ML20155C004

Compliance Evaluation Rept Supporting Amend of Coc GDP-2 Re Low Cylinder Pressure Shutoff

ML20155C004
Person / Time
Site:	Portsmouth Gaseous Diffusion Plant
Issue date:	10/27/1998
From:	NRC
To:
Shared Package
ML20155C003	List: ML20155C000 ML20155C004 ML20155C013
References
NUDOCS 9811020037
Download: ML20155C004 (10)

Text

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[ji#*%9A t UNITED STATES j j t

NUCLEAR REGULATORY COMMISdlON WASHINGTON, D.C. 20655 0001

%,*****/ October 27, 1998 '

DOCKET: 70-7002 CERTIFICATE HOLDER: United States Enrichment Corporation Portsmouth Gaseous Diffusion Plant Portsmouth, Ohio

SUBJECT:

CERTIFICATE AMENDMENT REQUEST - LOW CYLINDER PRESSURE SHUTOFF BACKGROUND '

i On May 26,1998, United States Enrichment Corporation (USEC) submitted a request to revise TSR Section 2.1.3.9, Low Cylinder Pressure Shutoff, to reduce the shutoff pressure level from 20 psia to 15 psia and to reflect an improved description of the system operation through 4 changes to the TSR's Surveillance Requirements and the Basis Statement wording. The proposed amendment describes how the low cylinder pressure shutoff system is intended to operate and to establish corresponding " Allowable Values" by replacing references to setpoints with allowable values.

The existing 2.1.3.9, Low Cylinder Pressure Shutoff, Surveillance Requirements state:

Frequency Surveillance Quarterly SR 2.1.3.9.1 Perform channel functional test to verify steam shutoff to the autoclave when after the first hour of heating the cylinder, pressure remains less than 20 psia.

Semiannually SR 2.1.3.9.2 Calibrate the low cylinder pressure shutoff system instrumentation.

The Basis states:

The heating of a UF cylinder having a closed or plugged valve would negate the protection afforded by the cylinder high pressure shutoff system. A UF. cylinder should not be heated if its pressure cannot be measured due to the potential of a hydraulic rupture. The exception is that 2S sample cylinders heated to 235 'F would have a void volume of over 9% with the cylinder valve closed. During the initial cylinder heating the system provides protection to prevent heating a cylinder with the cylinder valve closed or plugged. This system only provides protection during initial heating and not at another time (SAR Section 3.2.1.1.1]. ,

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E USEC has proposed to replace TSR 2.1.3.9, Low Cylinder Pressure Shutoff, Surveillance  ;

Requirements with the following:

l Frequency Surveillance Quarterly SR 2.1.3.9.1 Perform channel functional test to verify steam shutoff

to the autoclave when after the initial allowable time of cylinder l l heating the cylinder pressure does not exceed the allowable value.

l Semiannually SR 2.1.3.9.2 Perform calibration with allowable values of 215.0 psia )

l and s 65 minutes.

1 The Basis states:

l l l The heating of a UF cylinder having a closed or plugged cylinder valve and/or pigtail  ;

would negate the protection afforded by the cylinder high pressure shutoff system due to the isolation of the cylinder from the high pressure instrumentation. A UF cylinder i should not be heated if its pressure cannot be measured because excessive internal cylinder pressures could potentially rupture the cylinder. The low cylinder pressure shutoff system will isolate the steam supply to an autoclave when after the initial l nominal hour (s 65 minutes Allowable Value) of cylinder heating the cylinder pressure indication does not equal or exceed the Allowable Value of 15 psia. UF, cylinders are not heated unless their cold pressure is s 10 psia which provides a 5.0 psia margin to  !

l the Allowable Value for the purpose of ensuring valve and line clarity to the cylinder pressure instrumentation. Setpoints established shall be consistent with ANSI /ISA- i 67.04 Part I, "Setpoints for Nuclear Safety Related instrumentation" and ANSI /ISA-67.Cb Part II," Methodologies for the Determination of Setpoints for Nuclea- Safety Related i Instrumentation." The exception is that 2S sample cylinders heated to 235 *F would have a void volume of over 9% with the cylinder valve closed. This system only j provides protection during initial heating and not at any other time [SAR Section j 3.2.1.1.1].

Accordingly, the pertinent Safety Analysis Report (SAR) section has also been modified to address this proposed change in operation of the low cylinder pressure shutoff system.

DISCUSSION PORTS uses thirteen cylindrical (6,7, and 8 foot diameter) steam autoclaves in buildings X-342, X-343 and X-344 to feed, transfer and sample UF contained in cylinders. Cylinder heating is accomplished by pressurizing the autoclave with live steam that can be delivered at two flow rates. The higher flow rate is used for initial autoclave and cylinder heatup if the system steam condensation rate is very high and/or the blowdown exhaust system air eliminators are open. The high flow corresponds to a steam pressure of 12 psig. The feed, i

transfer and sample operations of the cylinders are protected against cylinder overpressure by j

! instrumentation that measures cylinder pressure directly through sensors downstream in the

. UF, process line. If the cylinder has either a plugged cylinder valve or pigtail, the protection ,

l afforded by the cylinder high pressure shutoff system would be negated because the high l

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3 pressure instrumentatior would be unable to measure the UF. cylinder pressure. The low j

cylinder pressure shutoff system's sole function is to ensure line clarity oy measuring for an expected pressure after a given time period (USEC is proposing a pressure of greater than 15 psia after a nominal hour--less than or equal to 65 minutes). This is performed early in tne heating evolution to ensure the availability of the pressure instrumentation well below the maximum allowable working pressure of the UF. cylinder (100 to 200 psig depending on the cylinder type).

Use of " Allowable Values" in lieu of setooints in the proposed amendment, PORTS has modified the surveillance requirements to change the action setting from a setpoint to an " Allowable Value," consistent with ANSI /ISA-S67.04 Part l-1994, "Setpoints for Nuclear Safety Related instrumentation," and ISA-RP67.04 Part ll-1994,

" Methodologies for the Determination of Setpoints for Nuclear Safety Related Instrumentation."

As defined in the ANSI standard, the allowable value is a limiting value that the trip setpoint may have when tested periodically, beyond which appropriate action shall be taken. By establishing an allowablo value, the trip setpoint can be established to account for instrument drift and uncertainty. For example, if the instrument drift and uncertainty amounts to 3.1 psi, then the low cylinder pressure shutoff system setpoint would be 18.1 psia. The trip setpoint becomes a procedurally controlled value. This is an acceptable application of this setpoint methodology.

The staff notes that the references in the proposed TSR Basis wording appear to be incomplete. It is suggested that the references be verified, and the TSR Basis wording be changed, accordingly.

l Revision of low oressure value from a setooint of 20 osia to an allowable value of 15 osia The trip setpoint is not only established to ensure that an instrument channel trip signal will occur to satisfy the safety function, it is also set to minimize spurious trips close to the normal operating point of the process. For the low cylinder pressure shutoff, the allowable value is set to provide a definitive means of assurance of suitable line clarity between the cylinder and the pressure instrumentation. The value is reduced from 20 psia to 15 psia to minimize challenges to the low cylinder pressure shutoff safety system actuation during the heating evolution without compromising functionality of the low cylinder pressure shutoff system. The triple point of UF.

is 22 psia at 147.3 F. During the heating evolution, there is a time period encorapassing a nominal hour in which the solid liquefies and sublimes at the triple point with a nominal pressure increase. A graph displaying the cylinder heatup profile is attached With the current setpoint at 20 psia and the uncertainty and drift associated with the instrumentation, the heating operation could be impacted because of the realized setpoint (actual setpoint plus instrument drift and uncertainty) being too close to the expected UF pressure profile at the nominal hour.

The heatup is a monitored evolution with an expected heating profile. As stated in Section 3.2.1.1.1 of the SAR, the cylinder low pressure cutoff system serves as a backup to the operator. The low pressure cutoff system willisolate the steam supply if the operator fails to manually stop the heating evolution earlier in anticipation that the required allowable value will not be reached in the allowable timeframe.

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4 By lowering the low pressure allowable value to 15 psia (the trip setpoint will be procedurally controlled to incorporate instrument uncertainty and drift), the operability of the heatup evolution is improved by effectively lowering the low cylinder pressure shutoff setpoint well below the expected pressure range occurring during the phase of latant heat of liquefaction. This change will not impact the safety function of the control system. As the cylinder is heated, there is a direct increase in pressure as sublimation of the solid occurs. The new allowable value of 15 psia represents a minimum change of 5 psia over the initial pressure of the cylinder (administratively controlled to less than or equal to 10 psia prior to heating). This change in pressure is sufficient in magnitude to demonstrate line clarity and operability of the pressure instrumentation. Both the quarterly and the semiannually surveillance requirements will ensure the functionality of the instrumentation to this revised allowable value of 15 psia.

Revision of a nominal hour to an allowable value of less than or eaual to 65 minutes The revision from "after the first hour of heating" to an allowable value of less than or equal to 65 minutes improves operability by providing a more explicit time reference for conducting the surveillance requirements during the heating evolution and by accommodating channel '

response time.

The change in providing a numericallimit will not negate the effectiveness of the low pressure cutoff system. After review of the UF heatup profile, the staff concludes that the five minute difference of the proposed change has negligible effect on functionality because the pressure profile is still encompassed by the latent heat of liquefaction phase which is well below the maximum allowable working pressure of the UF, cylinder.

Occuoational Radiation Exoosure The staff has not identified any significant credible occupational rauiation exposures that may result from proposed TSR 2.1.3.9 and SAR changes.

Criticality The staff has not identified any credible criticality accidents that may result from proposed TSR 2.1.3.9 and SAR changes.

Safeauards and Security The staff has not identified any safeguards or security related implications from the proposed amendment.

ENVIRONMENTAL REVIEW lssuance of the requested amendment to the Portsmouth Certificate of Compliance (GDP-2), to amend TSR 2.1.3.9, is subject to the categorical exclusion provided in 10 CFR 51.22(c)(19) and will not have a significant impact on the human environment. Therefore, in accordance with 10 CFR 51.22(b), neither an environmental assessment nor an environmental impact statement is required for the proposed action.

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CONCLUSION USEC's proposed changes to TSR Section 2.1.3.9, Low Cylinder Pressure Shutoff, Surveillance Requirements would tend to challenge the low cylinder pressure safety system actuation to a lesser degree with negligible impact to safety. By changing from a setpoint value of 20 psia to an allowable value of 15 psia, USEC has accommodated instrument uncertainty and changed the setpoint from being too close to the expected pressure around the triple point. The revised limit still provides a sufficient increase in measured pressure to assure functionality of the low cylinder pressure shutoff system. In addition, USEC provided a definitive timeframe to replace the phrase "after a nominal hour." An allowable value of less than or equal to 65 minutes is still within the latent heat of liquefaction phase. Based on the information provided in this CER, the NRC staff recommends approval of this amendment.

Region 111 staff has no objection to this proposed action.

Attachments:

1. Figure 1 Diagram of a TypicM Feed and Sample Autoclave

2. Figure 2 Typical Cylinder Hea;up - Pressure vs. Time Princioal Contributor Stephen Koenick l

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Figure 1 Diagram of a Typical Feetl an<l Sample Autoclave

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CONCLLJSION ,

USEC's proposed changes to TSR Section 2.1.3.9, Low Cylinder Pressure Shutoff, Surveillance Requirements would tend to challenge the low cylinder pressure safety system actuation to a lesser degree with negligible impact to safety. By changing from a setpoint value of 20 psia to an allowable vaiue of 15 psia, USEC has accommodated instrument uncertainty and changed the setpoint fre,m being too close to the expected pressure around the triple point, The revised limit still prov.' des a sufficient increase in measured pressure to assure functionality of the low cylinder pressure shutoff system. In addition, USEC provided a definitive timeframe to replace the phrase "after a nominal hour." An allowable value of less than or equal to 65 minutes is still within the latent heat of liquefaction phase. Based on the information provided in this CER, the I NRC staff recommends approval of this amendment. )

Region ill staff has no objection to this proposed action. l Attachments:

1. Figure 1 Diagram of a Typical Feed and Sample Autoclave

2. Figure 2 Typical Cylinder Heatup - Pressure vs. Time Princioal Contributor Stephen Koenick DISTRIBUTION Docket 70 7002 NRC FILE CENTER PUBLIC NMSS r# NMSS Dir. Off. r/t FCSS r/f SPD r4 KVBnen, Rlll CCox WScttwmk, FCOB PHiland. Rlli DHartland. Riti

• See previous concurrence OFC *SPB *SP9 *SPS C SPB SP h NAME SKoeruck 4 DHoadley YFarar ay F prson DATE 10/ /98 10/8 /98 10/7/98 h /98 hb C = COVER E = COVER & ENCLOSURE N e NO COPY '

G WMD5268C POR OFFICIAL RECORD COPY l

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', nIgligibla impict to s fsty. By changing from a satpoint valus of 20 psia to an allowable value of 15 psia, USEC has accommodated instrument uncertainty and changed the setpoint from being too close to the expected pressure around the triple point. The revised limit still provides a requir 50% increase in measured pressure to assure functionality of the control system. In addition, EC provided a definitive timeframe to replace after a nominal hour. An allowable value of less an 65 minutes is still within the latent heat of liquefaction phase. Based on the information pro ed in this CER, the NRC staff recommends approval of this amendment.  :

Region 111 staff ha o objection to this proposed action. I Attachments:

1. Figure 1 Diagram of a Typi Feed and Sample Autoclave l

2. Figure 2 Typical Cylinder Heat - Pressure vs. Time '

Princioal Contributor Stephen Koenick l

OtSTRIBUTION Docket 70 7002 NRC FILE CENTER PUBLIC NMSS rn NMSS Dir OR r# FCSSrM SPO r# K'00ren, Rill CCox WSchunk, FCOB PHiland. Rill DHartland, Rlil

• Sen premous concurrence OFC 'SPO SPEI ) *SPB C SP8 SPO NAME SKoenick it arfiey YFaraf MGa!Ioway RCherson DATE 10/1/98 / /98 10/ 7/98 / /98 / /98 C e COVER E e COVtR & ENCLOSURE N = NO COPY G %MOS266C POR OFFICIAL RECORO COPY

5

+.

n:g gibl3 imp ct to safsty. By ch:nging from a sttpoint valus of 20 psia to an allow bla valus USEC has accommodated instrument uncertainty and changed the setpoint from of being 15toop'sia(lose c to the expected pressure around the triple point. The rev a required 50%iqcrease in measured pressure to assure functionality of the control system. In addition, USEC provided a definitive timeframe to replace after a nominal hour. An allowable value of less than 65}hiqutes is still within the latent heat of liquefaction phase. Based on the information provided in thEd'CER, the NRC staff recommends approval of this amendment.

Region 111 staff have no objectliertto this proposed action.

Attachments:

1. Figure 1 Diagram of a Typical Feed and S' ample Autoclave

2. Figure 2 Typical Cylinder Heatup - Pressure vs. Time Princioal Contributor Stephen Koenick j l

l 1

l DISTRIBUTION.

Docket 70 7002 NRC FILE CENTER PUBLIC NMSS r4 NMSS Dr. O#. r# FCSSrd SP8r4 K'08nen, Rlli CCox WSchwulk. FCOB PHiland, Rill OHartland, Rill l

• See prevous concurrence OFC SPB SPB SP8 b SP8 SPB \

NAME I Koenckij OHoodley YFaraz MGalloway RPierson DATE / 0 / 7 /98 i /98 lat Y 198 1 /98 i /98 C = COVER E = COVER & ENCLOSURE N = NO COPY G WMD6268C POR OFFICIAL RECORD COPY l

l l