ML20214R508
| ML20214R508 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 09/19/1986 |
| From: | Murphy W VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| FVY-86-85, IEB-80-11, NUDOCS 8609290195 | |
| Download: ML20214R508 (10) | |
Text
(
s --
VERMONT YANKEE NUCLEAR POWER CORPORATION FVY 86-85 RD 5, Box 169, Ferry Road, Brattleboro, VT 05301
,,,,y,o.
p ENGINEERING OFFICE 1671 WORCESTER ROAD FRAMINGHAM MASSACHUSETTS 01701 TELEPHONE 617-872-8100 September 19, 1986 U.S. Nuclear Regulatory Commission Region I 631 Park Avenue King of Prussia, PA 19406 Attn:
Dr. Thomas E. Murley Regional Administrator
References:
a)
License No. DPR-28 (Docket No. 50-271) b)
Letter, USNRC to VYNPC, dated 5/8/80, IE Bulletin 80-11 c)
Letter, VYNPC to USNRC, WVY 80-97, dated 7/7/80 d)
Letter, VYNPC to USNRC, WVY 80-157, dated 11/10/80 e)
Letter, USNRC to VYNPC, NVY 83-262, dated 11/15/83 f)
Letter, VYNPC to USNRC, FVY 83-126, dated 12/22/83 g)
Letter, VYNPC to USNRC, FVY 84-23, dated 3/15/84 h)
Letter, VYNPC to USNRC, FVf 84-72, dated 6/28/84 i)
Letter, USNRC to VYNPC, NVY 85-240, dated 11/18/85
Dear Sir:
Subject:
IE Bulletin 80-11, Masonry Wall Design
Background
The subject IE Bulletin 80-11 [ Reference b)] was issued by the NRC to address the concerns regarding the adequacy of design criteria used for the design of masonry walls. References c) through i) document Vermont Yankee's response to the Bulletin, NRC's review, and Safety Evaluation Report issuance.
As a result of our monitoring industry experiences and efforts relative to masonry walls, an internal review was initiated of Vermont Yankee's archived documentation. This review indicated that, although our activities in the 1980-81 time frame were conducted in accordance with our interpretation of the Bulletin requirements, our documentation files could be deemed inadequate com-pared to our current practice. This result caused us to immediately commence a prograa to provide a documentation base, to current practices, which substan-tiated our original IE Bulletin 80-11 conclusions.
The scope of this activity essentially resulted in a complete re-evaluation of Bulletin 80-11 applicability to Vermont Yankee. Elements of this re-evaluation included:
j l
8609290195 860919 k
(j'k\\
PDR ADOCK 05000271 P
PDR t l )
i
VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclear Regulatory Commission September 19, 1986 Page 2 1.
Developing a comprehensive walkdown procedure and performing a plant walkdown to document that all walls relevant to the scope of IE Bulletin 80-11 have been addressed.
2.
Dispositioning any outliers identified as a result of Item No. I above such that Vermont Yankee could assure full compliance with the Bulletin requirements.
3.
Writing a routine surveillance procedure to require that all walls within the scope of the Bulletin are periodically checked to ensure that all analytical assumptions remain valid.
(In progress) 4.
Formulating design controls to ensure that the concerns and require-ments stated in the IE Bulletin 80-11 are adhered to during the course of any design or maintenance work at Vermont Yankee.
(In progress)
Issue
~
Vermont Yankee responded to IE Bulletin 80-11 [ Reference b)] by letter dated July 7, 1980 [ Reference c)]. This letter identified a significant scope limiting assumption inherent in our IE Bulletin 80-11 evaluation by stating, "The turbine building is nonseismic, and with the exception of the diesel generator rooms, was not surveyed." The implied reasoning was that it would not be relevant to evaluate masonry walls for seismic qualification in a building that was not designed to withstand a design basis earthquake. Subsequently, the NRC in Bulletin 80-11 Safety Evaluation Reports dated November 15, 1983 and November 18, 1985 [ References e) and i)], did not take exception to Vermont Yankee's design basis for excluding block walls in the turbine building from the scope of Bulletin 80-11.
During our recent re-evaluation process to augment the documentation available to support the conclusions we had made regarding IE Bulletin 80-11, no deficiencies were noted within our original defined scope. Accordingly, we concluded our responses made to IE Bulletin 80-11 [ References c), d) and f) through h)] were accurate and consistent, and are now supportable by documen-tation to be consistent with today's practices.
However, in performing this de novo review, we reconsidered the validity of excluding masonry walls in non-seismic areas of the turbine building from IE Bulletin 80-11 evaluation. Accordingly, to ensure we had not excluded signifi-cant masonry walls from censideration, we expanded our original IE Bulletin 80-11 re-evaluation scope to include block wallt within the turbine building that were adjacent to safety related equipment.
This review of masonry walls within the turbine building included assessment of the additional systems in the vicinity of block walls that were upgraded to safety class status subsequent to NRC approval of the original plant design basis. For example, Vermont Yankee's original Control Room HVAC System
VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclear Regulatory Commission September 19, 1986 Page 3 was not " safety-related", as evidenced by equipment specifications and the FSAR.
In the late 1970's, this system was intentionally enhanced, and designated as
" safety-related" for the sole purpose of ensuring replacement parts procurement, maintenance activities and modifications were adequately controlled under the auspices of the QA Program. Accordingly, Vermont Yankee's Control Room HVAC System is now considered " safety-related" (i.e., within the scope of IE Bulletin 80-11), but is not considered seismically designed per the plant's licensing basis (and hence is arguably beyond reasonable consideration of seismically induced failure mechanisms).
Four specific instances, including that described above, were identified during our re-review of IE Bulletin 80-11, where " safety-related" equipment is i
potentially impacted by turbine building masonry wall failure, as follows:
1.
Control Room HVAC controls, control cables, air handlers and ductwork.
2.
Diesel ventilation controls and cor. trol cables for ventilation fans in both diesel rooms.
3.
Reactor Building RHR corner room ventilation units (RRU's 5, 6, 7, 8) control and control cables.
4.
Reactor Protection System, Containment Isolation System input cables for high radiation / rain steam lines.
We have individually evaluated the potentiai operational impact of each of
~
these four items and have concluded that there is no immediate safety concern (refer to Attachment A).
However, we have also concluded that these areas should be upgraded. Consecuently, we have initiated a program to carefully assess options that could be taken to protect the noted systems.
Conclusion As a result of Vermont Yankee'sBulletin 80-11 re-evaluation of safety-related equipment in proximity to masonry walls in the turbine building, Vermont Yankee has concluded the following:
1.
The impact assessment (Attachment A) documents that the four iden-tified walls in the turbine building pose a minimal impact on plant safety and continued plant operation in the event of a design basis carthquake.
2.
A near-term program will be established to address the
" safety-related" equipment identified in the re-evaluation program by either relocating equipment and/or structural support of the walls.
VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclear Regulatory Commission September 19, 1986 Page 4 Schedule Based on evaluations done to date, it appears that the diesel generator HVAC issue will be addressed by a design change that was prepared to address a previously identified Appendix R concern. This design change is currently in the plant review cycle with installation scheduled for the first quarter of 1987.
1 It is our intent to have conceptual designs for the other areas, and remaining open corrective actions, developed by the end of the year. Shortly thereafter, we will be prepared to provide you with our installation /
implementation schedule.
In order to fully address the issues and concerns identified during the IE Bulletin 80-11 inspection at Vermont Yankee, we request a meeting at your con-venience to discuss this issue and Vermont Yankee's position with regard to the other issues raised during the inspection.
Should you have any questions or require additional information concerning this matter, please contact us.
Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION i
Warren P.
urphy l
Vice Pres dent and Manager of Operations
/dm cc:
U.S. Nuclear Regulatory Commission Office of Inspection & Enforcement Washington, D.C.
20555
ATTACHMENT A MASONRY WALLS - OPERATIONAL IMPACT ASSESSMENT REFERENCES 1.
Calculation VYC-415 2.
Calculation VYC-39, Rev. 2 3.
Calculation VYC-515 4.
Memorandum (OPVY 525/85, S.R. Miller to A.C. Kadak, dated July 17,-1985 5.
Memorandum (VYE 03/86), P.R. Johnson to R.E. Swenson, dated January 3, 1986 6.
Drawing G191237, Rev. 14 DISCUSSION Tr.e following constitutes an impact assessment for Vermont Yankee given the loss of various safety-related equipment located in the HVAC rooms of the Turbine Building due to seismically-induced failure of masonry wall room par-titions.
ASSUMPTIONS 1.
A seismic event occurs with sufficient magnitude to cause block wall damage.
2.
One or more block walls which separate the various fan rooms in the Turbine Building collapse.
3.
Falling walls / blocks impact or otherwise damage safety-related equipment such that it cannot perform its safety function.
t SAFETY-RELATED EQUIPMENT INVOLVED 1.
Control Room HVAC - includes air handler, ductwork, isolation damper, cables and controls.
l l
2.
Diesel Ventilation - cables and controls for ventilation (fans) in both diesel rooms.
3.
RRU's 5, 6, 7, 8 - control cables for cooling units in the four RHR corner rooms.
4.
Reactor Protection System (RPS) and Primary Containment Isolation System (PCIS) - input cables for high-radiation / main steam lines.
IMPACT ASSESSMENT A.
Control Room HVAC The Control Room HVAC System performs two safety functions:
Attachment A Page 2 1)
Cooling of Control Room for equipment during normal and any abnormal conditions.
2)
Recirculation mode during a core damage accident to comply with Control Room habitability requirements.
The Control Room HVAC System is designated as a Safety Class 3 system.
It is Seismic Class II in accordance with Section 12.2.1.1.4 of the Vermont Yankee FSAR.
In order to satisfy Safety Function #1 above after a seismic event in which the Control Room HVAC System is rendered inoperable, the doors to the Control Room can be opened and portable fans set up to provide cooling until repairs can be made. Based upon design air flow rates as detailed on the flow diagram of Reference 6, and the calculation of Reference 3, it is estimated that temporary ventilation sufficient to maintain the Control Room at an acceptable level for equipment operation can be established by placing two (2) - 5000 CFM smoke ejector fans in the main doorway of the Control Room, and opening the rear Control Room doors and doors to the Turbine Deck.
Safety Function #2 above is required for a core-damage accident as deter-mined by the calculation of Reference 2, which calculates dose rate assuming the TMI source term and maximum MSIV leakage according to Appendix J Type C testing. However, a seismic event with a LOCA and resultant core damage accident is beyond the design bases of Vermont Yankee (see Reference 4).
Thus, Safety Function #2 is not required after a seismic event.
B.
DIESEL ROOM (S) VENTILATION The safety function of Diesel Room (s) Ventilation is to maintain room tem-perature at an acceptable level in the diesel rooms in suport of reliable diesel operation.
Diesel Room Ventilation consists of air-operated dampers for supply and a fan for exhaust in each of the two diesel rooms.
Reestablishment of power to the diesel room exhaust fan (s) through the use of lifted leads and jumpers, could be developed in the unlikely event that existing contols are rendered inoperable due to seismically-induced block wall failure.
In addition, an Engineering Design Change Request (EDCR) is currently being prepared for Appendix R concerns which will permanently modify the controls for the diesel room exhaust fan (s) such that failure of the control cables in question, either due to fire or seismic event, will not affect operability of the fan (s).
]
Attachment A Page 3 C.
RRU's 5, 6, 7, 8 The safety function of the RHR room coolers (RRU's 5, 6, 7, 8) is to main-tain room temperature at an acceptable level in the four RHR corner rooms in support of RHR and Core Spray pump operation.
RRU's 5, 6, 7 and 8 are seismically mounted and form a Safety Class 3, Seismic Class I portion of the Service Wate. System.
If a seismic event were to render the controls for RRU's 5, 6, 7, and 8 inoperable, the following actions could be taken to restore cooling until repairs are effected:
a) the doors to the corner rooms could be opened and portable fans set up to provide ventilation from the Torus Area.
b) a procedure is in place to wire the RRU's locally to restore operabi-lity (lifted leads and jumpers).
Calculations which have been performed for Appendix R for RHR roor,heatup (Reference 1) show that for the first two hours, with no ventilation, doors closed, and core spray running for a total of one hour, room tem-perature would rise to 128*F.
With doors opened and portable fans pro-viding approximately 10,000 CFM of forced ventilation at two hours into the event, with core spray running 50% of the time (1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> out of 2) and RHR running 67% of the time (2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> out of 3), room temperatures would stabilize between 108'F and 113*F for an indefinite period of time (until repairs are made to RHR room coolers).
Reference 5, which was prepared to support ultimate equipment capabilities for a scenario which is beyond design basis, estimates that RHR room equipment would remain operable for the following temperature excursions:
a)
RHR and Core Spray Pump Motors - 2.5 years at 176*F or 1.25 years at 194*F b)
RHR Service Water Pump - 1.4 years at 176*F or 1.25 years at 194*F c)
RRU's 5, 6, 7, 8 - 2.5 years at 176*F or 1.25 years at 194*F A LOCA senario with seismic event would differ from an Appendix R scenario in that it would require RHR pump operation within the first two hour period. However, the one-time accident temperature excursion values noted above provide additional margin such that time would be available to open doors, followed by either setting up portable smoke ejector fans or re-establishing RRU operation by local wiring (lifted leads and jumpers) before temperatures that would jeopardize RHR room equipment operation would be reached.
Attachment A Page 4 D.
RPS/PCIS - INPUT FOR HIGH RADIATION / MAIN STEAM LINES The safety function of the Reactor Protection System (RPS) is to provide protection against the onset and consequences of conditions that threaten the integrities of the fuel barrier and nuclear system process barrier.
The safety function of the Primary Containment Isolation System (PCIS) is to provide protection against the onset and consequences of accidents involving gross release of radioactive materials from the fuel and nuclear system process barrier.
In particular, the Main Steam Line High Radiation monitors (4 inputs) provide a scram signal for the following accidents:
a)
Core damage accident (gross fuel failure) b)
Control Rod Drop Accident (single rod drop)
For the core-damage accident, loss of the Main Steam Line High Radiation monitors due to a seismic event is acceptable due to the following:
a) the scenario leading up to a core damage accident would involve a low water level signal into RPS, causing a scram, b) a seismic event with LOCA annd core-damage accident is beyond the design basis of Vermont Yankee (see Reference 4).
c)
Section 7.2.4 of the Vermont Yankee FSAR states that if any portion of the Reactor Protection System were to fail due to an earthquake, it would only fail in a direction which would cause a reactor scram when subjected to extremes of vibration and shock.
For the control rod drop accident, Section 14.6.2 of the FSAR states that a scram signal would be generated from the APRM's.
A high radiation alarm would also be received from A0G system, thus alerting the operators.
Additionally, any components that would need to fail as part of the control rod drop scenario are of Seismic Class I design (Control Rods, Control Rod Drives, Hydraulic Control Units).
Thus, it is concluded that sufficient redundancy exists within the RPS/PCIG to compensate for the loss of Main Steam Line High Radiation Monitors due to a seismic even, in order to scram and isolate the reactor for either a core-damage accident or a control rod drop accident.
A control rod drop accident is a very unlikely event for which the proba-bility of occurrence is made even smaller by the rod coupling tests per-formed in the CRD surveillance procedure used during startup.
Attachment A Page 5 a
CONCLUSION It is, therefore, concluded that there is no immediate safety concern for the interim period while upgrades are made to eliminate the potential for damage to equipment discussed above due to seismically-induced masonry block wall failure.
A seismic event resulting in block wall induced damage to the subject equipment has not occurred, and the probability of it occurring in the future is l
unlikely.
If such an event were to occur, the plant could, in a timely manner, be placed in a condition not requiring operability of the subject equipment.
Note that all areas discussed above would be accessible from a habitabi-i lity standpoint to take interim measures (such as opening doors and setting up portable fans (or ventilation) or to make repairs following a seismic event, since a seismic event with a core damage accident is beyond the design basis of Vermont Yankee. Vermont Yankee's design basis assumes successful ECCS operation following a seismic event, including LOCA.
.g-,
.a m-w -
rw-r--w-
~-
w-r*-. -.,
w
~-4-+
w
-