ML18037A130
| ML18037A130 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 09/10/1991 |
| From: | Sylvia B NIAGARA MOHAWK POWER CORP. |
| To: | Martin T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| CON-IIT07-603-91, CON-IIT7-603-91, CON-IIT7-603-92 CAL, NMP2L-1314, NUREG-1455, NUDOCS 9109160243 | |
| Download: ML18037A130 (6) | |
Text
~ NIAGARA 0 MOHWfK NIAQAAAMOHAWKPOWKA COAPOAATlOM>"i1~'i4i'"'CAO.=.'~AC'=. 4KA'"< i."=;< -'i'R".,>>'ic.
>>'~Q7 t
> ~ I Mr, Thomas T. Martin Regional Administrator, Region I U.
S. Nuclear Regulatory Commission 475 Allendale Road King oi Prussia, PA 19406 Re:
Nine Hile Point Unit 2
Docket No. 50-410 NPF<<69
Dear Hr. Hartin:
On August 13, 1991> Niagara Hohavk Paver Corporation's Nine Mile Point Unit 2 Nuclear Station declared a Site Area Emergency due to loss of control room annunciators vith a plant transient.
The loss of control room annunciators resulted from a loss of five n'on-safety related Uninterruptible Pover Supplies (UPS's) when the 8 phase main step-up transformer failed.
?ower vas restored to the annunciators within 34 minutes and a safe shutdown oi the Nine Mile Point Unit 2 reactor vas achieved, cold shutdown vas reached after approximately 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br />.
In response to this event, the Nuclear Regulatory Commission issued a
Confirmatory Action Letter on August 13, 1991 dispatching an Augmented Inspection Team (AIT).
This letter vas superseded by a Confirmatory Action Letter dated August 15, 1991.
The NRC also upgraded the investigation by forming an Incident Investigation Team (IXT).
Niagara Mohawk cooperated fully vith the AIT and the IIT and folloved the actions outlined in the August,15, 1991 letter to support the IIT investigation.
On August 30, 1991 you provided plans to conduct a special team inspection to support an NRC restart decision.
This inspection began on September 3, 1991.
This letter summarizes Niagara Mohavk's evaluations and corrective actions that have been taken such that safe restart and continued safe operation of the Nine Hilt Point Unit 2 Nuclear Station vill be assured.
Niagara Mohawk immediately established an Action Plan and a Recovery Organization reporting to the Executive Vice President, Nuclear prior to the end of the Site brea Emergency.
The Recovery Plan consisted of specific problem assessments in the areas of plant response, operator response>
emergency preparedness<
safety and equipment failure analysis>
vhich included the Uninterruptible Power Supplies, main transformers and the electrical
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f the assessment reports vere revie ed by
'e' the Site distribution system, ac o
Operations Review Committee, ia ara Mohawk met '-ith you and your staff :o provide a
'3 t
Yi il tion into the August t.
x e
Z rovided an overviev of the UPS circuitry, t..e ne e
prov he on oin assessment of the event.
. re-star re areoness items outage restart ass essment items, pre-startup emergency preparedness i ems, ations from the Safety Assessment
- ere sn items along vith recommendation rom h
su tonvalvshave been he s ecific re-startup assessment tems av d
h iated with the teeawater corrected and the lessons learned nod have been appx e
to s' scram.
The RCIC flov controller malfunct on chan e has also been made to pro it clos feedvater suction valves af ter s
a e
has been addressed by checking the co Some air vas found in the flov transmitter and remove s
a contributed to the flov oscillation problem.
The system v during startup at different reactor pressures, as essment contained a summary vhich outlineo the sequence h
P ant spo e assessmen of events associated with the aluat plan t an ie co si and that at o time during the vi'thin the bounds of current transient analysis an t at event was the plant in an unsafe condition.
onse and actions during and immediately An assessment of Operator
Response
an a
olio g teS aEmerg y
enc found operator an sta appropr atete and commendable.
Operator training vas e
ec operators for events of this nature.
Pre aredness activities concluded that the he a s ent o
the Emergency p
n rocedures.
All pre-startup corrective actions he Site Area Emergency vas time y an var A
ssment report provided to the NRC identified in the Emergency Preparedness Assessment re on Au ust 28, 1991, are complete.
8 s
re ared to provide a safety reviev of the Site Area a is.
The Safety A sessment on iud d that y
g g
at no time during this event v a vaa there any release o
ra oa d
Thi Safety Assessment also vas the health and safety of the public affecte s
t desi n improvements.
provided recommendations for post startup plant es gn mp ilure Analysis, separate assessment reports vore lectrical distribution system and tfh kh o ldd th t
'B" h
i te -
t.
sformer.
The f
h i
i tio tod t in transformer 1 be tra sport ed offsite for urt er n
the root cause of the fault.
The electrical str h
os actuated and performed their conclu e
t a d d h t the protective relaying schemos actua intended function to isolate the transforme r fault.
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corn leted a root cause eva~uation of the loss of the five p ibl P
r Supplies and their failure to safety re~ated Unint p
errupt e Power ause m ti with Dr.
Thorn s M
y of th intenance
{alternate 1
eNRCon h
ting Niagara Mohawk has concluded Septembe 4,
1991.
As er the simultaneous tripp'pping of the UPS's is imprope that the root cause for t ate a
ru tible Power Supplies vere n
l'ot designed-:o accommoda 1C es gn.
.he un e
p h
1 o1 h
circuit does not actuate unti
- Aso, as 1
1 h
i ver supply svitching circus
'll use the logic to trap.
A so, a
d ith b
d h
the a result oi discussions with the UPS ven or, i ned to mitigate a degraded voltage logic backup batteries vere not designe to m
condition.
4 1991 meeting, Niagara Mohavk vk has taken A
discussed in the September s
to revent recurrence of a similar common mode'e T e UPS logic power supp y rrective actions necessary p
1 has been modified to mak h
p p
ou
.nverter an e eliminates the vulnerabi ty o 1 o io of the UPS's.
to transients on the AC system during norma s assessed all erl to the Site Area Emergency, has asse k
h i
this event and has ta en Ie a
h 1
d 11 o eration.
e ave c actions for continued safe p
d vith the n orma i f tion provided to the NRC tart star h
the Encident invest ga ted i
o id d to M
S, V
i 1 tt ldd h
Ni Hil Poi U
September 10, 1991 Niagara Mohavk has conc u e 8
Nuclear Station is ready for restart.
Very truly yours, Exec. Vice President-Nuclear ffi of Nuclear Reactor Regulation xc:
Dr. T. E. Murley> Director, 0
ce o
Mr. R. A. Caprai Fxo)ect Director, NRR B inkman, Senior Prospect
- Manager, NRR Eeh R
tor Pro)ects Section No.
Eeh3., Director, eac actor Pro)ects Section Ho.
18 M
D. R. Haverkamp, Chief, Reactor ro r ~
s
~
1 Chief, Reactor Operations a
Mr. J.
E. Rosentha
,Division o a
e y Document Control Desk Records Management BRS/NAS/krc 001740GG