ML19326D749
| ML19326D749 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 07/01/1980 |
| From: | Hoffman D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8007030268 | |
| Download: ML19326D749 (9) | |
Text
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e Oe Commm Power 5
Company O
D General Off6ces: 212 West Michigan Avenue, Jackson. Michigan 49201
- Aree Code 517 788-0550 h
LJ July 1, 1960 Director, Nuclear Reactor Regulation Att Mr Dennis M Crutchfield, Chief Operating Reactors Branch No 5 U S Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPR 6 -
BIG ROCK POINT PLANT - REVIEW OF GENERAL ELECTRIC RESPONSES TO ACRS CONSULTANT CONCERNS General Electric Company (R Buckholz) letter to NRC (D Ross) dated February 21, 1900, discussed concerns raised by an ACRS consultant regarding post-accident operating conditions at light water reactors.
GE's discussion vae on a generic basis addressing these concerns for all boiling water reactors.
HNC letter dated May 7, 1980, requested Consumers Power Company to specifically evaluate the applicability of GE's discussion to Big Rock Point.
Consumers Power Company has completed the evaluation requested by the May 7, 1900, NRC letter. The attachment to this letter discusses the applicability of each concern addressed in GE's February 21, 1980, letter and provides infor-mation specific to Big Rock Point where appropriate.
David P Hoffman (Signed)
David P Hoffman Nuclear Licensing Administrator i
NRC Resident Inspector - Big Rock Point Attachment (8 pages) 8007030 A I
L' Question 1 Fressurizer level is an incorrect measure of primary coolant inventory.
Response.
This concern is not applicable to Big Rock Point.BRP measures primary coolant inventory directly using differential pressure sensors attached to the primary vessel and primary steam drum.
Question 2 The isolation of small breaks (e.g., letdown line, PORV) not addressed or analyzed.
Response
At BRP automatic isolation only occurs for steam line breaks outside of con-tainment.
Such breaks are addressed in Section 3.1.1.1.2 of NED0-24708.
Question 3 Pressure boundary damage due to loadings from: a) bubble collapse in subcooled liquid and; b) injection of ECC water in steam-filled pipes.
Response
The GE response is applicable to BRP.
BRP has no geometry equivalent to a
. pressurizer surge line and pressurizer, and ECCS water is injected at low pressure into the vessel rather than into pipes, hence this concern is not applicable to BRP.
Question 4 In determining need for steam generators to remove decay heat, consider that the break flow enthalpy is not core exit enthalpy.
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Response
BRP has no steam generators, and no credit is taken in Appendix K LOCA analysis for heat removal through the emergency condenser, therefore this concern is not applicable to BRP. The GE modeling of break flow is discussed in NED0-20566.
Question 5 Are sources of auxiliary feedwater adequate in the event of a delay in cooldown subsequent to a small LOCA?
Response
BRP does not rely on feedwater to remove decay heat following a LOCA, therefore, this concern is not applicable to BRP.
BRP has an essentially infinite supply of emergency core cooling water (Lake Michigan). However, once the containment has been filled to the 590 ft. elevation, the operator is directed to switchover to the recirculation mode of long term cooling.
In this mode, water from containment is pumped through the core spray heat exchanger and back to the reactor, and no further makeup water is required (although it would be available if required).
Question 6 Is the recirculation mode of operation of the HPCI pumps at high pressure an established design requirement?
Response
BRP does not have a high pressure injection system that can be used for recir-culation, 'therefore this concern is not applicable to BRP.
The core spray pumps used in the long term cooling recirculation mode at BRP. are low head i
Pumpswithdesignrequirementslbasedspecificallyonthatservice.
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. Question 7 Are the HPCI pumps and RHR pumps run simultaneously? Do they share common piping?
Suction? If so, is the system properly designed to accommodate this mode of operation (i.e., are any NPSH requirements violated, etc.?).
Response
The BRP "RHR" pumps, or shutdown cooling pumps, are not, and presently cannot, be used for long term cooling after a LOCA. Further, the shutdown cooling pumps do not share piping or suction with the established means of long term cooling, i.e..the core spray pumps. Therefore, this concern is not applicable to BRP.
Question 8 Mechanical effects of slug flow on steam generator tubes needs to be addressed (transitioning from solid natural circulation to reflux boiling and back to solid matural circulation may cause slug flow in the hot leg pipes).
Response
BRP does not have steam generators therefore this concern is not applicable to BRP.
BWR post-LOCA cooling modes are addressed in NEDO-24708. The only com-ponent 'at BRP which is similar to a steam generator is the emergency condenser.
The emergency condenser is a steam condensing device which is located above the highest point on the BRP primary coolant loop. Transition to solid natural circulation will never occur unless the operator inadvertantly overfills the primary coolant loop after a small LOCA or other transient and the primt ry system safety valves fail to lift. This is considered highly unlikely.
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Question 9 Is there' minimum flow protection for the HPCI pumps during the recirculation mode of operation?
Response
As noted in response to Question No. 6,- BRP does not have a high pressure injec-tion system that can be used for recirculation, and therefore this concern does not apply to BRP. Minimum flow protection for BRP safety injection pumps (i.e.
fire pumps and core spray pumps) is provided by relief valves on the fire system piping and on the core spray piping inside of containment.
Question 10 The effect of the accumulators dumping during small break LOCAs is not taken into account.
Response
BRP does not utilize accumulators to mitigate LOCAs. Therefore, this concern does not apply to BRP.
Que.stion 11 hhat is the impact of continued running of the RC pumps during a small LOCA?
Response-
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l The impact of continued running of the recirculation pumps has been addressed in Sections 3. 3. 2. 2, 3.2. 2. 3, and 3.5. 2.1.5.1 of NED0-24708.
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_ Question'12
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.During a small break LOCA in which offsite power is lost, the possibility and impact of pump seal damage and leak has not been evaluated or analyzed.
l Respont.
The seals of the BRP fire pumps and core spray pumps are cooled by the pump primary process water. No external cooling from auxiliary support systems, such as service
' water or room air coolers,ils required for the pump seals.
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5 Question'13'-
- During transitioning from solid natural circulation to reflux boiling and back again, the versel level vill be unknown'to the operators, and emergency pro-
.cedures andLoperator training may be inadequate. This needs to be addressed and evaluated.
Response
There is no'similar transition in BRP's case. In addition, vater level measure-ments in the. vessel (within the " shroud") and in the primary steam drum (down-comer region)'are incorporated into the operator guidelines.
Consequently, this concern does not apply to BRP.
-Question lh--
The'effect of non-condensable gas accumulation in the steam generators and its possible disruption tof decay heat removal by natural circulation needs to be addressed.
Response
The effect' on non-condensable gas accumulation is addressed in Section 3.3.1.8.2
.of NEDO-24708. For BRP non-condensable gases vould collect in the top of the primary steam' drum where-they vould have no significant effect on natural circula-
-tion within the primary coolant loop. However, non-condensable gases collecting
- in the top of. the steam drum-could incapacitate the. emergency condensor. To mitigate this effect Consumers Power Company has ccemitted to provide the capabil-
-ity to remotely vent the emergency condensor tube bundles.
-Question 15-Delayed cooldown following a. small-break LOCA-could raise the containment pressure and activate th'e containment spray system. ~ Impact and consequences need addressing.
- Response L BRP has. an automatically actuated enclosure (dryvell) spray system. Essential epiment in the enclosure has been qualified for the environment that vould Lexist,after'a'LOCA.
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Question 16*
This concern relates to the possibill.; that an operator may be inclined and perhaps even trained to isolate, where possible, a pipe break LOCA without realizing that it might be an unsafe action leading to high pressure, and short-term core bakeout. For example, if a BWR should experience a LOCA from a pressure boundary failure somewhere between the pump suction and discharge valve for either reactor recirculation pump, it would be possible for the operator to close these valves following the reactor blowdown to low pressure and thereby isolate the break, stop the blowdown, and rep;cssurize the reactor coolant system. Before such isolation should be permitted, it is firs: re:::aory to show by an appropriate analysis that the high pressure ECCS is adequate to reflood the uncovered core without assistance from the low pressure ECCS which can no longer deliver flow because of the repressurization. Otnerwise, such isolation action should be explicitly forbidden in the emergency operating instructions.
Response
If a BWR should experience a LOCA from a pressure boundary failure somewhere between the recirculation pump suction and discharge valves, it is possible for the operator to close these valves following the reactor blowdown to low pressure and thereby isolate the. break.
In reference 2, the NRC concluded based on information provided by GE that recirculation break isolation is not a problem.
In order for the BRP primary coolant system to repressurize following isolation of a recirculation line break, the isolation would have to occur prior to RDS actuation.
RDS actuation occurs or. coincident low steam drum water level, low
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Excerpt from Reference 1.
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reactor water level, and high fire header pressure. Containment pressure is not included in the'RDS actuation logic.
If br ak isolation were to occur prior to reaching
',w reactor water level, the vessel would repressurize to normal operating pressure if the main steam line was not isolated, and to the emergency condenser ac*.uation setpoint if the steam line was isolated.
If sufficient high pressure makeup was available, the primary systec would refill and the plant-would be returned to a stable mode of operation with no
. further loss of inventory to the containment. Without sufficient high pressure 'uxeup (either CRD pumps or main feedwater pumps) levels would continue to fall, resulting in automatic RDS actuation. This would depressuri:e the vessel and allow the low pressure ccie spray system to function. Thus isola-tion of a recirculation line break has no adverse effect on the course of the acci-dent.
In fact, it would favorably preclude RDS actuation given the availability of adequate high pressure injection flow for decay heat removal.
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- References -
1.
Memo, C. Michelson to D. Okrent, "Possible Incorrect Operator Action Such
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as Pipe Break Isolation," June 4,1979.
2.
Letter, D. G. Eisenhut to R. L. Gridley, " Potential for Break Isolation and Resulting-GE-Recommended BWR/3 ECCS Modifications," June 14, 1978.
P 3.
" Additional Information Required for NRC Staff Generic Report on Boiling Water Reactors," NEDO-24708, August 1979.
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