ML082730684
| ML082730684 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 09/26/2008 |
| From: | James Smith Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML082730684 (13) | |
Text
U.S. Nuclear Regulatory Commission Page 3 September 26, 2008
Enclosure
cc (Enclosure):
Mr. Brendon T. Moroney, Project Manager
U.S. Nuclear Regulatory Commission
Mail Stop 08G-9a
One White Flint North
11555 Rockville Pike
Rockville, Maryland 20852-2739
U.S. Nuclear Regulatory Commission Page 4 September 26, 2008
JDS:ZTK:PMB
Enclosure
cc (Enclosure):
G. Arent, EQB 1B-WBN T. J. Bradshaw (NSRB Support), BR 4X-C
C. R. Church, POB 2B-SQN
WBN Site Licensing Files, ADM 1L-WBN
I:License/ Discretionary Enforcement /Disc Letter CRACS Sept 2008.doc
E1 TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT (SQN)
UNIT 1 AND 2 DOCKET NOS. 327/328 REQUEST FOR ENFORCEMENT DISCRETION FOR TECHNICAL SPECIFICATION (TS)
LIMITING CONDITION FOR OPERATION (LCO) 3.
==0.5
BACKGROUND==
TVA is requesting enforcement discretion for SQN Units 1 and 2 for TS LCO 3.0.5.
Enforcement discretion was needed to prevent an unnecessary plant shutdown as a result of
unplanned failure of the B train main control room (MCR) air handling unit (AHU) motor in
conjunction with the planned maintenance to replace the batteries for the 1A-A emergency
diesel generator (EDG).
On September 24, 2008, at 1705 Eastern daylight time (EDT), Technical Specification (TS) LCO 3.8.1.1, "A/C Sources," Action (b) was entered for scheduled maintenance of the 1A-A
emergency diesel generator (EDG) 125-volt battery bank. At the time of entering the LCO, both
Unit 1 and Unit 2 were operating in Mode 1. The scheduled battery bank maintenance was
expected to take approximately 64 hours7.407407e-4 days <br />0.0178 hours <br />1.058201e-4 weeks <br />2.4352e-5 months <br />. On September 25, 2008, at 2255, LCO 3.7.15, "Control Room Air-Conditioning System (CRACS)," Action (a) was entered due to the loss of the
associated "B" train MCR AHU. Under this condition both units entered TS LCO 3.0.5, which
requires within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, action to be initiated to place a unit in a mode of condition in which the
applicable LCO does not apply. In this case, the LCO action would be satisfied by placing each
unit in hot standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, hot shutdown within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and cold
shutdown within the subsequent 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
This notice of enforcement discretion (NOED) requests discretion for Units 1 and 2 from
compliance with SQN TS 3.0.5 for the condition of the CRACS train "A" being inoperable solely
due to its emergency power source unavailable (i.e., EDG 1A-A) and its redundant train being
inoperable. Within this NOED, TVA is requesting an additional 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> from the expiration
time of LCO Action 3.0.5 to be in hot standby to return the EDG 1A-A battery bank and its
associated EDG to operable status.
SQN TS LCO 3.0.5 currently states:
"When a system, subsystem, train, component or device is determined to be inoperable solely because its emergency power source is inoperable, or solely because its normal power source
is inoperable, it may be considered OPERABLE for the purpose of satisfying the requirements
of its applicable Limiting Condition for Operation, provided: (1) its corresponding normal or
emergency power source is OPERABLE; and (2) all of its redundant system(s), subsystem(s),
train(s), component(s) and device(s) are OPERABLE, or likewise satisfy the requirements of this Specification. Unless both conditions (1) and (2) are satisfied, within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> action shall be
initiated to place the unit in a MODE in which the applicable Limiting Condition for Operation
does not apply by placing it as applicable in:
- 1. At least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />
- 2. At least HOT SHUTDOWN within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, and
- 3. At least COLD SHUTDOWN within the subsequent 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
E2 This Specification is not applicable in MODES 5 or 6."
The CRACS provides temperature control for the control room during normal operation and
following isolation of the control room. The Unit 1 and Unit 2 control room is a common room
served by a shared CRACS.
The CRACS consists of two independent and redundant trains that provide cooling of
recirculated control room air. Each train consists of a chiller package, cooling coils, air handling
unit, instrumentation, and controls to provide for control room temperature control. A single train
will provide the required temperature control.
TVA has reviewed the "NRC Regulatory Issue Summary 2005-01, Changes to Notice of
Enforcement Discretion (NOED) Process and Staff Guidance," and "Inspection Manual, Part
9900: Technical Guidance, Operations Notices of Enforcement Discretion," and has concluded
that Section 2.1, Situations Affecting Radiological Safety-Regular NOEDs, Criterion 1.a is
satisfied. This criterion applies to plants in power operation desiring to avoid unnecessary
transients as a result of compliance with the license condition and, thus, minimize the potential
safety consequences and operational risks. The basis for this conclusion and other information
required to support a request for NOED is provided below.
- 1. The TS or other license conditions that will be violated.
With CRACS train "A" inoperable solely due to its emergency power source unavailable (i.e., EDG 1A-A) and then its redundant train becoming inoperable, application of TS
LCO 3.0.5 is required. TS LCO 3.0.5 mandates within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, action to be initiated to
place a unit in a mode in which the applicable LCO does not apply. This would require
placing both units in hot standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, hot shutdown within the following
6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and cold shutdown within the subsequent 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
- 2. The circumstances surrounding the situation: including likely causes; the need for prompt action; action taken in an attempt to avoid the need for an NOED; and
identification of any relevant historical events.
At 1705 on 09/24/08, EDG 1A-A was declared inoperable in preparation for EDG 125-volt
direct current (dc) battery bank maintenance.
At approximately 2250 on 09/25/08, a swap of CRACS train "A" to "B" was attempted, at
which time the "B" train AHU tripped when attempting to start. Train "A" continued to
operate.
At 2255 on 09/25/08, CRACS "B" train was declared inoperable from an investigation
where smoke and a burnt smell from the B-B MCR AHU motor were indicated.
At 2255 on 09/25/08, TS LCO 3.0.5 was entered with both units required to be in hot
standby at 0655 on 09/26/08.
At 2345 on 09/25/08, the NRC Resident was notified.
E3 At 0038 on 09/26/08, a maintenance work order had been written to repair the B-B MCR AHU motor.
At 0507 on 09/26/08, the EDG 1A-A battery bank was aligned to the 125-volt dc
distribution board and charger.
At 1400 on 09/26/08, EDG 1A-A was declared operable.
Maintenance work order number 08-779987-000 was written at 0038 on 09/26/08 to repair
the B-B MCR AHU motor. A maintenance team was promptly dispatched to investigate
the B-B MCR AHU motor. It was concluded the motor would need to be replaced and
further investigation of the failed motor would need to be performed. Subsequently, CRACS "B" train was returned to operable status at 1608 EDT.
The likely cause of the motor failure is unknown at this time. However, the cause for the
unplanned entry into LCO 3.0.5 was the unplanned motor failure in conjunction with the
planned maintenance activity on EDG 1A-A. Prompt action was needed to preclude a
2 unit shutdown.
In addition, no avenues were available to restore the EDG from its scheduled maintenance
activity prior to exceeding LCO 3.0.5 allowed outage time.
No recent events have been noted in regards to the MCR AHU motors.
- 3. Information to show that the cause and proposed path to resolve the situation are understood by the licensee, such that there is a high likelihood that planned actions
to resolve the situation can be completed within the proposed NOED time frame.
At the time of the NOED request, the 1A-A EDG battery had been replaced with a new
battery, but was still considered inoperable. The EDG battery was scheduled to be
returned to service at 0900 on September 27, 2008. The return to service of the1A-A EDG
battery has been expedited to restore the EDG 1A-A operable within the proposed 36-hour
timeframe.
If a loss of off-site power occurs, the EDG battery provides control power during the
blackout period and field flash current for excitation during a EDG start. Prior to expiration
of the time limit of LCO 3.0.5, the diesel battery was made available and was sufficiently
charged to assure that the battery would perform its function in support of EDG 1A-A. A
TVA calculation provides assurance that based on as-left battery charger value, adequate
voltage would be available for devices to function properly.
B-B MCR AHU is inoperable due to an unanticipated failure of the motor. Maintenance
work order 08-779987-000 was written and made Priority 1 to repair the B-B MCR AHU
motor. Replacement of the motor and return to operable of the "B" CRACS train was
expected to be within the proposed 36-hour timeframe. Subsequently, CRACS "B" train
was returned to operable status at 1608 EDT.
- 4. The safety basis for the request, including an evaluation of the safety significance and potential consequences of the proposed course of action.
- a. Provide the incremental conditional core damage probability (ICCDP) and incremental conditional large early release probability (ICLERP) associated with the period of enforcement discretion.
E4 From the SQN Revision 4 PRA model, the ICCDP was determined to be 5.0351E-08, which is much less than the 5.0E-07 threshold. The ICLERP was determined to be
2.2798E-9, which is below the threshold of 5.0E-08
- b. Discuss the dominant risk contributors (cut sets/sequences) and summarize the risk insights for the plant-specific configuration the plant intends to operate in during the period of enforcement discretion.
CRACS has no impact on the calculated core damage frequency (CDF) or LERF at
SQN. CRACS and specifically the control room chillers are not included in the level
one probabilistic risk assessment (PRA) model. From TVA calculation
MDQ00003120020121, the time it takes the MCR to reach the 104°F environmental
design temperature, from a normal temperature of 75°F, during a design basis LOCA
is 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> (with outside temperatures at the design basis ambient temperature of
97°F). The relay and switchgear room adjacent to the MCR is also cooled by the
CRACS. The relay room would not reach the design basis temperature of 104°F in a
24-hour time period on loss of cooling. Since this is a slowly evolving transient, this
system has been screened out as either an initiating event or a support system failure. Also the plant can be maintained in hot standby from the remote shutdown
facility, in the unlikely event that MCR conditions would necessitate abandonment.
With 1A-A EDG in maintenance, the largest contributor to CDF is the loss of off-site power (LOOP) initiating event; the top sequence being the loss of the B-train EDG
resulting in a station blackout. Due to the fact that the 1A-A EDG is available, which
was not accounted for in the PRA model runs, this risk analysis is conservative for
the actual plant condition during the enforcement discretion period.
Additionally, the loss of off-site power would also result in the loss of power to the A train CRACS. However, it has been determined that the 1A-A EDG is available
and could supply power to the A-A CRACS within the 18-hour timeframe mentioned
above. The impact of the CRACS on the HRA actions in the PRA was reviewed.
Specifically, the RAW values of the human actions in the PRA were reviewed and all
of the HEPs with a RAW greater than 1.0 were assessed for long-term impact due to
delayed room heat-up from CRACS. All of the dominant HEP contributors are short-term actions and would be completed significantly prior to the worst-case, 18-hour
room heat-up described above.
- c. Explain compensatory measures that will be taken to reduce the risk associated with the specified configuration.
The following compensatory measures will be taken to reduce plant vulnerabilities to
preclude event mitigation and initiating events during the period of the NOED:
- 1. Protect the CRACS "A" train and associated equipment.
- 2. Protect the off-site power source by deferring nonessential switchyard and transformer yard activities where human error could contribute to the likelihood of
a loss of off-site power.
- 3. Verify breaker alignment in accordance with LCO 3.8.1.1, Surveillance Requirements 4.8.1.1.1.a.
E5 4. Defer nonessential activities on each unit where human error could contribute to the likelihood of a plant transient and subsequent demand on mitigating systems.
- 5. Nonessential surveillances or other maintenance activities on other risk significant equipment were deferred.
- d. Discuss how the proposed compensatory measures are accounted for in the PRA. These modeled compensatory measures should be correlated, as applicable, to the dominant PRA sequences identified in item b above. In addition, other measures not directly related to the equipment out-of-service may also be implemented to reduce overall plant risk and, as such, should be explained. Compensatory measures that cannot be modeled in the PRA should be assessed qualitatively.
The compensatory measures above were not accounted for in the PRA analysis
performed for this NOED. Protection of the A train CRACS will increase the
probability of maintaining the MCR environmen
- t. Protecting off-site power systems will reduce the possibility of a LOOP initiating event, reducing probability of the loss
of power to A train CRACS. Since the compensatory measures are in direct relation
to the equipment out-of-service, they should result in a significant risk reduction
during the NOED period, such that the proposed NOED does not result in any net
radiological increase to the public. .
- e. Discuss the extent of condition of the failed or unavailable component(s) to other trains/divisions of equipment and what adjustments, if any, to the related PRA common cause factors have been made to account for potential increases in their failure probabilities. The method used to determine the extent of condition should be discussed. It is recognized that a formal root cause or apparent cause is not required given the limited time available in determining acceptability of a proposed
NOED. However, a discussion of the likely cause should be provided with an associated discussion of the potential for common cause failure.
No common cause failure modes of the CRACS were considered in the PRA analysis; therefore, no adjustments to the common cause analysis are required. The
only common cause failure to be considered would be the failure of the MCR AHU
motor on the A train unit. Since the A train AHU is in operation and the B train AHU
motor failed on start-up, a common cause failure of the motor is unlikely.
EDG 1A-A was in maintenance and not failed, therefore no common cause failure due to the unavailability on this EDG is calculated. Common cause for the remaining
EDGs was adjusted to a 3-component group in the risk analysis.
- f. Discuss external event risk for the specified plant configuration. An example of external event risk is a situation where a reactor core isolation cooling (RCIC) pump has failed and a review of the licensee's Individual Plant Examination of External Events or full-scope PRA model identifies that the RCIC pump is used to mitigate certain fire scenarios. Action may be taken to reduce fire ignition frequency in the affected areas or reduce human error associated with time-critical operator actions in
response to such scenarios.
Review of the potential risk relative to fire safe shutdown identified only one known
deficiency in the SQN fire detection system, and a continuous fire watch is in place to
compensate. Only one SQN suppression sy stem is currently unavailable, EDG CO 2 tank leak, an hourly fire watch is in place and operable hose stations in the area are E6 serving as backup suppression. The compensatory measures in place are adequate to prevent any increase in external event fire risk due to the discrepancies.
The EDGs and the MCR CRACS are designed to withstand a design basis
earthquake. Since the 1A-A EDG has been determined to be available it could be
manually started and supply power to the A train CRACS after a DBE within the
18 hour2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> timelimit for the MCR to reach the environmental design temperature.
Therefore, the increase in risk from an earthquake would be very small.
A review of the weather forecast for SQN during the period that the NOED would be
in place did not indicate any severe weather (high winds, tornados, or flooding).
Therefore the risk of additional external events is considered negligible.
- g. Discuss forecasted weather conditions for the NOED period and any plant vulnerabilities related to weather conditions.
No severe weather is forecasted for the period of the NOED that could cause a plant transient. The forecast for the period of the NOED request:
Mostly cloudy with a 20 percent of rain, with a high near 77 and lows around 60. North wind between 5 and 10 miles per hour becoming calm.
- 5. The justification for the duration of the noncompliance.
The requested 36-hour extension from the time TS LCO 3.0.5 was entered, which requires
each unit to be in hot-standby, at 0655 on September 26, 2008, was viewed to be
adequate for completing the restoration activities of the EDG 1A-A battery bank and for the
unlikely event additional maintenance would be required of this battery bank.
- 6. The condition and operational status of the plant (including safety-related equipment out of service or otherwise inoperable).
Both SQN Units 1 and 2 are in Mode 1 at 100% power. The following safety-related
equipment is inoperable: EDG 1A-A is inoperable due to the associated EDG battery being inoperable for a scheduled maintenance activity (replacement of all battery cells). Both Units
entered TS LCO 3.8.1.1 Action (b) on 9/24/2008 at 1705. Currently, the new
battery for EDG 1A-A is installed and has been recharged following a discharge
test (which was completed satisfactorily). Based upon an evaluation by SQN
Engineering, the battery was capable of performing its support function to start
and flash the field of EDG 1A-A when the battery was untagged (on 9/26/2008 at
0507) following its discharge test. Therefore, EDG 1A-A would have been capable
of performing its function during a loss of off-site power and was considered to be
available. B-B MCR AHU is inoperable due to a failed motor. Both units entered TS LCO 3.7.15 Action (a) on 9/25/2008 at 2255. Additionally, both units entered LCO 3.0.5 due to the emergency power source to the redundant (Train A) MCR AHU
being inoperable. Boric Acid Transfer Pump 1B-B is inoperable due to failing itsSection XI pump performance test on 2/21/2008. This pump is part of the possible boration flow
paths, which can be used to satisfy Technical Requirements Manual TR 3.1.2.2 for E7 Unit 1. No LCO entry is required for this component since redundant boration flowpaths from the Unit 1 refueling water storage tank are operable.
- 7. The status and potential challenges to off-site and on-site power sources.
As described above, EDG 1A-A is inoperable, but available. All other EDGs are operable
and no activities are being conducted which could challenge operability of the remaining
EDGs. The off-site power sources for SQN Units 1 and 2 are operable. The off-site power grid is
stable in a green risk status. The weather at SQN is currently partly cloudy with a
20 percent chance of rain. There are no high winds or storms forecast over the next
48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. There are no switchyard or grid activities being conducted that would threaten
grid stability or off-site power source operability.
The 500 kilovolt (kV) to 161 kV intertie transformer located in the SQN switchyard is
currently out-of-service for maintenance. This maintenance activity has been terminated
until EDG 1A-A has been restored to operable status. Having this transformer
out-of-service imposes more restrictive reactive load limits to assure acceptable off-site
power voltage during an accident at SQN. These limits are being complied with and off-
site power operability and stability are not affected.
- 8. The basis for the licensee's conclusion that the noncompliance will not be of potential detriment to the public health and safety.
The increase in allowed outage time of an additional 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> will not be a potential detriment to the health and safety of the public based on the following:
The EDG 1A-A was available (capable of performing its design function) prior to
exceeding the LCO action time to perform its intended function. Hence the normal and
emergency power supply was available to the A-A MCR AHU train during the 36-hour
extension time.
Compensatory measures were in place to ensur e no activities would take place that could affect the supporting systems and equipment, including off-site and on-site power
sources, for the A-A MCR AHU train that could adversely affect risk during the 36-hour
extension time.
In the unlikely event the A-A MCR AHU was lost, TVA evaluations have determined that
the control room temperature rise from 75°F in the MCR takes at least 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> to reach 104°F in the MCR. As such, more than 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> exist before the MCR would become an
uninhabitable environment and shutdown of both units can be accomplished from the
backup control room. The backup control room is located outside the MCR and is
supplied by a different air-conditioning system that was available during the 36-hour
extension time.
There was no net increase in radiological risk to the public by avoiding the unnecessary
transient imposed by compliance with LCO 3.0.5 and safety continued to be assured by
the A-A MCR AHU, which was performing its intended function of maintaining control
room temperature.
E8 9. The basis for the licensee's conclusion that the noncompliance will not involve adverse consequences to the environment.
TVA has evaluated the NOED request against the criteria for identification of licensing and regulatory actions requiring environmental assessment in accordance with 10 CFR 51.21.
TVA has determined that the requested action meets the criteria for a categorical
exclusion set forth in 10 CFR 51.22(c)(9). This determination is based on the fact that the
proposed action is being requested as an enforcement discretion to a license issued
pursuant to 10 CFR 50, and that the change involves no significant hazards
considerations. Although the proposed action involves noncompliance with the
requirements of an LCO:
- i. The proposed action involves no significant hazards consideration.
ii. There is no significant change in the types or a significant increase in the amounts of any effluent that may be released off-site, since the proposed action does not affect
the generation of any radioactive effluent nor does it adversely affect any of the
permitted release paths.
iii. There is no significant increase in individual or cumulative occupational radiation exposure. The action proposed in this request for enforcement discretion will not
affect plant radiation levels; therefore, does not adversely affect dose rates and
occupational exposure.
Accordingly, the proposed action meets the eligibility criteria for categorical exclusion set
forth in 10 CFR 51.22(c)(9).
- 10. A statement that the request has been approved by the facility organization that normally reviews safety issues (Plant On-site Review Committee, or its
equivalent).
The basis for the request for enforcement discretion was reviewed and approved by the
Plant Operations Review Committee on September 26, 2008.
- 11. The request must specifically address which of the NOED criteria for appropriate plant conditions specified in Section B is satisfied and how it is
satisfied.
The enforcement discretion request meets NRC Inspection Manual, Part 9900:
Section B, Paragraph 2.1, Criterion 1.a. This criterion applies to plants in power
operation and is intended to avoid unnecessary transients as a result of
compliance with the license condition and, thus, minimize potential safety
consequences and operational risks. The safety consequences and operational
risks for SQN were reviewed as part of this NOED request and are documented
within this submittal.
- 12. Unless otherwise agreed as discussed in Section B, a commitment is required from the licensee that the written NOED request will be submitted
within 2 working days and the follow-up amendment will be submitted within
4 working days of verbally granting the NOED.
E9 This written NOED request meets the requirement for submitting the request within 2 working days of the NRC verbal approval (September 26, 2008). As agreed during oral
NOED request teleconference, a follow-up license amendment is not needed.
- 13. In addition to items 1-12 above, for severe weather NOED request the licensee must provide the following information.
This proposed enforcement discretion is not in regards to a severe weather or nature phenomena-related emergency.