0 f
Rin6 P
Steam Line 85 02 26.5 s15.0 64.0 i
" Level = 0 ft at bottom of pump suction' piping.
= 62 ft at bottom of stenn drum.
= 25.86 ft at core midplane.
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= 65 ft.at drum midplane.
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3 Once the drum has e=ptied, the only source of top entry steam wou3 d be the flash-ing of water in the downcomers.
The SAFE run indicates that between the time the drum empties and the vessel depressurization ceases (115 secondsT, the rate of energy addition to the saturated water in the vessel lower plenum is at least twice the rate of energy addition to saturated water in the downcomers. Once thd depressurization ceases, the rate of energy addition to the saturated water ir.bhe lover plenum continues to exceed the rate of energy addition to the satu-rauf+1 vater in the downcomers but by a lesser amount.
Iiovever, after 115 seconds,
the rate of ccre spray water evaporation vould be about the same as the steaming rate' in the downcomers; nence again it can be concluded that the amount of top entry steam would 'oe no more thsn 33% of the total amount of steam generated in the system.
Thus, Consumers Power Company concludes that under any postulated LOCA conditions Eig Rock Point the percentage of steam classified as top encry is bounded by at the ccmbined entry steam tests conducted at the Bartov, Florida test facility.
Further, it is expected that this response adequately alleviates staff concerns relating to this issue.
David A Bixel Iluelear Licensing Administrator CC: JGKeppler, US?!RC
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NRC DISTRIBUTION 'on PART 50 DOCKET MATERIAL 70-Mr. Don K. Davis Consumers Power Co.
^7'*#U"C'**"I 10/05/77 Jackson, Michigan 49201 l
David A. Bixel C^J 8 "'C'8 V ' O 10/11/77 j Earran C NcTenizg3 PMOP sNeurpopu NyussR CP CcPets MEcgsv30-I dcasa'NAD CuscLessipiso CccPv l,$ pf, p &
- sscri;TioNQonsists of additional information in regard to Itr dtd. 09/19/77 concerning
- evaluation of the adequacy of the redundant core spray system at Big Rock Po'.nt based on actual
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bundle spray flows and bundle evaporation rates...
w/att table 1 3p + 1p PLANT N!JtE:
, BIG ROCK POINT 2
jcm 10/11/77 40 sac #
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