ML19305E718

Safety Evaluation Supporting Amend 33 to License DPR-61

ML19305E718
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Site:	Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png
Issue date:	04/24/1980
From:	Office of Nuclear Reactor Regulation
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ML19305E706	List: ML19305E705 ML19305E714 ML19305E718 ML19305E720
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NUDOCS 8005200306
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 33 TO FACILITY OPERATING LICENSE NO. DPR-61 CONNECTICUT YANKEE ATOMIC POWER COMPANY HADDAM NECK PLANT DOCKET NO. 50-213_

l.0 INTRODUCTION By letter dated January 3,1978, Connecticut Yankee Atomic Power Company (CYAPCO)* requested changes to the Technical Specifications for the Haddam Neck Plant. The proposed changes would estcblish requirements related to prevention of low temperature overpressurization events.

Supporting information was sutraitted by letters dated September 3, 1976, October 15, 1976, December 3,1976, March 1,1977, March 21, 1977, April 26,1977, June 1,1977, September 7,1977, November 30, 1977 and March 6,1978. The CYAPC0 submittals are in response to NRC requests related to the generic issue of PWR overpressure protection.

2,0 BACXGROUND Over the last few years, incidents identified as pressure transients.

have occurred in pressurized water reactors.

This term " pressure transients," as used in this report, refers to events during which the temperature pressure limits of the reactor vessel, as shown in the facility Technical Specifications, are exceeded.

All of these incidents cccurred at relatively low temperature (less than 200 degrees F) where the reactor vessel material toughness (resistance to brittle failure) is reduced.

The " Technical Report on Reactor Vessel Pressure Transients" in NUREG-0138 (Reference 17) summarizes the technical considerations relevant to this matter, discusses the safety concerns and existing safety margins of operating reactors, and describes the regulatory actions taken to resolve this issue by reducing the likelihood of future pressure transient events at operating reactors.

A brief discussion follows.

• also referred to as the licensee

. 2.1 Vessel Characteristics Reactor vessels are constructed of high quality steel made to rigid specifications, and fabricated and inspected in accordance with the time proven rules of the ASME Boiler and Pressure Vessel Code.

Steels used are particularly tough at reactor operating conditions.

However, since reactor vessel steels are less tough and could possibly fail in a brittle manner if subjected to high pressures at low temperatures, power reactors have always operated with restrictions on the pressure allowed during startup and shutdown operations.

At operating temperatures, the pressure allowed by Appendix G limits is in excess of the setpoint of currently installed pressurizer code safety valves.

However, most operatina PWRs were not originally designed to have pressure relief devices to prevent pressure transients during cold conditions from exceeding the Appendix G limit.

2,2 Regulatory Actions By letter dated August 11,19h., (Reo

1) the NRC requested that CYAPC0 begin efforts to design ana lant systems to mitigate the consequences of. pressure transien.

ow temperatures.

It was also requested that operating prt e examined and administrative changes be made to guard against - tiating overpressure events.

It was felt by the staff that proper a.ministrative controls were required to assure safe operation for the pacica of time prior to installation of the proposed overpressure mitigatiN hardware.

CYAPCO participated as a member of a 6

' whouse (W) user's group which was formed to support the analys:. # fort required to verify the adequacy of the proposed Overpressure Prcuection System.

Using input data provided by the members, T1 licensee's in the user's group.

W perfsrmed transient analysis (Reference 18) applicable to a CYAPC0 responded (Reference 2 and 3) with information describing their interim measures to prevent pressure transients.

Based on some " scoping" calculations done by Westinghouse for the user's group, the licensee presented (Reference 4) a discussion of the hardware modifications which were to be proposed pending after further analyses.

These hardware changes assumed the ability of the existing pressurizer power (air) operated relief valves (PORV), to mitigate all pressure transients.

By letters dated January 10 and February 14, 1977, we requested additional information.

By letter dated April 1,1977 (Reference 9), we requested CYAPC0 to ensure that the likelihood of an overpressure transient as a result of improper RCP operation was minimized.

'CYAPCO's April.26,1977 submittal (Reference 10 ) addressed the staff's concerns regarding RCP operation.

. After meetings, conference calls and detailed RCS pressure transient analyses, CYAPC0 rejected their initial intent to rely on the existing PORV's, and presented a report describing the preposed installation of new low pressure spring loaded safety valves (SLSV's) and associated motor operated isolation valves (MOV's) on the pressuri:er.

The finai Overpressure Protection System (OPS) report (Attachment 2 to Septemcer 7, 1977 submittal, Reference 19) indicated, however, that CYAPC0 had not analyzed the RCS pressure response resulting frem the single HPSI pumo mass input event.

This was not in accordance with the staff's criteria, discussed in Section 2.3 herein. Therefore, we requested (Reference 13) the licensee to provide an analysis of the event.

If the Appendix G maximum allowable pressure was predicted to be exceeded with the proposed OPS, CYAPCO was to propose system modifications meeting our design criteria, and to provide a value - impact assessment to make these modifications.

We visited the plant on November 17, 1977, observed the OPA components and controls being installed and discussed with the plant staff the administrative and procedural controls taken to preclude the HPSIP mass input transient.

Installation and testing of the nPA was completed prior to startup following the Fall 1977 refueling outace.

CYAPCO's November 30, 1977 and March 6,1978 submittals (Reference 14 and 16) provided an analysis of the HPSIP mass input event and the staff requested value-impact assessment. CYAPC0 proposed Technical Specifications in support of the Haddam Neck OPS in their January 3,1978 submittal (R2ference 15).

2.3 Design Criteria Through a series of meetings and correspondence with PWR vendors and licensees, the staff developed a set of criteria for an acceptable overpressure mitigating system.

The basic criterion is that the mitigating system will prevent reactor vessel pressures in excess of those allowed by Appendix G for the design basis events discussed in Sectica 2.4.

Specific criteria for system performance are:

D) Operator Action:

No credit can be taken for operator action for ten minutes after the operator is aware of a transient.

(2) Sincie Failure:

The systen must be designed to relieve the pressure transient given a single failure of an active component in addition to the failure that initiated the pressure transient.

(3) Testability:

The system must be testable on a periccic basis consistent with the system's employment.

(4) Seismic and IEEE 279 Criteria:

Ideally, the system should meet se!smic Cateogry I ano IEEE-279 criteria.

The basic objective is that the system should not be vuberable to a common failure that would both initiate a pressure transient and disaole the overpres-sure mitigating system.

Events such as loss of instrument air and loss of offsite power must be considerec,

. We also required in the design of the pressure mitigating system that the electrical, instrumentation, and control systens provide alarms to alert the operator to (1) properly enable the system at the appr)priate temperature during cooldowns and (2) indicate if a pressure transient is in progress.

In the initial letters to all PWR licensees (Reference 1) we also required the installation and use of pennanent RCS pressure and temperature recording devices.

2.4 Design Basis Events The incidents that have occurred to date have been the result of operator errors or equipment failures.

Two varieties of pressure transients can be identified:

a mass input type from charging pumps, safety injection pumps or safety injection accumulators; and a heat addition type, which causes thermal expansion, from sources such as steam generators, reactor coolant pumps, pressurizer heaters or decay heat.

On Westinghouse designed plants, the most common cause of the over-pressure transients to date has been isolation of the letdown path.

Letdown during low pressure operations is via a flowpath through the RHR system.

Thus, isolation of RHR can initiate a pressure transient if a charging pump is left running.* Although other transients occur with lower frequency, those which result in the most rapid pressure increases were identified by the staff for analyses.

The most limit; ing mass input transient identified by the staff is inadvertent injec-tion by the largest safety injection pump.

The most limiting thermal expansion transient is the start of a reactor coolant pump with a 50 degree F temperature difference between the water in the reactor vessel and the water in the steam generator (secondary).

• For example, one RCS pressure excursion was caused by the securing of the RHR pumps while the RCS was in a cold, shutdown and water-solid v

condition.

The RCP's were left operating (heat input of about 4.2 MW) and the core was generating about 13.6 MW of decay heat.

The los: of the low temperature heat removal capability, plus i

the possible partial icss of letdown, caused the pressurization.

i Based on the historical record of overpressure transients and the imposition of strict administrative controls, we conclude that the limiting events described above and in Section 4.0 form acceptable bases for the analysis of the OPS.

3.0 SYSTEM DESCRIPTI0fl Afl0 EVALUATION The Haddam Neck OPS consists of two spring loaded safety valves (SLSV) on new piping added to the pressurizer.

Each SLSV line includes two motor operated isolation valves (M0V) upstream of the SLSV.

Both SLSVs are set to open at 380 psig.

When all four MOVs are open, a pressure transient is terminated below the Appendi.<

G limit by opening of one or both SLSVS. During RCS cooldowns, the four MOVs are electrically opened, and to ensure proper OPS lineup, an enabling alarm annunciates (audible and visual) when RCS pressure is below 380 psig, temperature is below 340 F, and any of the four OPS MOV are closed.* To ensure the MOVs are not prematurely opened, the MOVs are electrically interlocked so that none can be opened unless RCS pressure is below 400 psig and RCS temperature is below 340'F. -To preclude erroneous MOV closure the CYAPCO removes all power from the MOV operators once the valves have been opened.

During RCS startup and heatups, power is manually reinstated to the MOVs and the four MOVs are shut when RCS tenperature is above 340 F.

Additional assurance that the MOVs are shut prior to system pressurization is provided by an alarm which annunciates whenever RCS tenperature is above 340 F and the MOVs are open.

l 3.1 Evaluation of Haddam Neck Using Design Basis Criteria Haddam Neck was evaluated under the guidance of the design basis criteria stated in Section 2.3 of this evaluation, and with specific attention given to various pertinent NRC staff positions resulting from these criteria. Sections 3.1.1 through 3.1.7 address conformance with the criteria.

3.1.1 Operator Action In each design basis transient analyzed, no credit for operator action was assumed until 10 minutes after the initiation of the RCS overpressurization transient and after the operator is made g

aware of the overpressure transient by the low temperature over-pressure transient alann.

Therefore, the system performance meets our design criteria with respect to operator action.

• This alann is supplemented by an "RCS pressure transient" alarm that annunciates when pressure is above 400 psig and temoerature below 340'F. These two alanns work in conjunction with administrative procedures in ensurin9 the CYAPC0 OPS is properly aligned.

a 6-3.1.2 Single Failure Criterion The Haddam Neck OPS is designed to protect the reactor vessel given a single failure in addition to the failure that initiated the overpressure transient. Redundant or diverse pressure protection channels are used to satisfy the single failure criterion.

3.1.3 Seismic Design and IEEE Std-279-1971 Criteria The design of the SLRV's and the associated instrumentation and control hardware which serve as the long-term mitigating system for low temperature RCS overpressurization are based on the existing applicable plant criteria and the following considerations:

(1) IEEE Std-279-1971 criteria have been implemented within the limitations of the original plant design and con-struction philosophy.

The control circuits for each valve train are independent of each other.

(2) The i sol ation MOV's and SLRV's were designed and manufactured in accordance with the AS?E Boiler and Pressure Vessel Code, Section !!! (1972 Ed ition).

Isolation MOV's are classified as Class 1 valves and the relief valves are classified as Cisss 2.

The subject valves were designed to be capaole of opera-ting during and after a seismic acceleration of 3.0 g in any direction.

Therefore, it is concluded that each valve assembly has been designed for Category I

]

seis.ic design conditions.

The electrical and control circuitry installation for the isolation M0V's are consistent with the require-ments of the original plant design philoso:hy.

We therefore conclude that the CYAPC0 Haddam Neck OPA satisfies our positions with respect to seismic design and IEEE Std-279-1971 criteria.

3.1.4 Alarm System CYAPC0 has added electrical and control provisions for the LTOP to be used during low RCS temperature conditions.

This system includes:

(1) A high pressure alarm to alert the operator of an impending overpressure transient, (2) An alarm associated with the plant cooldown process to ensure that the SLSVs will be operable in accordance with the Technical Specifications, (3) Indicttions to confirm the openina of the SLSV isolation valves at the main control board, and (4) An alam that will activate to alert the operator that SLSV isolation valves are in the "open" position to ensure system isolation once the RCS temperature exceeds 340'F.

8 e We have concluded that CYAPC0 has provided all necessary alanns and indications for reliable LTOPS operation.

We have also concluded that the added alarm features are of the audio / visual type, capable of providing the operator unambiguous information associated with the LTOPS operations. We, therefore, find the alarm system to be acceptable.

3.1.5 Pressure Transient Reportina and Recording Requirements Our position is that pressure-recording and temperature-recording instrumentation are required to provide a permanent record of the pressure transient. The response time of the pressure / temperature recorders shall be compatible with pressure transients that increase at a rate of approximately 100 psig per second.

CYAPC0 states (Reference 19) that appropriate instrumentation MJ recording equipment exists at the Haddam Neck Plant which will provide a continuous and permanent record over the full range of primary system pressure and temperature. The sensino and recording equipment will be in service during startup and shutdown operations as well as during long periods of cold shutdown operations.

We conclude that this implementation satisfies the NRC staff position.

l 3.1.6 Testability Our position on testability is that the system be tested prior to any reliance upon it for overpressure protection.

CYAPC0 has stated that the four OPS M0V's will be mechanically tested in accordance with the requirements specified in Section XI of the ASME Code, and will be eletrically tested by confirming proper motor and valve movement in response to an input signal (e.g., opening or closing).

A channel functional test associated with the MOV interlocks and controls will be conducted once per refueling shutdown. The SLSV's setpoint will also be verified each refueling outage by either a bench test, (removal of the SLSV for test a testing facility), or by an in-place test done by pressurizing the RCS up to the SLSV setpoint with alternate sets of M0V's open so that each SLSV can be checked. Testing req' vementa have been incorporated into the technical specifications as discussed in Section 5.2 herein, and are acceptable.

. 3.2 Apoendix G The Appendix G curve submitted by CYAPC0 for purposes of overpressure transient analysis is based on fourteen (14) year period of full power operation.

The licensee has utilized the zero degree heatup curve (isothermal curve), which is acceptable since most pressure transients have cccurred during isothermal metal conditions.

Margins of 60 psig and 10*F are included in the curves to account for possible instrument inaccuracies.

The Appendix G limit at 100*F according to the 14 EFPY isothermal curve is 590 psig.

The staff finds that the use of the isothermal,14 EFPY Appendix G curve is acceptable for OPS performance design.

3.3 RCS Transient Pressure Analyses RCS overpressure transient analyses were performed by Westinghouse for the members of the owner's group.

The one loop "ersion of the LOFTRAN code (Reference WCAP 7907) was used for the analysis of mass input type transients and the four loop version was used for the heat input transients.

Both versions required some changes to the input modeling and initialization.

LOFTRAN is currently under review by the staff and is judged to be an acceptable code for treating problems of this type.

The Westirghouse generic analyses (Reference 18) provided sensitivity studies that enabled PWR licensees to calculate the pressure overshoot (P

-P for both types of transients (mass and heat input) with a b iety bf) plant parameters.

The pressure overshoot is due to the 3

effects of PORV delay and stroke times.

CYAPC0 used the sensitivity studies to evaluate the OPS performance using their existing PORV and specific plant parameters (pump flowrate, system volume, PORV stroke time and S/G heat transfer area).

The CYAPC0 calculations (shown in Appendix A of Reference 19) demonstrated the inability of the existing PORV's to mitigate the design base events because of their relatively slow stroke time.

Therefore, the licensee designed and installed an OPS utilizing passive SLSV's.

.o.

Since the Westinghouse sensitivity studies were performed assuming the use of a PORV to relieve system pressure and since the time dependent flow characteristics of the PORV and SLSV differ,* the licensee could not use these studies directly to affirm OPS performance without making additional assumptions (see Section 3.3.1).

However, the portion of the RCS pressure transient prior to PORV opening is applicable to Haddam Neck, and the licensee and staff used this part of the analyses in verifying the,oroposed OPS performance.

Certain assumptions in the Westinghouse transient analysis are conservative relative to the actual Haddam Neck RCS and associated system parameters.

Some of these are listed below:

1.

The RCS was assumed to be rigid with respect to metal expansion.

2.

No credit was taken for the reduct'on in reactor coolant bulk modulus at RCS temperatures above 100 F (constant bulk modulus at all RCS temperatures).

3.

No credit was taken for the shrinkage effect caused by low temperature SI water added to higher temperature reactor coolant.

4.

The entire volume of water in the steam generator secondary was assumed available for heat transfer t3 the primary.

In reality, the fluid immediately adjacent and above the tube bundle would be the primary source of energy in the transient.

5.

The overall steam generator ' aat transfer coefficient was assumed to be the free convective heat transfer coefficient of the secondary side.

The forced convective heat transfer coefficient of the primary side, and the tube metal resistance have been ignored thus resulting in a conservative (high) coefficient.

6.

The RCP flowrate assumed in the heat input analysis was 95,000 gpm whereas the actual Haddam Neck RCP flow is about 62,000 gpm.

• The PORV and SLSV relief rates depend on upstream pressure and flow area.

Both the PORV and SLSV upstream pressures are pressurizer pressure.

The PORV flow area is independent cf upstream pressure once the setpoint has been reached, and depends only on the air operator's stroking characteristics whereas the SLSV flow area varies directly with upstream pressure until the value is fully open at 110% of PSET-

The staff agrees that these assumptions are conservative.

Another significant conservatism associated with the determination of the OPS performance is the assumption that only one SLSV is available for pressure relief.

Unlike the PORV, the SLSV is free of actuating circuits and pilot valves and is considered a passive device.

The upstream isolation valves are opened during plant cooldown and have their power removed, and are therefore also passive devices.

Verification of the licensee's proposed OPS is described below with respect to each of the limiting design base events.

3.3.1 Mass Input Case The mass addition from a single centrifugal charging pump (CCP) with a concurrent total loss of letdown and the RCS in a water-solid condition was identified by CYAPC0 as the most limiting mass input case requiring mitigation by a SLSV.* Based on this event, the licensee calculatea the required SLSV setpoint such that the Appendix G limits are not exceeded. We verified CYAPC0's calculations and performed independent checks.

Both CYAPC0's and our calculations are discussed below.

CVAPCO determined the CCP flow at discharge pressures below about 1300 psig by extrapolating tne head-flow curve ** (Figure 5 of Reference 19) then calculated the SLSV capacity using manufacturers data and assuming the valve to be fully open (Figure 6 of Reference 19).

From these curves, CYAPCO estimated that at a RCS pressure of 380 psig, the CCP flow into the system is about 860 gpm and the SLSV relieving rate is about 890 gpm, thus showing that the maximum RCS pressure during this event would be below 380 psig.

Since the Appendix G pressure limit at 100*F is about 590 psig, this calculation shows that if the SLSV satpoint is sufficiently below 590 psig, the SLSV will mitigate this ev ent. The SLSV setpoint was chosen to be 380 psig and CYAPC0 determined the overall SLSV flow performance curve. We note that using this curve, the peak RCS pressure for this event is about 418 psig.

• As discussec in Section.4.0, the licensee has not considered the HPSIP mass input event as one of the design base events used to determine the SLSV setpoint and OPS performance acceptability.

• • Extrapolation of CCP flow data will give a maximum but possibly unrealistic flowrate.

The pump flowrate is limited by the avail-aole NPSH and the motor overcurrent trips.

CYAPC0 estimates that CCP flow can't go above about 640 gpm due to the maximum available suction head.

. We examined the possible effects of liouid flashina by using data supplied by a SLSV manufacturer for a valve design similar to the Haddam Neck SLSV.* This data indicates that a flow reduction of about 60% could be experienced if 350'F liquid flashed in the SLSV throat.** Using this data, we estimated the relief rates from one and both SLSV's.

Based on these estimates and the extrapolated CCP head-flow curve, the peak RCS oressure is about 1220 psig with a single SLSV and about 625 psig with both SLSV's operating.

The maximum allowable pressure at a RCS temperature of 350*F is above 1220 psig, so we conclude that, for a mass addition event, flashing does not compromise the OPS performance.

As a further check, we used the Westinahouse sensitivity studies (Reference 18). Although these studies assume the operation of a PORY rather than a SLSV, the capacities of the reference PORV and SLSV are similar,*** and the opening characteristics of the SLSV are su p er ior. **** Therefore, if the predicted peak RCS pressure using the W studies is acceptable, then the peak pressure with the SLSV will also be acceptable.

Using actual or conse:vative plant snecific parameters, we calculated the peak RCS pressure to be about 445 osig which is below Appendix G limits at 100 F.

We conclude that the W sensitivity studies also support the proposed SLSV setoc7nt and perfomance, and therefore, based on the arguments and calculations presented above, the Haddam Neck OPS mitigates the design base mass addition event.

Cros:y, tne manufacturer of the RHR safety valve used by Kewaunee supplied this data to Wisconsin Public Service Company, who then submitted it to the staff in support of the Kewaunee overpressure protection system.

Since the pressurizer liquid '.emcerature is allowed to be as much as 200*F hotter than the RCS, i, is possible for the SLSV discharge to be hotter tnan 350*F.

However, the pressurizer is cooled down using spray flow which is at the RCS cold leg temperature.

Since the spray nozzle is at the top of the pressurizer, which is where the SLSV penetrates the pressurizer, the staff considers 350 F a sufficiently conservative zemperature for estimating flashing effects.

• • • Comparing the SLSV flow perfomance curve to Figure 2.2.1 of Reference 18, the PORV flow is about 50 gpm qreater than the SLSV flow at 380 psig.

• • • • CYAPC0 states that the SLSV " cons" open in less than 500 msec.

a 12 -

3.3.2 Heat Input Case Inadvertent startup of a single reactor coolant pump (RCP) in an idle, water-solid RCS with a primary to secondary temperature difference (across the steam generator tubes) of 50*F was identified by CYAPC0 as the most limiting heat input case.

The SLSV setpoint and performance were substantiated by noting that the PORV and SLSV have similar capacities and in all W heat input analyses (Reference 18) the PORV was shown to have sufficient capacity even though overshoots were experienced due to PORV delay and stroke times.

Since the SLSV's stroke time is much less than the PORV's and there is virtually no delay time, the licensee concluded that the performance of the SLSV was acceptable.

We used the Westinghouse predictions of RCS pressure response before PORV operation to determine the SLSV capacity requirements for the limiting heat input event.

The determination was made by coupling two calculations:

1.

Using the Westinghouse predictions of the RCS pressure response for various mass input rates into a water-solid RCS of volume similar to Haddam Neck, we determined the relationship 1

between mass input rate (gpm) and the rate of RCS pressure rise (psi /r-c).

2.

Using the Westinghouse predictions of the RCS pressure response due to the startup of a reactor coolant pump (RCP) in an idle water-solid RCS of volume similar to Haddam Neck's and with an RCS/SG AT of 50*F, we detennined the relationship between initial RCS temperature ( F) and the rate of RCS pressure rise (psi /sec).

Once these relationships were determined, the RCS expansion rate versus initial RCS temperature, (for a constant RCS/SG aT), during the RCP startup transient was calculated, to determine the necessary SLSV relieving capacity.

Using Figures MIS, Hll and H12" of the Westinghouse analyses (Reference

18) the relationships described above were determined.

3

• ThesefiguresassumeaRCSvolumgof6000ft rather them the Haddam l

Neck RCS volume of about 8400 ft.

Other curves in the W study show the pressuri:ation rate to decrease markedly with larger RCS volumes.

l t

. Based on these relationships, and the SLSV relieving characteristics, the following table sunrnarizes the staff calculations:

Pressuriza-Initial Allowable tion Expansion PEAK PRESSURE (psig)

Temp Pressure Rate Rate 1 SLSV 1 SLSV 2 SLSV's (oF)

(psig)

(psi /sec)

(gpm)

(no flashing) (flashing)

(flashing 100 590 33 240 382 408 390 140 680 52 380 387 425 400 180 810 76 570 400 940 415 250 1350 115 860 417 1700 550 Based on the arguments and calculations presented above, the staff concludes that the SLSV's and their associated setpoints provide sufficient relieving capacity to mitigate desian base heat input events.

4.0 HPSIP MASS INPUT EVENT As noted ir. Section 2.4, the most limiting mas input transient is the inadvertent injection by the largest safety injection pump.

The largest safety injection pump at Haddam Neck is the high pressure safety injection pump ('IPSIP) which has a flowate above 2100 gpm at a discharge pressure of 500 psig (from Figure 4, Reference 19). This is more than double the maximum flowrate of the HPSIP in other plants designed by Westinghouse.* Que to the very large relieving capacity necessary to mitiaate the Haddam Neck HPSIP mass input event, and other plant specific considerations described and evaluated below, CYAPC0 has designed the OPA to mitigate all credible mass and heat inputs with the exception of the HPSIP mass input.

Since the proposed desian did not mitigate the most limiting mass transient we requested CYAPC0 to propose modifications that would mitigate the event and provide a value-impact assessment based on the installation j

of this modification.

j

• From Fiqure 2.3.3 of Reference 18, other HPSIP's in W designed plants (with the exception of Yankee-Rowe and San Onofre) have flowrates ranging from 500 to 900 gpm at 500 psig.

. In response to our request, CYAPC0 determined the likelihood of the HPSIP mass addition event by considering the various operator errors and/or equipment malfunctions which must take place for the event to occur.

The expected peak RCS pressure was also calculated based on the existing OPS (two newly installed SLSV's) and revised calculations of the RCS, ECCS and OPS piping frictional losses.

CYAPCO then examined the various equipment changes which, together with the newly installed OPS, would totally mitigate the HPSIP mass addition event.

From those various equipment changes, the most viable was selected and its cost and installation schedule were estimated.

From this information the licensee concluded that the protection afforded by the most viable equipment fix did not warrant the cost and impact on plant operations. CYAPCO's assessments and our evaluations are described below.

4.1 RCS Pressure Transient Analysis CYAPC0 calculated the peak RCS pressure that would be experienced during the HPSIP mass addition transient and presented the results in their Reference 16 submittal.

These calculations included the effects of piping frictional losses and therefore more ~1alistically represent the mass addition rate than the calculations assumed in Section 3.4.1.

The following table presents CYAPCO's calculations alona with the maximum allowable RCS pressure permitted by the 14 EFPY Appendix G Isothermal curve and 10 EFPY Appendix G Hydrostatic Test curve.

Peak RCS Pressure Max. Allowable Pressure Backoressure 1 SLSV 2 SLSV Isothermal Hydro Test 10 psig 930 psig 575 psig 590 psig 1000 psig 100 psig 955 psig 625 psig 590 psig 1000 psig We note that the possible effects of flashing were accounted for by assuming a backpressure of 100 psig.

Further, we note that if both SLSV's are assumed to operate, which is reasonable since they are passive components, the RCS peak pressure exceeds the Isothermal Appendix G curve by 35 psig and is significantly below the maximum pressure permitted by the Hydrostatic test curve.

4.2 System Modifications To Fully Mitiaate the HPSIP Event CYAPCO has reviewed the possible system additions / alternations which in addition to the newly installed OPS, would totally mitigate the HPSIP mass addition event.

Eacn is described along with our assessment.

a 15 -

a.

Increasing the Capacity of the Existing OPS This modification could be accomplished by the replacement of the newly installed two inch (00) pipes, MOV's and SLSV's with larger pipes, MOV's, and SLSV's.

b.

Installation of Relief Devices in the ECCS Piping Between the riPSIP and the RCS A system composed of safety valves or PORV's could be added to the ECCS piping such that the RCS pressure would bc limited by relieving HPSIP pressure.

This modification would have to be accompanied by control circuitry or isolation valves which i

insured that the relief devices would not operate when the HPSIP's are required during a LOCA.

CYAPC0 rejected this alternative since it could affect the ECCS performance and since it would require a more extensive design, procurement and installation effort (and cost) than the modification described in item (e) below.

We agree with this conclusion, and also note that this change would have to be accompanied by an ECCS failure modes and effects analyses (FMEA) which ceuld require a re-analysis of the Haddam Neck ECCS/LOCA performance.

c.

HPSIP Control Circuits CYAPC0 evaluated the viability of ECCS modifications that would either limit HPSIP flow or trip the HPSIP in the event of an inadvertent injection.

CYAPCO concluded that the hardware changes, control circuitry and extra administ ative measures to accompany these changes were such that the ECCS performance could be degraded.

We reviewed this alternative and thatthismodificationwouldalsorequireanexkoncludedensive tCCS FMEA since the control systems for LOCA mitigation could be compromised.

d.

RHR System Modifications Some PWR licensees are utilizing the RHR system code safety valves for either a part of or as the total OPS.

In Reference 19, CYAPCO discusses their evaluation of this alternative.

The RHR safety valve setpoint would have to be lowered from the present 500 psig to about-380 psig.

However, due to the RHR system configuration and pressure limitations, this adjustment in setpoint would compromise the RHR system's ability to provide

, continuous core cooling below 300"F. The staff and CYAPC0 agree that the RHR system does not present a viable alternative for mitigation of the HPSIP mass addition event.

e.

Additional Pressurizer SLSV The installation of another relief piping train, (2 MOV's and SLSV) similar to the ones recently installed would provide enough relieving capacity so that the HPSIP mass addition event would be completely mitigated, (by the operation of all three SLSV's).

Tne two inch (CD) pipe would tie into the three inch (00) lateral between the pressurizer and the high pressure code safety valves.

The new SLSV discharge would be connected to the ten inch (00) discharge pipe as near as possible to the pressurizer relief tank.

This addition would provide a redundant and independent relief path which does not compromise the design functions of the ECCS or RHR systems.

CYAPC0 has estimated that the total installation cost of the additional relief train and associated control circuitry would be abwt $675,000. This figure does not include any estimate of the cost of replacement power.

We find the factors described below pertinent in our evaluation of CYAPCO's request that this event need not be considered when detemining the needed relief capacity.

1.

If a HPSIP mass addition event were to occur at a RCS temperature of 100*F, the Appendix G curve (isothermal) would be exceeded by, at most, 35 psig (100 psig back pressure and both SLSV's).

The staff notes that there is a 60 psig and 10*F instrument error included for conservatitra in the calculation of the Appendix G isothermal curve.

Also, if the RCS temperature is above about 120*F, the Appendix G limit increases such that these is no violation during the HPSIP mass a 9ition event.

The amount of time spent between 120*F and 100 F is normally quite small (based on staff conversations with other licensees).

2.

If the HPSIP mass addition event were to occur at a RCS tempera-ture below 120*F, the Appendix G isothermal curve (14 EFPY) would be exceeded.

However, the hycrostatic test curve would not be exceeded and the peak RCS pressure would be at least 330 osig below the hydrostatic test curve. We are not allowing OPS design uased on the Appendix G hydrostatic test curve, but we note that the RCS is allowed to be pressurized once per year up

to these limits during a slow and controlled test.

The HPSIP mass addition event is certainly not a " slow and controlled" test, nevertheless, we note that the peak pressure of a j

relatively improbable event is significantly below the allowable pressure of a relatively frequent test.

3.

Since the present pressure setpoint of the RHR code safety valve is 500 psig, if the RHR and RCS systems are connected, it is probable that the actuation of this valve would reduce the peak RCS pressure during the HPSIP mass addition event to about 600 I

psig.

4.

The most viable addition to the newly installed OPS which would result in an OPS that totally mitigates the HPSIP mass addition event would cost an estimated $675,000 and would not add appre-ciably to the plant safety.

We note also that CYAPC0 -

states they.have already spent in excess of $1,000,000 on the newly installed OPS.

4.3 Conclusion Regarding HPSIP Mass Addition CYAPCO's administrative controls significantly lower the likelihood of a HPSIP mass addition event.

However, even if the event occurred, the peak RCS pressure would not exceed the staff's OPA design limits (Isothermal Appendix G curve) by more than 35 psig and would not exceed the Appendix G hydrostatic test curve.

In addition, the instrumentation conservatisms associated with the Isothemal curve are such that the real isothermal curve would not likely be exceed. Based on these arguments and the factors discussed in 4.2 above, we conclude that HPSIP mass addition event can be omitted from consideration as an OPS design basis transient.

5.0 ADMINISTRATIVE CONTROLS To supplement the hardware modifications and to limit the magnitude of postulated pressure transients to within the bounds of the analyses provided by CYAPCO, a defense in depth aoproach is adopted using procedural and administrative controls.

Those specific conditions required to assure that the plant is operated within the bounds of the analysis are included in the Technical Specifications.

5.1 Procedures A numbu of provisions for the prevention of pressure transients are contained in the Haddam Neck operating procedures.

(1) The plant operating procedures for shutdown, cooldown and heatup operations have been modified to reduce to a minimum the time the RCS is in a water-solid condition.

(2) The plant procedures for RCP startup have been modified to require that when the first RCP is to be started in a water-solid system, the steam generator and RCS temperatures must be within 20 F, even though the licensee's OPS has been designed to mitigate the RCP startup transient with a 50 F AT.

(3) To reduce the probability of a RCP start causing a thermal expansion due to temperature asymmetries, at least one RCP is kept running during normal plant cooldowns for as long as possible.

(4) The safety injection logic.is blocked while in a shutdown condition.

(5) Additionally, the ECCS components which are capable of causing an overpressureeventaredisabledduringplantshutdownandcooldowns when the RCS temperature is below 340 F, and are not re-enabled (unless required for surveillance tests), until RCS startup (RCS temp > 340*F).

Specifically, the following actions are taken:

Open power supply breakers to the HPSIP's and LPSIP's, and place their control switches in the " pull-lock" position.

Remove the HPSIP power supply breaker and lock closed the cover door.

Shut, lock shut, remove power and " danger tag" the MOV's between the HPSIP's and the RCS.

Also, place their control switches in the " pull-lock" position.

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We conclude that the procedural and administrative control _ __ _ ___

described are acceptable.

How_ever, we detennined that certain procedural and administrative controls should be included in the Technical Specifications.

These are listed in the following section.

. 5.2 Technical Specifications To assure operation of the overpressure protection system (OPS), the licensee has submitted (Reference 15) proposed technical specifications to be incorporated into the license for Haddam Neck.

These specifications are summarized below.

(1 ) The OPS must be operable whenever the reactor coolant system temperature is below 340*F and the reactor coolant system is not vented.

If this condition is not met the licensee must conform to specified action statements.

(2) When starting a reactor coolant pump, and the reactor coolant cold leg temperature in any nonisolated loop is at or below 340*F, the secondary water temperature of each nonisolated steam generator must be no more than 20*F higher than the water temperature of each of the nonisolated reactor coolant cold legs.

(3) The High Pressure Safety Injection Pumps and one centrifugal charging pump must be disabled whenever the reactor coolant system temperature is below 340'F and the rea-tor coolant system is not vented.

(4) During the core cooling system periodic tdu, the RCS shall be vented by a minimum opening of at least r rw inches (00) with the OPS operable, or by two openings, each a minimum of three inches (00) if both OPS are inoperable.

(5) The OPS shall be tested each refueling outage.

We have reviewed CYAPCO's proposed Technical Specifications as revised by us and concluded that they are acceptable based on the analyses and methods described in Section 3.3 and Section 4.0.

We have discussed our revisions with the licensee's representatives and they have agreed with them.

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6.0

SUMMARY

The administrative controls and hardware changes made by CYAPC0 provide protection for Haddam Neck from pressure transients at low temperatures by reducing the probability of initiation of a transient and by limit-ing the pressure of such a transient to below Appendix G limits. We find sufficient justification for the exclusion of the HPSIP as a consideration in the OPS relief cacacity design and that the OPS meets the staff criteria and is acceptable as a long term solution to the problen of overpressure transients. However, any future revisions of Appendix G limits for Haddam Neck must be considered and the over-pressure system setpoint adjusted accordingly with corresponding adjustments in the license.

7.0 ENVIRONMENTAL CONSIDERATION

We have determined that the amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact.

Having made this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact and, pursuant to 10 CFR Section 51.5(d)(4), that an environmental impact statement or negative declaration and environmental imoact appraisal need not be prepared in connection with the issuance of this amendment.

8.0 CONCLUSION

We have concluded, based on the considerations discussed above, that:

(1) because the amendment does not involve a significant increase in the probability or consequences of accidents previously considered and does not involve a significant decrease in a safety margin, the amendment does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in canpliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security or tc the health and safety of the public.

Date:

April 24, 103C l

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9.0 REFERENCES

1. NRC (Schwencer) letter to CYAPCO (Switzer) dated Au9ust 11,1976.

2. CYAPC0 (Switzer) letter to NRC (Schwencer) dated September 3,1976.

3. CYAPCO (Switzer) letter to NRC (Schwencer) dated October 15, 1976.

4. CYAPCO (Switzer) letter to NRC (Schwencer) dated December 3,1976.

5. NRC (Schwencer) letter to CYAPC0 (Switzer) dated January 10, 1977.

6. NRC (Schwencer) letter to CYAPCO (Switzer) dated February 14, 1977.

7. CYAPC0 (Switzer) letter to NRC (Schwencer) dated March 1,1977.

8. CYAPCO (Switzer) letter to NRC (Schwencer) dated March 21, 1977.

9. NRC (Schwencer) letter to CYAPCO (Switzer) dated April 1,1977.

10. CYAPC0 (Switzer) letter to NRC (Schwencer) dated April 26, 1977.

11. CYAPC0 (Switzer) letter to NRC (Schwencer) dated June 1,1977.

12. CYAPCO (Switzer) letter to NRC (Schwencer) dated September 7,1977.

13. NRC (Schwencer) letter to CYAPC0 (Switzer) dated November 1,1977.

14. CYAPC0 (Switzer) letter to NRC (Schwencer) dated November 30, 1977.

15. CYAPC0 (Switzer) letter to NRC (Schwencer) dated January 3,1978.

16. CYAPCO (Switzer) letter to NRC (Schwencer) dated March 6,1978.

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17. " Staff Discussion of Fifteen Technical Issues Listed in Attactment G, November 3, 1976 Memorandum from Di rector NRR to NRR St a f f,"

NUREG-0138, November 1976.

18. " Pressure Mitigating System Transient Analysis Results," prepared by Westinghouse for the Westinghouse User's Group on Reactor Coolarit System Overpressurization, July 1977 (submitted as Attachment I to reference 12 above).

19. " Specific Pl ant Re po rt, Low Temoerature RCS Over:ressure Protection for Connecticut Yankee," August 1977 (sutnitted as Attactnent 2 to-Reference 2 above).