IR 05000336/1981026
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UNITED STATES NUCLEAR REGULATORY COMMISSION
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e a WASHINGTON, D. C.20655
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" -This is an internal, pre-t decisional document not
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- FEB 2 2 J982 necessarily representing a
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position of AE00 or NRC.
. MEMORANDUM FOR: Carlyle Michelson, Director Office for Analysis and Evaluation of Operational Data
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FROM:
Eugene V. Imbro Office for Analysis and Evaluation of Operational Data
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SUBJECT:
LER 50-336/81-26:
INVESTIGATION OF THE RELATIVE FREQUENCY OF VALVE OVERTRAVEL ANOMALIES THAT COULD RESULT IN A POTENTIAL
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CENTRIFUGAL PUMP RUN0VT EXCEEDING NPSH At the Millstone Nuclear Power Station, Unit 2, L5R 81-26 describes an event
where seven of the eight high pressure. safety injection (HPSI) motor-operated
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valves overtravel from to one inch further than the required position. The
LER states that. valve overtravel results in smaller HPSI pump runout margins. The overtravel was caused by the variable coastdown of the Limitorque motor-operated valves and the small margin of. acceptable valve position.
It was noted ;in this LER that valve 2-SI-616 overtraveled on four successive test days
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c (after~being reset each time), and valves 2-SI-626 and 627 each overtraveled on two separate test days during 'recent adjustments in June 1981.
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The HPSI safety injection valves have regularly overtraveled in the yearly surveillance test at Millstone.
In 1979 (LER 79-41),' valves 2-SI-616 and 626 Apparently, frustrated by the repeated surveillance failures of the valve to,ch overtraveled by 3% and in 1980 (LER 80-41), MOV 2-SI-616 overtraveled by % in
cycle to a correct opening,'the licensee manually opened the valves to the
required position and set each " fully open" limit switch in.the Limitorque-motor operator to be electM cally open at this point to prevent any further
remote opening of valves.
In this configuration, the valve can be closed i
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If, during power operation, the valve is. inadvertently in the closed position, it will open on an SIAS, but again, may overtravel.
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The HPSI injection valves are two-inch nominal pipe size globe valves with 3
turns between the full closed ar.d full open position. There are two marks corresponding to a minimum and maximum acceptable.techni' cal specification flow rate. The two reference. marks are on an approximate two-inch diameter circle so
that one inch of overtravel would result in about 5% change in valve stem travel.
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The technical specification requiring the valve travel test became effective
in spring 1978.
2M
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O 820628 ADR
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UDELL82-261 PDR
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2-Carlyle Michelson
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The valve operator is a Limitorque-type 1MB-00 powered by an. AC. electric motor with both limit and torque. switches to define the potential valve stem travel.
On valve closure, the torque switch.should provide the initial cut-off of electrical power with the thennal overload device as a backup.
(After the valve has seated, stem travel has virtually. ceased and closing torque is increasing rapidly.) On full opening of the valve, the limit switch should first cut-off electricit'y to the motor operator before the valve stem starts to reach the limit of its travel in the full open position and the torque switch is activated. A Limitorque adjustment manual implies.that the " fully open" limit switch can be activated from 90 to 100%.of the valve's full open position. The desired valve opening necessary to get acceptable HPSI flow for the injection valves at Millstone 2 is 21s turns or a " fully open" limit switch. setting of about 71% of valve stem travel. Limit switch adjustments in this vicinity are somewhat more difficult to
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set than at the recommended 90-100% position.
Further, all Limitorque actuators are designed to reach full motor speed before applying torque to turn the valve stem.
This results in an impact to the valve stem at energization that should result in.less p'recise initial stem movement.
In addition, the motor speed during valve movement is not constant but is load dependent and may be influenced by the relative valve packing tightness on the test date. Also, the~re is a certain amount of play or lost motion in the wonn gear linkage to the limit switch. Finally, -
the Limitorque operator is relatively large in comparison to the HPSI valve it is driving.. Each of these conditions further exacerbate.the difficulty in reaching repeatable valve positions while trying to stop valve movement in a narrow band at about 70% of stem travel. '(The acceptable range of HPSI flows is on average 157 to 168.75 gpm per injection line.)
To continue the investigation of valve overtravel conditions, an LER search was performed to determine how prevalent valve overtravel conditions are within the
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nuclear industry. The search span was limited to calendar years 1980 and
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1981 and used combinations' of code and text searches sufficiently generalized l
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to capture 188 LERs in this time frame. Each of these LERs was read and only two of these events involved valve overtravel situations; they were the two known LERs submitted by Millstone 2.
The relevant Millstone technical specifications were compared to the Combustion Engineering standard technical. specifications and the technical specifications of each of the other seven Combustion Engineering designed plants to detennine if.there was something unique in the Millstone 2 technical specifications that caused the valve overtravel to be reported. Although the technical specifications are somewhat different, most required verification that each ECCS throttle valve would actuate to its correct position on an SIAS once per 18 months. The exceptions are Palisades and Ft..Calhoun, these require testing during each refueling outage. Apparently, overtravel of ECCS throttle valves is unique to Millstone 2.
Finally, each of the resident inspectors at the Combustion Engineering plants was contacted. The intent of the survey was to determine the correct position of the HPSI injection valves following a SIAS at other CE plants and to determine if the pump runout problem at Millstone 2 could be an unrecognized generic problem at the other CE sites. The salient points of this survey were:
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i Carlyle Michelson-3-
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The HPSI. injection. valves go full open on a SIAS.
Only at Millstone 2 are the. valves required to open to a throttled position. This is probably due to unusually low HPSI system line losses.
(There may have been an interface problem between CE and the A/E during plant construction.)
2.
At~ all CE plants, a provision exists whereby some of the containment spray flow discharged from the containment spray HXs can be diverted into the HPSI pump suction lines.
If inadequate NPSH.is postulated on recirculation flow, the containment spray system could provide a source of cool water to the HPSI pump suction.
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Each plant has some indicating device; e.g., a low suction pressure alarm, HPSI pump amperage, etc., together with a flowmeter on each HPSI leg to inform
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the operator of a pump runout condition.
We have discussed our observations and findings in a series of telephone conversations with site personnel at Millstone 2.
The licensee is continuing to study the problem to determine a satisfactory inethod for restoring remote position operability.to these valves.
Neither.the resident inspector nor AE0D
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observe a safety problem in operation of the facility with the HPSI injection
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valves manually open.to the technical specification position. A possible corrective action could be the installation of a flow restricting device; e.g.,
i another orifice or a more restrictive flowmeter orifice or a different plug or reduced trim on the HPSI injection valves.
In any case, it is expected that the final configuration will be identical with the.other CE plants, i.e., the
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rated HPSI flow is. achieved at the full open HPSI valve position. No further AE0D action is requir_ed.
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Eugene V. Imbro Office for Analysis and Evaluation of Operational Data
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Econner, NRR JShedlosky, RI l
EBrown, AE00 l
FAshe, AE00 MChiramal, AE00
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2 The CE design basis for.the HPSI system is such that pump NPSH requirements would not be exceeded during post-LOCA recirc~61ation flow from the containment sump with the injection valves wide open.
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LER SCREENING / DISPOSITION SHEET Docket No. O (o LER No. f/-2 0 g OM - O go Engineer:
Ts A fl:319 I 3R 1/or[9I GD 1.
Add'l Info.
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h No Yes Required?
Yes (circle one)
iF V4 W R C o pfAl If YES, describe pga y
.,a yn, neovicemrars as
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M LCCA 2.
Is this event significant?
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l If yes, why?
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4-5; f
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Abnormal Occ'urrence?
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.Yes (Appendix E)
Yes (Circle one)
If yes, why?
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Reportable to NEA?
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(AppendixC)
Yes Yes o
Yes
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If yes, why?
pes.61c Fo ugj'n IV 5.
Recomended Action:
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I Category (circle one) I II I
II III IV
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Lead Engineer (NSSS) Disposition (Category III only):
Lead Engineer:
Category: I II IV Coments:
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Final Acti n/ Disposition E/mv
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Af ECTICUT 06101
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July 16, 1981 MP-2-4849 4,,.h..--k..b
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Mr. Boyce.
E3. JUL 2 3IbW ~~J Director, Region I u. #A [' h/
Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission
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b-631 Park Avenue
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King of Prussia, Pennsylvania 19406 N
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Reference:
Facility Operating License No. D.PR-65 Docket No. 50-336 Reportable Occurrence R0-50-336/81-26/3L-0
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Dear Mr. Grier:
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This letter forwards Licensee Event Report 81-26/3L-0 required to be submitted within thirty days pursuant to Millstone Unit 2. Appendix A Technical Specifications, Section 6.9.1.9.b, conditions leading to operation in a degraded mode permitted by a limiting condition for operation. An additional three copies of the report are enclosed.
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Yours truly,
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NORTHEAST NUCLEAR ENERGY COMPANY
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M E. J. Mroczka
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Station Superintendent Millstone Nuclear Power Station EJM/JDB:bjo Attachment:
LER R0-81-26/3L-0 cc:
Director, Office of Inspection and Enforcement, Washington, D. C.
(30)
Director, Office of Mar,agement Information and Program Control, Washington, D. C.
(3)
U. S. Nuclear Regulatory Commission, c/o Document Management Branch, Washington, D. C.
20555
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St I 07290050)B10716 DR ADOCK'05000336 m
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3, LICENSEE EVENT REPORT
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75 REPORT oATE
S EVENT DESCRIPTION AND PROB AELE CONSEQUENCES h
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While performing TS 4.5.2.e surveillance' testina between June 16 and Juiv 9.
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g ; 7 of the 8 HPSI MOV's overtraveled from 1/4 to 1 inch past the reouired position.
In each case the plant was operated in accordance with the action specified in
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TSAS 3.5.2.a.
The overtravel would have resulted in higher injection' flow rates I
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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS e variable coastdown times of the motor and g
The overtravels were a result of
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I the small margin of acceptable valve position. To eliminate the potential for i
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future overtravel events, the valves are opened to the. required position and
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, maintained at that position.
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i ATTACHMENT TO LER 81-26/3L-0
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I NORTHEAST NUCLEAR ENERGY COMPANY MILLSTONE NUCLEAR POWER STATION - UNIT 2 PROVISIONAL LICENSE NUMBER DPR-65 DOCKET NUMBER 50-336 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES While performing T.S.4.5.2.e. surveillance testing between June 16 and July 9, 7 of the 8 HPSI MOV's overtraveled 1/4 to 1 inch past the required position.
In each. case the plant was operated in accordance with the action specified in T.S.A.S.3.5.2.a.
The overtravels would have resulted in higher injection flow rates and smaller HPSI pump runout margins.
The overtravels occurred as follows:
Date Valve F13-81 F5F626'
6-19-81 2-SI-616)
6 Suc4.ar56 vf 78M Y
~6-21-81 2-51-616l
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6-22-81 2-SI-616t
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6-23-81 2-SI-616)
6-25-81 2-51-646
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6-28-81 2-SI-626Y2-SI-636 7-2-81 2-SI-6275*-
7-7-81 2-SI-62T2-SI-637 7-9-81 2-SI-647
Similar events were reported in LER 79-41 and 80-41.
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