ML20236R241
| ML20236R241 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 07/14/1998 |
| From: | Ohanlon J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 98-179A, NUDOCS 9807210315 | |
| Download: ML20236R241 (5) | |
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YIRGINIA Euccinic ANI> Pownca Cm1PANY RCit MONI), VIIMilNI A 23261 l
July 14, 1998 U. S. Nuclear Regulatory Commission Serial No.
98-179A Attention: Document Control Desk NL&OS/ETS R2 Washington, D.C. 20555 Docket Nos.
50-338 50-339 License Nos. NPF-4 1
NPF-7 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 PROPOSED TECHNICAL SPECIFICATIONS CHANGE REVISED LOOP STOP VALVE OPERATION j
On November 6,1996, Virginia Electric and Power Company (Serial No.96-532) requested amendments, in the form of changes to the Technical Specifications, to Facility Operating License Numbers NPF-4 and NPF-7 for North Anna Power Station Units 1 and 2, respectively. The proposed changes will modify the requirements for isolated loop startup to permit filling of a drained isolated loop via backfill from the Reactor Coolant System through partially opened loop stop valves.
In a June 9,1998 letter, the NRC staff requested additional information to continue review of the proposed Technical Specifications change. The Attachment to this letter j
provides the information requested by the staff.
Should you have any questions or require additional information, please contact us.
Very truly yours, James P. O'Hanlon Senior Vice President - Nuclear
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l Attachment l
Commitments made in this letter; C \\
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None
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l 9807210315 900714 PDR ADOCK 05000338 P
PDR l
w____-___-__________-_____
Unithd States Nuclear Regulatory Commission cc:
Region ll Atlanta Federal Center 61 Forsyth Street, SW Suite 23T85 Atlanta, Georgia 30303 Mr. M. J. Morgan NRC Senior Resident inspector North Anna Power Station Commissioner l
Department of Radiological Health Room 104A 1500 East Main Street Richmond, VA 23219 l
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Response to Request for Additional Information Revised Loop Stop Valve Operation North Anna Power Station, Units 1 and 2 (TAC Nos. M97187 and M97188)
I NRC Question i
The response to questions 3 and 4 from the original set of RAls dated April 14,1998, indicates that the loop stop valves will not be opened with any of the reactor coolant pumps (RCPs) operating and the analyses assume free convection rather than forced convection associated with RCP operation. The basis provided to justify no RCP operation is that the design differential pressure for the loop stop valves is only 200 psi and the RCP seals require 300 to 325 psi to operate properly. The set of initial conditions where this evolution can be accomplished safely should not be derived solely from the design limitations on the individual components but rather established in the TS allowing the evolution. As a result, if the opening of a loop stop valve can only be accomplished safely with no RCPs running and RCP operation is permitted in Mode 5 where the specification applies, the specification should be modified to preclude RCP operation.
Virginia Power Response The analyses performed for the loop backfill evolution examined both natural convection and forced convection heat transfer on the primary side of the steam generator tubes as discussed in our April 15,1998 response to NRC question number 4 of your March 16,1998 request for additional information. The forced convection case is representative of one or more reactor coolant pumps operating.
The case simulated in the analyis was intended to represent start of the reactor coolant pump in the backfilled loop just after completion of the evolution. However, the heat transfer, volume surge and reactivity effects discussed in that response would bound the case of opening the stop valves with a reactor coolant pump running in another loop. The analysis which shows that loss of RHR suction would not result from opening the loop stop valve would also apply to the case of one or more RCPs running.
Based on the heat transfer analysis performed for both natural and forced convection, opening of a loop stop valve with one or two reactor coolant pumps running has been adequately analyzed and can be performed safely. However, as discussed in our previous submittals, practical operational limitations as well as concern for protecting the integrity of the reactor coolant pumps and motors would preclude performing the backfill evolution with RCPs operating.
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NRC Question Question 5 from the original RAI requested a description of how the gas from the empty loop was vented. Please provide this description.
Virginia Power Response Station operating procedures address filling and venting of isolated reactor coolant system (RCS) loops using either the Containment Vacuum System or the Process Vent System. A vacuum is drawn on the RCS loop using the containment vacuum pumps or process vent blower. The two methods currently used are as follows. The containment vacuum pump is connected to the RCS high point vent to draw a substantial vacuum on the RCS loop to remove as much of the gas as possible and pull water into the steam generator tubes when fill is initiated. The other method installs a spoolpiece between the RCS high point vent and the Process Vent system. The Process Vent blower develops a slight negative pressure to pull the gas from the loop. The first method is preferable because it removes more of the gasses and reduces the number of reactor coolant pump starts to obtain a water solid loop to return to service. The gasses that are displaced while filling the reactor coolant system (RCS) loops are vented to atmosphere through the Process Vent System.
For both methods of venting, the RCS loop is filled until water reaches the high point
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vent, and the gasses extracted from the RCS loop are discharged to the Process Vent System to ensure a monitored release path.
NRC Question The response to question 6 indicates that level instrument uncertainties are not included in the 450 ft' specification and that no channel uncertainty has been calculated because of the conservatism ir the analysis.
Although there is a good deal of conservatism in the analysis, using this conservatism to bound the instrument uncertainties is not appropriate because neither the conservatism nor the instrument uncertainty has been quantified.
Please include instrument uncertainties in the development of the pressurizer water volume specification.
Virginia Power Response Virginia Power quantified the conservatism associated with assuming that all three loops were unisolated simultaneously when the proposed 450 ft' specification was developed. This conservatism was calculated as follows:
i For the loops not under a vacuum:
1.
The volume on the steam generator side of the loop stop valves below mid-loop was catculated. This volume was multiplied by two to obtain the volume that Page 2 of 3
would drain into the two loops assuming those two sets of loop stop valves are
opened simultaneously. This volume is identified as V%,.
2.
The RCS loop piping water volume on the reactor vessel side of the loop stop valves above mid-loop elevation was calculated. The volume was again multiplied by two to account for two loops. This volume is available for filling drained loop volumes in the two loops and is identified as b%,.
.3.
The difference in these two volumes is the additional RCS volume that is needed to fill these two loops to the mid-loop elevation.
l The additional volume was calculated to be 340.4 ft'.
Review of North Anna level instrument channels of a design similar to the cold calibrated pressurizer level channel (differential pressure transmitter based) shows that this type of channel has a level indication accuracy of better than 3% span, which corresponds to about 40 ft'.
Since this quantified conservatism of 340.4 ft' is significantly greater than the 40 ft' I
estimate for the level channel instrument accuracy as noted in our April 15,1998 letter, instrument accuracy effects are considered to be already included in the 450 ft' specification. There is no need for further specific quantification of the cold pressurizer level channel accuracy.
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