ML20024B221
| ML20024B221 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/13/1978 |
| From: | Janis J BABCOCK & WILCOX CO. |
| To: | Smythe C METROPOLITAN EDISON CO. |
| References | |
| TASK-10, TASK-GB GPU-2490, NUDOCS 8307070365 | |
| Download: ML20024B221 (5) | |
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.D4 ft Puzo Discharge Bre ak As a result of a: sal.1 break analyses on the 20STA planta, a concern was raised that the worst smal.1 break on tha 177FA plants may not have been evaluated. As a result of this concern, an analysis of a small break LOCA (0.04 square foot) at the reactor coolant pum:p discharge has just been completed. The results show thac the core is uncovered for an extended period of time.
The most recent previous analysis of the.04 ft braak for the 17771 lowered loop plant is reported in BAU-10103A, Rev. 3, "ECCS Analysis of DW'o 1777A Lowered-Loop NSS " July 1977. Both 10103 analysis and the most recent sus 11 break analyses were performed with the small break evaluation
2 Previous analyses of the'.04 ft break for the 1777A lowered loop plant
- howed acceptable results.,These analyses (EAU-IOO52 and BA9-10103), however,
- snaned the breal to be at the RCP scetion.
These earlier investigations
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[sCGl-10052) damit with the differences between puw discharge and suction i
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1reaks.
The investigation, however, was performed for a 0.1 square foot break.
lis break being larger allows the RCS to depressurize to a value at which the
.?J. sad C7T systems are functional.
The result was that the puq section was helfied as a worst case.
The r-ining break spectrum cases were then erfor=ed for punp section breaks.
It is ccw evident that the very s mall
- e. aks, those for which the HPI is the only system in.jacting water, should be
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= at tha pu=p discharp.
g ggg The recently completed analysis assumes a reactor trip and flow coastdown
= ring which Mw the fuel sensible beat is removed. This portion of the ramsient lasts about 100 seconds.
During the next several hundred seconds, 2033 pockets form in tho upper, or et. ped, ragions of the RCS (reactor i
mlant system) and loop draining occurs. No core tenperature transient will 99e=I.( mmm.n& O %,9A%.D%4
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~2-(for a 2772 25tt power), the fluid levels have fallen to the beight of the l
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- reactor vessel nozzle belt and a boiling pot situation exists.
In this moda, 4,,
8.u miti;ll;stion of the accident requires injection of vetor at a rate equal to or[fcrS greater than boil off Boil off rates in excess of the injection rates will /L
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- fluid levels to drop.
This analysis showed that injection rates did
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,v').h set equal boil off rates until 8200 seconds for the 0.04 square foot pump did=m break.
Am hnation of Yagure I shows why the pump discharge break is a worst czae.
Ccmaider a break at the pump suctica.
Two EPIs would nor==117 be octuated, but in the evaluation, only one is allowed because of single failure.
Still, because of the pump vair effect, all EPI water will flow to the reactor i
vessel.
h s, 200% of the actuated HPI can be used for core cooling. This flow is sufficient to provide continuous core cooling.
Bow consider a break at the pump dischargs, specifically on the lower half of the pipe. Any EPI
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Zwster injected into the broken cold leg will pass by the rupture prior to
-wissel penetratica. This flow can pass occ the break and thus not be utilized 2cr cora cooling.
Becacne of the single failure, the EPI in the enbroken locy is assened not to function.
The EPI attached to the broken loop will
-indect50: into the intact leg and 50% into the broken le:.
Thus, only 50%
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'be.C4 ft break appears to be very near tha largest size btnak in which
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caly tha E?I system would be utilized, and thus the ecst limiting small break of thin category.
y 2CS68 lE'i has identif.ied and is actively evaluating potential solutions to this er =11 LCCA problem.
To date, these solutions pri:narily deal with potentist l
CJys to intresse effective E7I flow (flow to the 2C cold legs not containin3 the IDCA) or to depressurize the Ec system to obtain 1.PI flow.
All solution *
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,ume a.04 ft break at the pump discharge, a loss of offsite power and a single active failure which results in the loss of one HPI train.
Thne potential solutions are being ""in*d:
(1)
Opening t$e BPI discharga crose-connects and injection valves to permit more of the flow from the operating pump to enter the reactor coolant system (2)
Actuating a standby EPI pump by eenmeeting it to the operating auxiliary power source (3)
Cpening the atmospheric damp valves to more rapidly depressurize the Primary system, thereby resulting in additional injection from the core FTag and low pressure injection systems.
The results of the evaluation to date have shown that securing flow from o secced HPI pump (item 2 above) or steam generator cooldown (item 3 above),
otarting at 20 ninutes in the TECA, will keep the core cov red with a mixtura E-med thus result in no temperature excurmica.
4 4/14/73, these solutions will have been more fully investigated and further decisicas should be possible regarding corrective actions.
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_ believea that plant operations abould be unaffected during the brief period l
J ef H w required to define correctim actions because of the e=t:nmely low l
probability that a break of this specific size will occur at the bottom portion of the p=mp discharge piping at the sane ti=e one EPI string is assumed not to function because of single failure assumptions.
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