ML20003E823
| ML20003E823 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 04/14/1981 |
| From: | Heider L VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | Ippolito T Office of Nuclear Reactor Regulation |
| References | |
| FVY-81-64, NUDOCS 8104170091 | |
| Download: ML20003E823 (3) | |
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f)J VERMONT Y AN K EM NUCLEAR POWER CORPOR ATION scvcNTv scvon cROvc sTRtcT 2.C.2.1 FVY 81-64 RUTLAND. VERMONT 05701 REPLY TO ENGINEERING OFFICE 1671 WORCESTER ROAD April 14, 198)R AMINGH AM. M ASSACHUSETTS O1701 TELEPHONE 017 872 9100 United States Nuclear Regulatory Commission 4
Washington, D. C.
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g Attention:
Office 01..uclear Reactor Regulation Mr. T. A. Ippolito, Chief
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44 Division of Licensing
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References:
(a) License No DPR-28 (Docket No. 50-271)
(b) Letter, VYNPC TO USNRC, WVY 80-146, dated 4
N October 14, 1980 tu l (c) Letter VYNPC to USNRC, FVY 81-14, dated Janua ry 27, 1981 (d) Letter, USNRC to VYNPC, dated March 6,1981 (e) Letter, USNRC to VYNPC, dated January 9.1981
Subject:
BWR Scram Discharge System - Long Term Modifications
Dear Sir:
Reference (d) requested that Vermont Yankee modify our commitments made in References (b) and (c) regarding the subject modifications to our scram discharge system. Our responses to these requests are presented below:
NRC Position (1)
"The modifications must be complete by December 31, 1982."
Response
Vermont Yankee has no refueling or maintenance outage scheduled during 1982. This makes it necessary f or Vermont Yankee to defer the installation of these modifications until the refueling outage scheduled to begin in March of 1983. We f eel that the addition of only three months to an implementation schedule of over two years is not significant.
Furthermore, we believe that continued operation of our f acility until March of 1983 is justified by the excellent operating history of our scram discharge system and the f act that modifications have already been incorporated to futher enhance the reliability of the scram system, such as additional water level monitoring instrumentation and control room indication of scram air header pressure. Modif ica t ions required by Reference (e) provide still another incremental increase in system reliability.
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United States Nuclear Regulatory Co sission April 14, 1981 Division of Licensing Page 2 NRC Position (2)
'The design must include our criterion on Diverse Instrumentation (Saf ety Criterion 3 in Generic SER on BWR SCRAM DISCHARGE SYSTEM, December 1,1980)".
Response
NRC Ceneric Letter 81-18, which provides further information on the staff's position on the above Generic SER, states "We consider diverse instrumentation for the automatic level sensing system on the Scram Discharge Volume to be a necessary and important provision that will enhance the overall reliability of the BWR Scram System".
This statement alone does not provide justification for us to design additional diversity into our systems. Before considerlag any changes to our planned modification, we need the data used by the staff to reach the conclusion stated above. This data should include a quantitative evaluction defining how much the system reliability is enhanced.
In addition, we would like to know how the staff intends to factor this new information along with other planned improvements to the SDV [see Ref rence (b) and (c)] into their scram f ailure probability models that support their ATWS conclusions.
We are disappointed with the NRC Position (2) above. The GE Owners Group criteria for SDV design review, which we endorse, was the result of a significant eff ort originally intended to restore confidence in the original scram discharge volume design. Implementation of the criteria that finally resulted f rom extensive interactions with the NRC staff is admitted by both the staff and the GE Owners Group to not only restore but to improve (in some cases significantly) the reliability of the SDV system and, consequently, the scram system. At no time during these interactions was any evidence provided that supported a staff desire for diverse instrumentation, nor was the Owners Group at all convinced that diversity added measurably to the other improvements already achieved. We are now even less convinced of the need for diversity af ter assessing our planned modifications to the scram discharge volume. These modifications will provide incremental improvements in the scram discharge volume reliability and make any potential f ailures extremely remote. These modifications which have been described in previous letters include the following:
Two independent instrument volumes versus the one in the orf.ginal design.
It is very unlikely that all eight level instrraercs (4 in each volume) in the two independent instrument volu;.e would fail at the came time.
There will be no pipe reductions between the volume header and the instrument volume. This insures that all water accumulates in the independent instrument volumes.
Modification to the vent and drain systems will reduce the probability of level instrumentation failures. With regard to level instrumentation f ailures, it is our opinion that failures to date have been site specific, and not generic in nature. Operating experience at Vermont Yankee indicates that these problems do not exist at our facility.
United States Nuclear Regulatory Commission April 14, 1981 Division of Licensing Page 3 t
Furthermore, we are concerned about the following statement made in NRC Generic Letter 81-18 with regard to ATWS:
"We are deleting the option that allows credit for operator action on the basis of an ATWS consideration that allows no credit for operator action for a minimum of 10 minutes." We disagree with this judgment since ATWS is not a design basis. To use ATWS as a basis for anything while it is not a regulatory requirement, is ina pp ropriate.
In addition, even if ATWS were a requirement, we certainly would not agree to "no credit for operator action for a minimum of 10 minutes".
We must also point out the fact that this statement is inconsistent with the staff's most recent draf t proposed rule on ATWS which does allow credit for operator action if it can be demonstrated that an operator vould have adequate information and could reasonably be expected to take proper corrective action within the time available.
NRC Position (3)
" Revised TS' may be required prior to operation with the modified systems and if so, must be proposed at least three months in advance of the modification completion dates".
Response
If Vermont Yankee determines that revised technical specifications are required prior to operation with the modified systems, proposed technical specifications will be submitted at least three months in advance of the modification completion dates.
In clor,ing, Vermont Yankee would like to formally request any data or information that the staff has which explicitly and quantitatively defines how diverse instrumentation will"... enhance the overall reliability of the BWR Scram System."
Please contact us if it is determined that this information should be requested via the Freedom of Information Act rather than through a letter of this sort.
We trust the information supplied above will be satisfacotry, however, should you have any questions, please contact us.
Very truly yours, i
I VERMONT YANKEE NUCLEAR POWER CORPORATION YY L. H. Heider Vice President 1
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