ML20056H389

LAR for License DPR-53 Revising Heatup & Cooldown Curves & LTOP Controls for Unit 1

ML20056H389
Person / Time
Site:	Calvert Cliffs
Issue date:	09/03/1993
From:	Denton R BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20056H390	List: ML20056H389 ML20056H397
References
NUDOCS 9309090241
Download: ML20056H389 (9)

Text

--

l 1

_W c j BALTIMORE  ;

• GAS AND  ;

ELECTRIC ,  ;

! 1650 CALVERT CLEFS PARKWAY . LUSBY, MARYLAND 20657-4702

) l l ROBERT E. DENTON

Vict PREstotNT

{

s NUCLEAR ENERGY

{

! (eso) teo eass i

September 3,1993 j

, I

U.S. Nudear Regulatory Commission  ;

i Washington,DC 20555  ;

J ATTENTION: Document ControlDesk i

SUBJECT:

Calvert Cliffs Nuclear Power Plant l l . Unit No.1; Docket Nos. 50-317 License Amendment Request; Variable Iow Temperature Overpressure i

Pmtection -!

! - i' I

REFERENCES:

(a) Letter from Mr. V. R. Evans (BG&E) to Mr. D. K. Davis, dated July 21,1977, Reactor Coolant System Overpressurization (b) Letter from Mr. G. C. Creel (BG&E) to NRC Document Control  ;

Desk, dated August 13, 1990, Unit .1 Emergency Licensing l Amendment Request -Iow Temperature Overpressure Protection

! (c) Iotter from Mr. G. C. Creel (BG&E) to NRC Document Control -

! Desk, dated February 6,1992, Unit 1 Licensing Amendment Request l j - Iow Temperature Overpressure Protection .  ;

(d) CEN-152, " Combustion Engineering Emergency Procedure ,

Guidelines," Revision 3 Pursuant to 10 CFR 50.90, the Baltimore Gas and Electric Company hereby requests an Amendment to Operating License No. DPR-53 by incorporating the changes described below into the Technical j Specifications for Calvert Cliffs Unit No. l.

l l

l DESCRIPTION The proposed amendment would revise the heatup and cooldown curves and the low Temperature Overpressure Protection (LTOP) controls for Unit 1 to support modifications to the LTOP system that are scheduled for the spring 1994 refueling outage. This proposed amendment is plant specific to Calvert Cliffs. This proposed change and the scheduled modifications are necessary to increase operating flexibility.

9309090241 930903

.PDR P ADOCK 05000317 - % I ppg l wp paej;9; r o'

i k o l Document Control Desk September 3,1993 Page 2 HACKGROUND On July 22,1977, a plant-specific report on Reactor Coolant System (RCS) LTOP was submitted to the NRC (Reference a). That report detailed the administrative controls and hardware modifications which were necessary to protect the 10 CFR Part 50, Appendix G, Pressure-Temperature (P-T) limits from an LTOP event for reactor vessel irradiation up to 10 Effective Full Power Years (EFPY). In our letter dated August 13,1990 (Reference b), we described additional measures required to continue 10 CFR Part 50, Appendix G, P-T protection for 12 EFPY. In Reference e, we described changes to the administrative controls needed to provide LTOP for neutron fluences up to 3.25x1019 n/cm2s (E > l MeV), which corresponds to approximately 22 EFPY based on current core loading patterns.

This License Amendment Request describes the Inodifications being made to the LTOP system to provide continued low temperature overpressurization protection. The significant changes are:

1) the fluence used to determine the heatup and cooldown rates was reduced to 2.61x1019 n/cm2 (E > 1 MeV) in order to increase plant operating flexibility in the LTOP region. This fluence corresponds to the Pressurized Thermal Shock screening criteria defined in 10 CFR 50.61; 2) a digital Power-Operated Relief Valve (PORV) actuation system is used to provide a variable PORV trip setpoint during low temperature operation, while retainin he single PORV trip setpoint during shutdown cooling (SDC) operations.

The proposed heatup and couldown cunes and rates are based on fluence with no reference to the I corresponding EFPY. As stated in Reference (c), the vessel embrittlement calculations are actually j based on fluence and not EFPY. Therefore,it is more appropriate to base the heatup and cooldown curves on fluence.

l l He current LTOP system utilizes two pressurizer PORVs. When the LTOP system is enabled, each

! of the two PORVs is set to open at a reduced pressure. The present configuration of the Minimum Pressure and Temperature (MPT) Enable temperature circuitry (with the single setpoint PORV),

combined with the reactor coolant pump (RCP) operating curves, gives a small operating window with a " knee" at the MPT Enable temperature. The MPT Enable temperature is the RCS temperature below which the LTOP controls are required to be in place to protect the Appendix G limits. Attachment (2) shows the current MPT Enable temperature and the RCP operating cunes.

In addition, the current LTOP system does not allow the use of one RCP in each coolant loop as recommended in CEN-152 (Reference d) for recovery from certain postulated accidents.

A variable-setpoint low temperature overpressure protection (VLTOP) system is being installed to i increase the allowable operating pressure band in the LTOP region and to increase our flexibility in the use of RCPs. The VLTOP system uses a variable PORV setpoint to take advantage ofincreased Appendix G pressure limits at increased RCS temperatures. The new system will allow operators to cooldown to SDC conditions while running one RCP in each loop. This system significantly increases l the operating window in the LTOP region.

The LTOP system will be modified in the spring 1994 refueling outage so that a programmable l microprocessor is used to determine the PORV trip setpoint. This modification has been resiewed under the controls provided in 10 CFR S0.59, and it has been determined that it does not involve an unreviewed safety question. He equipment necessary to implement the VLTOP system will meet or exceed the hardware requirements of the existing LTOP equipment. He microprocessor that will be used for the control system has been purchased as Class 1E and will be classified in the Q-List as Augmented Quality-PORV to be consistent with the current classifications of the LTOP system.

i 4 ,

Document Control Desk September 3,1993 Page3 i

Issues such as verification and validation of the program software and the effects of eledromagnetic interference were evaluated to provide reasonable assurance that the new equipment would not result in a common-mode failure.

The temperature input for the system is taken from the RCS cold leg. The system continually monitors the coldest RCS temperature during forced and natural circulation. However, due to the plant configuration, these temperature sensors are not in the flow stream during SDC operation.

The SDC water enters the RCS through the safety injection nozzles downstream of the cold leg temperature sensors. Therefore, the cold leg temperature sensors may not reflect the reactor vessel temperature when on SDC. To account for this, the VLTOP system maintains an extra single pressure setpoint that is independent of RCS temperature. The single setpoint is equal to the lowest variable setpoint to conservatively protect the Appendix G limits at all temperatures when on SDC.

The single setpoint is manually selected from the PORV handswitch when the operators aliga the SDC System and is maintained until forced circulation is re-established. Both the variable and single setpoint are manually activated via handswitch position in the Control Room. The manual action to enable the variable LTOP system remains the same as the current LTOP system.

REOUESTED CIIANGE Change the Unit 1 Technical Specifications as shown on the marked-up pages attached to this transmittal. These changes to the Technical Specifications include the following items:

1. IIcatup and Cooldown Curves and Rates

a. Change Technical Specification Limiting Condition for Operation (LCO) 3.4.9.1.a, maximum allowable heatup rates, as follows:

Maximum Allowable Heatun Rates RCS Temperature FROM Fin any one hour period 70 to 164 F 30, Fin any one hour period >164{F to 328,F

, 40, 10 Fin any one hour period >328,F10,355 F l

60, Fin any one hour period >355 F TO t

30* Fin any one hour period 70 F to 164

• 40, Fin any one hour period >164 F10,256{F

, 60 Fin any one hour period >256 F l

I i

i i

1 i .

Document Control Desk September 3,1993 Page 4 i

b. Change Technical Specification LCO 3.4.9.1.b, maximum allowable cooldown rates, as follows:

i Maximum Allowable Cooldown Rates RCS Temperatures 4

FROM 100 Fin any one hour period y 254*F 20, Fin any one hour period 254 Fto {84,F 10 Fin any one hour period < 184 F TO 100 Fin any one hour period y 270 F 20, Fin any one hour period 270 F to {84,F 10 Fin any one hour period < 184 F 4

i

c. Replace Technical Specification Figures 3.4.9-1 and 3.4.9-2, RCS P-T Limits, with a new figures. The revised curves and rates are based on the lower fluence value of 2.61 x 1019 n/cm2 (E >1 MeV). 'Ihis change in the fluence value makes it necessary to revise the Adjusted Reference Temperatures (ART) for 1/4 T position and 3/4 T position ip the Bases Accordingly, the ART for 1/4 T position has been changed from 253.7 F,to 241.4,F, and the ART for 3/4 T position has been changed from 193.8 F to 181.0 F.

2. LTOP Controls

a. Change Technical Specifications 3.4.93.a.1 and 2 from "s 429 psia" to 'below the l curve in Figure 3.4.9-3*" to account for the variable LTOP system that will be installed. The footnote, "When on shutdown cooling, the PORV trin :etpoint shall be s 429 psia," has been added to account for SDC operation.

b. The MPT Enable temperature has been changed from 355*F to 365 F. The Technical Specifications effected by this change are 3.1.2.1, 3.1.23, Table 33-3, >

3.4.1.2,3.4.13,3.4.93,4.5.2,3.53, Bases 3/4.4.1, Bases 3/a.4.9, and Bases 3/4.5.2.

c. Due to the higher MPT Enable temperature, the transition region at which the high pressure safety injection (HPSI) pumps are placed under manual control on cool 355,down F-375 and F, to restoreq 365 F - 385to automatic status F. This affects on heatup Technical has been3.53 Specification changed and from Table 33-3. <

d. The allowable HPSI pump flow rate has been changed from "less than or equal to l 200 gpm" to "less than or equal to 210 gpm" when used to add mass to the RCS. This j affects Technical Specification 3.4.93, Bases 3/4.4.9, and Bases 3/4.5.2.

l I

l l

l

• . j i Document Control Desk September 3,1993 Page 5 i

l 3. Technical Specification Hases l Revise the Technical Specification Bases 3/4.4.1, Coolant loops and Coolant Circulation, and Bases 3/4.4.9, Pressurefremperature Limits, and Bases 3/4.5.2, ECCS Subsystem, to be consistent with the above changes and to clarify some of the existing material.

SAFETY ANAIXSIS ne LTOP system, including the administrative controls, ensures that the Appendix G P-T limits for

. the reactor pressure vessel will not be violated while operating at low temperatures. The heatup and cooldown curves are conservatively developed in accordance with the fracture toughness requirements of 10 CFR Part 50, Appendix G, as supplemented by the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section III, Appendix G. The reactor vessel material Adjusted RTmyrvalues are based on the conservative methodology provided in Regulatory Guide 1.99, Revision 2.

The proposed change to the Technical Specifications will revise the existing heatup and cooldown curves and rates. The fluence was decreased from 3.25x1019 n/cm2(E > 1 MeV) to 2.61x1019 n/cm2 (E > 1 MeV) in order to increase plant operating flexibility in the LTOP region. The fluence of 2.61x1019 n/cm2 (E > 1 MeV) corresponds to the Pressurized Thermal Shock screening criteria defined in 10 CFR 50.61 for weld 2-203, A,B,C.

1 The proppsed change to the Technical Specifications will increase the MPT Enable temperature from 355 F to 365 F. De new MPT Enable temperature is determined using the guidance in 4

Standard Review Plan 5/(,2. He temperature is based on a fluence of 2,61x1019 n/cm2 (g > 1 gey) and a heatup rate of 60 F/hr. The current LTOP system used a 10 F/hr soak during heatup to decrease the MPT Enable temperature. This is no longer needed because increasing the MPT  ;

Enable temperature .mes not adversely impact Ge LTOP operating window with the new system.  ;

Due to the higher MPT Enable temperature, the range of temperatures where the HPSI pumps are l placed on manual cont The old range wasF 355 to 375{ol F, on andathe cpoldown new range and is 365returned F to 385 F.toHeautpmatic stajus on a heatup new range maintains the current temperature span of 20 F for performing the required actions. Analyses have shown that there is sufficient time (> 10 minutes) for an operator to manually start a HPSI pump and pregent core damage during a Ioss-of-Coolant-Accident when the RCS temperature is less than 400 F. i ne selection of the proposed heatup and cooldown curves and rates and the use of variable setpoint for the PORV ensures that the Appendix G P-T limits will not be violated when operating at low l temperatures. His will also increase the operating window in which the plant may operate during heatup and cooldown. To conservatively protect the Appendix G limits at all temperatures when on SDC, the VLTOP system will maintain an extra single setpoint that is independent of RCS temperature and is equal to the lowest variable setpoint. j i

I The proposed change will increase the throttled HPSI flow rate frora 200 gpm to 210 gpm when the LTOP controls are required to be in place. He limiting Appendix G pressures are increased due to the lower reactor vessel embrittlement allowed under the new P-T limits. His increases the allowable pressure during PORV liquid discharge, which in turn increases the allowable HPSI flow rate during a design basis mass-addition event.

l l

I l

i Document Control Desk September 3,1993 Page 6 Additional analyses were conducted to ensure the LTOP administrative controls protect the  !

Appendix G P-T limits for all anticipated initial conditions in MPT Enable. The RCS pressure response was modeled using, where required, RELAPS/ MOD 3. 'Ihis program was chosen over the previous use of hand calculations and RETRAN in order to more realistically model the integrated system response, including the interaction between the RCS and the pressurizer. Also, RELAP was i

able to model complex phenomena, such as primary-to-secondary and secondary-to.primasy heat transfer, for the wider range of L-itial conditions including conditions initiated while on SDC. In j addition, RELAP allowed use of a multi-node pressurizer to more accurately model the temperature stratifications during the insurge. As with the previous analysis, the PORV flow using RELAP was benchmarked against data from the Electric Power Research Institute PORV qualification tests.

DETERMINATION OF SIGNIFICANT IIAZARDS  ;

The proposed change has been evaluated against the standards in 10 CFR 50.92 and has been determined to not involvc a significant hazards consideration, in that operation of the facility in accordance with the proposed amendments:

1. Would not involve a significant increase in the probability or consequences of an accident previously evaluated.

The Low Temperature Overpressure Protection (LTOP) system, including the administrative l

controls, ensures that the 10 CFR Part 50, Appendix G, Pressure-Temperature (P-T) limits for the reactor pressure vessel will not be violated while operating at low temperatures. The heatup and cooldown curves are conservatively developed in accordance with the fracture toughness requirements of 10 CFR Part 50, Appendix G, as supplemented by the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section III, Appendix G. The reactor vessel material Adjusted RTNDT values are based on the conservative methodology provided in Regulatory Guide 1.99, Resision 2.

Analyses show that the proposed use of a variable LTOP system will not result in a significant increase in the probability of an inadvertent opening of a Power-Operated Relief Valve (PORV) causing a small break Loss-of-Coolant-Accident. The proposed heatup and cooldown curves and associated limits continue to provide conservative restrictions on Reactor Coolant System (RCS) pressure to minimize material stresses in the RCS due to  ;

normal operating transients, thus minimizing the likelihood of a rapidly propagating fracture due to pressure transients at low temperatures. Because the proposed heatup and cooldown curves and rates are based on conservative Appendix G methods, and because the LTOP controls protect the Appendix G P-T limits, the proposed curves and limits do not involve an increase in the probability of accidents previously evaluated.

The proposed use of a variable PORV trip setpoint and the decrease in the allowable fluence at the reactor vessel wall results in the changes to the heatup and cooldown curves and rates, the Minimum Pressure and Temperature (MPT) Enable temperature, high-pressure safety  !

injection (HPSI) pump flow limit, and HPSI pump manual control transition temperature. ,

These proposed changes continue to provide sufficient margin to accommodate postulated j pressurization from mass and energy addition transients. Calculations have been performed i' that prt dict the response to such transients. Because the results of the analyses remain well l within the conservative acceptance limits of Appendix G, these changes do not increase the ,

consequences of accidents previously evaluated. I i

Document Control Desk September 3,1993 Page 7 Herefore, the proposed changes do not imolve a significant increase in the probability or ,

consequences of an accident presiously evaluated.

2. Would not create the possibility of a new or differer;t type of accident from any accident previously evaluated.

The new variable LTOP control system along with the proposed changes to the Technical Specifications will ensure that the Appendix G P-T limits will not be violated during low temperature operations. While setpoints and curves have changed, this proposed change does rsot introduce any operator actions that are significantly difTerent from current operator actions used at the plant. The variable LTOP system will continue to have redundant channels to ensure that no single equipment failure or operator error will result in violation of the P-T limits. The use of a variable LTOP system does not create a new failure

-cA=; m for the PORV. The failure mechanism for the PORV continues to be an '

inadvertent opening or the failure to open during a pressure transient which has been previously evaluated. Herefore, the proposed change does not create the possibility of a new or different type of accident from any accident previously evaluated. t l

3. Would not involve a significant reduction in a margin of safety.

This change will ensure that the margin of safety is maintained with respect to energy or mass 1 addition events in that none of the events postulated could challenge the Appendix G limits.  !

He proposed use of a variable PORV trip setpoint and the decrease in the allowable fluence i at the reactor vessel wall necessitate the changes to the heatup and cooldown curves and rates. the MPT Enable temperature, HPSI pump flow limit, and HPSI pump manual control transition temperature. Rese changes ensure that the margin of safety is maintained by protecting the Appendix G limits for all postulated transients. Therefore, the proposed change does not imolve a significant reduction in a margin of safety.  ;

1 i

1 i

Document Control Desk September 3,1993 Page 8 FNVIRONMENTAL ASSESSMENT The proposed amendment would change requirements with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 or changes to an inspection or surveillance requirement. We have determined that the proposed amendment imolves no significant hazards consideration, and that operation with the proposed amendment would result in no significant change in the types or significant increases in the amounts of any effluents that may be released offsite, and in no significant increase in individual or cumulative occupational radiation exposure. Therefore, the proposed amendment is eligible for categorical exclusion as set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no emironmental impact statement or  ;

emironmental assessment is needed in connection with the approval of the proposed amendment.

SCilEDULE This change is requested to be approved and issued by March 1,1994. His schedule will allow for "

the implementation of both the hardware and the revised heatup and cooldown curves during the 1994 Unit 1 Refueling Outage. Due to the hardware modifications to the LTOP system, implementation of these Technical Specifications cannot occur until after the RCS is vented and the '

pressurizer manway is removed. This is currently scheduled to occur around February 20,1994.

However, issuance of this amendment is not currently identified as impacting outage completion or continued plant operation.

SAFIm' COMMITTEE REVIEW l These proposed changes to the Technical Specifications and our determination of significant hazards ,

have been reviewed by our Plant Operations and Safety Review Committee and Offsite Safety ,

Review Committee. They have concluded that implementing these changes will not result in an undue risk to the health and safety of the public. ,

l l

i

l 1

Document Control Desk l September 3,1993 Page9

?

l  :

Should you have any questions regarding this matter, we will be pleased to discuss them with you. l

%trulyyours, ,

3 ,

l STATE OF MARYLAND : I

TO WIT : I COUNTY OF CALVERT  : '

I hereby certify that on the day of 6/n , 993 before m , the subscriber, a Notary Public of the State of Maryland in'and for C4 ON v'  !

personally appeared Robert E. Denton, being duly sworn, and states that he is VicePresident of the j Baltimore Gas and Electric Company, a corporation of the State of Maryland; that he provides the -

foregoing response for the purposes therein set forth; that the statements made are true and correct to the best of his knowledge, information, and belief; and that he was authorized to proside the ,

response on behalf of said Corporation.

WITNESS my Hand and Notarial Scal:

Notary Public 1

I My Commission Expires:

Dat/

[ f .

t RED /DJM/djm/ dim Attachments: (1) Unit 1 Technical Specification Revised Pages (2) RCS Pressure / Temperature Operating Limits & RCP Operating Limits  ;

cc: D. A.Brune, Esquire J. E. Silberg, Esquire  !

R. A. Capra, NRC  !

D. G. Mcdonald, Jr., NRC l T. T. Martin, NRC .

P. R. Wilson, NRC  !

R.1. McLean, DNR J. H. Walter, PSC l-t

> - ,, , , - _. .. . . . . , . , , , < . . . , . . , . .