05000336/LER-2009-003

LER-2009-003,

Docket;Nqmber
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(V)(D) 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
3362009003R01 - NRC Website

,Event .Description On October 7,. 2009, while Millstorte :Power -Station Unit 2 (MPS2) was in Mode 5 at .0% -power, operators conducting a control board walk-down at turnover-noted that the Inhibit"„)(eys for under voltage (UV) protection were in place and the sensor channels for both vital buses were .bypassed.

This condition existed .for approximately seven flours and,rendered,both emergency diesel .generators (EDGs) [EK] inoperable, however the EDGs were available to be remotely started. Upon-discovery, the channels were taken out of "inhibit" restoring UVprotection 'and operability of theEDGs.

Upon investigation it was determined that the ;channels were bypassed 'under .a work order earlier in the day while 'MPS2 was ,in Mode 4. The Instrument & Controls -(I&C)lechnicians bypassed all of the Engineered Safety Feature Actuation System (ESFAS) [JE] sensor inputs ;including the UV protection.

The UV protection should not have been bypassed 'until the plant was in Mode .5. The:plant Technical Specification (TS) 3.8.1.1 for Modes 1,2, 3, and 4, requires two separate andlndependentEDGs, and invokes various surveillance, equirements

• {SR) that must be met ,to meetthe operability requirements for them. SR 4.8.1.1.2.c.2, c.5, c.7 and c:8 all invokeauto-start requirements for the EDGs. Since the auto-start feature for both EDGsVas inhibited 'in

• Mode 4, these surveillance acceptance criteria could not T met. Therefore, 'both'EDGs were rendered 'inoperable While in Mode:4.

This event is being reported in accordance with 10,0FR 50.73(0)(2)(0(B), 10 CFR

• 50.73(a)(2XVXD) and 10 CFR 50.73(a)(2)(vii). This is a supplement to LER_2009-603-00 to ,report this condition in accordance with 10 CFR 50.73(a)(2)M(D).

Background

The ESFAS panel consists of 4 channels, each with sensor inputs,(e.g., containment:pressure, containment radiation levels, and steam generator level) for generation of the following protection/actuation signals: containment isolation (CIAS), safety injection (SIAS), enCloSure building filtration (EBFS), main steam isolation (MSI), sump redirulation (SRAS), and UV. The UV signal Joad sheds the vital bus and starts the EDG and sequences the loads on in the event of a.loss of normal power. The CIAS, SIAS, EBFS, 'MSI, and SRAS signals are not required below'Mode 3 per TS 3.3.2.1 and table 3.3-3, and can be bypassed (placed in `Inhibit") in Mode 4. The UV protection is not required below Mode 4 per TS 3.3.2.1 and table 3.3-3, and can.be bypassed (placed in "inhibit") in Mode 5.

Cause

The cause of the event was less than adequate written:instructions for performing the task performed by instrument and controls technicians.

Assessment of Safety Consequences

This event is considered to be of low safety significance. The plant was in Mode 4 approximately 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> after an orderly reactor shutdown when the ESFAS UV channels were inadvertently placed in "inhibit". In this condition, the;EDGs would not have automatically started and/or loaded in the event of a loss of power. There was no actual loss of offsite power during the timeframe the under voltage channels were in "inhibit". During the time these channels` were 'in inhibit, core and Reactor Coolant System (RCS) heat removal transitioned from the reactor coolant pumps and steam generators to the low pressure safety injection pumps and the shutdown Cooling heat .exchangers.

in the -event of a tOSS -ofdffsite -power:With RCS .heat ,removaryia the _steam .generators, -continued core.

and RCS beat removal-would :have been :assured ;by .natUraf,:t_irtulatiOn iand continued steam :generator beat removal :Via The atmospheric dump-"valves.

If the ;loss of :offsite 7power bad occU:rred 'with :shUtdOwn--coOlingestablii,hed, -the;EDGs would,not"have automatically started.. However, 'That ,conditionis readily,a,pparent to,the operators,,and existing proceduratguidahcawould-direct starting 'and.loading.ditheEpG. :AdeqUate time would baye_been available-to 'reestablish -shutdown --cOoling flOw .by-manUally starting .aiow pressure .safetyinjeCtion pump and adjuSting tlow-througbthe -shutdown ,.coOling.beatexchangers as necessary.� .

In the event that a Joss of offsite power 'ct>cturred.along'With :loss of:RCS inventory with the !automatic diesel generatorstarrinhibited, the RCS.Inyentory and-pressure control safety funCtions would.have been capable of ,being maintained.: Based:on operator � and 'procedural guidance, there would have:been adequate time to restOre'pOwerlo -a vital 'bus and manually start a high pressure safety injection 'pump to reeStablish _RCS 'inventory control.

Based on the above dismission; thereiwasno -adverseeffectonThe..bealth andsafetyof the public.

Corrective. Action Upon discovery, the channels were taken out of Inhibit" restoring IN protection and Operability of the emergency diesel generators. An extent of condition review .concluded 'that:no other trains or channels that were required to be operable were inappropriately "inhibited" for the ESFAS and the RPS.

The operations crew and IAC technicians were briefed the next day to'review the,event. The briefs included a discussion on bypassing undervoltage and ;how it affects emergency power availability. A statement was added to IBC's standard brief for this task to ensure That undervoltage protedtion is NOT bypassed. Additionallywork control documents have,bee'nOodified to-provide guidance as to the ESFAS sensor inputs which could be,bypassed, so that,the development of future work orders will capture the lessons learned from this event. Improved procedure guidance :has been developed governing bypassing/inhibiting ESFAS, RPS, ATWS and AAFWIS and is in the review process. These actions are being addressed under the station's corrective action 'program.

Additional corrective actions are being taken in accordance with the station's corrective action program.

.Previous Occurrences No previous similar eventsiconditions were identified.

Energy Industry Identification System (EDS) codes are identified in the text as {XX].