ML20024D301
| ML20024D301 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 07/28/1983 |
| From: | Kay J YANKEE ATOMIC ELECTRIC CO. |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.F.2, TASK-TM FYR83-69, NUDOCS 8308040479 | |
| Download: ML20024D301 (7) | |
Text
T:lephone (617) 8724100 TWX 7103807619 YANKEE ATOMIC El. ECTR!C COMPANY via83-s9 2.C2.1 h*
1671 Worcester Road, Framingham, Massachusetts 01701 Yauxes
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July 28, 1983 United States Nuclear Regulatory Commission Washington, D. C. 20555 Attention:
Mr. Dennis M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing References; (a) License No. DPR-3 (Docket No. 50-29)
(b) USNRC Letter to YAEC, dated June 27, 1983 (c) YAEC Letter to USNRC, dated March 18, 1974 (Proposed Change #114)
(d) USNRC Letter to YAEC, dated July 5, 1974 (e) YAEC Letter to USNRC, dated March 10,1983 (FYR 83-28)
(f). YAEC Letter to USNRC, dated November 24, 1981 (FYR 81-155)
Subject:
Response to Request for Additional Information on Inadequate Core Cooling Instrumentation
Dear Sir:
In response to Reference (b), the following information is presented.
This information provides detailed information on the incore thermocouples, their qualification and distribution in the core, and the proposed modifications in response to the requirements of NUREG-0737, Item II.F.2,.
1.
NUREG-0737, Item II.F.2, Attachment 1, requires a minimum of 4 environmentally qualified instrumentation channels per quadrant.
This is not provided, why?
Yankee Response The original Yankee Incore Instrumentation Systen consisted of flux wires and 24 incore thermocouples. The thermocouple arrangement contained 19 in one quadrant (complete coverage of all assemblies within the quadrant) and the remaining five located in the other three quadrants.
In the early years of operation, the thermocouples provided a means of monitoring the radial power distribution between flux wire runs.
In 1974 the Incore Instrumentation System was upgraded to movest.le fission chambers and 26 incore thermocouplesn I
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United States Nuclear Regulatory Commission July 28, 1983 Attention:
Mr. Dennis M. Crutchfield Page 2 The thermocouple arrangement was essentially the same as the original system.
Nineteen thermocouples were located in one quadrant to provide full quadrant coverage. The remaining seven were distributed two per quadrant in the high power regions and one was located on the periphery. With only 76 assemblies in the total core, this arrangement provides at least an equivalent thermocouple coverage per fuel assembly as in the larger plants.
The existit:g incore instrumentation configuration was proposed to NRC in Reference (c) and approved in Reference (d). In Reference (d), the Staff Safety Evaluation stated the following:
"The present distribution [ pre-1974] of core locations for flux mapping and for monitoring core outlet coolant temperatures with the incore instrumentation is arranged to provide a detailed map of one quadrant with a few monitoring positions in other quadrants for checking symmetry. This distribution will be changed [as proposed in Reference (c)] for the new incore instrumentation to provide a more uniform coverage of the core. We have concluded that the proposed number of monitoring locations (26 thermocouple positions and 22 flux path positions) is acceptable for the Yankee Rowe core that contains 76 fuel assemblies."
Note: Subsequent to this modification, two (2) additional thermocouples were inserted in the sealed flux tubes and positioned in the upper plenum to bring the total number of thermocouples to 28.
2.
The backup display should receive temperature inputs from 16 thermocouples, 4 from each quadrant. The map of thermocouple locations discloses that 2 of the 4 quadrants only have 3 thermocouples, and 1 quadrant only has 2 thermocouples. Will additional units be installed?
YAEC Response The distribution of thermocouples is discussed in response to Questions 1 and 3.
Based on these discussions, it is our position that the number and location of thermocouples is sufficient for the Yankee Plant core size. Furthermore, it is also our position that the NUREG-0737 objective to provide indication of radial distribution of the coolant enthalpy (temperature) rise across representative regions of the core is met.
United States Nuclear Regulatory Commission July 28, 1983 Attention:
Mr. Dennis M. Crutchfield Page 3 3.
The backup display should be entirely powered by Class 1E power sources.
In addition, the backup display should have a minimum range of 2000F to 2300 F.
The table provided indicates that there are insufficient thermocouples provided which have both adequate range and also have 1E power. Will a backup display be provided?
YAEC Response A backup display (two 3 pen recorders per train) will be provided, powered by redundant lE power sources, and will satisfy the above temperature range requirements. The backup display will record (on dedicated recorders) the temperatures of eight (8) thermocouples arranged such that there are two (2) qualified thermocouples per quadrant, with one per quadrant associated with each power source.
For further details, see the attached block diagram.
0 4
A primary display with a range of 2000F to 1800 F, the ability to display a spatially-oriented core map of temperature distributions, a temperature-time history, and an alarm capability is required. Will a suitable primary display be provided?
YAEC Response The Safety Parameter Display System (SPDS) will provide the primary display and will fulfill the above requirements.
It is planned that all incore thermocouples be input to the SPDS with exception of two thermocouples dedicated to the LTOP recorder and two dedicated for the proposed Hot Shutdown System. For further details, see the attached block diagram and core map.
5.
Is instrumentation for ICC indication available at all times, not just during power operation?
YAEC Response All ICC instrumentation is' available except during routine surveillance or when disconnected during refueling operations as with the incore thermocouples.
6.
Half of the core exit thermocouples used for the primary coolant saturation margin monitor are not qualified. When will the remaining thermocouples be qualified? If they will not be qualified, provide justification for that decision to NRC.
Will additional qualified thermocouples be installed in each quadrant of the reactor c9re?
United States Nuclear Regulatory Commission July 28, 1983 Attention:
Mr. Dennis M. Crutchfield Page 4 YAEC Response A total of fourteen (14) thermocouples will be qualified once the installation of qualified connectors is complete. This will result in the following qualified thermocouple distribution:
two (2) thermocouples per quadrant with four (4) additional thermocouples in the fourth quadrant, and two (2) thermocouples in the upper head.
These thermocouples will be inputs to the SPDS, Backup Display, and Saturation Monitor.
We are evaluating the qualified life of the existing QDHT connectors presently installed on six (6) thermocouples. Based on the results of this evaluation, we will make a determination whether to install additional QDHT connectors or investigate the possibility of obtaining other qualified connectors now undergoing qualification testing. Other core locations will be fitted with qualified thermocouples such that fourteen (14) thermocouples will be LOCA qualified. For the proposed core locations for qualified thermocouples, see the attached incore distribution map.
7.
Describe your plans for upgrading the reactor vessel upper head thermocouples consistent with ICC instrumentation design requirements. Discuss your plans for inclusion of upper head thermocouples information into Yankee Rowe emergency procedures, especially those procedures relevant to the SGTR event, to improve the basis for operator actions.
YAEC Response In discussions with NRC, subsequent to the meeting of April 26, 1983, we identified the existence of two elevated thermocouples. These thermocouples were described as being located below the upper guide tube support plate and inserted into sealed flux tube paths. These thermocouples, at this location, are more correctly identified as in the upper plenum than in the upper head and were originally inserted at this elevation for evaluating a potential failure mechanism (i.e., thermal cycling) for the flux monitoring paths.
Since these thermocouples are not in contact with reactor coolant (as are the core exit thermocouples), and because they are located below the guide tube support plate, two (2) upper head thermocouples will be installed. Procedures will be revised appropriately to incorporate their use.
The Yankee emergency procedures presently consider information from the incore thermocouples to provide a basis for operator actions:
both the Inadequate Core Cooling procedure, as discussed in
United States Nuclear Regulatory Commission July 28, 1983 o
Attention:
Mr. Dennis M. Crutchfield Page 5 Reference (e) and in the Steam Generator Tube Rupture (SGTR) procedure. The SGTR procedure specifically alerts the operator to the possibility of void formation and cautions against false level conditions in the pressurizer. The procedure states the importance of maintaining overpressure above the corresponding saturation pressure. In addition, the Yankee plant is equipped with loop isolation valves that can be used to rapidly isolate the primary leak through a ruptured tube. The loop isolation valves reduce the need to depressure the primary system during a SGTR, thus, reducing the likelihood of void formation.
Void formation in the upper head during natural circulation cooldown at the Yankee Plant has been evaluated by RETRAN analysis [see Reference (f )].
Results from the analysis were used to develop guidelines to prevent void formation during cooldown on natural circulation. Procedures limit the cooldown rate under natural circulation conditions to 200F/hr. This in conjunction with the requirement to maintain a 1000F subcooling margin, based on present instrumentation, is sufficient to preclude void formation in the upper head during potential natural circulation operating conditions.
We trust this information is satisf actory. Should you have any questions, please contact us.
Very truly yours, YANKEE ATOMIC ELECTRIC COMPANY J
A. Kay Senior Engineer - Licensing JAK/dsm
CONCEPTUAL BLOCK DIAGRN!
Sh. 1 of 2 ICC DETECTION SYSTEli Vital Bus 1 Power Vital Bus 2 Power 4
1 8
4 1
8 Thermocouples UHT Thermocouples Thermocouples UHT Thermocouples Z_
Qualified
_Z Connectors 5
8 13 Single Output Dual Output Single Output Transmitters Transmitters Transmitters 8
-} Sat.
- to Back up Back up Recorde r Mon.
Recorder NY Y
Y S,V y
v
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j
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t j
q v
Via TEC isol. (4 T/C)
Via TEC 1 sol.
(8 T/C)
Cabinet Cabinet (4 T/C)
(4 T/C)
LOCATIONS Saturation Monitor inputs (Oualified)
G-3 /H-7 / D-8 / E-3 / B-4 / E-5 / C-5 / D-2 Backup Recorder Inputs (Qua_1_i f ied )
G-3/H-5/F-7/11-7/B-7 /D-8/E-5/C-3/ Head Thermoeouples All thermocouples will be input to the SPDS with exception of:
G-10/D-1 liot Safe Shutdown C-6 /ll-2 1.-Top Recorder
- Upper head thermocouple
I ROWE INCORE THERMOCOUPLE LOCATIONS Sh. 2 of 2 A
B C
D E
F G
H J
K
() x x
@ x
()
x x
x g
X X
X x
4 0
X X
X @
x s
6 X
X 7
8 Upper llead X
Thermocouple Upper Head Thermocouple 10 i
Sat ura t ion Moni tor Inputs (Qualified) liack Up Recorder Inputs (Qualified)
X tan"t t" seos
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