ML080870349

Watts Bar, Unit 1 - Technical Specifications (TS) Change - TS-07-18 - Revision of the Allowable Value for the Containment Purge Exhaust Radiation Monitors - Limiting Condition for Operation (LCO) 3.3.6, Containment Vent Isolation Instrument

ML080870349
Person / Time
Site:	Watts Bar
Issue date:	03/27/2008
From:	Brandon M K Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TVA-WBN-TS-07-18
Download: ML080870349 (13)

Text

March 27, 2008 TVA-WBN-TS-07-18 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Gentlemen:

In the Matter of the ) Docket No. 50-390 Tennessee Valley Authority ) WATTS BAR NUCLEAR PLANT (WBN) - UNIT 1 - TECHNICAL SPECIFICATIONS (TS)

CHANGE - TS-07 REVISION OF THE ALLOWABLE VALUE FOR THE CONTAINMENT

PURGE EXHAUST RADIATION MONITORS - LIMITING CONDITION FOR OPERATION (LCO) 3.3.6, "CONTAINMENT VENT ISOLATION INSTRUMENTATION" Pursuant to 10 CFR 50.90, Tennessee Valley Authority (TVA) is submitting a request for a TS change (TS-07-18) to License NPF-90 for WBN. The proposed TS change revises the allowable value listed for Function 3, "Containment Purge Exhaust Radiation Monitors," in Table

3.3.6-1, "Containment Vent Isolation Instrumentation," of LCO 3.3.6. The Containment Purge

exhaust radiation monitors (1-RE-90-130-A and 1-RE-90-131-B) initiate containment vent

isolation to mitigate the potential release of radioactive effluents via this flow path following a

postulated Small Break Loss of Coolant Accident (SBLOCA).

The current allowable value is appropriate when the containment purge exhaust filters are

credited. However, that value was deemed nonconservative in Modes 1 through 4 operation

because the containment purge exhaust filters are not credited in the WBN design and licensing

basis and are not required to be operational in those operating modes by the WBN Technical

Specifications. Administrative controls hav e been implemented to impose a more conservative allowable value and setpoint that does not credit the containment purge exhaust filters. WBN

procedure 1-ODI-90-15, "Containment Purge Release" Revision 26 has been implemented with

precautions and specific notes to restrict the setpoint for these monitors. This setpoint has been

established through approved instrumentation accuracy calculations for these monitors to

ensure the proposed allowable value will not be exceeded. This administratively controlled

allowable value and setpoint will ensure compliance with the WBN U.S. Nuclear Regulatory Commission Page 2 March 27, 2008 design and licensing basis during the processing of this request. Review of past setpoints for this function concluded that the settings were always lower than the proposed allowable value

and the associated setpoint. The setpoint for this function has been maintained well below the

proposed allowable value.

TVA has determined that there are no significant hazards considerations associated with the

proposed change and that the TS change qualifies for categorical exclusion from environmental review pursuant to the provisions of 10 CFR 51.22(c)(9). Additionally, in accordance with 10

CFR 50.91(b)(1), TVA is sending a copy of this letter and enclosures to the Tennessee State

Department of Public Health.

TVA requests approval of this TS change by the beginning of the Cycle 9 refueling outage which

is currently scheduled to begin in the fall of 2009. TVA intends to implement the revised TS

within 30 days of NRC approval.

There are no regulatory commitments associated with this submittal.

If you have any questions about this change, please contact me at 423-365-1824.

I declare under penalty of perjury that the foregoing is true and correct. Executed on this 27 th day of March, 2008.

Sincerely, Original signed by M. K. Brandon Manager, Site Licensing and Industry Affairs

Enclosure:

Evaluation of the Proposed Change cc: See page 3 U.S. Nuclear Regulatory Commission Page 3 March 27, 2008 Enclosure cc (Enclosure): NRC Resident Inspector Watts Bar Nuclear Plant 1260 Nuclear Plant Road Spring City, Tennessee 37381 ATTN: Margaret H. Chernoff, Senior Project Manager U.S. Nuclear Regulatory Commission Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation MS O-8 H4-A Washington, DC 20555-0001 U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Mr. Lawrence E. Nanny, Director Division of Radiological Health 3rd Floor L & C Annex 401 Church Street Nashville, Tennessee 37243

ENCLOSURE EVALUATION OF THE PROPOSED CHANGE

Subject:

Watts Bar Nuclear Plant (WBN) Unit 1 - Technical Specifications (TS) Change -

TS-07 Revision of the Allowable Value for the Containment Purge Exhaust Radiation Monitors - Limiting Condition for Operation (LCO) 3.3.6, "Containment

Vent Isolation Instrumentation."

1.0

SUMMARY

DESCRIPTION This evaluation supports a request to amend Operating License NPF-90 for WBN Unit 1.

The proposed TS change revises the allowable value listed for Function 3, "Containment

Purge Exhaust Radiation Monitors," in Table 3.3.6-1, "Containment Vent Isolation

Instrumentation," of LCO 3.3.6, during Modes 1 through 4. The current allowable value

remains acceptable during movement of irradiated fuel assemblies within containment.

The Containment Purge exhaust radiation monitors (1-RE-90-130-A and 1-RE-90-131-B)

initiate containment vent isolation to mitigate the potential release of radioactive effluents

via this flow path following a postulated Small Break Loss of Coolant Accident (SBLOCA). The isolation of this flow path serves to limit radiological consequences of

the design basis SBLOCA to well within the limits of 10 CFR 100, "Reactor Site Criteria."

These monitors and the associated TS allowable value are not used to protect the

nuclear fuel or the Reactor Coolant System safety barriers; therefore, the allowable value revised by this change is not a 10 CFR 50.36, "Technical Specifications," limiting

safety system setting.

The current allowable value was determined to be non-conservative for operating Modes

1 through 4, and this condition has been documented in TVA's corrective action

program. The allowable value was determined to be non-conservative because the

basis for the specified value inappropriately credited the containment purge exhaust

filters, when the TS LCO 3.9.8 only requires these filters during movement of irradiated

fuel assemblies within containment. Administrative controls have been implemented to

impose a more conservative allowable value that does not credit the containment purge

exhaust filters. This administratively controlled allowable value will ensure compliance

with the WBN's design and licensing basis during the processing of this request.

2.0 DETAILED DESCRIPTION The Containment Purge exhaust radiation monitors are gaseous effluent monitors which continuously monitor the radioactivity in the exhaust air from the containment

atmosphere as required in 10 CFR 50, Appendix A, GDC 60 and 64. The two redundant

safety-related monitors perform a primary safety function for mitigation of the offsite dose

consequences for a limited break size spectrum of SBLOCA events. A high radiation signal from either noble gas monitor automatically generates a Containment Vent

Isolation (CVI) signal which in turn shuts down the Reactor Building Purge Ventilation

System (RBPVS) fans and isolates the syst em by closing its respective dampers and butterfly valves. The automatic isolation func tion of these monitors is a primary safety function, since it mitigates the potential release of radioactive material to the

environment following a postulated design basis event which satisfies the requirements E1-1 described in 10 CFR 100. Note for the design basis large break LOCA, a safety injection signal is credited for generation of the CVI signal.

The analytical limit (activity level in the flow stream) established for the Containment

Purge exhaust radiation monitors is based on isolating the Containment Purge exhaust

before reaching 10 percent of the exclusion area boundary dose limit for a SBLOCA. In

establishing the analytical limit, the Containment Purge exhaust filters were credited.

The Containment Purge exhaust radiation monitor allowable value in TS Table 3.3.6-1 is based on the analytical limit. Since the analytical limit and allowable value credits the

Containment Purge exhaust filters for accident mitigation, filter testing in accordance

with R.G.1.52 is required. Based on the preceding, TVA documented in its corrective

action program that there is no Surveillanc e Requirement (SR) for Containment Purge exhaust filter testing in Modes 1 to 4 even though the allowable value specified in TS

Table 3.3.6-1 Item 3 for the Containment Purge exhaust radiation monitors takes credit

for purge exhaust filtration during Modes 1 to 4.

In order to resolve this condition, the Containment Purge exhaust radiation monitor analytical limit for Modes 1 to 4 was conservatively reduced to a value that will initiate a

CVI to control releases to well within 10 CFR 100 limits without the need to take credit

for the Containment Purge exhaust filters. No change was required during movement of

irradiated fuel assemblies within containment, as TS LCO 3.9.8 requires operability of

the Containment Purge exhaust filters during such movement. This change resulted in

keeping the analytical limit of 1.87 E-01 Ci/cc (Containment Purge exhaust filters credited) only for movement of irradiated fuel assemblies within containment, and using

a limit of 4.3 E-02 Ci/cc (Containment Purge exhaust filters not credited) for Modes 1 to

4. Based on this modification to analytical limits, the Containment Purge exhaust

radiation monitor allowable value in TS Table 3.3.6-1 is being revised to be consistent

with the new analytical limit. The proposed revision retains the current allowable value

of less than or equal to 8.41E-02 Ci/cc (8.41E+04 cpm) during movement of irradiated fuel assemblies within containment, and adds a new allowable value of less than or

equal to 2.8 E-02 Ci/cc (2.8E+04 cpm) in Modes 1 to 4.

3.0 TECHNICAL EVALUATION

Containment Purge exhaust radiation monitor analytical limit and allowable value ensures that the monitor will isolate the C ontainment Purge exhaust to limit the offsite radiological consequences of a postulated SBLOCA. The analytical limit for the monitor

is conservatively determined such that the monitor will isolate the Containment Purge

exhaust before exceeding 10 percent of the offsite dose limits for a SBLOCA. In

establishing the analytical limit, the purge exhaust filters may or may not be credited. If

the purge exhaust filters are credited in establishing the monitor analytical limit, a higher

activity concentration can be allowed in the flow stream upstream of the Containment Purge exhaust filters since the filters will remove a significant percentage of the activity

in the exhaust. If the filters are not credited, the allowable activity concentration in the

flow stream upstream of the filters is reduc ed since none of the activity is assumed to be removed by the exhaust filter.

The allowable value is a limiting value for the setpoint. The allowable value is more conservative than the analytical limit and ensures that sufficient margin exists to account for instrument uncertainties that either are not present or are not measurable during

testing (i.e., unmeasurables). The actual setpoint is more conservative than the E1-2 allowable value, and is chosen to ensure that actuation will occur prior to exceeding the analytical limit.

For the proposed amendment, the allowable value for the trip setpoint for the containment ventilation isolation signal in itiated by the Containment Purge exhaust radiation monitors (loops 1-R-90-130-A and 1-R-90-131-B) is being decreased from

8.41E-02 Ci/cc to 2.8E-02 Ci/cc for Modes 1 to 4. This is necessary due to the lower analytical limit required if the Containment Purge exhaust filters are not credited with

decreasing the released concentration. The analytical limit used to establish the

allowable value proposed in the TS change was calculated in WBN design calculation

WBNAPS3079, "Safety Limit for the Containment Purge Exhaust Monitors." This is the

same calculation used to calculate the analytical limit used to establish the current

allowable value. This same calculation was used to determine the analytical limits for

both crediting and not crediting the Containment Purge exhaust filters.

The methodology used to determine the allowable value (AV) is a conservative variation of Method 3 of ISA-RP67.04.02-2000, "Methodologies for the Determination of Setpoints

for Nuclear Safety Related Instrumentation." This methodology is defined in TVA's

Technical Instruction EEB-TI-28, Setpoint Calculations.

The high AV is determined based on the following equation:

AV < (AL - (Adbe-Anf))

Adbe = design basis accident accuracy Anf = normal measurable accuracy.

The low AV is determined by the following equation:

AV > (SP + Anf)

SP = the setpoint.

The AV specified in TS Table 3.3.6-1 is set half way between these two values. This assures that there is additional margin for non-statistical unmeasurables. The

Containment Purge exhaust radiation monitors initiate containment vent isolation to assure that releases are well within 10 CFR 100 limits. Because the monitors are not

used to protect the reactor fuel or the Reactor Coolant System safety barriers, the

allowable value specified in the TS for this device is not a 10 CFR 50.36 limiting safety system setting.

Only the AV is provided in TS Table 3.3.6-1 because the actual setpoint is conservatively determined by WBN's Chemistry staff in accordance with the Offsite Dose

Calculation Manual (ODCM) prior to every pur ge of containment. The limiting (highest) setpoint, as well as instrument loop and component accuracies, and the AV are

determined by instrument accuracy calcul ation 1-RE-90-130, "Demonstrated Accuracy Calculation for Containment Building Purge Air Exhaust Monitors." The setpoint and AV

are based on the AL provided in design calculation WBNAPS3079. In addition to the

conservatisms of the AV determination as discussed above, the setpoint determination is

conservative in that it assumes all gaseous radiation is from the isotope to which the

monitor is least sensitive, and additionally assumes the monitor is no more accurate than

the required accuracy, both of which work to force the setpoint lower. WBN's Chemistry staff determines the setpoint for the release based on containment samples in E1-3 accordance with procedure 1-ODI-90-15, "Containment Purge Release." WBN's Maintenance staff performs setpoint calibration in accordance with 1-SI-90-5, "92 Day

Channel Operational Test of the General Atomic Containment Purge Air Exhaust Radiation Monitor Loop 1-LPR-90-130," and 1-SI-90-7, "92 Day Channel Operational

Test of the General Atomic Containment Purge Air Exhaust Radiation Monitor Loop 1-LPR-90-131," which refer to setpoint and scaling documents 1-R-90-130 and

1-R-90-131. These setpoint and scaling documents provide the limiting setpoint value

determined in calculation 1-RE-90-130. WBN procedure 1-ODI-90-15 contains

restrictions that will not allow the setpoint for containment purge activities to be adjusted

higher than the maximum allowable setpoint as determined in calculation 1-RE-90-130.

Eighteen month channel calibrations 1-SI-90-6, "18 Month Channel Calibration (Source Calibration) of the General Atomic Contai nment Purge Air Exhaust Radiation Monitor Loop 1-LPR-90-130," and 1-SI-90-8, "18 Month Channel Calibration (Source Calibration) of the General Atomic Containment Purge Air Exhaust Radiation Monitor Loop 1-LPR-

90-131," assure that the monitor instrumentation and setpoints are within the required

limits and accuracies. These calibration procedures test the entire loop through

containment ventilation isolation. The procedures include performance calibration of the

radiation ratemeter to a known radiation source, calibration of the bistable setpoint (by

reference to procedures 1-SI-90-6 and 1-SI-90-8), and testing the ratemeter bistable

interlocks with alarms, annunciation, and containment ventilation isolation. Channel

operational tests, performed every 92 days by 1-SI-90-5 and 1-SI-90-7, include

verification that the bistable which initiates containment ventilation isolation is within its

as-left calibration accuracy. Any tested compliance component found outside of the as-left calibration accuracy is reset prior to exiting the procedure.

In summary, the allowable value for the Containment Purge exhaust radiation monitors listed in TS Table 3.3.6-1 is being revised to be consistent with the analytical limit that does not credit the Containment Purge exhaust filters for Modes 1 to 4, and to keep the

analytical limit that does credit the Containment Purge exhaust filters during movement

of irradiated fuel assemblies within containment. The revised analytical limit and

allowable value will ensure the Containment Pu rge exhaust radiation monitors will isolate the Containment Purge exhaust consistent with the plant's design and licensing basis for

mitigating the consequences of SBLOCA to well within the dose limits of 10 CFR 100.

4.0 REGULATORY EVALUATION

4.1 Applicable Regulatory Requirements/Criteria Containment Purge exhaust radiation monitor analytical limit and allowable value ensures that the monitor will isolate t he Containment Purge exhaust in the event

of a small break loss-of-coolant accident (SBLOCA). For the design basis large

break LOCA, this function is accomplished by a Safety Injection initiation. The

analytical limit for the monitor is conservatively set such that the monitor will

isolate the Containment Purge exhaust to limit the associated offsite radiological

consequences to well within the limits of 10 CFR 100 for the design basis

SBLOCA event. Two analytical limits have been established by calculation, depending on whether the purge exhaust filters are or are not credited. If the

purge exhaust filters are credited in establishing the monitor analytical limit, a

higher activity concentration can be allowed in the flow stream upstream of the

Containment Purge exhaust filters since the filters will remove a significant

percentage of the activity in the exhaust. If the filters are not credited, the E1-4 allowable activity concentration in the flow stream upstream of the filters is reduced since none of the activity is assumed to be removed. This TS change

requests the revision of an allowable value in the TS to a value that does not

credit the exhaust filters for Modes 1 to 4 operations, while maintaining the

existing allowable value for movement of irradiated fuel assemblies within

containment.

4.2 Significant Hazards Consideration The proposed Technical Specification (TS) change revises the allowable value listed for Function 3, "Containment Purge Exhaust Radiation Monitors," in Table

3.3.6-1, "Containment Vent Isolation Instrumentation," of LCO 3.3.6. The

Containment Purge exhaust radiation monitors (1-RE-90-130-A and

1-RE-90-131-B) initiate containment vent isolation to mitigate the potential

release of radioactive effluents via this flow path following a postulated Small

Break Loss of Coolant Accident (SBLOCA). The proposed change corrects a

non-conservative allowable value in Modes 1 to 4 where the Containment Purge

exhaust filters were inappropriately credited for the mitigation of the radiological

consequences associated with a SBLOCA. The proposed TS allowable value

ensures the monitors will isolate the Containment Purge exhaust and ensures the

consequences are well within the applicable regulatory limits. This change does

not affect any accident doses reported in the FSAR.

TVA has evaluated whether or not a significant hazards consideration is involved with the proposed amendments by focusing on the three standards set forth in

10 CFR 50.92, "Issuance of Amendment," as discussed below:

1. Does the proposed amendment involve a significant increase in the probability or consequences of an accident previously evaluated?

Response: No.

The proposed change is associated with radiation effluent monitoring and isolation of Containment Purge exhaust flow in the event of a design

basis SBLOCA. The change is not associated with equipment or

processes which can initiate a design basis accident. Consequently, this

change does not affect the probability of an accident previously

evaluated.

The revised purge exhaust monitor allowable value will ensure the monitors isolate the purge exhaust and will limit the offsite doses

associated with a SBLOCA to well within the limits of 10 CFR 100. This

change serves to ensure the consequences of an accident previously

evaluated remain bounded by the plant's current licensing basis.

Therefore, the consequences of accidents previously evaluated are not

increased by this change.

Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.

2. Does the proposed amendment create the possibility of a new or different kind of accident from any accident previously evaluated?

E1-5 Response: No.

The proposed change is associated with radiation effluent monitoring and isolation of Containment Purge exhaust flow in the event of a design basis SBLOCA. The change is not associated with equipment or

processes which can initiate a design basis accident. The change does

not introduce new accident initiators or physical changes in plant

equipment.

Therefore, the proposed change does not create the possibility of a new or different kind of accident fr om any previously evaluated.

3. Does the proposed amendment involve a significant reduction in a margin of safety?

Response: No.

The proposed change involves a conservative change in the Containment Purge exhaust radiation monitor allowable value in TS Table 3.3.6-1. The

new allowable value reflects a change in the monitor analytical limit which

does not assume credit for the Containment Purge exhaust filters. The

proposed allowable value will ensure the monitors will isolate the purge

exhaust as assumed in the existing design basis SBLOCA analysis.

Therefore, the proposed change does not involve a significant reduction in a margin of safety.

Based on the above, TVA concludes that the proposed amendment does not involve a significant hazards consideration under the standards set forth in 10

CFR 50.92(c), and accordingly, a finding of "no significant hazards consideration"

is justified.

4.3 Conclusions

In conclusion, based on the considerations discussed above, (1) there is reasonable assurance that the health and safety of the public will not be

endangered by operation in the proposed manner, (2) such activities will be

conducted in compliance with the Commission's regulations, and (3) the

issuance of the amendment will not be inimical to the common defense and

security or to the health and safety of the public.

5.0 ENVIRONMENTAL CONSIDERATION

A review has determined that the proposed amendment would change a requirement with respect to installation or use of a facility component located within the restricted

area, as defined in 10 CFR 20, or would change an inspection or surveillance

requirement. However, the proposed amendment does not involve (i) a significant

hazards consideration, (ii) a significant change in the types or significant increase in the

amounts of any effluents that may be released offsite, or (iii) a significant increase in

individual or cumulative occupational radiation exposure. Accordingly, the proposed

amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR

51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), no environmental impact E1-6 statement or environmental assessment need be prepared in connection with the proposed amendment.

E1-7

6.0 REFERENCES

None ATTACHMENTS

1. Technical Specifications Page Markups E1-8 A1-1 ATTACHMENT 1 TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT (WBN)

UNIT 1 PROPOSED TECHNICAL SPECIFICATION CHANGES (MARK-UP)

I. AFFECTED PAGE LIST Unit 1 3.3-56 II. MARKED PAGES See attached.

Containment Vent Isolation Instrumentation 3.3.6 Watts Bar-Unit 1 3.3-56 A1-2 Table 3.3.6-1 (page 1 of 1)

Containment Vent Isol ation Instrumentation FUNCTION REQUIRED CHANNELS SURVEILLANCE REQUIREMENTS ALLOWABLE VALUE 1. Manual Initiation 2 SR 3.3.6.6 NA 2. Automatic Actuation Logic and Actuation Relays

3. Containment Purge Exhaust Radiation Monitors 2 trains 2 SR 3.3.6.2 SR 3.3.6.3 SR 3.3.6.5 SR 3.3.6.1 SR 3.3.6.4 SR 3.3.6.7 NA 8.41E-02 Ci/cc (a) (8.41E+04 cpm) 2.8E-02 Ci/cc(b) (2.8E+04 cpm)

4. Safety Injection Refer to LCO 3.3.2, "ESFAS Instrumentation," Function 1, for all initiation functions and requirements.

(a) During movement of irradiated fuel assemblies within containment (b) Modes 1, 2, 3, and 4