ML20155C165
| ML20155C165 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 10/03/1988 |
| From: | Hariston W ALABAMA POWER CO. |
| To: | NRC OFFICE OF ENFORCEMENT (OE) |
| References | |
| EA-88-113, NUDOCS 8810070264 | |
| Download: ML20155C165 (37) | |
Text
i S Alabama Power Company ,. .
600 North 18 h Street Post Off.ce Bom 2641 B rm:ngham, Alabama 35291-040o Te:ephone 205 2501837 W. G. Hairston, lla Senior V ce President N uc' ear Operabons g) ,
October 3,1988 t+ satun **c swem Docket Nos. 50-348 50-364 Enforcement Action 88-113 Director, Office of Enforcement U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Vashington, DC 20555 centlemen Joseph H. Farley Nuclear Plant NRC Inspections of February 22 - March 11, 1988 RE: Notice of Violation and Proposed Imposition of Civil Penalty This letter transmits Alabama Power Company's response to the Staff's transmittal letter and Notice of Violation and Proposed Imposition of Civil Penalty dated August 3, 1988. Attachments 1 and 2 to this letter, together with their enclosures, pro Alabama Power Company's "Reply to the Notice of Violation" (see 10 CFR 2.201) and "Ansver to the Notice of Violation" (see 10 CFR 2.205), respectively.
Alabama Power Company denies that it has violated the requirements of Technical Specifications or the Final Safety Analysis Report (FSAR) for Farley Nuclear Plant as it relates to this issue. This denial is based upon an independent evaluation of the as-found condition by Vestinghouse and Dr. Elemer Hakay, a nationally recognized nuclear industry pump consultant. Alabama Pover Company would like to reconstruct the facts surrounding this issue in belief that these concerns are only reasonable in view of what is nov knovnt that it it only with the benefit of hindsight that criticism can be levied. Alabama Power Company contends that a review of the facts and circumstances surrounding the phenorenon of hydrogen accumulation in the Train A RHR to charging pump suction line (without the benefit of current information) should conclude that management acted prudently during the pertinent time period. Such actions were not indicative of a "significant breakdown in the management controls" of our corrective action program as asserted by 0810070264 380928 F'DH ADOCK O'3000348 O PDC i g
i
, 5 8 8 Director, Office of Enforcement U. S. Nuclear Regulatory Commission Page 2 the Staff. Should the Staff maintain its position that a violation occurred, ve conclude that because this phenomenon was discovered, reported and promptly addressed by Alabama Power Company, full mitigation, not escalation, of any civil penalty is varranted.
Alabama Pover Company encourages the Staff to give due consideration to its Reply and Ansver and after doing so, issue an order in accordance with 10 CFR 2.205(d) dismissing the Notice of Violation.
Alabama Power Company is also concerned that the NRC's August 4, 1988 press release did not present a fair characterization of the facts and issues involved in the subject Notice of Violation. Ve are distressed that the press release presented the NRC's opinion regarding High Head Safety Injection System (HHSIS) operability without indicating that Alabama Power Company disputed the NRC's conclusions. Further, the NRC press release states "... NRC inspectors identified the fact that the Company had performed an inadequate engineering analysis of the emergency cooling system's operability." This statement implies that the NRC inspectors discovered a condition which Alabama Power Company had overlooked. To the contrary, Alabama Power Company discovered the condition and reported it to the NRC. The press release further stated that "the Company was avare of indications that hydrogen gas coming out of solution in the reactor cooling vater was accumulating in pipes to the extent that there was a potential that charging pumps which vould be needed to inject cooling vater into the reactor during certain abnormal occurrences vould not vork." This was not the case. The only indication of gas accumulation prior to March 1, 1988 vas in the Unit 2 B (2B) charging pump suction piping. The accumulation of gas in the 2B charging pump suction was addressed operationally to ensure the 2B charging pump vas maintained operable. Through this operational control, Alabama Pover Company ensured the 2B charging pump vas operable as far as gas accumulation in the suction piping was concerned.
Hydrogen gas had not been vented from the Train A RHR to charging pump suction line. Therefore, the only concern known to Alabama Pover Company, the accumulation of gas in the 2B charging pump suction, had been adequately addressed. Additionally, this portion of the press release vas vorded to convey major safety consequences to the public because of the assertion that "... charging pumps needed to inject cooling vater... vould not work." This description is misleading because it ignores that only one redundant train vas affecteo, that the injection phase was unaffected by the issue, and that this vat only a potential concern for a limited cpectrum of small break sizes. Had the press release been aore accurate in this regard, an entirely different view of safety significance vould have been conveyed. The press release continued to state that "a Company recommendation for a change in the system remained open for six and one-half years and was finally canceled without the recommended analysis being performed." The design change referred to addressed gas accumulation in the Unit 2 B charging pump suction only. It did not state or hypothesize the accumulation of gas
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I Director, Office of Enforcement U. S. Nuclear Regulatory Commission Page 3 l !
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at any other location in the system. rinally, the press release states !
l "NRC officials said management contr As at Farley resulted in 'the operation of the plants in a degraded condition. for an extended period l of time'." Alabama Power Company does not believe that the failure to ;
identify the source of the hydrogen, a complex technical issue which is j not yet fully understood today, can be construed as "problems in management controls." Instead, the operation of Farley with the ;
accumulation of hydrogen was the result of an inadequate knowledge base l throughout the industry. Alabama Power Company was thus not in a position to detect such an off-normal condition.
NRC press releases are often relied upon by the local media as the -
principal source of information when reporting on enforcement action !
taken against a licensee. Any mischaracterizations in the NRC press i release vill likely be repeated and perhaps magnified in local news l accounts. This can have a detrimental etfeet on the general public's !
perception of a licensee, which ultlicately can lead to distrust and lack j of cooperation. For these reasons, ve urge the NRC to ensure that press ,
releases accurately report the facts and do not judge the guilt or i innocence of a licensee prior to the conclusion of the administrative !
process.
If there are any questions, please advise. ;
Respectfully submitted, !
, ALABAHA POVER COMPANY l i l
t KM he &
V. G. Hairston, III l VGH.III/REHidst-V8.4 I
cc: Mr. L. B. Long Dr. J. N. Grace Mr. E. A. Reeves Mr. G. F. Maxwell SVORN TO AND SUBSCRIBED BEFORE ME THIT k DAY 0 Oc.hh t- , 1988 1
Notary lyic Hy CoYmission Expires h- N-- N
. s ATTACIIMFNP 1 Alabama Power Company Joseph M. Farley Nuclear Plant Reply to Notice of Violation Enforcement Action 88-113 j Inspection Report Numbers 50-348/88-05 and 50-364/88-05 A. Summary of Position In accordance with the Commission's Rules of Practice and Procedure, as described in the Notice of Violation transmittal letter dated August 3, 1988, Alabama Power Company (sometimes hereinafter referred to as "APCo" or "the company") hereby replies to the Notice of Violation and i Proposed Imposition of Civil Penalty. See, 10 CFR 2.201. As more fully discussed belov, Alabama Power Company does not believe that the ;
Train A Cmergency Core Cooling System (ECCS) charging pumps on Units 1 and 2 vere inoperable for use in the recirculation mode. Instead, -
Alt.bama Power Company, having conducted an appropriate evaluation, and 1 consulted with an industry-recognized pump consultant, concludes that the affected systems vould have performed their required safety functions. Moreover, Alabama Power Company believes that the heavy reliance which the Staff apparently placed on the Vestinghouse letter of March 4, 1988, to support the Notice of Violation vas misplaced.
That letter identified a vorst case, "very improbable" scenario, which appears to focm the basis for the Staff's conclusion that the ECCS subsystem vas inoperable. APCo asserts that any conclusion based on a very improbable sceuprio necessarily entails undue speculation and should be rejected In the alternative, and assuming that the Staff maintains its position that a violation of Technical Specifications /FSAR requirements has occurred, APCo believes that the alleged violation has minimal safety significance. Thus, any violation should not be issued at more than a Severity Level IV. Moreover, since prompt corrective action was taken by APCo, mitigation, not escalation, of the base civil penalty is appropriate.
- Neither the transmittal letter nor the Notice of Violation provided any other technical analysis to support the Staff's position. Since March 4 1988, Vestinghouse has refined its earlier evaluation and such refinemeni has been utilized by APCo in preparing both its Peply to the Notice of Violation and its Ansver.
1
. s Attschm:nt 1 ' '
Page 2 B. Discussion 1 1
This attachment refers to the Notice of Violation which states: '
During the Nuclear Pegulatory Commission (NRC) inspection conducted l on February 22 - March 11, '.988, a violation of NRC requirements was l identified. In accordan & with the "General Statement of Policy and l Procedure for NRC Enforcer:.?nt Actions," 10 CFR Part 2, Appendix C (1988), the Nuclear Re g atory Commission proposes to impose a civil penalty pursuant to Scaion 234 of the Atomic Energ; Act of 1954 as amended (Act), 42 U.e,.r. 2282, and 10 CFR 2.205. The particular violation and associated civil penalty is set forth below:
Technical Specifiestion 3.5.2 requires that two independent emergency core cooling system (ECCS) subsystems shall be OPERABLE in Mode: 1, 2. and 3, with each subsystem comprised of, in part, one OPERABLE centrifugal charging pump and an OPERABLE flow path capabic of taking suction from the refueling vater storage tank on a safety injection signal and transferring suction to the containment sump during the ,
recirculation phase of operation. OPERABLE is defined by Technical Specification 1.18 as, in part, "capable of performing its specified functions."
The functions of the charging pumps as high head safety ;
injection (HHSI) pumps are delineated in the Final Safety Analysis Report (FSAR). FSAR Chapter 6, Emergency Core '
Cooling Systems, Section 6.3.2.2.7, System Operation, l paragraph B, Recirculation Mode, states, "la] portion of each ,
one of the RHR pump's discharge flov vould be used to provide '
suction to tvo operating charging pumps which vould also deliver directly to the RCS cold legs," and, "[this] mode of operation assures flov in the event the depresmrization proceeds more slovly so that the reactor coolant system pressure is still in excess of the shutoff head of the residual heat removal pumps at the onset of recirculation."
Contrary to the above, the licensee operated the reactors in Modes 1, 2, and 3 and failed to maintain two independent ECCS subsystems OPERABLE as defined in Technical Specification 3.5.2 and FSAR Section 6.3.2.2.7 because the "A" train ECCS subsystems on Units 1 and 2 vere rendered inoperable for use in the recirculation mode due to the presence of substantial amounts of hydrogen gas in the crossover piping from the RHR pumps to the centr ifugal charging pump suctions. ,
l Specifically, on February 26, 1988, approximately fifty-six cubic feet of hydrogen gas was discovered in the crossover piping of Unit 1, and on February 29, 1988, approximately I forty cubic feet of hydrogen gas was discovered in the crossover piping of Unit 2.
This is a Severity Level III violation (Supplement I). ,
Civil Penalty - $100,000
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. s Attach =2nt 1 '
- Page 3
- C. Denial of the Allt..d Violation Alabama Pover Company denies that, for cach unit, the Train A charging pump, or its associated flow path. vas inoperable in the recirculation mode duting the petiod that hydrogen gas was entrapped in its RHR to che.rging pump suction line. Attachment 2, paragraph B.1, and Enclosure 1 1 pro-ide evidence that the charging pump and its associated flow path .
vere operable in the recirculation mode.
D. Corrective Steps To Avoid Additional Gas Accumulation Periodic venting of the Train A RHR to charging pump suction line on l both units was implemented to limit future hydrogen accumulation. The ,
periodic venting is conducted frequently enough so that any accumulated '
hydrogen is less than that recommended by the NSSS supplier and pump vendor.
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E. Actions Taken to Ir. prove Plant Design and Results Achieved A loop seal has been installed on the Unit 1 RHR to charging pnap suction line at approximate elevation 109. The loop seal is designed to preclude hydrogen migration f rom the A charging pump st etion line i towards the Train A RHR to charging purp suction line. Based on the results of subsequent, periodic venting of the subf.ct line, this loop t
seal has significantly retarded hydrogen accumulation. Alabama Power Company vill install a similar loop seal on Unit 2 during its sixth refueling outage.
In order to verify the re duction of hydrngen accumulation, a venting
, program developed by the NSSS supplier is being implemented. The .
! prohram vill determine the effectiveness of the loop seal under various I operating conditions and configuratione. The results of the venting l 1
program vill determine if additional corrective action is required. i J
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, s ATTACllMENT 2 1
Alabama Power Company Joseph H. Farley Nuclear Plant Answer to Notice of Violation Enforcement Action 88-113 Inspection Report Numbers 50-348/88-05 and 50-364/88-05 A. Summary of Pocition In accordance with the Commission's Rules of Practice and Procedure, as described in the Notice of Violation dated August 3, 1988 Alabama Power Company hereby ansvers the Notice of Violation and Proposed Imposition of Civil Penalty. See, 10 CFR 2.205. Alabama Power Company denies that the subject violation occurred as stated and contends that the NRC Staff has not provided an adequate basis to justify its NOV, and the associated civil penalty. Based on an evaluation of the as-found condition, Alabama Power Company and its consultant, Dr.
Elemer Makay, with system analysis by Vestinghouse, have concluded that there vas no significant loss of performance of the Train A ECCS charging pump Dr. Hakay has determined that if the recirculation mode vere initiated the charging pump would shortly purge itself of the hydrogen and then resume normal operation.
Even if the hydrogen reached the pump as a solid slug (a condition deemed very improbable by both Vestinghouse and Dr. Hakay), and such an improbable occurrence resulted in temporary gas binding of the charging pump, Alabama Pover Company has determined through engineering evaluation and consultation that such a condition vould not cause catastrophic failure of the pump. Vestinghouse has calculated that the vorst case, maximum time that it is anticipated the pump vould be without vater for lubrication is 12.5 seconds. Based on Dr. !!akay's evaluation and Vestinghouse's calculations as described in Enclosure 1, it is shown that the ECCS system performance vould have been acceptable.
Therefore, it is Alabama Power Company's position that the accumulation of 56 cubic feet of hydrogen in the Train A RilR to charging pump suction line of Unit 1, vould not render this pump "inoperable." It follows that the accumulation of 40 cubic feet of hydrogen in the same suction line of Unit 2 vould not render its ECCS subsystem inoperable either. ;
l Additionally, the con < i'ision reached in the NOV, and its transmittal letter, that the EC' absystem vas inoperable in the recirculation mode, is not suppo: A sy engineering analysis. The Staff apparently placed heavy relia.4- vn the Vestinghouse letter of March 4, 1988 to justify the violate.. and that reliance vas misplaced. The letter simply does not afford an adequate basis to conclude that catastrophic pump failure vould have occurred.
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1 Attechtsnt 2 - '
Page 2 Alternatively, should the Staff maintain its position regarding the existence of the violation, 100 percent escalation of the base civil penalty is not warranted and, in fact, full mitigation of the civil penalty is appropriate. When the totality of facts and circumstances surrounding this occurrence are re'rieved, without the advantage of current knowledge, it is clear that Alabama Power Company neither knew nor should have known of the accumulation of hydrogen in the Train A RHR loop. Additionally, the as-found condition was not safety significant as it relates to a Level III violation, defined by 10CFR Part 7, Appendix C. Hitigation of the civil penalty is also appropriate since Alabama Power Company took prompt and extensive corrective action once the event was discovered and provided prompt reporting to the NRC.
B. Discussion l The following discussion addresses each of the above positions.
Alabama Pover Company has examined (1) technical specification requirements regarding charging pump operability, (2) the safety significance of the as-found condition, (3) the events which led to the discovery of the alleged deficiency and (4) the Enforcement Policy (10 CFR Part 2, Appendix C) regarding the above iscues. The Company has also interviewed numerous people who vere associated with this issue during the relevant time period and engaged Dr. Elemer Makay and Vestinghouse to perform certain technical evaluations.
- 1. The Technical Specification /FSAR Operability Requirements Vere Not Violated As discussed belov, Alebama Pover Company concludes that the Unit 1 !
and 2 emergency core cooling system subsystems remained operable j notvithstanding the existence of hydrogen in the Train A RHR to charging pump suction line. Technical Specification 1.18 defines OPERABLE-0PERABILITY as whenever a system, subsystem, train, component or device is capable of performing its specified function (s) and when all support components are also capable of performing their related functions.
In pertinent part, Section 3.5.2 of the Farley Technical Specifications provides:
Two independent Emergency Core Cooling System (r.CCS) subsystems shall be OPERABLE [in Modes 1, 2, 3] vith each subsystem comprised of:
- a. One OPERABLE centrifugal charging pump, i
- b. One OPERABLE residual heat removal heat exchanger,
- c. One C?ERABLE residual heat removal pump, and
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. Attechuant 2 .
Page 3 h
! d. An OPERABLE flow path capable of taking suction from the refueling vater storage tank on a safety injection signal and transferring suction to the containment sump during the recirculation phase of operation.
While preparing its response to the NOV, Alabama Power Company consulted with Vestinghouse to obtain a more precise understanding ,
of operability of the ECCS subsystem as it pertains to this issue.
Vestinghouse stated in a letter dated September 8, 1988r !
j Operability of the ECCS system is addressed in plant T-Spec
! 3/4.5.2. The LCO requires 1) one operable CCP, 2) one operable RHR heat exchanger, 3) one operable RHR pump and 4) a flovpath capable of taking suction from the RVST and transferring suction to the containment sump during recirculation. ;
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. In addition, surveillance requirement 4.5.2.1 requires HHSI -
- Single Pump Flov > 193 gpm (each injection line). E a .
It is the position of Vestinghouse that this flovrate applies i j only to flow requirements during the injection phase. This ;
specification does not address flow requirement during j
recirculation. i
- For recirculation, operability is defined as an available ;
i flovpath from the containment sump including an operab
- andchargingpump,andanoperableRHRheatexchanger.}eRHR l I ;
j Alabama Pover Company has also consulted with Dr. Elemer Makay ,
i regarding the effect of the as-found hydrogen gas on the charging l j pumps in the recirculation mode. Although APCo acknowledges that !
j the operation of Train A vith gas pockets for a limited period of 1 time is not a desired operating condition, the Company does not
, agree that the charging system was inoperable under the Technical i l Specification / FSAR definition. This conclusion has been based on :
Alabama Power Company's review and consultation with Dr. Hakay. {
l Regarding operability of the charging pumps, recent evaluation has j shovn that the amount of trapped gas discovered in Train A RHR to l charging pump suction line piping (56 cubic feet in Unit 1, 40 l cubic feet in Unit 2) vould not have caused the destruction of the !
q pump prior to the gas being completely pumped out of the system. In 3 addition, pump testing performed on similar pumps at Palo Verde
- (1985) and a fossil plant (1980) confirm that this type of pump can operate under similar conditions for at least several minutes j) vithout any pump damage. (See Enclosure 1.) Alabama Power
] Company's evaluation of what the charging pump is expected to 1
{ *Flovrate requirements for recirculation are addressed in 10CFR50.46.
Specific requirements for Farley Nuclear Plant are addrest.ed in Enclosure
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. s Attachmsnt 2 '
Page 4 experience as a result of the presence of hydrogen gas in the RHR to charging oump suction header is that although the pump may stall (see Enclosure 1, Reference 4), the system vill re-flood the pump suction. This vill happen within a relatively short time, estimated to be less than 13 seconds. The system rapidly purges the suctioa piping of all hydrogen gas, and normal operation resumes without significant loss of performance (or perhaps no loss at all). Enclosure 1 provides a more detailed description and references two test reports that support the conclusion that gaseous flow or gas / vater flov is tolerable for a limited period of time. The reports illustrate that gas / vater or intermittent gas flow causes instability in the pump, but that the pump can be expected to pass the gas and recover to its full operational capabilities. As stated in a 1970 article by Dr. Makay, "... air trapped in suction and discharge piping is an occasional cause of instability. Hovever, this is not of a permanent natures eventually it is vashed out and smooth operation is resto.ed."'
i Alabama Power Company maintains that, consistent with the Technical Specification requirements, the flow path was always capable of taking suction from the refueling vater storage tank. While ve acknowledge that during the recirculation phase intermittent water / gas pockets entering the pump for a short period of time vould not be the most preferable or efficient vay to operate the r pump, the flow path vas never blocked sufficiently to render the l charging pump "inoperable." ;
o Even assuming that the charging pump failed to deliver its full l capacity flov to the reactor coolant system (RCS), Alabama Power Company's analysis of RCS conditions at the time of switchover to t recirculation concludes that such full capacity flov as dictated by the initial injection phase is unnecessary during the subsequent recirculation phase. This is because enough time has passed since the initiation of the LOCA such that decay heat levels are greatly reduced. Consequently, the need for HHSI flow into the RCS is greatly reduced. The function of the ECCS subsystem during the 7 recirculation mode is satisfied if the core remains covered at all i times. This dictates that either flovrates be maintained st greater than the boil off rate or that flov is not degraded or ,
ceased for long enough periods to allov core uncovery. Enclosure 2 i provides a discussion regarding the effect of hydrogen gas accumulation on the Train A RHR to charging pump suction line and its impact on flow requirements. In the enclosure, Vestinghouse !
states, "Given the systems evaluation and assuming the pump i continues to operate, Vestinghouse has concluded that the hydrogen l gas is not capable of degrading HHSI flov for a long enough time to :
result in core uncovery. Therefore, more than adequate HHSI flov (
vould be available." ,
'"Eliminating Pump-Stability Problems", by E. Hakay, Franklin Research Laboratory, Pover, July 1970 at 62. '
Attech:snt 2 Page 5 In the NOV, the Staff implies that the ECCS charging pumps and/or flow path was inoperable solely due to the presence of hydrogen gas in the Train A RHR to charging pump suction line. Based on :
additional consultations with Vestinghouse and Dr. Hakay, Alabama Pover Company contends that such an implication is incorrect.
Indeed, absent in the NOV is any technical analysis or basis for the Staff's summary determination that the mere presence of hydrogen automatically renders the ECCS subsystem inoperable.
Alabama Pover Company believes nov, of course, that such a summary determination is not justified.
i The logic referenced in the Staff's transmittal letter was
! apparently predicated on Vestinghouse's March 4, 1988 letter; and more specifically, a "vorst case," very improbable scenario. The Staff fails to acknowledge the more likely scenario identified in t the letter (and nov confirmed by Dr. Hakay) that "hydrogen vould -
normally be expected to mix vith the vater prior to reaching the pump suction." The Staff ignores the important part of the letter ,
where Vestinghouse says that in such an event, "enough lubrication '
is provided to prevent pump failure" and that once the gas is purged, "pump performance vill recover." Vestinghouse adds:
4 Vestinghouse believes this is acceptable since pump performance is less stringent during recirculation than during injection.
Therefore, a slight degradation of charging pump flov for a short period of time at the initiation of recirculation is acceptable. (Emphasis Added)'
Vieved in its proper context, the Staff's conclusion that the
- charging pump vas inoperable is inconsistent with the Vestinghouse i Vestinghouse developed the March 4, 1988 letter in letter.
l respc.nse to the urgent need of Alabama Pover Company for quantitative guidelines for hydrogen ventina Therefore, it was necessary that Vestinghouse forego a detaileu, rigorous evaluation and, instead, develop a conservative, safe criteria for venting by l making safe, very conservative assumptions. This approach, while ;
vell suited for restoring acceptable operating conditions in the shortest possible time, is not appropriate as the basis for enforcement proceedings. Enforcement action should be based on evaluations which give due consideration to actual pump and system :
response to the accumulation of hydrogen as opposed to evaluations [
intended to define a condition for operation which assures no '
question as to pump and system capability. Enclosure 1 provides I the results of a more balanced evaluation of the effects of the hydrogen. Since no other technical basis supporting this l
< conclusion is offered by the Staff, it follovs that the conclusion ,
J of inoperability is not justified. '
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'It is readily apparent from Enclosure 1, based on a system response evaluation by Vestinghouse and a pump response evaluation by Dr. Elemer Hakay, that Alabama Power Company has greatly refined this early evaluation.
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1 Attechsent 2 *
- Page 6 Based on the above, Alabama Power Company concludes that (1) the Train A charging pump would have remained operable throughout gas / vater flow conditions and (2) gas entrapment in the Train A RHR to charging pump suction line did not render the flow path inoperable. Therefore, Technical Specification conditions vere always satisfied in that the pump and flow path vere operable, and further, FSAR provisions vere not violated.
- 2. Alternatively. Assuming A Violation Occurred, It Vas Not Safety Significant And Does Not Justify A Severity Level III Violation And A $100,000 civil Penalty should the Staff remain convinced that a violation occurred as stated in the NOV, Alabama Power Company maintains that the alleged deficiency does not warrant escalated enforcement action because the as-found condition lacks the requisite safety significance.
Farley Emergency Event Procedures (EEP) and operator training would have guided operators to assure adequate core cooling with or without HHSI pumps.
As more fully explained in Enclosure 1, a 4 inch or above loss of coolant accident (LOCA) results in such a rapid depressurization of the RCS that RHR injection occurs before the recirculation mode is initiated. For small break (SB) LOCAs of 1 inch or belov, no containment spray initiation is assumed and operator action vill result in the RCS reaching cold shutdown before the P.VST reaches the setpoint for recirculation. Therefore, a SBLOCA that assumes ECCS subsystem operability is in the range of 1-4 inches, since it is only there that the RVST vould reach its setpoint for recirculation before the RCS pressure decreased to less than RHR discharge pressure for RCS injection. Switchover to the recirculating mode is performed well into the accident scenario after decay heat has lessened: therefore, time is not as much a critical factor and procedural guidance specifies manual operator actions.
In such a case, Farley oper. tor procedures for both units, which are based on and consistent with N"C-approved Vestinghouse Ovner's Group guidelines, provide specific instructions for cooldovn and depressurization of the RCS both with or without HHSI pumps.
Specifically, the Vestinghouse Ovner's Group guidelines as described in a letter to the NRC state:
'FSAR 6.3.2.2.7 provisions are substantially the sanm u thusw appearing in Technical Specification 3.5.2.
Attachtsnt 2 ' '
Page 7 For LOCA scenarios characterized by RCS pressures greater than the shutoff head of the RHR pump, EEP-1 transitions the operator to procedure ESP 1.2. This procedure provides guidance to cooldovn (at rates up to 100*F/hr.) and depressurize the RCS to cold shutdown conditions. For the more probable case where the HHSI pumps are running, procedure ESP 1.2 provides guidance to reduce and terminate HHSI pump flov in combination with the plant cooldovn and depressurization. For the case where HHSI pumps are not operating, procedure ESP 1.2 functions to cooldovn and depressurize the PCS. Since RCS pressure vill follov saturation pressure for RCS temperature, this RCS cooldown vill result in delivery of the safety injectiop accumulator contents followed by delivery of the RHR flov Because these guidelines address the scenario of a complete absence of HHSI charging pumps and still effectively resolve the SBLOCA, safety significance is minimal. Even assuming inoperability of the charging pumps, there never has been any unacceptable risk that endangered the public health and safety.
For this reason an escalated Severity Level III Civil Penalty is I
not warranted. The determination that the HHSI charging pump vas I inoperable vould justify at most a Severity Level IV Violation.
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- 3. Alabamp Power Company Had Neither Actual Nor Constructive Knowledge of Hydrogen Accumulation in the RHR Line The NOV is based upon the assumption that the company "performed an inadequate engineering analysis of system operability based on indications of hydrogen gas coming out of solution for reactor coolant in the HHSI system." The Staff increased the base civil i
penalty by 100%, "because of the failure of Alabama Power Company management to act on available information concerning the 1 !
1 occurrence of gas generation and its potential accumulation in the 1 crossover piping." Alabama Power Company believes that its position was adequately stated in the Enforcement Conference, but {
i it appears that the Staff may not have had a clear understanding of 1
'This quote (with Farley procedure nomenclature substituted for generic nomenclature) is taken from a letter dated August 29, 1985 to D. G. t i
Eisenhut, Director, Division of Licensing, NRR, from L. D. Butterfield, !
Chairman, Vestinghouse Ovner's Group. In response to the guidelines ;
referenced here, the NRC, in a supplemental SER dated December 26, 1985, said: "Based on our review of the above guidelines, ve conclude that the Revision 1 ERGS provide adequate guidance for the loss of high pressure makeup before the occurrence of inadequate core cooling."
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Attcch::nt 2 *
- Page 8 our position and the relevant facts. Ve therefore vill set out our position and the facts more clearly below. This review shows actual hydrogen accumulation in the RHR line had never been previously identified as a concern and that there was no actual or constructive knowledge of a problem with hydrogen in the RHR line until March 1988.
- a. Unit 2 Startup At the time of Unit 2 s'zartup in 1979, Alabsma Power Company and Vestinghouse vere investigating generic concerns with shaft failures in charging pumps. During this period, an Operating Change Request (OCR) vas initiated to address "Problems associated with proper venting of the charging /HHSI pumps." This OCR identified the following actual problems: (1) gas accumulation on the 2B charging pump suction loop when the 2B charging pump vas idle; and (2) venting arrangements with pump seal coolers and mini-flow piping. Specifically, the OCR reported on the cold hydro test on Unit 2 where "gas was found to accumulate in the suction loop of idle 'B' charging pump."
However, in addition to these actual problems, the OCR speculated that the inability to vent the suction of the "A" pump back to the VCT vas a "potential problem ... during safety injection operation." There was also more speculation and hypothesis about gas accumulation in the "A" and "C" charging pump suctions when thepumpsvereidleandinthe"A,""g,"and"C"chargingpump suctions when the pucps vere running Alabama Power Company has recently discussed these events with the author of the OCR vho stated that his concern was caused by finding gas in all three charging pump suctions prior to starting the pumps; however, only accumulations in the 2B charging pump suction vere identified in the OCR. The author attributed the gas collection to the extensive maintenance being done on the system prior to startup, and noted that the charging pumps had no significant run time when the OCR vas written. The author also hypothesized that the gas accumulation vould be a problem in the running pumps because the fluid velocity in the pump suctions vould not be high enough to sveep any gases not in solution through the pumps. The result vould be that the c J vould l accumulate in the pump suction high points during operation, which could impair the performance of the pump. As indicated in the OCR, the only documented evidence of gas accumulation was in
'It is important to observe that the OCR vas prepared by a startup engineer involved in pre-operation testing and maintenance. In it, he hypothesized "potential" problems that vere later never seen when actual operations began.
Attech:cnt 2 *
- Page 9 the 2B charging pump suction line. Since the configuration of the 2B charging pump suction piping is significantly differeit from that of the other two charging pumps, the gas accumulation can be justifiably attributed to the unique configuration. Consequently, when the maintenance on the system was completed and the charging pumps were run for significant periods of time, gas was not fouad to accumulate in the suctions of the running charging pumps.
Therefore, the major problem identified was gas accumulation in the 2B charging pump suction, a problem that was eliminated by running the 2B charging pump continuously.
To place the OCR in proper context, several considerations must be borne in mind. First, the state of knowledge within the industry at the time vas such that the potential for hydrogen stripping (see paragraph 3.d) was not considered to be a technical concern. For example, a report prepared in September, 1979 by Dr. Elemer Hakay, a recognized independent consultant on pump operation, to address pump shaft concerns at Farley did not identify the formation of gas pockets damage ,in suction lines as a factor contt'ibuting to pump shaft Westinghouse also circulated a questionnaire to utilities in October, 1979 vhich, among other things, asked the question: "Does the suction piping from VCT, RVST or the makeup control system contain gas traps..." Significantly, the questionnaire did not mention the need to consider the RHR system piping. In any event, Vestinghouse did not indicate that any further potential concerns needed to be addressed as a result of the response to the questionnaire.
Moreover, in September, 1980 the NRC itself inspected the design, installation and operation of the gharging pumps at Farley and found no violations or deviations. The NRC reviewed a vealth of documents associated with the charging pump issues and did not identify hydrogen accumulation as a potential issue affecting charging pump operability. According to the Inspection Report, the NRC Inspection Specialist from the Performance Apprais.nl Branch
' Determination of the Causes of the "Charging and Safety Injection" Pump Failures and Operating Difficulties in Vestinghouse "PVh" Nuclear Units, (September 4, 1979). This report included an Appendix I which contained the results of a telephone survey with Vestinghouse "PVR" plant ovners using charging pumps similar to those i.t Farley. Nothing in this survey identified hydrogen accumulation in the Train A RHR to chargina pump suction line as either an actual or potential problem. See also, Hakay, "Eliminating Pump-Stability Probless," Pover, July 1970 at 6T -
! ' Inspection Report No. 50-348/80-28, dated November 14, 1980 l
4 Attcchscnt 2 '
4 Page 10 I
reviewed "various correspondence between NRC (NRR), Vestinghouse, j Pacific Pumps and the Licensee concerning pump problems and corrective action" and did not identify the problem which Alabama Power Company is nov cited for failing to resolve.
l It is our belief that this is convincing evidence that the state of 1
knowledge at the time, including the NRC's own reviews, was such '
, that hydrogen accumulation was not considered a concern. Given the l state of knowledge and the fact that only the 2B charging pump i shoved any evidence of gas accumulation, it is not reasonable to conclude that Alabama Power Company knew or should have known of a concern regarding gas accumulation in the Train A RHR to charging pump suction line.
j At the time the OCR vas initiated, Unit 2 vas in startup. During j startup, a tremendous number of issues are discovered or a hypothesized and are brought to management's attention.
i considering the level of activity during startup and the absence of ,
objective evidene snat gas accumulation was a significant problem, the approach taken in response to the OCR vas reasonable. j
- b. The 1981 PCR On June 5, 1981, while performing a routine surveillance test i procedure (STP) on the 2B charging pump, plant personnel started j the pump and noticed low running amps. The pump was secured .
{ immediately and a procedure change was initiated that required [
] venting the suction piping. After such venting, the STP was ,
performed satisfactorily. All three pumps for each unit vere then !
l evaluated and no gas accumulation was found other than on 2B charging pump. Since only this pump had the unique piping configuration, the event served to re-enforce the conclusion that
! gas accumulated in only the 28 charging pump suction loop and only i j vhen it was idle. On June 6, 1981, operations night orders were written as follovs ,
! Unit 2 I
. i i
2B charging pump has gas trap -- pipa with vertical U in !
A . tion. Hence run 2B charging pump at on service pump.
If secure it then vent suction vent to floor drain prior j
j to starting. '
{ On June 10, 1981 Production Change Request 81-2-2064 vas j initiated and accordingly focused on this known problem. The OCR ;
vas considered superseded after initiation of the FCR, This is l l
clear evidence that no deficiencies er.isted "in the design l deficiency reviev process or the production change request :
i process..." as suggested by the August 3, 1988 transmittal letter.
I I
f i
1 j I
Attach:cnt 2
- Page 11 As a result of the experience of June 5, 1981, a valkdown of both units' charging pump suction loops occurred. The suction line for the 2B charging pump vas the only line identified where there was evidence of a problem and the only line with the unique pipiiig configuration. Therefore, the focus of the PCR vas properly on resolving this apparent problem. At that time, nothing in the expertenee of Alabama Power Company, Dr. Hakay, Vestinghouse, Bechtel or the NRC suggested that gas accumulation was occurring in an area other than that of the unique piping configuration.
Accordingly, it was within that framework that Alabama Pover Company considered the solutions proposed by Bechtel and Vestinghouse over the next fev months. This is additional evidence of the prudence of Alabama Pover Company's actions in 1982.
By letter dated March 22, 1982, Vestinghouse proposed permanent modifications which included installation of vent lines on the 2B charging pump and 2C charging pump suction lines and a vater seal and a vent line for the 2A charging pump suction line. While Vestinghouse's proposal included modifications for all three pumps, no evidence vas cited of gas accumulation for charging pumps other than 2B. In fact, the Vestinghouse letter stated that the vater seal modification was not necessary for Train A in Unit 1. This implied to Alabama Power Company that the problem was isolated to the 2B charging pump, because the design of the Train A is similar in both units, with the exception of a slight difference in elevation.
After the Vestinghouse proposal was evaluated by Alabama Power Company, it was determined that the permanent modifications vould not be beneficial. The technical reasons for this were twofold First, it was not clear that gas vould vent back to the VCT given the pressure differential between the VCT and the suction lines.
Second, the modifications vould have introduced the risk of faulty automatic valve actions and vould have entailed installing a check valve in the common vent line--a change that was considered by plant management to be undesirable from the standpoint of reliability of a safety related system. In addition, the modifications were determined to entail considerable cost without a corresponding safety benefit. Given what was believed about the lack of cafety significance of the issue and the ability to control the 2B charging pump accumulation by having the 2B charging pump on service, the modifications ver the PCR vas eventually voided.g determined to be unjustified and 1 l
i
'The PCR vas held in abeyance (along with a number of others) beginning in 1983 while better means to modify the system vere sought. Eventually the PCR vas voided on February ll, 1988.
I l
1
Attcch::nt 2 Page 12 It is evident, therefore, that far from failing to perform an adequate evaluation of the issue, the known problem was appropriately pursued, and prompt corrective action was taken.
Contrary to the NOV, plant management did not perform an inadequate engineering analysis of the known problem nor did it fail to act on available information.
- c. 1987 Incident Report On March 2, 1987 an Incident Report was filed to report cavitation of charging pump A in Unit 1. Cavitation of the pump was found to be due to gas or air in the suction line. Subsequent analysis, as described in the Incident Report and LER No. 88-006-01, dated April 25, 1988, determined that the probable cause of the gas accumulation in the suction piping was due to a VCT pressure drop resulting from failure of the VCT hydrogen pressure regulator (dropping from 20 psig to 15 psig). It was believed that the pressure drop resulted in gas coming out of solution.
The NOV faults Alabnma Pover Company for not implementing the corrective actions of Incident Report 1-87-88 vhich, in part, recommended that PCR 81-2-2064 be considered for implementation on Unit 1. On the contrary, Alabama Power Company did repair the hydrogen pressure regulator, which was thought to be the cause of the condition. The addition of a PCR similar to 81-2-2064 to the "Permanent Corrective Action" recommendation was made because the Farley Staff was not absolutely sure that the hydrogen regulator was the root cause for the gas accumulation. Vhat was known was that gas did accumulate in the 2B charging pump when it vas idle and, in this instance, gas accumulated in the 1A charging pump when it was idle. It was also known that the Vestinghouse proposed resolution for PCR 81-2-2064 included vents for each Unit 2 l charging pump suction. Consequently, it was proper to suggest that a similar PCR be evaluated for Unit 1. However, operating for almost eleven months with no gas accumulation in any idle pump other than the 2B charging pump confirmed for the Farley Nuclear Plant Staff that the reason for the gas accumulation in the 1A charging pump vas the failure of the hydrogen pressure regulator.
Therefore, the voiding of PCR 81-2-2064 and the failure to write a similar PCR for Unit 1 vas proper,
- d. Source of Hydrogen The NOV states that it is a particular concern to the NRC Staff that no detailed engineering analysis was performtd to evaluate why hydrogen was being stripped from the fluid in the HHSI system.
Use of the term "stripping" here by the NRC is based on hindsight, i
Hydrogen stripping was only hypothesized and used by Alabama Power Company after the March 1, 1988 discovery of the hydrogen accumulation.
Attcch::nt 2 ' '
Page 13 since that term was not used until after Alabama Power Company's discovery of the accumulation. Additionally, the Staff vas concerned that tests vere not performed to determine hov much gas was being generated or the location of the gas. Alabama Power Company would like to reconstruct the facts surrounding this issue in belief that these concerns are only reasonable in view of what is now knovnt that it is only with the benefit of hindsight that this criticism can be levied. Consideration of the available observations at the time Alabama Power Company had to evaluate the situation yields a different perspective.
Alabama Power Company discovered during Unit 2 startup testing that gas vould accumulate at the high point location of the Unit 2 B charging pump suction. In evaluating this finding, it stood to reason that if gas was desorbing at videspread locations in the suction system or if gas entrainment vere occurring from the VCT, it vould be accumulated at the C charging pump suction high point when the C charging pump was idle. The accumulation vould be due to buoyancy. The fact that the suction header is horizontal vould allov for migration of gas toward the C charging pump, for example when the A charging pump is running. However, accumulation was not occurring in the C charging pump suction, thereby indicating that there was something unique about the 2B charging pump that caused gas to be formed.
Since the aforementioned observation indicated that gas accumulation was not occurring at videspread suction locations but rather at the 2B charging pump and due to the fact that ae:umuistion in the 2B charging pump could be understood in terms of buoyancy effects and 2B's charging pump unique physical arrangement, it naturally folloved that Alabama Power Company's concerns were with addressing the 2B charging pump accumulation.
Additionally, given the fac,t that gas accumulation had not been observed at any other locations, except as a result of perceived equipment problems, on either unit aespite numerous opportunities to be detected, there appeared to be no justification for pursuing further the difficult question of vhy the gas was accumulating at the 2B charging pump. Nor did there appear to be indications that the problem spanned beyond the 2B charging pump.
The source of the hydrogen gas which accumulates in the Trdin A RHR to charging pump suction remains only a hypothesis. Following the March 1988 discovery of the hydrogen gas, Vestinghouse and Ecchtel l vere requested to assist in determining the source of the hydrogen.
To date, although fully cognizant of the fact that hydrogen accumulates, neither has conclusively determined the source.
Although the source of hydrogen has not been concretely identified, one primary source has been hypothesized. "Hydrogen stripping",
characterized by hydrogen desorbing at localized high velocity, lov pressure points within the charging pump supply piping, is believed 4
Attachunt 2 *
- 1 Page 14 to be the primary source. Fluid supplying the charging pump suction from the Volume Control Tank (VCT) is saturated with dissolved hydrogen. This is accomplished by spraying the fluid into the VCT through a hydrogen atmosphere, maintaining a 15-20 psig hydrogen overpressure in the VCT, and by bubbling makeup hydrogen through the liquid in the VCT. As the hydrogen saturated fluid exits the VCT, the parameter keeping the hydrogen in solution is increasing pressure due to the decreasing elevation of the suction piping, i.e., the VCT is higher than the charging pumps.
Based on engineering experience, it is expected that the additional pressure due to elevation vould keep hydrogen from desorbing. The installed piping configuration is not just a straight run of pipe.
System requirements, such as connecting the RHR pump discharge and the VCT to the charging pumps suction header and NRC requirements such as train separation, require the use of elbows and T-connections. System operation requires the use of valves for the recirculation mode. As the fluid traverses the charging pump supply piping, it flows through numerous elbovs T-connections, and valve bodies. It is hypothesized that these mechanical members cause flow perturbations in the fluid. These perturbations may result in high velocity, lov pressure points which offset the pressure increase due to elevation. Consequently, some hydrogen could be desorbed at localized sites and become entrained in the fluid. As the entrained hydrogen flovs through the charging pump supply piping, it collects at the system high points, such as the 2B charging pump suction piping or the Train A RHR to charging pump suction piping, or is pumpeJ through the charging pumps vhere it is forced into solution by the large pressure increase.
Alabama Power Company did not knov, nor do ve nov knov, the ::m ee of the hydrogen accumulating in the 2B charging pump suc'. ion piping. Our only conclusion is that once it is there, bu)yancy vill cause it to accumulate in the high point of the 2B chargng pump 1 suction. It was not until after gas was discovered in the Train A l RHR line that speculation developed that localized pressure effects at various locations in the suction system could cause some 1 hydrogen to desorb, thereby suggesting that accumulations vould not i l be unique to the 2B charging pump. '
I This illustrates vhy the original Vestinghouse resolution to the problem (four air operated valves, a loop seal, and associated piping) vas considered an unnecessary design, i.e., vent beyond the
{
conditions that vere known to exist. Consequently, Alabama Power Company's reluctance to implement a design change of major l 7 proportions which complicated a safety-related system, and
) introduced additional failure modes, can be better understood. Of l even greater significance is the fact that the source of the l 1
hydrogen is still not fully understood today. Therefore, it is i unreasonable to fault Alabama Pover Company for inability to ,
I identify the initial condition or for the lack of industry )
knowledge on hydrogen desorption over nine years ago. ,
i 4
1 l 1
i
}
Attech: nt 2 '
Page 15
- e. Summary From the above discussion, it is apparent that once deprived of the advantages of clear hindsight, it is neither fair nor reasonable to say that because a concern with hydrogen accumulation in the B charging pump of Unit 2 was recognized in 1979, all other potential pockets for trapping gas should have been recognized and action taken to foreclose any possibility of gas accumulation. The hydrogen accumulation phenomenon was not recognized as a significant concern at the time, nor was the presence of gas in the 2B charging pump suction line considered a problem for pump operability. Given the state of knowledge at the time within the industry and the NRC and the fact that concerns vere properly focused on the 2B charging pump Alabama Pover Company's actions were reasonable and should not now--in the light of subsequent events--be second-guessed and considered unreasonable.
Accordingly, Alabama Power Company believes that escalation of the civil penalty for the alleged failure to act on available information was not appropriate.
- 4. Hitigation of the Civil Penalty is Varranted
- a. Prompt and Extensive Corrective Actions Upon discovery, at approximately 1700 on March 1, 1988, that a hydrogen gas entrapment condition existed which resulted in hydrogen accumulation in the Train A RHR to charging pump suction line, Alsbama Pover Company promptly instituted corrective actions that remedied the problem. At approximately 1620 on March 2, 1988, Alabama Povt.r Company implemented a periodic venting program on the i RHR to charging pump suction lines of both trains on both units to I minimize the quantity of hydrogen allowed to accumulate.
- b. Prompt Identification and Reporting Once the existence of the accumulation of hydrogen gas ias originally recognized on March 1, 1988, Alabama Power campany promptly alerted the NRC Resident IIspector. Alabama P>ver Company also notified the industry of its finding in a Nuclear Network notification. Significant research into the effects of this finding was performed end provided in a promptly issued and I detailed 1.ER dated April 25, 1988. I
Attachmint 2 ' '
Page 16 1
C. Conclusion There is objective scientific evidence that supports the finding that the Train A ECCS charging pumps on Units 1 and 2 vere operable for use in the recirculation mode. The assertions in the NOV that Alabama Power Company suffered a significant breakdown in management controls is unjustified and unsupported. Instead it is apparent that if tested against the state of knowledge in the nuclear industry and the NRC during the pertinent time frame, Alabama Power Company acted prudently, responsibly, utilized good engineering judgment, and adhered to NRC Regulations. Accordingly, the Staff should enter an order, in accordance with 10 CFR 2.205(d), dismissing the Notice of Violation.
I t
I r
i
i
! ENCLOSURE 1 i
EVALUATION OF HYDROGEN GAS IN THE RER TO CHARGING PUMP SUCTION LINE ,
a Objectives i The goal of this evaluation is to outline the fluid systems evaluation as
- to what the charging pump is expected to experience as a result of the i presence of hydrogen gas in the RHR to charging pump HHSI suction header.
This gas is pulled into the charging pump at the start of cold leg '
recirculation. Therefore, the discussion provided vill address that time
- from just prior to alignment for cold leg recirculation until the time that the gas is entirely purged from the system.
Transients of Consideration:
The vorst case scenario is a solid slug of gas reaching the charging pump '
with no mixing occurring. Because of the piping configuration, the A pump is expected to have the least mixing (i.e., highest void fraction) at its 4 suction. The B pump, with approximately twice as many elbows and ,
I T-connections as the A pump to promote mixing, is expected to have a much lover void fraction at its suction. Consequently, this analysis is based on the A pump as the vorst case.
t j A 4 inch or above Loss of Coolant Accident (LOCA) results in such a rapid l l depressurization of the RCS that RHR injection occurs before the !
recirculation mode is initiated. For Small Break (SB) LOCAs of 1 inch or ;
belov, no containment spray initiation is assumed and operator action vill ;
result in the RCS reaching cold shutdown before the RVST reaches the ;
setpoint for recirculation. Therefore, a SBLOCA th y requires ECCS
, recirculation subsystem operability is in the range of 1-4 inches, since it .
i is only there that the RVST vould reach its setpoint for recirculation :
j before the RCS pressure decreases to less than RHR discharge pressure for j
therefore lovest HHSI flow is the one inch LOCA that results in a RCS J i pressure of 600 psig with a HMSI flovrate of 550 rpm, based on operator I l action approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> following the break when the RVST level j reaches the setpoint for recirculation.
4 l
l Initial Conditions and Key Parameters
) - Refer to the attached sketch No. 1
- Valve 8706A closed
- RHR pump is not operating 4 - Flov from RVST to charging pump = 550 GPM i - Pressure at point D = 10-20 psig
- Discharge head of charging pump = 1680 psig 1
l i
l l
Enclosure 1 '
- Page 2 4 l j - 56 f t' of hydrogert exists in pipe section A to B. Note this represents t
an almost 100% void of this section I - Reactor Coolant System pressure is > 600 psig !
- - The maximum developed head of the RHR is 150 psid
- The maximum developed head of the charging pump is 2680 psid i
- Charging pump minimum flow paths vill be isolated ;
i Evaluation:
The effect of switchover to recirculation on the charging pumps is presented in phases. Following is a discussion of each stage.
P_hase 1:
I Initial conditions
, i l Phase 2:
2 Valve 8706A is opened :
I Phase 3:
I The RHR pump is turned on i i
] - As the pump comes up to speed, the pump begins to deliver vater in ;
- section A to F tovards the charging pump suction. j e
- - As vater traverses from point A to B it has the effect of }
! compressing the gas and carrying the gas from point B to point C. [
' i i)'
- Vhile the gas is being carried and compressed, the charging pump vill <
continue to deliver 550 GPM flov. Suction flov vill be drawn from i i both the RVST and the RHR pump supply lines. j l
i :
j Phase 4: l
] Vhen the gas front reaches point C, a mixture of gas and vater vill ;
have been created. This mixture vill represent some void fraction.
i If I this void fraction is less than 20%, the pump performance actually i
! improves as reported in Ref. I and the gas vill be purged in a short !
time period. The case when the void fraction is above 20%, which is
- the most pessimistic case, is discussed below.
I Phase 5: 5 I
This mixture of gas and vater reaches point D (Inlet to the charging pump). ,
I i
l 2
i i 4
, . _ _ - - - _ _ - - - - - - - - , _ - _ . ___ , . . , , , - _ , _ . . . . , - _ ____,_--_n_-_, _ . . . . - _ , - . ~ . , . . . . - - - - -
Enclosure 1 Page 3 Phase 6:
Vhen the void fraction becomes higher than 20%, the charging pump ,
generated head vill be lovered, but pumping continues. When the void i fraction reaches a very high number, say approaching 100% due to the i amount of gas present in the pump, the pump do.veloped head vill fall t off, such as during the Palo Verde Nuclear Auxiliary Feedvater pump ;
test, shown as test point No. 11 in Reference 2. Once the discharge ;
pressure of the charging pump falls belov Reactor Coolant System t
- pressure (600 psig) the pumping process vill stop and the flov in the
- suction piping vill stagnate. The charging pump vill continue to run. l l Some vater is contained inside the pump passages that vill provide <
adequate lubrication to all close clearance surfaces such as the wear-rings at the impeller eye, and the balancing drum. Since the RHR pump is running, the suction pressure vill increase to near the At this time the gas is shut-offheadoftheRHRpump(159.psig).
compressed to approximately 12 ft Check valve 8926 closes due to a ,
positive closing head.
I Phase 7:
A reviev of the piping layout for the charging pump suction notes the pump suction piping to be self venting. During the time that the system is not pumping, some amount of gas vill escape back up to the
] higher points and the lover elevation piping vill be re-flooded. This results in re-flooding / priming of the first stage of the charging pump.
1 As this occurs, the pump developed head vill begin to increase and the charging pump vill start pumping again. An excellent example is shown in Figure 3 of Reference 3 during a start-up operation of the Martins
- Creek Power station, where the start-up boiler feed pump is similar in design. The large amount of turbulence is expected to result in a fairly homogeneous gas / vater mixture. This mixture could be postulated i in sectioits A-B, B-C, C-D and E-C. The void fraction of this ,
j homogeneous mixture is predicted to be less than the initial void I
- fraction the pump experienced in Phase 5. The amount of gas trapped inside the charging pump hydraulic passages is purged out of the charging pump into the discharge piping. ,
i l
- Phase 8
- ;
) As the pumping process is re-initiated, the charging pump vill pull '
- this homogeneous mixture back into the charging pump suction. The charging pump vill continue to run, thereby purging the system of gas. l l The pump performance may fall again due to the presence of gas in the
! pump; however, each time the pump stalls (see Reference 4), the system l vill self correct itself by venting and re-flooding the pump inlet, t such case was demonstrated at the Palo Verde Nuclear plant with the j
- Auxiliary Feedvater (AFV) pumps that are of comparable design. After
- re-flooding the AFV pump, normal operation of the pump resumed without i
{ any damage to the AFV pump internals, and without any loss of f l _ performance. ;
j !
Enclosure 1 Page 4 i
l 1
! Each time the pump is pumping fluid, a significant amount of gas passes th,ough the pump and is purged from the system. Following each occurrence of pump stall and re-initiation, the volume of gas to purge from the systeis decreases. Event'2 ally, the amount of gas present vill decline to an acceptable pumping level.
Key Points:
- Some water or Vater. gas mixture is always present inside the charging pump which provides lubrication to the close clearance wear surfaces.
The charging pump is not expected to see a solid slug of hydrogen gas.
- The charging pump may stall; however, if this occurs the system vill re-flood the charging pump suction. Reflooding vill happen within a i relatively short time period, estimated to be sithin 12.5 seconds. Vhen compared with the Palo Verde test in vhich AFV pumps of similar design vere operated in the run-out mode with loss of head for 8 minutes, including total loss of head for 2 minutes, with no mechanical damage to the pump, no damage to the charging pumps is expected. (See Reference 2)
- Eventually the system purges the suction piping of all hydrogen gas, and normal operation resumes, without significant loss of performance (or perhaps no loss at all as presented in Reference 2 after Test Point No.
12 and 13 and the Palo Verde nuclear plant). Starvation of the pump for l
longer time periods is reported in Reference 3 vithout failure. Martins
- Creek pump speed is 5900 rpm. The pump experienced a complete loss of j head several times for "several minutes" (once for 7.5 minutes, twice for 5-6 minutes, several times for over 1 minute). See Figure 3 of Reference
- 3.
i 1
4 I References ;
I l j 1. "1/3 Scale Air-Vater Pump Program Analytical Pump Performance Model",
] EPRI Report No. NP-160, October 1977.
! 2. "Performance Behavior of The Auxiliary Feedvater Pumps In The Normal i And Extreme Run-Out Operating Modest Actual Testing Performed On The l Motor Driven Pump of Unit 1 At The Palo Verde Nuclear Station" by E.
- Makay, March 28, 1985.
- 3. "Start-Up Pump System Vibration Study." DeLaval Technical Report No. l RP-36 by Soete and Peck January 26, 1979 (Prepared for PA. P & L Co., !
Martins Creek Pcver Station.). I
- 4. "Eliminating Pump-Stability Problems" by E. Hakay, POVER, July 1970, p.
i 62. i l
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, REFERENCE 1 I
1/3' SCALE AIR WATER PUMP PROGRAM, ANALYTICAL PUMP PERFORMANCE MODEL
'EPRI NP.160 ,
(Research Project 598) .
Key Phase Report Volume 1 ,
1 OCTOBER 1977 Prepared by BABCOCK & WILCOX Power Generation droof, NucJear Power Generation Division Lynchburg, Virginia 24506 L
PRINCIPAL INVESTIGATOR J. J. Cudlin 1
' PROGRAM MANAGCR C. E. Parks Proper,ed for Electris Power Research institute 3412 Hithiew Avenue Pato Alto, Californla 94304
. . , . EPRI Project Manager Kjell A. Niiston I
. to e 6
r O
d I 9 4 5
{
single-phase characteristics through the pump average vold fraction. It was proposed that the difference between the single- and two-phase charaa.
f teristics could be calculated by applying a multiplier 'to the' single-phase homologous carves. The multiplier, to be a fur.ction of the pump average *
, void fraction o, was defined as M(a) = (C): ge); (C)2 ,
(1) where 3 .
(c); = single-phasecharacteristicsh/v,b/oj,etc.,
2
. [
2 q
(C)2
- two-phaec characteristics h/v , b/oj, etc. [
)
It was presumed that the variation of M with void fraction would depend I on flow direction. Consequently, separate correlations were undertaken L
! for the first and second quadrant data, surthermore, the approxicate
) characteristics reported in Reference 1, reproduced here for the first i
quadrant as sigsres 2-2 and .1-3, exhibited a difference in trends between the positive and negative characteristics. Head and terque were observed j
to decrease with increasing void traction in the region where the charac-I f' 1
teristics were positive for all void fractions. However, where the head and torque curves were negative for both single- and two-phase flows. tne :
] magnitudes of head and torque at two-phase operating points actually j
showed an increase at void fractions less than 3Cs4 Therefore, it was i I
1 censidered necessary to develop N(a) separately for positive and negative '
I performance characteristics in the first quadrant. l 1 -
j Values of Mto) were competed for first- and second-quadrant two-phase j
performance charaeseristics using the reduced homologous data and poly- l nomial fits to the single-phate head and terque curves.
l l
i tach multiplier was assumed to be a polynoudal in the average void frac- I tien, a, of the foru l
}
1 M(a) = ag + ago + 23 82 , ,,, ,,3 ,an, g,3 1
4 the coefficients, S g, were determined by least-squares fits to the calcu-lated values of M. The babcock & Wilcox R:n> curve-fitting program
)
1 (Peterence 3) was used.
i
t 5
DM PUMP WO-PMSE PLAF03MAtiCE PACGFAA REPORTS 1.
C-E 1915,Quarterly Technical Progress Report No.1, January 1 - March 31, EPRI RP301.
- 2. C-E Cuarterly Technical Progress Report No. 2, April 2
. 1975, EPRI RP301. June 30, 3.
C-E quarterly Technical Progress Reprt No. 3, July 1 - Eeptember 30,1975. EPM RP301.
4.*
Wo-Phase Ptrtp Perforzuce Program, Preliminary Test Plan, W. G.
Kennedy et. el. , EPRI NP-128, September 1975.
5.
C-E Quarterly Technical Progress Report No. 4, octeter 1 - Decen.ter 31, 1975, EPRI RP301.
4.
Review and Analysis of State-of-the-Art of Multiphase Purp Tachnology,
' P. W. Runsta&ler, Jr. , EPM HP-14 9, Pebruary 1976.
7.
C-E Cuarterly Technical Progress 74Mrts No. 3 & 6. January 1 -
Jane 30,1976. EPM RP301.
8.
Two-Phase Purp Perfornance Program, Punp Test Pacility Description, J. D. Pishburn et. al. , EPM NP-175, Nevereer 1976.
9.
C-E Cuarterly Technical Progress Report No. 7 & 8, July 1 - Cecember 31,1974, LPM 3P301.
10.
1/20 Scale Model Purp Test Program, Preliminary Test Plan, P. W.
Ruy.stadler, Jr. ant T. x. Dolan, EPRI NP-292, Pobruary 1977.
11.
1/30 scale Model Purp Test Program, Pacility Description Deport, P. W. Anstadler, Jr. and P. X. Dolan, EPRI NPa293, March 1977 it.
Analytical Models and Experimental Studies of Centrifugal Pump Perforunce January 1917In Two-Thase
' Plow, D. C. Wilson et. al. , WM NP-170, 13.
1/3 scale Air-Water Pure Program, Test Progran and Pwie Performance, R. W. Winks EPRI WP-138, Pobruary 1977.
e y u $W
REFERENCE 2 .
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./ [khU REPORT NO: D.CO-10,75 6.
KGCH 28,1985 Report PERTOFF.GCE BD!AVIOR OF THE AUXILIARY TEEDWATER PUMPS IN THE NORMAL AND EXTRDE RUN-OUT OPERATING HODES: ACTUAL TESTING PERTOPMED ON nlE HOTOR DRIVEN TUMP OF UNIT 1 AT THE PALO VERDE !?JCLEAR STATION.
BY ELDER REAY TECHNICAL DIRECTOR PREPARED TOR ARIZONA PUBLIC SERVICE CO.
AND i BECHTEL POWER CORPORATION !
l l
t -
ENEltGY RESEAllCil & CONSULTANTS C0llP.
900 OV ERTON AVENyt . MQmmisviLLE, PA 19067 i
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- TEST FLOW
j l 18:58 0 24.5 1790 1766' 4078 0.5 ~ 72 !
2 74 0 22 1480 1458 3370 0.4 12 5 .
{ f 3_ 990 21 ~ 1270 1249- 2885 135 l ; 4 19 : 21 1070 20 119 0 117 0 2703 13g j 5 1200 19 1080 106l 2451 14 0 i 6 1270 18.5 998 979 2262 14 0 7 19 !2 3 1380 18 870 852 1968 0.8 142 l b 8. A 1470 16.5 690 673 1556 1.5 138 .
9 l
] 1510 16.5 520 503 116 3 132 -.
8 MIN .
) 10 '
1510 16.5 410 393 909 130 ~
.i i ii e 'm"". 1520 16 300 28'r 656 25 128 l , 12 -750 22.5 1470 1447 3343 0.5 12 5 l
- 13 !9:34 0 i 26 1785 1759 l 4063 o.s 72 j 14 COAST DOWN TIME: 1Mm. 25 Gec. -
0 S- ABO 250 CFM 70R CONTINt)00$1,Y RECIRCUIATING MINIMDM ROU TD CET TOTAL FEDF FLou AT NICE PRESSURES. {
h% VIBRAIICII 1845 MMtITORfD IN THE I-Y-Z DIRECTICIIS. ONLY MAX. AprLITBES SN06B5. -
{
i TABLE 1: AUKILIARY FEEITJATER Fme (AFB-POI) RINE-0UT TIDt TESTING AT THE PA14 VERDE -
NUCLEAR CENEBATING STATICK 11 NIT NO.1 Ott MARCu 6,1985. [
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Energy Research & Consultants Corp.
aonmem = =uc-. = wur.m s o P
3-28-BS:EM. EFF2 w .u. in 90-1 EFF.$
40000g-
. !t , , -
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3500- 3 ,- s ~ ,2 TESTED AT BIN 6HAHo o 70 .
3000 a
11
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A g>.
I y . FrXED ORIFICE 8
'g20 ug[ .
2500- [ g .. RECIRC F1.0W /
gj- ,
1
, g 23o0. 1 g .
3560 RPM g,g . .-
- l. 1500 I O OttGINAL FAcroRY TEST POWr6. \, '
l 8000~ 9 3-6-85 TESTIMG AT PA1D VERbE: ROM-OUT TEST, k'$, '
g ,.
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'D* k O 3- G- 65: REPEAT PERF. TEST DolRTS.AFTER RUN- OUTTES .
smEM ^RE5WTA*K g -6 a MRUN OUT PolHTS T W W
- 4 o
3 g 200 400 soo 800 1000 1200 1400 1s00 3 '
isoo 20do FLOW - GPM -
4x6x ich. B MSD 8 STG.
, FIGURE 7: EINCRAM-MADE NUCLEAR AUKILIARY FEEDWATER PLMP "ITSTING AT TIIE PALO VERDE NUCLEAR CINERATING STATION, UNIT 1.
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REFERENU 3 i . -
1
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- N;. . '
DELAVdL TuflBINE INC.
j TRENTON, N.J. 08602 auraeas ve. irs =C c64.l i nica no .
< G. W. SOETE / R. J. PECK
- f.Tu Start-Up Pump - System Vibrations Study Pa. Power & Light, Martins Crack Sta., 705812-13 s,.. oiv.aa ir. o4ve o. e. a si -
RP-36 Jan. 26, 1979 0' Pumps aestnacts h ring start-up and shutdown, on a daily basis, tevere cavitation occurs on the motor / gear driven pumps in a routine manner. Proper in-strumentation can be installed and, with surveillance, will prevent this.
These instruments may also be used to automate the opening and closing of the recirculation salve at proper flow points tc more positively protect the pump.
Cavitation and failure to properly operate the non-automatic recirculation valves were the -
major contributors to the failures experienced by these pumping units.
. Future monitoring of shaft vibration and axial position is a positive step towards measuring the-operating, pump characteristics in terms of a praventative maintenance program.
,,,,,,,,,,,,, Pennsylvania Power & Light 3 ,
_ _, ___ 4 r e a r. . or .v. G _. W. Soeta, R. J. Peck, W. A. M'c CrM .,
U ,
< e #. v a n ti ni.c o: Mn or Engineering onpantus v, Pu p Engineering
...c.,., Service-Dept. ,6),
( A. Gortz (1) ,_ circulato Library copy tot F. W. Belt =, Jr., R. J. Jackson, R. P. Kolb, R.
J. G. Popok/W. F. Y o ung*, G. W. J. Peck, Soete, and Library.
No. 283 (R.2) 443
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.. mt g y REFERENCE 4 , , , i 5
._ !E Ed~
\
AIR, GAS and LIQUID HANDLING Eliminating pump-stability problems Boiler feed pump vibrations can be reduced considerably, perhaps eliminated, by selecting hydrostatic bearings over conventional hydrodynamic bearings nonuniform flow upstream of the blades or manufacts ing Competition in the boiler feed pump (BFP) market has created a situation where desired pump efficiencies are ex- inaccuracies, one channel stalls before the others.
Breakdown of flow in this passage causes a deflection of ceeding current technological capabilities. Though per-formance figures appear somewhat infiated now, competi- the inlet fluid stream. Thus, one neighboring passage re-ceives fluid at a smaller incidence angle and another at a tive position in the future demands that higher eHiciencies be delisered without creating operational problems, larger angle. Result: Passage with the larger incidence h!any phenomena tax safe operation, e pecially at partial angle stalls, and cyclic rotation of the phenomenon begins.
loads. They include vibration from hydraulic forces, higher For centrifugal pumps with blades bent backward (where noise lesels, larger and unpredicted asial thrust, damping inlet angle is less than 90') stall rotates in the direction of eHects on critical speeds and nonsynchronous response of impeller rotation at high loads and in the opposite direction the fiesib!c rotor. Further, pressure pulsations in the impel- at low loads. Similarly, stall can occur in diffuser channels ler and hydraulic passages hase been greatly magnified in from a change in incidence angle during low load condi-high-output, high speed pumps. A frequent result of these tions. If diffuser is not properly desig d, stall also will be
' ons is f atigue failure of the impeller. evident at fullload.
.iough research continues, no concrete solutions for Vibratlon is strongly influenced by pump-stage geometry pt. . sibration problems have yet been found. The total (figttre in center of column at right). Conclusion based on problem of pump instability involves complex interactions many laboratory and field tests is that the following areas among hydraulic, geometric and mechanical features of a should be carefully designed if induced vibration, cau particular unit. itation and generalinstability are to be reduced:
To locate the causes and solve vibratory problems, you o Geometry of the inlet guide vanes must examine carefully both the failure mechanism and
- Impeller eye geometry and shaft size pump geometry. Seseral mechanisms leading to intolerable
- Impeller discharge geometry, exit angle and vanes vibrations are: (1) rotating stall in the impeller, (2) stall
- Wearing ring elearance in the ditiuser and guide channels, (3) secondary flows, o Radial gap between the impeller and the diffuser (4) casitation from a low net positive suction head
- Impeller / diffuser alignment (NPSH), and (5) oscillations es sed by rotor dynamlet.
- Diffuser geometry The first four situations are g,nerally obsersed during
- Axial gap betweer. tbe impeller and stator.
low NPSH conditions and transient partialload operation. Also, air trapped in suction and discharge giping is an The fifth, somewhat independent of flow aad NPSH, is occasional cause of instability. However, this is not of a strongly dependent on speed variation and bearing charac- permanent nature: eventually it is washed out and smooth teristics. Pump tests at varying speeds have shown that, at oneration is restored, any flow and NPSH condition, there is at lesst one critical Degree of instability is determined by observing: (1) speed where pressure oscillations are most pronounced. frequency and amplitude of fiow pressure oscillations, (2)
Frequency of these oscillations depends on design quality. lateral vibration, whkh induces pressure wases, (3) axial ,
A thorough understanding of srcIl is important if you vibration-this, too, induces pressure waves, and (4) vari- l I
have excessive BFP vibration (figure, lower right). Rotat- ations in axial thrust induced by pressure oscillations.
ing stall in impellers occurs this way: When the lor d condi- Poor design or wear at any one of the locations listed l Jion of a centrifugal machine changes, directioti of flow above may be responsible for these oscillatory disturbances. ]
also changes in the casca$e of blades. That is, as the in- Realize that frequency range and peak to peak amplitudes cidene angle-d:fference between flow angle and pump- depend on magnitude of axial thrust, level of efficiency and impeller or diffuser vane inlet angle-increases, you get head stability, flow separation first, then stalling. However, because of Pressure pulsations can be defined as low and high-frequency response of fluid particles to complex, unsteady, ,
nonlinear forces. Low frequency, high amplitude pressure )
By E Makay, Franklin Institute Research Laboratory pulsations result in visually observable movement of pump Power, Jwly 1970 J 62
l ,
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- Scyf= , Propostv /enpM : Sar/ Ape y '
Hydrostatic bearings offer s'[nificarrt *
- j
~~~" ~
reduction in boiler feed pump size
,_ g e
4 and cost.Their load carrying capacity c S c-a R O /*"/ is malmained by an externally
[ s pressurized ftuld. Heace, fluid film N
4.,,,_ L q p ,/ 'y separates shaft from bearing even at ero speed.
c g p p Bearings must be pressurized:
\ Speed of rotation is too slow to
';d
'- ' (J [J y '/ lL
$;d qg f,,,, N / give sufficient load carrying capacity
" '~ '
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rq" Ii f from hydrodynamic action alone
-recall, viscostty of water is f I I I
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I 88 /*** /
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very low at high temperature.
in hydrodynamic bearings, fluid pressure supporting a load is s
W# __ generated within the bearing by Asta//wp kn/M '
relative motion of bearing and shaft.
d and connecting pipe. They also cause gross fluctuation in .) .
[
discharge flow. High frequency, high. amplitude pressure pulsation degrades pump performance somewhat; more im- A//sser --- 3 ~ w - j,/Ct/t d tnoor portant, it causes accelerated damage to the rotating a;4 Qf,2 gI j stationary cascades. 7 : ag r /
A//usre/ g Many pump instability problems can be eliminated, or at .. T Msokp ev least reduced,if hydrodynamie, oillubricated journal bear. '##f##' N jigf;gd[" 6
' 'g em#e'N// user ings are replaced by hydrostatic bearings using pressurized gMfg y boiler feedwater as the lubricant. There are many advan. #f , xM tages to be gained by selecting hydrostatic bearings. For C'#'4--~
@~~-J~ -~
1 St'0'h */'
- cxample, overall length of a feed pump can be shortened M 6$ N by approximately 40'"1. Reasons: Water lubricated bear-ings can be enclosed within the pump barrel, and seals can C. A s
s be climinated (figures in tinted area).
Further, when a shorter bearing span is employed, shaft no, a
( l [*""'f e o
'"'9 deflection does not dictate the shaft diameter; it is deter.
mined by stress lesels alone. To illustrate: For an 80.000-hp.
J h "@r jg,c,.3,,fg.
f%e stage unit, shaft diameter is estimated at 9.5 in. when Shc// -
hydrodynamic bearings are used. Hydrostatic bearings per-mit an 8.25 in. diam shaft with its favorable influence on pump performance and life. Other adsantages: V'bration, cavitation, and instability can generally be trac d " $ " " '" 8
- Smaller impeller eye produces a better flow path, yield- p ps age.'For e r ng r n cle rance ih e ing increased emeiency and NPSH excessive or perhaps the impeller / diffuser is out of alignment
- Longer blade path offers more favorable blade loading
- Smaller diameter wearing ring causes less leakage, giving higher pump emeiency
- Smaller clearances at the wearing surfaces she better \
partial load performance and less danger of instability # \
- Secondary flow at the impeller eye during low loads is ;Mer PO ' .
decreased, reducing vibration caused by pressure pulsation
- Smaller impeller produces the same bead, lowers disc friction and reduces barrel stresses 8' ave -- N ,
- Higher speeds are possible, reducing unit size d ' O h,
- Oillubrication system is eliminated 1,, -l, -~ iP ~ Jtourva rs %
- Capital cost is reduced. //c # ?-
Although most BFP bearing experience has teen with #O#"" V s hydrodynamle journals in the larrJnar regime, the tech-k nology for turbulent bearings is well established and has a g betn apphed successfully to other demanding applicatism in rotating machineryc Recently developed computer pro- \ f, grams sehe hydrostatie t<aring problems to improve per.
formance predictions for both dynamic and static loading.
(
and determine the effects of turbulence in the bearing film. $talling occurs when the incidence angle-difference betweer' fl'" angle and pur p impeller or d ffuser. vane intet angle-These programs ha\e been strified experimentally for gen- increases above a specific critical value. Stalled area.
eral modes of operation, o which eventually washes out, reforms as rotation continuel Pe or Jw's Isro AIR. gas ans UQuio HANDLINo s1
a .
o . .
ENCLOSURE 2 The following discussion provides information regarding the effect of hydrogen gas accumulation on the RHR to CCP suction line and its impact ori flow requirements.
Operability of the ECCS system is addressed in plant Technical Specification 3/4.5.2. The LCO requires 1) one operable CCP, 2) one operable RHR heat exchanger, 3) one operable RHR pump and 4) a flovpath capable of taking suction from the RUST and transferring suction to the containment sump during recirculation.
In addition, surveillance requirement 4.5.2.1 requires HHSI - Single Pump flov > 193 gpm (each injection line). However, this flovrate applies only to flow requirements during the injection phase. This flovrate does not address flow requirements during recirculation.
However, requirements for flovrates during recirculation are addressed in 10CFR 50.46. In general terms, it is necessary that the ECCS operation be able to support long-term cooling of the reactor core. This includes limiting PCT and providing for decay heat removal. In specific terms, demonstrating complete coverage of the core during the time period of interest vill ensure acceptable long-term cooling.
The operative parameters for evaluating adequate core coverage include flov delivered to the core, water inventory in the core, and decay heat levels.
A calculation was performed which focused on that period of time after the accident when recirculation might be required until such time that the RCS pressure could be reduced belov the RHR cut-in pressure. This evaluation determined (1) flovrate required to maintain a steady state water level, (2) initial excess inventory available to prevent core uncovery, (3) total tolerable loss of all ECCS flovrate, and (4) total tolerable partial loss of ECCS flovrate.
The key parameter in maintaining a steady state water level is the decay heat present in the core. To maintain a constant vater level, inventory must be added to account for vater inventory lost due to boil off. Of course, as the decay heat is diminished, the flow requirement decreases.
The ANS 1971 + 20% decay heat was used, in keeping with the decay heat ,
model employed in the Farley SBLOCA analysis of record. The question, then, i was to establish the flov that vould have to be made up to compensate for ,
potential boil off and thus assure the core vould remain covered long-term. ;
Several very conservative assumptions vere taken with respect to general l cooling of the vessel vater inventory.
Vith this basis established, the following table was developed to shov flov versus time after an accident.
TIME FLOV (LBM/SEC) FLOV(GPM)
I hr. 57.2 428.1 2 hrs. 45.5 340.6 3 hrs. 40.0 299.4 4 hrs. 36.6 273.5
" s
'
- a a Enclosure 2 Page 2 l The second issue was to identify the amount of excess inventory available prior to recirculation. Excess inventory is defined as the amount of water !
available above the top of the core. It was verified based on analysis trends that the reflooding of the core / vessel during injection vould be sufficient that the water level vould reach the hot leg elevation prior to i i the initiation of recirculation. The vater above the core up to the hot ;
leg elevation vould represent an inventory that could be boiled off in t dissipation of decay heat before the core vould be in jeopardy of being uncosered.
I Knoving the available water inventory and decay heat levels, it is possible f
- to determine the total tolerable loss of all ECCS Flovrate. This evaluation was conservative in nature taking no credit for hot leg filling above the hot leg (bottom) elevation nor was downcomer filling factored in. ;
J The total tolerable loss of all ECCS vas calculated to be as follows:
TIME TOLERABLE HHSI INTERRUPTION TIME (SEC)
I hr. 272 r 2 hrs. 349 t 3 hrs. 400 4 hrs. 440 i i The final issue vas to evaluate the total tolerable partial loss '
! (degradation) of HHSI flow. This vould occur if the gaseous void reduces i the delivered HHSI flovrate, but does not result in total cut-off. This cvaluation defined a family of curves which would look like the following ,
curve defined for the 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> time point. (This represents the most :
limiting curve due to the highest decay heat level). l t
As previously identified the minimum expected flovrate during switchover to ;
j recirculation is expected to be approximately 550 GPM (RCS pressure - 600 .
psig). Based on the curve belov, two extremes of the curve can be !
evaluated for comparison (flov delivered equals 50 GPH and 400 GPH). The i
first case (50 GPH) represents a 91% reduction in flow and can be tolerated ,
- for 5.1 minutes. The second case (400 GPH) represents a 27% reduction in [
i flov and can be tolerated indefinitely. t i
- Given the systems evaluation and assuming the pump continues to operate, i Vestinghouse has concluded that the hydrogen gas is not capable of !
i degrading HHSI flow for a long enough time to result in core uncovery. !
Therefore, more than adequate HHSI flov vould be available. +
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