ML20245B457
| ML20245B457 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 06/16/1989 |
| From: | Morris K OMAHA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LIC-89-432, NUDOCS 8906230184 | |
| Download: ML20245B457 (6) | |
Text
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Omaha Public Power District 1623 Harney Omaha. Nebraska 68102 2247 4
402/536-4000 I
June 16, 1989 LIC-89-432 U. S. Nuclear Regulatory Commission i
ATTN: Document Control Desk i
Mail Station PI-137 Washington, DC 20555 l
References:
1.
Docket No. 50-285 2.
Operations Support Analysis Report (0SAR) 88-36 "Effect of High Pressure Safety Injection Cross-Connect Valves on Hot Leg Injection" 3.
Letter from NRC (P. D. Milano) to OPPD (K. J. Morris) dated January 10, 1989 i
Gentlemen:
1
SUBJECT:
Response to Questions on OSAR 88-36 "Effect of HPSI Header l
Cross-Connect Valves on Hot Leg Injection" Enclosed is Omaha Public Power District's (OPPD) response to the questions raised in the Safety Evaluation Report which was transmitted in Reference 3.
As stated in Reference 2, inability to operate the HPSI header and I
cross-connect valves following loss of instrument air has little effect on the l
implementation of hot and cold leg injection after a large break LOCA.
Calculations have indicated that the existing system can provide adequate flows to the hot and cold leg to prevent boron precipitation.
If you have any questions concerning this matter, please do not hesitate to contact us.
Sincerely,
/ MMk K.
. Morris Division Manager Nuclear Operations KJM/jak Attachment c:
LeBoeuf, Lamb, Leiby & MacRae R. D. Martin, NRC Regional Administrator A. Bournia, NRC Project Manager P. H. Harrell, NRC Senior Resident Inspector g
g, 8906230184 090616 i
PDR ADOCK 05000205 1\\
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RESPONSE TO THE QUESTIONS RAISED BY THE NRC IN THE SAFETY EVALUATION ADDRESSING THE FCS OSAR 88-36
1.0 INTRODUCTION
Operations Support Analysis Report (0SAR) 88-36, "Effect of High Pressure Safety Injection Cross-Connect Valves on Hot Leg Injection," was developed to demonstrate that adequate simultaneous hot and cold leg injection can be implemented after a large break Loss of Coolant Accident (LOCA), if instrument air is not available to operate the High Pressure Safety Injection (HPSI) header valves (HCV-304, 305, 306, 307).
The NRC Safety Evaluation raised questions about the solution outlined by OPPD to be used if instrument air is not available. The following response answers the questions raised by the NRC, clarifies some aspects of the OSAR and i
demonstrates that simultaneous hot and cold leg injection as proceduralized for use at Fort Calhoun Station is a viable method of preventing boron precipitation following a large break LOCA.
f 2.0
SUMMARY
OF THE SIMULTANEOUS H0T AND COLD LEG INJECTION ANALYSIS Long term response to a large break LOCA requires that, in order to prevent boron precipitation in the core, simultaneous hot and cold leg injection is to be initiated no later than 23 hours2.662037e-4 days <br />0.00639 hours <br />3.80291e-5 weeks <br />8.7515e-6 months <br /> after the accident.
The Long larm Core f soling (LTCC) study performed by Combustion Engineering,Inc.WE)hasestablishedthattheLTCCrequiremengsfor lagge and small breaks overlap for breaks ranging from 0.005 ft to 0.02 ft.
In other words, the small break guidelines as outlined by CE in 2
the LOCA analysis can be used for breaks as large as 0.02 ft,
Furthermore, in a later study performed by CE it was stated that fuel rupture,andthereforepossibilityofpersonnelexposuregohigh radiation, does not occur for breaks smaller than 0.03 ft thereby l
l allowing for local operation of the valves.
l l
From a boron precipitation standpoint the limiting break size is the 2
double ended guillotine break (6.3 ft ) which results in low pressures and temperatures in the RCS and requires the maximum hot leg flow in order 1
to prevent boron precipitation.
The assumptions used are the same as in the CE LTCC study, i.e.
pressurizer pressure 5 psig (20 psia), containment pressure 0 psig, and containment sump temperature 212*F.
i Instructions for implementing the hot and cold leg injection are outlined in E0P-03 " Loss of Coolant Accident".
The procedure requires realignment of the HPSI header valves either by closing the air operated header isolation valve HCV-304 or by throttling the motor operated loop injection j
valves until prescribed flows to the hot and cold legs are achieved.
I Specific instructions are described depending on which HPSI pumps are j
available.
In addition to this existing hot leg injection path, the modification noted in the NRC SER as being planned was implemented during the 1988 l
Refueling Outage to allow remote operation of valve SI-186 in the Low Pressure Safety Injection (LPSI) system to provide a back-up injection Page 1 l
' path into the RCS hot leg. This back up path was intended to be used in the event that a large break LOCA occurs, with loss of instrument air (and inability to restore the instrument air) and a failure of the solenoid valve HCV-249.
This scenario would result in a loss of the hot leg injection path at the end of 25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br /> when the air supplied by the accumulator serving HCV-240 is expected to be depleted. This path becomes available for hot leg injection any time the RCS pressure is lower than 140 psia.
3.0 CONCERNS RAISED BY NRC IN THE SAFETY EVALUATION REPORT 1.
Question The licensee should provide reasonable assurance that multiple HPSI pump operation will not occur if such operation would cause valve throttling capability to be exceeded.
Response
At the time of the OSAR 88-36 analysis, implementation of the hot and cold leg injection by E0P-03 (LOCA) required that the HPSI flow be equally split between the hot and cold legs. The procedure also prescribed separt..ing the 2 HPSI headers (one to the cold leg and one to the hot leg) if multiple pumps are available.
The LTCC analysis performed by CE shows that in order to keep the boron concentration below the precipitation limit it is necessary to provide a hot leg side flow which exceeds the core boil-off rate by at least 5 l
gpm.
The cold leg flow must be equal to at least the boil-off rate at a given time.
Equal flow split between the hot and cold legs is not necessary as long as the above requirements are met.
Calculations performed by 0"PD have confirmed that operation of only one HPSI pump is the limiting case for implementing hot and cold leg injection because the pump flow must be split by introducing additional hydraulic resistance in the cold leg injection path (4" line) in order to match the pressure drop through the auxiliary spray line (2" line).
The additional resistance is introduced by throttling the loop injection valves.
If two or more HPSI pumps are available, the total safety injection flow becomes approximately double.
Since the hot leg injection flow requirements remain the same, the additional flow will be directed to the cold leg therefore resulting in higher flow losses, a lower pressure drop across the loop injection valves and minimal, if any, throttling required by the loop injection valves.
Procedural changes to E0P-03 (Loss of Coolant Accident) have been implemented to provide operator guidance for recommended hot and cold leg injection flows during multiple pump operation, when instrument air is not available. As detailed under response to Questions 2 and 3, multiple HPSI pump operation is preferred over single HPSI pump operation and requires less throttling of the loop injection valves.
Page 2 l
2.
Question A pressure drop calculation of flow through the two inch portion of the pressurizer spray line path should be performed.
If an approximate calculation of pressure drop shows a substantial safety factor, a precise calculation need not be performed and the minor, potential nonconservatism discussed in Section 2.4.1 (Items 3 and 4) need not be addressed.
Response
OPPD had performed a detailed pressure drop calculation for various flows through the auxiliary spray line.
The flows used for calculation were taken from the actual pump curves (item 3, Section 2.4.1 of the SER). The OPPD calculation shows that there is not a substantial safety factor from a pressure drop standpoint if only one HPSI pump is in operation. Hot leg injection flow of 175 gpm via the auxiliary spray line becomes limiting from both a pump capacity standpoint and an excessive loop injection valve throttling requirement.
In view of these results, CE was requested to reevaluate the LTCC analysis and quantify the minimum hot leg injection flow which will prevent boron precipitation in the core for all the break sizes.
Results of the CE evaluation show that a hot leg side flow of 100 gpm (via the auxiliary spray line) is sufficient to prevent boron precipitation, and the LTCC analyses remain valid for this reduced flow, as long as the total flow from the pump remains unchanged.
Further uncertainties related to one pump operation were eliminated by procedural changes requiring that a minimum of 2 HPSI pumps be used during hot and cold leg injection. This operating mode provides a substantial safety factor in that no operating limits are approached and Item 4 of Section 2.4.1 of the SER was not addressed.
3.
Question The licensee should perform a better determination of the throttling conditions to which the valves may be exposed and should better verify valve suitability unless the mode of operation is established as far removed from the vicinity of potential valve challenge.
Resoonse OPPD has performed detailed calculations to determine the pressure drop through the auxiliary spray line at various flow rates for one and multiple pump operation. The pressure drop through this line together with the flow rate to the cold leg determines the extent to which the loop injection valves may require throttling.
For one pump operation and 175 gpm flow to the pressurizer, the pressure drop becomes high enough that a limit is approached both on the pump delivery capability and the need for extensive throttling on the loop l
l injection valves.
In order to resolve these potential problems, the
{
following steps were taken:
Page 3 v
l
'a)
CE was contracted to evaluate the minimum required hot leg flow necessary to prevent boron precipitation for the whole spectrum of large breaks.
The analysis performed by CE indicated that boron precipitation will not occur as long as the hot leg injection flow is not decreased below 100 gpm, and the total pump flow remains unchanged, b)
The lcop injection valve manufacturer was requested to evaluate the suitability of the valves for the calculated operating conditions.
Discussions with the manufacturer indicated that the valves are designed for satisfactory operation with considerable throttling and even flashing across the seat. The manufacturer has provided OPPD with a Cv curve versus percent valve opening which allows verification of the valve operating range. However, the manufacturer has stated that there is an uncertainty about the valve capability for fine flow control at the lower Cv range (50-60 gpm flow). This condition has the potential for occurring during operation with only one HPSI pump.
To eliminate the uncertainties related to operation of only one HPSI pump (throttling capability of the loop injection valves)
E0P-03 was revised to require operation of 2 HPSI pumps for implementation of hot and cold leg injection, or if only one HPSI pump is available to use the altornate hot leg injection path via the LPSI pump.
Calculations show that operation of 2 and 3 pumps provide adequate hot and cold leg injection flow and is well within the loop injection valve operability range.
4.
Question These are not normal valve alignments, particularly if low head pumps are to be used.
For example we did not see that pump miniflow requirements had been addressed. We suggest suitable documentation be prepared which addresses such topics so that potential problems are avoided.
Response
An additional hot leg injection path has been provided by a modification installed during the 1988 Refueling Outage.
This path uses the shutdown cooling warm-up line via valve SI-186 and into the hot leg through the isolation valves HCV-347 and HCV-348. A complete hydraulic evaluation of this line has been performed by CE and it was found to be an acceptable path provided the pump minimum ficw requirements are met.
OPPD's response to NRC Bulletin 88-04 states that since the manufacturer of the pump was unable to provide sufficient flow information, OPPD performed a test with the LPSI and HPSI pumps operating in a simultan-eous miniflow mode for a period of 30-45 minutes, with calculated LPSI miniflow rates of 150 gpm each. Operating parameters of the pumps were closely observed during the run and no signs of abnormal operation were detected.
Page 4
In addition, a pump performance test performed in November 1988
-(SP-SI/CS-2) showed that no discernible degradation of any of the SI pumps has occurred over the long term due to use of the miniflow line for quarterly pump testing. The calculated miniflow during the quarterly individual pump test is approximately 200 gpm.
The testing described above provides reasonable assurance that the LPSI pumps can be safely operated at flows of 200 gpm. A caution statement incorporated in E0P-03 (LOCA) warns the operator of possible pump damage if the pump is operated at flows below 200 gpm and RCS pressures above 140 psig.
It should be noted that this alternate hot leg injection path is intended to be used only if the auxiliary spray line path is not available or if only one HPSI pump is operable.
The above documentation provides assurance that the pump miniflow requirements have been addressed for this mode of operation,
4.0 CONCLUSION
S j
Detailed calculations performed in support of OSAR 88-36 have indicated that the failure of the air operated valves on the HPSI headers in the open position and inability to operate them following loss of instrument air has little effect on implementing the hot and cold leg injection required for LTCC.
The calculations have; however, indicated thht there may be.a potential problem in accomplishing simultaneous hot and cold leg injection if only one HPSI pump is operating, due to uncertainees about the fine flow control capability of the loop injection valves in the low Cv range.
In order to prevent any potential for problems during this mode of operation, the Emergency Operating Procedure for LOCA (E0P-03) has been revised to require operation of 2 HPSI pumps or (if only one HPSI is available) use of the alternate injection path to implement simultaneous hot and cold leg injection. Additional guidance for operation of 2 HPSI pumps when instrument air is not available was also included in E0P-03.
Based on the calculations performed and procedural controls established, the hot and cold leg injection guidance as proceduralized at FCS is a' viable method of preventing boron precipitation following a large break LOCA with loss of offsite power, failure of I diesel and/or loss of instrument air.
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