ML20058N497
| ML20058N497 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 12/17/1993 |
| From: | Hutchinson C ENTERGY OPERATIONS, INC. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-92-04, GL-92-4, GNRO-93-00158, GNRO-93-158, IEB-93-003, IEB-93-3, NUDOCS 9312220077 | |
| Download: ML20058N497 (3) | |
Text
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1 Entsrgy Operations,Inc.
ENTERGY maa Ryt G6 son, M9 3960 r
W CD1437 2800 C. R. Hutchinson vec heuwd (WaWG Gra-(f GJ NuCMJir QJW1 Dec ed>cr 17, 1993 U.S. Fjt 'ecr Regulatory Commission Mail S at an F1-37 Washingtta, D.C.
20555 Attention:
Document Control Desk
Subject:
Grand Gulf Nuclear Station Docket No. 50-416 License No. NPF-29 Grand Gulf Nuclear Station Final Response to NRC Bulletin 93-03 GNRO-93/00158 Gentlemen:
On July 30, 1993, Entergy Operations submitted the Grand Gulf Nuclear Station (GGNS) response to NRC Bulletin 93-03 and Generic Letter 92-04.
That submittal described the short term compensatory actions and planneu hardware changes to address the concerns associated with reactor water level' measurement inaccuracies as a result of potential degassing of reactor water level instrumentation reference legs. NRC Bulletin 93-03 required that a. written report be submitted within 30 days of completion of the requested hardware modifications, confirming completion and describing the modification completed. This submittal completes the remaining action of NRC Bulletin 93-03.
During-Refueling Outage 6 (RF06), GGNS implemented a. design modification to provide a continuous purge to all1four channels of the reactor vessel. water level indicating system reference legs. This continuous purge supply, provided by the Control Rod Drive System (CRD) pumps, will effectively serve to prevent the concentration of noncondensible gases in the reference legs. This is accomplished by providing a source of water that is not saturated with noncondensible gases to continuously purge the reference legs.
This change will enhance reactor vessel level instrumentation reliability for both rapid and slow depressurization events.
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The GGNS design consists of a line tapped from the CRD pump' j
~
discharge that branches into four separate purge lines, each j
going to one of the vessel level instrumentation reference legs. Each line contains two check valves in series, a-1 restricting orifice to limit flow, and a' flowmeter as well as' additional manual valves for maintenance. The manual block valve downstream of-the transmitters and before the condensing chamber on each line has been modified'to prevent inadvettent closure as described in NRC Information Notice 93-89. This modification consists of a pin inserted through' a hole drilled in the root valve stem and yoke and then tack-welded in place. A flowmeter installed in each-line is monitored by operators as part of their normal rounds to ensure the purge flow is maintained at required levels.-
j GGNS plans to continuously operate this system during plant.
- operation.
Post-modification testing demonstrated the system design flowrates were achieved.
In addition to the continuous backfill system, GGNS
[
installed a modification that-provides-indication of level in the core zone range. This modification ~ employs the current fuel zone monitoring instrumentation,cbut instead of using a condensing pot as a reference leg source ~, it uses.
the variable leg of the' narrow range transmitters. This-ensures that the variable leg of this instrument does not l
become saturated with noncondensibles,.thus providing an accurate indication of reactor level within the range of the transmitter (the indicated range was increased.by 100-inches). This~ modification addresses only the degassing 1
concerns associated with rapid depressurization scenarios, not low pressure controlled shutdowns.
In the event the continuous backfill system described-becomes inoperable, GGNS plans to rely on this core. zone monitor and a manual reference. leg backfill prior to controlled shutdowns (slow depressurizations)-in order to support level instrumentation operability.
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December 17. 1993
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GNRO-93/00158 Page 3 of 4 i
This letter confirms GGNS implementation of the hardware modifications as described above to address RPV level instrumentation reference leg degassing and completes the reporting requirements of NRC Bulletin 93-03, item (3).
Should you have a.ly questions or comments, please feel free to contact Ricky Patterson at (601)437-6466.
I Yours truly i
M f_
CRH/RLP/mtc cc:
Mr.
R.
H.
Bernhard Mr. H. W.
Keiser Mr. R. B. McGehee Mr. N.
S. Reynolds Mr. H.
L. Thomas Mr. Stewart D.
Ebneter Regional Administrator U.S. Nuclear Regulatory Commission Region II 101 Marietta St.,
N.W.,
Suite 2900 Atlanta, Georgia 30323 3
Mr.
P. W. O'Connor, Project Manager (w/2)
Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop 13H3 Washington, D.C.
20555 5
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4 G9312072