ML20027D536
| ML20027D536 | |
| Person / Time | |
|---|---|
| Issue date: | 10/25/1982 |
| From: | Sheron B Office of Nuclear Reactor Regulation |
| To: | Fraley R Advisory Committee on Reactor Safeguards |
| Shared Package | |
| ML20027A678 | List:
|
| References | |
| FOIA-82-543 NUDOCS 8211040527 | |
| Download: ML20027D536 (5) | |
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DISTRIBUTION Central Files RSE R/F RSE S/F GAlberthal R/F EGoodwin TSpeis 007 f.' 5 ;;pp l
ESheron i
GMazetis WJensen GAlberthal 12iOR/dlD'Jit FOR:
Raymond F. Fraley, Executive Director, ACRS FR0it:
Brian W. Sheron, Chief, Reactor Systems Branch', DSI, i:5R
SUBJECT:
ACRS C0!'CERNS ON RCS VEliTS, FEED AND BLEED In the September 28, 1982 ACP.S subco:sittee meeting, J. Ebersole raised questions about the topics of RCS high point vents and feed and bleed.
To address these questions, Reactor Systems Sranch has prepared discussions in the attached enclosures.
921 1:a1 sig 3
5 Brian W. Sheron, Chief Reactor Systems Branch Division of Systems Integration Office of Nuclear Reactor Regulation
Enclosures:
As stated cc:
R. I'attson RSB S/Ls U. Lyon
Contact:
G. Alberthal x29407 (2 // O Y
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ENCLOSUEE 1 POST FEED & BLEED RECOVERY OF A EEK REACTOR All B&W plants, with the exception of Davis Besse, have safety grade HPI-purps capable of pumping sufficient water at the reactor safety valve set point to provide core cooling in the event that all steam generatcr cocling is lost (feed and bleed).
The HPI system at Davis Besse has a shut off head well belcw that of the safety valves and the PORY is too staall in capacity to lower reactor system pressure below the HPI shutoff head in the event of a comalete loss of feedweter.
Based en current staff evaluation, Davis Besse therefore, cannot be cc.oled by feed and bleed.
The plants with high pressure HPI can be cooled for an indefinite period by feed and bleed at the safety valve setpoint.
Feed and bleed could evertually be established in the recirculation moce by connecting the HPI system to the discharge of the LPI system.
The LPI system can be aligned to take suction from the reactor building sump.
For long term -
high pressure feed and bleed operation, HPI flow would have to be periodically adjusted to provide subcooling of the reactor system water l
end to prevent excessive cooling of the reactor vessel.
3-Complete recovery from the event recuires that the reactor system be eventually depressurized.
Depressurizatien could be acconplished by
- 1) reestablishing steam generator cooling er 2) venting the reactor f
- ystem (FORV, high point vents, and letdowr).
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Abrertal Transient Operator Guidelines (ATOG) for Oconee 3 are currently under review by the staff.
The Guidelines instruct the cperator to.
" bump" a reactor coolant pump following feed and bleed operation fcr which feedwater has been restored.
This action may be required even though feedwater has become available since steam fornation in the reactor ccolant hot legs may prevent the self-initiatior; cf natural circulation.
If a reactor coolant pump cannot be " bumped" or if feedwater is unavailable, the Guidelines instruct the operator to continue to depressurize and, cooldown the reactor system by venting thrcugh the PORV.
lio guidance is given fcr the possibility that the PDF.V will not open (presumably, high pressure feed and bleed would continue). Although not in the Guidelines, another course of action would be to open the high point vents to exhaust the trapped steam in the hot legs.
When sufficient steam were exhausted and replaced with HPI water, natural circulation cooldown would be established if; feedwater were available.
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ENCLOSUP.E 2 RCS VENTS
':UREG-0737 " Clarification of Tl'.I Action Pl?n Pequirecents" Item II.B.1, "Pcactor Coolcnt System Vents" provides the staff guidance on the i
required design features for RCS vents.
As steted in 10 CFR 50.44, the purpose of the vents is "to provide improved operaticnal capability to.
raintain adequate core cooling following an accident...".
The primary purpose of the II.B.1 requirement to install vents was for removal of ten condensible gases that could impede na ural circulation under degraded core conditions.
The purpose of the vents was never considered to be for renoving decay heat, depressurization, or other functions which are perferned by other equipment used to mitigate accidents.
i Accordingly, clarification iten 3 in UUREG-0737 states that "the size of the RCS vents is not a critical issue".
Clarification item 4 states that "where practical, the RCS vents should be kept staller than the
-size corresponding to a LOCA" to minimize challenges to the ECCS.
Based j
on this guidance, nearly all PWR's orifice the vent. system to limit the liovid discharge rate to less than the capacity of one charging pump at system pressure.
Typical ficw rates of an crificed vent on a PWR at l
pressure is about 30-100 gpm liquid, and abcut 500-1200 gpn Hydrogen gas.
This permits the venting of approximately one half of the RCS l
volune in one hcur.
Lower pressures will not significantly affect the volumetric gas discharge rate because flow would be choked.
f l-itbcugh the vent paths are not required to be redundant at each RCS hich point, the isolaticr of a vent path is required to be redundant to a
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rir.irize the censequences of a stuck oper. valve or ir.cdvertert actuation.
The reasons for these vent system criteria are based on.the cbservaticn that RCS vents have not been identified as necessary to rc.itigate the consequences of any Design Basis Event. Thus the use of vcnts is presumed necessary only for Deyond Desien Easis events.
Partini venting of the RCS would be possible if cne vent trcin failed because the other vent train must be poviered by a different power supply.
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