ML20058A828
| ML20058A828 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 10/18/1990 |
| From: | Sieber J DUQUESNE LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9010290222 | |
| Download: ML20058A828 (9) | |
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i N,$N,. c.,u, o mtm October 18, 1990 U. S. Nuclear Regulatory Commission Attn Document Control Desk Washington, DC 20555 Reference Beaver Valley Power Station, Unit No. 1 Docket No. 50-334, License No. DPR-66 Request for Temporary Waiver of Compliance Gentlemen:
The purpose of this letter is to request NRC approval of a request for a
temporary waiver of compliance in meeting the Beaver Valley Unit No.
1 Technical Specifications.
Specifically, the Limiting Condition for Operation (LCO) for the containment
?
recirculation spray system (RSS) requires a
minimum flow of 8000 gallons per minute through RSS subsystems which includes two heat exchangers in each subsystem.
This value has not been met and it has been determined that the flow through the "C" heat excht.nger of the "A"
Train subsystem is experiencing unexpected increases in flow resistance.
This is a result of tube plugging due to asiatic clams and other river water debris.
This request is to perrait redefining the minimum required river water flow through the RSS h< sat exchangers while still satisfying the safety analysis wita respect to containment depressurization and offsite dose consequences.
During performance-of quarterly pump and valve testing it was observed that flows through the RSS heat exchangers experienced an unexpected drop.
In order to better quantify the extent of flow degradation, we performed our refueling frequency surveillance test which ostablishes DBA flow paths.
This resulted in concluding the "C"
heat exchanger could not pass the required flow and wo entered the seven day action statement of Specification 3.6.2.2.
Several parallel efforts were established to resolve the inoperability status of the heat exchanger.
An inspection of the tube sheet through the use of a remote operated video camera was performed' to identify the extent of tube plugging.
The tube sheet does not show an excessive amount of plugging, however, plugging is evident.
- Also, it is expected that plugging inside the tubes has occurred to some extent but cannot be verified with a video camera inspection.
This inspection has been conducted by inserting a remotely-operated video camera through an open valve located outside of containment and guiding it through approv.imately 60 feet of pipe to observe the tube sheet inside tbo heat exchanger inside l
containment.
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'. Tcpp rcry Waivcr of C:cplitnca Page 2 Cleaning the heat exchangers was attempted by allowing reverse flow via a
draining evolution on the "C" heat exchanger.
There is only sufficient pressure in the reverse direction when doing a gravity drain to obtain a flow rate of approximately ten gallons per minute.
The result was relatively clean water being discharged from the heat exchanger.
Further cleaning efforts are complicated due to the sub-atmospheric design of our containment.
River water flows through the tube side of the vertically mounted heat exchangers.
Access to the tube sheet is through a seal welded diaphragm on the end of the heat exchanger.
Removal of this diaphragm requires
- grinding, while reinstallation is accomplished through welding.
This cannot be done without entry to mode 5
since this diaphragm represents a containment boundary.
We also initiated an evaluation of parameter changes within the RSS to determine if operability could be re-established based on new accident analysis assumptions.
This has been completed and forms the basis for this request for a temporary waiver of compliance.
I The long term corrective action is to submit a
Technical Specification Change Request to revise the river water flow requirements through the RSS heat exchangers and include other operating restrictions regarding river water temperature and containment air partial pressure which supports the analysis assumptions.
This submittal will be forwarded to the NRC by November 2, 1990.
Therefore, this request for temporary waiver of compliance is to allow Unit No.
1 to continue to operate while not meeting the existing flow requirements defined in specification 4.6.2.2.e.3.
This request is for the period of time it takes for the Technical Specifications to be revised approving the changes discussed above.
Additional details supporting this request are located in the Enclosure which addresses the current understanding of the level of detail required with respect to requesting a temporary waiver of compliance.
The contents of this request have been discussed with members of the NRC staff during a 7enference call on this date.
If you have any questions.egarding this submittal, please call me or members of my staff.
Sincerely, D
e hr hicePresident Nuclear Group cc Mr. J. Peall, Sr. Resident Inspector Mr. T.
T. Martin, NRC Region I Administrator i
Mr. A. W. DeAgazio, Project Manager Mr. R.
Saunders (VEPCO)
ENCLOSURE Evaluation Supporting a Temporary Waiver of compliance (ret Recirculation Spray Heat Exchanger River Water Flow) 1.
Discuss the requirements for which a waiver is requested:
This waiver addresses Technical Specification Limiting condition of Operation (LCO) 3.6.2.2
" Containment Recirculation Spray System:
The surveillance requirement (4.6.2.2.e.3) defines a flow rate of at least 8,000 gallons per minute (gpm) through each River Water subsystem and it's two associated recirculation spray i
heat exchangers.
A recent surveillance test has demonstrated a flow rate less than required in the "C" recirculation spray heat 1
exchanger and has resulted in Unit No. 1 entering the LCO 3.6.2.2 action statement.
We must restore this component to operable status within seven days or be in hot standby within the next six hours.
The seven day action statement expires at 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> on October 19, 1990.
We request permission to operate with a i
reduced flow requirement of 2 6000 gpm through the recirculation spray heat exchangers for the period of time it takes to process a change to the Technical Specifications for Unit No.
1.
2.
Discuss the circumstances surrounding the situation including the need for prompt action, and why the situation could not have been avoided:
Surveillance requirement (4.6.2.2.e.3) is performed once per 18 months to demonstrate adequate flow exists through the recirculation spray heat exchangers.
During seventh refueling
- outage, which ended December 25, 1989, this test was performed and a
flow of 8400 gpm was recorded through each recirculation spray Train A and B subsystems.
Other surveillance testing is performed on a.'arterly frequency to demonstrate pump and valve operability in accordance with the Inservice Test Program requirements.
Since flow is established through the recirculation spray heat exchangers during this quarterly testing, we incorporated a flow measurement step within the' surveillance test in December of 1989.
This provides an opportunity to more closely monitor changes in flow conditions through the heat exchangers.
It was observed during the quarterly test conducted October 3,
- 1990, that the "A"
Train (1A and 1C heat exchanger) flows were approaching the limits of surveillance requirement 4.6.2.2.e.3.
As a
- result, additional testing was performed on the "A" Train using the swing river water pump.
This also indicated a
significant reduction in flow as compared to the last completed test performed with this arrangement.
In order to better quantify the apparent degrading flow conditions we performed the 18 month surveillance test which provides a more representative alignment of plant equipment for DBA conditions.
This testing was conducted on October 12, 1990, and provided the basis for declaring the "C" heat exchanger of the "A" Train inoperable.
l
4
. EnglC uro, c:ntinu d Temporary Waiver of compliance Page 2 During this
- cycle, the "B"
Train recirculation spray heat exchangers continued to show acceptable flows with only minor flow degradation observed.
Flow information is shown on TABLE 1 for each quarterly pump test.
TABLE 1 A Train (GPM)
B Train (GPM)
Notes A PumD C Pump B Pumo C Pumo 12/89 9,400 9,400 1
01/90 8,900 02/90 8,600 8,700 9,200 05/90 8,700 8,700 9,100 08/90 7,400/8,500 8,700 8,600 2,
3 10/90 7,900/8,050 7,600/8,100 3
Note 1:
Clean system following refueling outage Note 2:
Peak clam infestations occurred during July, August, and September Note 3:
Flushed system for 1
hour and obtained adequate gpm flow rate The test data suggests that the peak clam infestion period had some impact on heat exchanger performance,
- however, video inspection of the tube sheets does not support excessive. flow blockage due to clams.
We cannot determine the extent of tube plugging beyond the tube sheet without shutting down and opening the heat exchangers.
The "C"
heat exchanger is downstream (parallel) of the "A" heat exchanger and has shown a propensity to foul earlier than the "A" heat exchanger.
We continued to
. run the system and flushed the heat exchangers after which flows returned to an expected level.
The "A" Train testing in October indicates a significant unexpected increase in system resistance following flushing of the heat exchangers.
This resulted in efforts which eventually lead to declaring the "C"
heat exchanger of the "A" Train inoperable.
It is intended to demonstrate that the flow requirements through tLe heat exchanger subsystems can be reduced to 6,000 gpm for th*
remainder of this cycle and still remain within the conclusions of the Safety Analysis Report.
NRC approval of this requeat is require / to permit continued operation of Unit No.
1, otherwise, we muut initiate steps to be in hot standby beginning at 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> October 19, 1990.
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EnclCCura, CCntinund i
Te'mporary Waiver of Compliance Page 3 3.
Discuss compensatory actions (if any):
This revised analyses demonstrate the ability of the recirculation spray system to depressurize the containment and maintain it sub-atmospheric.
We will administratively control plant operation to assure new analyses assumption are satisfied, otherwise, we will reduce plant mode such that we are no longer in an action statement.
Additionally, we will monitor system performance monthly instead of quarterly by initiating flow through the heat exchangers and recording flow data.
This i
compensatory action will remain in effect until such time that the Technical Specifications are approved and implemented.
4.
Provide a
preliminary evaluation of the safety significance and potential consequences of the proposed request:
Reduction of the river water flow thru the recirculation spray heat exchangers does not effect the containment peak pressure analysis from a
- LOCA, but does effect the capability of the containment depressurization system to depressurize the containment following the accident.
A re-analysis of the containment depressurization following a LOCA has been performed using LOCTIC computer code (details of analysis are contained in Attachment 1).
This analysis reduced the assumed river water flow for one train of recirculation spray heat exchangers to 6,000 gpm.
The results of this analysis demonstrated that the design basis requirement for the containment Depressurizati7n System continue to be met at a reduced river water flow of 6,007 gpm provided additional resttictions are placod on allowable river water temperatures and allowable operating containment air partial pressure.
As seen in Figure 3.6-1, attached, (Maximum allowable primary containment air pressure versus river water Temperature),
when the river water flow to the recirculation spray heat exchangers is less than 8,000 gpm but greater than or equal to 6,000
- gpm, the maximum allowable river water temperature is 75*F and the maximum allowable containment air partial pressure is 10.1 psia.
With these additional restrictions on plant parameters, analysis has shown that with a river water flow to one train of recirculation spray heat exchangers reduced to 6,000
- gpm, the Containment Depressurization System continues to be capable of reducing the containment pressure to sub-atmospheric pressure within one hour and maintaining the containment pressure sub-atmospheric following a LOCA.
Therefore, this request does not result in an increase in the potential consequences of any postulated accident.
5.
Discuss justification for the duration of the request:
Current testing demonstrates the recirculation spray system cannot satisfy existing Technical Specification surveillance requirements.
This Temporary Waiver of Compliance needs to remain in effect until a Technical Specification change can be approved by the NRC incorporating changes to river water flow and maximum allowable primary containment air pressure vs river water temperature.
Eqcic ura, cantinu:d Temporary Waiver of Compliance Page 4 6.
Provide a
basis for the conclusion that the request does not involve a significant hazards consideration:
The change in allowable river water flow to the recirculation spray heat exchangers will not increase the probability of an accident previously evaluated.
An evaluation has been performed to determine that the design basis requirements of the containment depressurization systems will continue to be met with the revised recirculation spray heat exchanger river water flow.
The capability of the containment depressurization system to depressurize the containment within one hour to a
sub-atmospheric pressure and maintaining it there remains unchanged.
Therefore, based on the above, this request does not involve a i
significant hazards consideration.
7.
The basis for the conclusion that the request does not involve irreversible environmental consequences:
The requested change does not involve irreversible environmental consequences based on the demonstration that the assumptions of the containment depressurization safety analysis will remain valid.
The containment peak pressure following a LOCA remains unchanged.
The capability of the containment to depressurize to a
sub-atmospheric condition and remain there within one hour following a
LOCA remains unchanged.
Therefore, based on the continuing ability of the containment to contain fission products and eliminate a
potential leak path within one hour following a
- LOCA, this change does not involve irreversible environmental consequences.
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o-ATTACHMENT 1 Beaver Valley Unit 1 Engineering Evaluation to Support a Reduced River Water Flow to the Recirculation Sorav Heat Exchancers BACKGROUND The containment at Buaver Valley Unit 1 consists of a concrete containment building which operates at sub-atmospheric pressures.
The containment depressurization system is designed to return the containment pressure to sub-atmospheric conditions within one hour after an accident and naintain these conditions for a minimum of 30 days.
The two main rubsystems of the containment depressurization system are the quench spray system and the recirculation spray system.
The quench spray system sprays cooled, borated water from the refueling water r.torage tank into the containment atmosphere via spray headers in the top of containment dome.
The recirculation spray system draws water from the containment sump and delivers it to spray headers.
The recirculated spray water is cooled by heat exchangers which r.se river water as a cooling medium.
There are two heat exchangers por train.
The heat removal provided by the heat exchangers augments the quench spray system during depressurization and provides long term heat removal to maintain sub-atmospheric conditions.
The systen design basis is defined by the minimum performance I
necessary to satisfy the acceptance criteria for the containment analyses.
These acceptance criteria are maintaining the peak containment pressure less than the design pressure of 45 psig for all accidents, achieving sub-atmospheric conditions within one hour following a
design basis accident, and maintaining sub-atmospheric for an extended period following depressurization.
Additional criteria are linked to this design basis due to dependencies on the system performance.
These are maintaining adequate NPSH for the low head safety injection pumps and the recirculation spray pumps.
Each criterion has specific limiting conditions which are comprised cf system configuration, assumed
- failures, operating limits, initial conditions, and safety system performance.
The effect of reduced river water flow to the recirculation spray heat exchangers was evaluated for each criterion.
Where necessary, compensating restrictions on operating limits were investigated.
EVALUATION Analyses were performed to demonstrate acceptable results for each case using the LOCTIC computer program.
The limiting cases have been established by sensitivity analyses.
The sensitivity to reduced heat removal capability by the recirculation spray system is generally well understood and can be evaluated qualitatively for I
some cases.
For other cases, LOCTIC program calculations must be L
made to determine the effects.
l The containment peak pressure analysis is not affected by changes in the recirculation spray system.
The peak pressure occurs at approximately 12 seconds post-accident while the recirculation spray system is not activated until 300 seconds following a CIB.
l The recirculation spray pump NPSH analysis is minimally affected by l
changes in the heat removal capability.
However, reduced heat removal tends to improve the results since the limiting case assumes maximum heat removal to reduce containment pressure,
. Att:chment 1, c:ntinund Reduced River Water Flow Page 2 For these two cases, no additional analyses are necessary.
For the remaining
- cases, LOCTIC runs were required due to the sensitivity of these cases to reductions in the heat removal.
The following discussion describes the approach taken to perform these analyses.
The LOCTIC input can be characterized by those paramotors which define the physical characteristics of the systems and those which are defined by operating limits and system performanco requirements.
This characterization is made to distinguish between those parameters which are basically fixed and those over which some control can be exercised within practical limits.
The river water flow limit is a
system performance requirement.
Allowance for degradation of the system is the only practical control that oxists without physically changing the system.
However, if this allowance cannot be shown to be acceptable within the envelope of all other current operating
- limits, then this allowance must be rejected unless other limits can be changed to compensate for the effects.
Therefore, the approach taken was to decido, based on past analysos; what other operating limits provide the greatest sensitivity to heat removal capability in the river water temperature range of interest and investigate what changes must be made to provide acceptable results at reduced flows.
This approach led to the conclusions that the depressurization time analysis was the limiting analysis for the River Water temperature range of interest and that the operating limit which is most sensitive to changes in heat removal capability is the containment air partial pressure.
This limit is shown on Technical Specification Figure 3.6-1.
The development of this curve ossentially maximizes the allowable air partial pressure by taking i
advantage of the increased heat removal provided at lower river water temperatures.
Therefore, lowering the limit reduces the heat removal requirement and allows reduced flow.
LOCTIC runs were performed to determine the new limits which provided acceptable results at reduced river water flow of 6000 gpm per train.
The results are shown as a new limit on Figuro 3.6-1 (attached).
Additional runs were made to demonstrate that the NPSH for the low head safety injection pump is adequate and that the peak pressure which occurs following RWST depletion remains sub-atmospheric.
For both casos the results were acceptable.
CONCLUSION Operation at reduced river water flows to the recirculation spray heat exchangers can be justified on the basis that operating limits on the containment air partial pressure and river water temperature can be adjusted to compensate for the reduced heat removal capability.
Therefore, the design basis of the system continues to be mot in that the containment analysis shows acceptable results.