ML19338D900
| ML19338D900 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 08/18/1980 |
| From: | Haller N NRC OFFICE OF MANAGEMENT AND PROGRAM ANALYSIS (MPA) |
| To: | Harold Denton, Dircks W, Murley T NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS), Office of Nuclear Reactor Regulation, NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| Shared Package | |
| ML19338D883 | List: |
| References | |
| NUDOCS 8009240134 | |
| Download: ML19338D900 (9) | |
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- UN!TED STATES '
-[ Y ~ t,( [' i NUCLEAR REGULATORY CO..*i/,lSSION
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. WASHINGTON, D. C. 2055ti 2
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AUG 13 1933 MEMORANDl% FOR:
. R. Denton, Director, NRR W. J. Dircks. Director, NMSS
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T. Murley, A.: ting Dire: tor, RES q
V. Stello, Jirector, IE s,
R. B. Mirogue, Director, SD H. K. Sh4 ar, Executive Legal Director J. J. Fouchard, Director, PA C. Michelson, Director, AE0D FROM:
Norman M. Haller, Director, MPA
SUBJECT:
PROPOSED ABN0?. MAL OCCURRENCE - REACTOR C00LANT' PUMP SEAL FAILURE
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Enciosed is a draf t Comission Paper witn a propcsed Federal Register Notice in regard to the failure of a reactor cooient pucp ssai at Arkansas (Nclear
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One - Unit 1.
The event is under emid 7 tin as an w:.rd ccccrrence since it appears to satisfy cre,tof_ tha =::ar.p;;s na:cd i-the abncn:ci occurrence policy state-ment; r.al0 Tcgra ds an of tr.; 'n.ar; c ;'i c.t tar...c.ry.
During preparaticr of trc Second Curter Abrar?.ai Occurrence Report tc Cc,ngress, 1
4 ECD proposad uis
/:.ot as er. acnornel occurrar.ce.
NRR and IE both previously suggastcd it c2 re;.;rted as i.n Ap;,cr:tix C event due to the publicity ragarding tha gcseous releat.E feca rcn.i"; ant.
Your revie7, co m:nt: =.rd writtee (or telephone) cnr.currence are recuested by clos 2 of busin2ss R 7.:t 22,1930.
We are :.ro:ns i:.g the evant sepcrately and will include it in che second 4.:rter Report to Congress if Corr;rission at;)roval is received in ti-^.
If requirc:,, "Pl. will arrcMe for an irfernD briefing of the Cercission.
4 Suggested participents are IE, MR, AE0D, and MFr..
It is suggested that AEOD take the lead at the briefing.
If you have questions or wish tc. discuss details, please contact P. Dobe er
~J. Crooks of my'offica at 49-27735.
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Norran M. Haller, Director, MPA
Enclosure:
Commission Paper
Contact:
P. Bobe/J.-Crooks, MPA 2773 8009240 IM.
f Mu,ltiple. Addressees ~ -
cc: ~ w/ enclosure W.' J. Dircks, ED0 T. A. Rehm, EDO D. G. Eisenhut, NRR (2)
D. Thompson, IE-(2)
R. L. Fonner, ELD'
_G. C. Gower, IE (5)
L. B. Higginbotham, IE G. G. Beveridge, NMSS H. H. Scott, RES R. E.. Alexander, SD M. A. Taylor, RES W. T. Russell, NRR J. Roe, f;RR (2)
R. L. O'Connell, NMSS R. H. Gramann,llMSS F. Ingram, PA R. A. Hartfield, FPA J. L. Crooks,';PA P. E. Bobe, M?/ (3)
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s NUCLEAR REGULATORY COMMISSION ABNORMAL. OCCURRENCE i
REACTOR COOLANT PUMP SEAL FAILURE Section 208 of. the Energy Reorganization Act of 1974, as amended, requires the NRC to disseminate information on abnormal occurrences (i.e., unscheduled incidents or events which'the Commission determines are significant from the standpoint of public health and safety).
The following incident was determined to be an abnormal occurrence using the criteria published in _the Federal Register on February 24,1977 (42 FR 10950). Appendix A (Example II.A.2) criteria.of i
l the Policy Statement notes that major degradation of the primary coolant pressure boundary can be considered an abnor:r.al occurrence.
The following _ description of the event also contiins the remedial action taken.
Date and Place - On May 10, 1930, Arkansas Power and Light Company reported that a reactor coolant pump seal had failed at Arkansas Nuclear One - Unit 1,* a pressurized water reactor (P'.lR), located in Pope County, Arkansas.
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_ Nature and Probable Ccoseauences - The nature of the failure of a reactor coolant a
pump seal, described below, is a degradation of the primary coolant pressure 4
boundary. This boundary is one of three barriers designed to contain radioactive materials generated by the nuclear reactor - the other two are the fuel cladding' and the primary containment boundary.
The primary coolant system circulates pressurized _ cooling water between the nuclear reactor core and steam generators for heat transfer via reactor coolant pumps.
Each reactor coolant pump has a.
Shaft / Seal / System which is to maintain essentially zero reactor coolant leakage.
Should seal leakage occur, however, it requires a reactor shutdown when the leak
- A similar incident occurred at.the H. B. ~ Robinson plant in May 1975.
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rate exceeds 10 gallons per minute.
Emergency coolant water makeup is available should small or intemediate sized loss of coolant accidents occur following pipe breaks, valve failures or coolant pump seal failures.
Safety systems exist to mitigate the consequences of these and similar malfunctions, but it is desirable to Icep the frequency of incidents to as low a level as practical.
The likely consequences of an incident that similarly degrades the primary coolant pressure boundary are (1) loss of prima'ry coolant into containnent, and (2) a controlled shutdoetn of the reactor to a cold shutdown condition.
Containment pres-sure ar.d gaseous radioactivity levels nay increase in proportion to conditions existing it the pla n priar to and during the incident.
If additional failures occur simultaneously duc to significent r,uip:cen*, poblems or personnel errors, the consequences can ir. crease in severity.
The following sequence of events occurred at Arkansas Nuclear One - Unit 1:
At 0145 on May 10, 1980, while the plant was at approximately SP: full pcwer, Operations personnei were taking Reactor Coolant System (RCS) leak rate data when a step decrease in makeup tank le~ l occuried, indicating an unusual RCS inventory loss. The "C" P, tactor Coolant Pump (RCP) seal instrumentation confirmed that a problem existed with the seal or associated piping. _ Based on this information, power was reduced in preparation for shutdown as required by the license.
Due to the observed indications, operations personnel actions were governed by the small break procedure.
After 3S minutes, RCS letdown was secured to reduce RCS inventory loss.
Lwe Operations staff were called in when it was decided to go to Cold Shutdown operation.
The NRC Resident Inspector and NRC Headquarters
i' Maryland were notified of the controlled shutdown. After 62 minutes, the Main Turbine Generator was tripped by the operators. The power reduction initially started at a rate of approximately 5% per minute decrease when the estimated RCS leak rate was 10 to 20 gpm; when the RCS-leak rate increased, the load reduction rate was increased to approximately 20 to 30% per minute. The 'C" RCP was stopped one minute after the turbine was taken off line with the Reactor still critical. The RCS leak rate than took a step increase to an estimate'd maximum leak rate of 350 gem. The "C" RCP lift pumps were started and stopped four times in succession and, after the fourth try, caused a decrease in RCS leak rate.
The Reactor stas shut down by the operators from approximately 10% full j
power 3 minutes after the "ain Generator shutdown.
In order to n.aintain pres:urizer level and RCS pressure during the subsequent transient, the tuo v;ditional High Pressure Injection punps were started, and all High Pressure Injection valves (CV-1219, CV-1220, CV-1227, and CV-1228) tiere j
manually opened.
The "C" RCP seal return was then isolated to prevent RCS in-l ventory lcss throug? the seal return line, and seal flow was increased to quench l
l the steen' vater that was leaking by the failed seal. At this time, operators c
noted that tne Reactor Building pressure had increased from 14.7 csia to 15.2 l
psia and that radiation levels had increased, confirming that RCS leakage was i
inside the containment.
The operators then put the Reactor Building Emergency Coolers in service to reduce the containment-building pressure increase.
Shortly l
thereafter, the operators secured the "A" Reactor Coolant pump and terminated l
High Pressure' Injection. !!ormal RCS Makeup was established with "A" and "B" i
i ih!.np Punps taking suction fr:r the B] rated Water Stor:.ge Tank (BWST).
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- RCS was then cooled down with a.'
- .1:tively high Reactor Coolant System cooldown rate, and depressurized to. minimize pressure on the RCP seals and thus' leakage through the seals.
Two and one-half, hours after being initially notified, the NRC requested.addi-tional.information regarding Reactor Coolant System conditions (pressure and
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temperature),':leactor Building. pressure and temperature, and the mode of cooldown.
To expedite the RCS depressurization, one perscn from the Operations staff 'nd one Health Physics technician entered the containment building to energize the Core Flood Tank discharge valvas controls, which are required to be locked out in certain operation.:1 c.i s.
The two persons were in the Reactar Building for about five ninutes.
Tna Health Physics tecanicicn received 53 nren and the operator retaiv:d 14 nrcn ex;.csures, 'Aiic in scr.eral radiation fields of between 400 and 1000 - % per n:a.r.
The State l> alth C2partent and the Office of E.rergenc3 Services were notified at 0050.
The RCS cccMc.;n urs essentially complete c.t 0900 with the Decap Heat Removal Syrtet: in service and all four Reactor Ccolant pumps off.
The margin to saturation in the RCS hot leg was always maintained greater than 100 F.
The total amosnt of wata transferred to the RCS from the CU5T was estimatcd to be -
64,000 gallons as of 0900:
approximately 25,000 gallons was required for make-up as a result of RCS shrinkage, and about 39,000 gallons collected in the Reactor Building basement during cooldown.
Subsequently,11,000 more gallons were drained from the hot-legs -to the containment building.
Radioactivity levels at the stachand Rcnn. bdlit.ry Cuilcing areas here at background levels.
There.
were no' personnel injuries or high radiation exposures.
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-*N' Following.NRC approval, the reactor containment building was vented on May 13, 1980. The. release was monitored by the EPA, the State of Arkansas, and the licensee. Venting was completed on May 15 and monitoring results detected traces of Xenon-133 that were a small fraction of the regulatory limits. The RCS leakage was reprocessed for use in the RCS.
Cause or Causes-A failure investigation was initiated,'uhich included:
(1)
Examination of the failed seal, the three remaining seals, and one spare seal. The finding, of this ernnir n Mon were as follows:
-(a)The RCP 'C' Seti 3rd stage demage was very severe.
The stationary carbon ring was des.rcyid, the tiuu
- a.! carbide rotating face ring was broken, cnd the rot:. ting fcce lect ring was distorted.
There was addi-tional related da: age.
The damcge to the 3rd stage seal was too ex-tensive to identify 'tish certainty the initiating cause or' failure mode. The failure tc the lower two seal stages most probably resulted from daqage cashii. ' oric; shaf t cncursions produced by the breakup of the upper (H) real LLage.
(b)The three +emaining ;: 13 udi:eted tiut high tenperature conditions _hhd been experienced.
(2)'
Revies of the seal failure history at Arkansas Nuclear One and other utilities of similar-' design.
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- Review o'f the'Jassible failure mechanisms:
(a)SomeLtypes of transients, such as operating with the controlled bleed-off valve shut, can initiate a damaging wear pattern leading to a. latent failure.
(b) Inaccurate setting of :the seal; specifically axial seal location,
- could produce' abnormal wear, resulting-in an increase in total closing force, sealing area, and total horsepower of the seal stage. -
all leading-tc failure.
(4)
Recommendations to prevent recurrence.
Actions Taten to Prtcent 8.currenc_e Licensco - The licc.sce replaced the sc :1; on tPe four Reccter Coolant Pumps at A"O Unit 1.
Th3 lic:cecc it erkir.; lcic!) s;it" Eyron Jc;ksen, the pump ranufacturcr. and 3:Execk and Milccv. tFL acle:r S e Systc1 Suppliar, on the failure analysis investigations.
The problem was reviewed with the plant cperatcrs and main uiance persent.el.
The licensce clso relocated the electrical breakers for the Cora Flood Tank Discharge Valves autside of the Reactor Con-1 tainment Building, for ease of access.
!;RC - The i:RC inve-tigated the various aspects of the incicent.
The tRC mat with the licensee and reviewed the planned corrective actions and the results of.the licensee!s preliminary analyses.
The NRC is continuing with these review efforts.
In conjunction, the. NRC has-been following the various types of seal
-failures.that have occurred on Reactor Coolant Purrps and the industry efforts w.n
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related to pump seal development to improve reliability and availability, including effo,rts to reduce failure modes and frequency.
In addition, the tiRC licensing staff is reviewing concerns on large amounts of water collecting in the containment during operational transients and dCCidents, since USOful Equipment Day beCO.T.e subir.ergad and fail to Operate.
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