ML20059B636
| ML20059B636 | |
| Person / Time | |
|---|---|
| Site: | 05200001 |
| Issue date: | 10/25/1993 |
| From: | GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20059B634 | List: |
| References | |
| NUDOCS 9310290035 | |
| Download: ML20059B636 (8) | |
Text
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f Wetwell-to-Drywell Vacuum Breakers 3.6.1.6 3.6 CONTAINMENT SYSTEMS 3.6.1.6 Wetwell-to-Drywell Vacuum Breakers LC0 3.6.1.6 Eight wetwell-to-drywell vacuum breakers shall be OPERABLE.
AND Eight wetwell-to-drywell vacuum breakers shall be closed.
APPLICABILITY: MODES 1, 2, and 3.
ACTIONS ,.
CONDITION REQUIRED ACTION COMPLETION TIME A. One wetwell-to-drywell A.1 Restore one vacuum 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> vacuum breaker breaker to OPERABLE ,
inoperable for status.
opening.
B.
One 6?
6@ll;slfwetwell-B.1 VEfifff61gsuf5Hfh{s }2TdUfs 1 to-drywe vacuum vacuum;brea_ker(s)?by !
breaker (s) not closed. laltbrri.stelmqthodsk C. Required Action and C.1 Be in MODE 3. 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> associated Completion
. Time not met. AND C.2 Be in MODE 4. 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> i-i
[
ABWR TS 3.6-20 10/21/93 9310290035 PDR 931025ADOCK T' 05200001'b A PDR yi
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. Wetwell-to-Drywell . Vacuum Breakers j 3.6.1.6 !
1 SURVEILLANCE REQUIREMENTS 1
SURVEILLANCE FREQUENCY !
SR 3.6.1.6.1 ------------------NOTE------ ------------
Not required to be met for vacuum breakers that are oper, due4eg ,
Garveillanees--ee-when performing their intended function.
Verify each vacuum breaker is closed. 14 days AND Within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after any discharge of ,
steam to the suppression chamber from the safety /
relief valves (S/RVs) or any operation that causes the drywell-wetwell differential pressure to be reduced by 2 .007 kg/cmzd.
SR 3.6.1.6.2 Perform a functional test of each vacuum 18 months breaker.
SR 3.6.1.6.3 Verifyeachrequiredvpcuumbreakerfully 18 months opens at 10.035 kg/cm d.
SR 3.6.1.6.4 Perform CHANNEL CALIBRATION of vacuum 18 months breaker position indication channel.
ABWR TS 3.6-21 10/21/93 m _ _ _ _ -
, Wetwell-to-Drywell Vacuum B 3.6.1.6 B 3.6 CONTAINMENT SYSTEMS B 3.6.1.6 Wetwell-to-Drywell Vacuum Breakers BASES BACKGROUND The function of the wetwell-to-drywell vacuum breakers is to relieve vacuum in the drywell. There are 8 internal vacuum breakers between the drywell and the wetwell, which allow gas and steam flow from the wetwell to the drywell when the drywell is at a negative pressure with respect to the wetwell. Therefore, wetwell-to-drywell vacuum breakers prevent an excessive negative differential pressure across '
the wetwell/drywell boundary. Each vacuum breaker is a self actuating valve, similar to a check valve.
A negative differential pressure across the drywell wall is caused by rapid depressurization of the drywell. Events that cause this rapid depressurization are cooling cycles, inadvertent drywell spray actuation and steam condensation from sprays or subcooled water reflood of a break in the event of a primary system rupture. Cooling cycles result in minor pressure transients in the drywell that occur slowly and are normally controlled by heating and ventilation equipment. Spray actuation or spill of subcooled water out of a break results in more significant pressure transients and becomes important in sizing the internal vacuum breakers.
In the event of a primary system rupture, steam condensation within the drywell results in the most severe pressure transient. Following a primary system rupture, gas in the drywell is purged into the wetwell free airspace, leaving the drywell full of steam. Subsequent condensation of the ;
steam can be caused in two possible ways, namely, Emergency Core Cooling System flow from a ruptured pipe, or containment spray actuation following a loss of coolant accident (LOCA). These two cases' determine the. maximum depressurization rate of the drywell.
In addition, the waterleg in the vertical vents of the vent )
system is controlled by the drywell-to-wetwell differential 1 pressure. If the drywell pressure is less than the wetwell :
pressure, there will be an increase in the vent waterleg. )
This will result in an increase in the water clearing '
(continued)
ABWR TS B 3.6-37 10/21/93 l
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. Weteell-to-Drywell Vacuum B 3.6.1.6 BASES BACKGROUND inertia in the event of a postulated LOCA, resulting in an (continued) increase in the peak drywell pressure. This in turn will result in an increase in the pool swell dynamic loads. The internal vacuum breakers limit the height of the waterleg in the vent system during normal operation.
APPLICABLE Analytical methods and assumptions involving the SAFETY ANALYSES wetwell-to-drywell vacuum breakers are presented in Reference 1 as part of the accident response of the primary containment systems. The vacuum breakers are provided as part of the primary containment to limit the negative .
differential pressure across the drywell and wetwell walls-that form part of the primary containment boundary.
The safety analyses assume that the internal vacuum breakers are closed initially and are fully open at a differential 2
pressure of 0.0352 Kg/cm d (0.5 psid) (Ref.1).
Additionally,1 of the 8 internal vacuum breakers are assumed to fail in a closed position (Ref.1). The results of the analyses show that the design pressure is not exceeded even under the worst case accident scenario. The vacuum breaker opening differential pressure and the requirement that all 8 vacuum breakers be OPERABLE are a result of the requirement placed on the vacuum breakers to limit the vent system waterleg height. Design Basis Accident (DBA) analyses require the vacuum breakers to be closed initially and to remain closed, with the drywell at a higher pressure relative to the wetwell.
The wetwell-to-drywell vacuum breakers satisfy Criterion 3 of the NRC Policy Statement.
LC0 All 8 of the vacuum breakers must be OPERABLE for opening.
All wetwell-to-drywell vacuum breakers, however, are required to be closed (except during testing or when the vacuum breakers are performing the intended design function). The vacuum breaker OPERABILITY requirement provides assurance that the drywell-to-wetwell negative differential pressure remains below the design.value. The requirement that the vacuum breakers be closed ensures that there is no excessive bypass leakage should a LOCA occur.
(continued)
ABWR TS B 3.6-38 10/21/93
i Wetwell-to-Drywell Vacuum l B 3.6.1.6 l BASES I i
APPLICABILITY In MODES 1, 2, and 3, a DBA could result in excessive negative differential pressure across the drywell wall, caused by the rapid depressurization of the drywell. The event that results in the limiting rapid depressurization of the drywell is the primary system rupture that purges the drywell of gas and fills the drywell free airspace with steam. Subsequent condensation of the steam would result in depressurization of the drywell. The limiting pressure and '
temperature of the primary system prior to a DBA occur in MODES 1, 2, and 3. Also, inadvertant actuation of the ,
drywell spray could result in rapid depressurization of the l drywell . The vacuum breakers, therefore, are required to be OPERABLE in MODES 1, 2, and 3.
In MODES 4 and 5, the probability and consequences of these events are reduced by the pressure and temperature limitations in these MODES; therefore, maintaining wetwell-to-drywell vacuum breakers OPERABLE is not required in MODE 4 or 5. t ACTIONS A.1 With one of the required vacuum breakers inoperable for :
opening (e.g., the vacuum breaker is not open and may be stuck closed or not within its . opening differential pressure limit, so that it would not function as designed during an event that depressurized the drywell), the remaining seven OPERABLE vacuum breakers are capable of providing the vacuum relief function. However, overall system reliability is ,
reduced because a single failure in one of the remaining vacuum breakers could result in an excessive wetwell-to-drywell differential pressure during a DBA.
Therefore, with one of the eight required vacuum breakers inoperable, 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is allowed to restore the inoperable vacuum breaker to OPERABLE status so that plant conditions are consistent with those assumed for the design basis
,, analysis. The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Completion Time is considered acceptable due to the low probability of an event in which the remaining vacuum breaker capability would not be i adequate.
(continued)
ABWR TS B 3.6-39 10/21/93 i
=
. . . . ~ . - - . . - - . - - . . . .
s .,
Wetwell-to-Drywell . Vacuum ;
c.. B 3.6.1.6 :
BASES ACTIONS IL1 ;
(continued)
Odif6Eid6F# open vacuum breakers allow communication between '
ths"dfisbil'andwetwellairspace,and,asa_ result,there'is the potential for wetwell overpressurization due to this bypass leakage if a LOCA were to occur. SlHEsithiTVicusiii '
breake?isifiyW6fWalTyrtifsis'd?Blaisdi6FfiFisithf6F617-~
C6hditioAIBj%iM}likelbel~intefediduelt6@65EF"~5u:i ihaldstishC 6stly s?~f,'tEc c '5TEh~EEEi; Tr a51tieg'"bc.
Bi~6s6d.~~T:hcrt' tiac is ellcwed tc close the vccuum brecher due to the icw probability of-ar, event thct would prc :urize pe4mery cent-ainment-r If vacuum breaker position ' indication is not reliable, an alternate method of verifying that the vacuum breakers are closedisbychE5lWnyitEst '
t
- iWstfUliissfitTbC ~ Ahothiniposj.iT6IQi5dlEitT66 altehhit#!issthedj i
.thidi&00mi bfiskFEinreicl osed stTSyT6Ee aldfE/iirifjggIfHitffEftr sMA 5~issid iboil6~thTsitwell pressure and .
verifying that the pressure differential.does not fall below- i 0.3 psid for 15 minutes without makeup. 'The required T2 !
hour Completion Time is considered adequate to perform"Ihis ,
test. If the stated criteria of this test-is not met, )
'Cond{tl6h?Cjiisaitjtisjynltif@.
C.1 and C.2 If the inoperable wetwell-to-drywell . vacuum breaker cannot ,
be closed or restored to OPERABLE status within the required >
i Completion Time, the plant must be brought'to a MODE.in which the LC0 does not apply. To achieve this status, the plant must be brought to at'least MODE 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and 1 to MODE 4 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. The allowed Completion Times are reasonable, based on operating experience, to reach the required plant conditions from full power conditions in-an orderly manner and without challenging plant systems.
SURVEILLANCE SR 3.6.1.6.1 REQUIREMENTS Each vacuum breaker is verified closed (except when.being -;
tested in accordance with SR 3.6.1.6.2 or when performing its intended function) to ensure that this potential large (continued) l o
ABWR TS B 3.6-40 10/21/93 8- e 5ma rp u " wp-- $y+ - *-_
Wetwell-to-Drywell Vacuum B 3.6.1.6 BASES SURVElLLANCE SR 3.6.1.6.1 (continued)
REQUIREMENTS (continued) bypass leakage path is not present. This Surveillance is performed by observing the vacuum breaker position i indication or by increasing the drywell pressure by 0.5 psid above the wetwell pressure and verifying that the pressure differential does not fall below 0.3 psid for 15 minutes l without makeup. The 14 day Frequency is based on engineering judgment, is considered adequate in view of the fact that the vacuum breakers are normally biased closed.by gravity forces. This verification is also required within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after any discharge of steam to the wetwell from the safety / relief valves or any operation that causes the drywell-to-we well differential pressure to be reduced by '
2 0.007 Kg/cm}d. A footnote is added to provide additional assurance of closure if position indication instruments indicate one or more vacuum-breakers are not closed.
SR 3.6.1.6.2 Each required vacuum breaker must be cycled to ensure that it opens adequately to perform its design function and returns'to the fully closed position. This ensures that the '
safety analysis assumptions are valid. The 18 month Frequency of this SR is based on the need to perform the surveillance during an outage. The vacuum breakers can~only be manually actuated and are only accessible during an outage.
SR 3.6.1.6.3 Verification of the vacuum breaker opening pressure is necessary to ensure thct the safety analysis assumption regarding vpcuum breaker full open differential pressure of :
0.035 Kg/cm g is valid. The 18 month frequency is based on the need to perform this Surveillance under the conditions that apply during a plant outage. The 18 month Frequency is acceptable based en the passive design of the vacuum breakers (no actuator required for opening).-
(continuco)
ABWR TS B 3.6-41 10/21/93. !
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, Wetwell-to-Drywell Vacuum B 3.6.1.6
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i BASES SURVEILLANCE REQUIREMENTS SR 3.6.1.6.4 (continued)
A CHANNEL CALIBRATION is a complete check of the instrument loop and the sensor. The test verifies the channel responds to measured parameter with the necessary range and accuracy.
The 18 month frequency is based on the ABWR expected refueling interval and the need to perform this Surveillance under the conditions that apply during a plant outage.
REFERENCE 1. ABWR SSAR, Section 6.2.
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ABWR TS B 3.6-42 10/21/93 1
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