ML20247C211
| ML20247C211 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 03/20/1989 |
| From: | Boyle M Office of Nuclear Reactor Regulation |
| To: | Mroczka E NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| TAC-60207, NUDOCS 8903300143 | |
| Download: ML20247C211 (6) | |
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March-20, 1989
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w-Docket No. 50-245 DISTRIBUTION C Docket; File a 0GC
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Mr. Edward J. Mroczka NRC'& Loial'PDRs EJordan Senior Vice President Plant File BGrimes Nuclear Engineering and Operations Glainas ACRS(10)
Northeast Nuclear Energy Company BBoger JLazevnick (SELB/ DEST)
P.O. Box 270 SNorris Hartford, Connecticut 06141-0270 MBoyle
Dear Mr. Mroczka:
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SUBJECT:
' REQUEST FOR ADDITIONAL INFORMATION - DEGRADED GRID PROTECTION (TAC NO. 60207)
By letter dated August 15, 1988 Northeast Utilities submitted its revised design for Millstone Unit.I degraded grid under voltage protection logic. On December 2, 1988, NU submitted a proposed change to the Technical Specifications reflecting the new design. The NRC staff has reviewed this information and requests that the additional information identified in the enclosure be submitted so that we may complete our review.
The reporting and/or recordkeeping requirements contained in this letter affect fewer than ten respondents; therefore, OMB clearance is not required under P.L.96-511.
Sincerely,
/s/
Michael L. Boyle, Project Manager Project Directorate I-4 Division of Reactor Projects I/II Office of Nuclear Reactor Regulation
Enclosure:
As stated cc w/ enclosure See next page
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1, Mr. Edward J. Mroczka Millstone Nuclear Power Station
. Northeast Nuclear Energy Company Unit No. 1 cc:
Gerald Garfield, Esquire R. M. Kacich, Manager Day, Berry and Howard Generation Facilities Licensing Counselors at Law Northeast Utilities Service Company City Place Post Office Box 270 Hartford, Connecticut 06103-3499 Hartford, Connecticut 06141-0270 W. D. Romberg, Vice President D. O. Nordquist Nuclear Operations Manager of Quality Assurance Northeast Utilities Service Company Northeast Nuclear Energy Company Post Office Box 270 Post Office Box 270 Hartford, Connecticut 06141-0270 Hartford, Connecticut 06141-0270 Kevin McCarthy, Director Regional Administrator Radiation Control Unit Region I Departmeni. of Environmental Protection U. S. Nuclear Regulatory Commission State Office Building 475 Allendale Road Hartford, Connecticut 06106 King of Prussia, Pennsylvania 19406 Bradford S. Chase, Under Secretary First Selectmen Energy Division Town of Waterford Office of Policy and Management Hall of Records 80 Washington Street 200 Boston Post Road Hartford, Connecticut 06106 Waterford, Connecticut 06385 S. E. Scace, Station Superintendent W. J. Raymond, Resident Inspector Millstone Nuclear Power Station Millstone Nuclear Power Station Northeast Nuclear Energy Company c/o U. S. Nuclear Regulatory Commission Post Office Box 128 Post Office Box 811 Waterford, Connecticut 06385 Niantic, Connecticut 06357 J. P. Stetz, Unit Superintendent Millstone Unit No. 1 Northeast Nuclear Energy Company Post Office Box 128 Waterford, Connecticut 06385 l
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4 REQUEST FOR ADDITIONAL INFORMATION MILLSTONE UNIT 1 UNDERVOLTAGE DETECTION ROUIFICATION 2
' 1.
The Load Shed & LNP Logic diagram provided in your August 15, 1938 letter shows multiple points where signals from redundant divisions are brought together into common logic gates.
Identify the isolation and separation you have provided between redundant circuits. Provide the actual. schematic diagram of the undervoltage detection logic.
2.
The Load Shed & LNP Logic diagram shows multiple points where a single failure of a logic gate can cause load shedding of both redundant divisions and starting and loading of the emergency generators even
'though offsite power is still available. Please justify.
3.
There is no signal identified in the Load Shed & LNP Logic that separates the onsite buses from the normal station service trans-former and the reserve station service transformer (trips NSST and RSSTbreakersonbuses14A,14B,14C,and14D)onalossofvoltage or degraded voltage signal. Please explain how this is accomplished.
i 4.
It appears from the Load Shed & LNP Logic diagram that a loss of power
(<70% voltage) can exist on a single division (14E or 14F) with no auto-matic action taken to correct it other than load shedding of the respec-tive buses and a degraded voltage annunciation. Does the load shodding also start the automatic connection of the emergency power sources to the buses? If not how does the plant respond to a LOCA with simul-
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taneous loss of offsite power to one division and a single failure of the redundant division?
5.
With respect to question 4 above the same situation applies to a degraded voltage condition (< 90% but>70% voltage) except the buses are not load shed. How then does the plant respond to a LOCA with simultaneous de-graded voltage on one division and a single failure of the reduncant division?
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6.
From the Load Shed & LNP Logic diagram provided, it appears that a single failure in 14E or 14F switchraar such as a switchgear fire I
that disables the switchgear undervoltage relays will also disable the undervoltage detection logic for the redundant division. The remaining division will then not be able to respond to a loss of voltage condition. Please justify this violation of the single failure criteria.
7.
Identify the source of power to the redundant 51 and S2 logic channels shown in the Load Shed & LNP Logic diagram. If the source of power is from the Class IE power system justify the connection of the Class 1E power between redundant divisions. Describe the separation and isola-tion provided between redundant systems.
8.
It is not clear from the logic diagrams you provided in your August 15, 1988 letter how the load shedding of the emergency buses will be bypassed during load sequencing and subsequently reinstated following load sequencing. Please provide an explanation of how this is accomplished.
9.
The Load Shed & LNP Logic diagram indicates that a signal with no time delay will be sent to the Load Shed & LNP actuation circuits whenever the NSST and RSST breakers to buses 14C and 14D are all simultaneously open. One of the actions this accomplishes is blocking of the fast
-s-transfer circuits. Will the logic interfere with a legitimate fast transfer when all the breakers to buses 14C and 14D are simultaneously open as part of the fast transfer sequence?
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- 10. The Load Shed & LNP Logic diagram shows 3-out-of-3 logic for the loss L
of voltage relaying and 2-out of-3 logic for the degraded voltage relaying. Why isn't 2-out-of-3 logic used for both?
- 11. With regard to Table 3.9.1 in the revised Technical Specifications you submitted in your December 2,1988 letter, the first part of that table
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identifies power available relaying on the emergency buses. This appar-ently replaces the power available relaying previously identified in tables 3.2.2 and 4.2.1, however, the relays identified in table 3.9.1 do not. appear to be the same as those relays identified in tables 3.2.2 I
1 and 4.2.1 since more buses and more relays are involved. No description i
however is provided for the new configuration. Please clarify whether
'l this is a new configuration and, in either case,' describe the actuation logic ahd function of these relays.
i 12.
Identify the function of the Train A and Train B Load Shed & LNP Circuit relays shown at the bottom of page 3/4 9-2a in Table 3.9.1 of the revised j
Technical Specification.. Are these the relays that provide the functional logic shown in the Load Shed & LNP Logic diagram?
- 13. Regarding the load shedding function identified on the logic diagrams pro-vided in your August 15, 1988 letter, clarify whether the phrase " Load Shed Bus" and " Load Sheds Buses" means separation of the loads from the buses 1
or separation of the buses from their power source.
If it means separa-tion of the loads from the buses then why is load shedding provided for the loads of buses 14B and 14D if these buses are not loaded to the emer-gency diesel or gas turbine generators, and why aren't the bus 14B load shed relays identified in technical specification table 3.9.1? If it means separation of the buses from their power sources then how is separa-tion of the loads from the buses accomplished prior to load sequencing?
- 14. a)
No instrument functional test, calibration, or instrument check frequencies are identified for the "Undervoltage/ Timer Relaying" J
in table 3.9.1 of the revised technical specifications. The sur-veillance frequencies for these items should be once per shift, once per month, and once every refueling outage respectively.
I Please add these surveillance requirements to the revised tech-nical specification.
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Also, the trip setpoints with minimum and maximum limits for the "Undervoltage/ Timer Relaying" are not specified in table 3.9.1.
This information should be provided in the revised technical specifications, and the basis for the'setpoint values should be
_provided to us for our review.
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In addition, there is no operability requirement identified for the "Undervoltage/ Timer Relaying" in table 3.9.1 when in the
" Refuel / Shutdown" mode.- This relaying should be operable in these modes whenever the safety-related equipment in the divi-sion it monitors is required to be operable. Please revise the technical specifications accordingly.
- 15. The undervoltage relaying that initiates transfer of the safety buses to the gas. turbine generator are all connected to bus 14E which is not connected to the same winding of the NSST that feeds bus 14A.
How then can you assure that a degraded condition on bus 14A will be detected by the relaying on bus 14E in order to automatically transfer bus 14A to the gas turbine?
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