ML17339A921
| ML17339A921 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 03/14/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17339A919 | List: |
| References | |
| NUDOCS 8004240276 | |
| Download: ML17339A921 (18) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATIOt<
RELATED TO AI'IEttDt'IENT -NO 55'O FACILITY OPERATING LICENSE HO DPR" 31 AHD AI~EHDtIEHT tl0.
47 TO FACILITY OPERATIt'G LICENSE HO.
DPR-41 FLORIDA POWER AND LIGHT COMPANY TURKEY POINT NUCLEAR GENERATING, UNIT NOS.
3 AND 4 DOCKET NOS.
50-250 AND 50-251 1.0 2.0 Int rodu ct i on By application dated December 11, 1978 the F.lorida Power and Light Company (FPL) requested amendments to Facility Operating License Nos.
DPR-31 and DPR-41 for the Turkey Point Plant Unit Hos.
3 and 4.'he application proposed amendments, which incorporate new limiting conditions for operation and surveillance requirements associated with the reactor vessel overpressure mitigating system (OHS).
By letter dated October 18, 1977 (Reference
- 1) Florida Power and Light Corpany
{FPL) submitted to the NRC a plant specific analysis in support of the proposed overpressure mitigating system (ONS) for Turkey Point Units 3 and 4.
This information,supplements documenta-ti'on submitted by FPL earlier {References 4-11).
We have completed our review of all information submitted by FPL
'n support of the proposed overpressure mitigating system and have found that the system provides adequate protection from overpressure transients and that acceptable Technical Specification changes have been proposed.
~Bk 1'ver the last few years, incidents identified as pressure transients
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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 vessell, as shown in the faci1ity Technical Specifications, are exceeded.
All of these incidents occurred at re1atively low temperature (less than 200 degrees F ) where'he reactor vessel materia 1 tougfIness (resistance to brittle failure) is reduced.
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2-2 ~ 1 The "Technical Report on Reactor Vessel Pressure Transients" in
'UREG 0138 (Reference,2) summarizes the technical. considerations relev'ant to this matter, discusses the safety concerns and existing safety margins of op'crating reactors, and describes the regulatory actions taken to resolve this issue by reducing the likelihood of
'uture pressure transient events at operating reactors.
A brief discussion is presented here.
Vessel Character'istics 2.2 Reactor vesselS are constructed of high quality steel made to rigid specifications, and fabricated and inspected in accordance with the time-proven ru'les of, the ASHE Boiler and Pressure Vessel Code; Steels used are particularly tough at reactor oper'ating conditi'ons.
- However, since reactor vessel steels are less tough and could possibly fail in a brit'tie manner if subjected to'igh 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'f the setpoint of currenly 'installed pressurizer code safety valves..However, most operating'PWRs did not have pressure relief devices to prevent pressure transients during cold conditions fron exceeding the Appendix G limit.
Re ulator Actions By letter dated August 1 1,
- 1976, (Reference
- 3) the f<RC requested that FPL begin efforts to design and install plant systems
-to mitigate the consequences of pressure transients at low=temperatures.
It was also requested that operating procedures be examined and administrative changes be made to guard against initiating:overpressure events.
It was
.felt by the staff that proper admi ni strati ve control s were re-quired to assure safe operation for t'e per'iod of time prior to instal-lation of the proposed overpressure mitigating hardware.
'I FPL responded (References.4 and.5) with preliminary...information des-.
cribing interim measures to prevent. these transients along with some discussion of proposed hardware.
The p'roposed hardware change was to install a
low pressure actuation setpoint on the pressurizer air operated relief valves.
3-FPL participated as a member, of a Westinghouse user's g'oup which was formed to support the analysis effort required to verify the adequacy of the proposed system to prevent overpressure transients.
Usi>>i, input data generated by the user's
- group, Westinghouse performed transient analyses (Reference
- 10) which are used as the basis for plant specific a na lysi s.
2.3 The l(RC requested additional information concerning the proposed pro-cedural changes and the proposed hardware'hanges.
FPL provided the required responses (References 6 and 7).
Reference 1 transmitted the plant specific analysis for Turkey Point Units 3
8 4.
c Through this series of meetings and correspondence with PWR vendors and licensees, the staff developed a set of criteria for an acceptabl'e overpressure mitigating system.
The basic criterion is that the mitigating system will prevent reactorvessel pressures in excess of these allowed by Appendix 6.
Specific criteria for system performance are:
2) 3)
~OA i:
l di ten minutes after the operator is aware of a transient-F 1:
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transient given a sin'gle failure in addition to the failure that initiated the pressure transient.
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d sistent with the system's errployment.
Seismic and IEEE 279 Criteria:,Idea'lly, the system should meet seismic Category I and IEEE 279 criteria.
The basic objective is that the system should not be vulnerable to a
common 'failure that would both 'initiate a pressure transient and disable the overpres-sure mitigating system.
Such events as loss of instrument air and loss of offsite power llust be considered.
The staff also instructed the licensee to provide an alarm which monitors the position of the pressurizer relief valve isolation
- valves, along with the low setpoint enabling switch, to assure that the overpressure mitigating system is properly aligned for shutdown conditions.
Design Basis Events The incidents t'hat have occurred to date have been the result of
. operator errors or'quipment faiIu'res.'wo'arieties of pressure-transie'n'ts can. be identified:
a mass input, type from charging
- pumps, safety injection pumps, safety injection accumulators; and a heat addition type which. causes. thermal expansion from sources su'ch as 'steam c 'nerators or decay heat.
3.0 On Westinghouse designed plants, the most comnon 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-
'HR system,
Although other transients occur with low frequency, those which result in the most rapid pressure
. increases were identified by the staff for analysis., The most'limiting mass in'put transie'nt identified by the staff is inadvertent injection by the, largest safety injection pump.
The most 1i'miting thermal ex-pansion transient is the start of a reactor coolant pump with a 50 degree F tempera'.ure,difference between the i<ater in the reactor
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" vessel and the=water in the steam generator.
I Based on the historical record of overpressure tra'nsients and the" imposition of. more effective administrative controls, the staff believes that the limiting events identified above form an'cceptable bases for analyses of the proposed overpressure mitigating system.
SYSTEM DESCRIPTION AND EVALUATION The proposed OllS includes
- sensors, actuating mechanisms,
- alarms, and valves to prevent a reactor coolant system transient from, exceeding the pressure and temperature limits included in the Turkey Point Units 3
and 4 Technical Specifications (TS).
'PL. adopted the "Reference Hitigating System" dev'eloped by Westinghouse and the user's group..The licensee proposed to modify tf>e actuation circuitry of the existing air operated pressurizer relief-valves to pro-vide a
low pressure setpoint during startup and,shutdown conditions.
The low pressure setpoint is a constant 415 psig at temperatures below 300 degrees F.,Above 300 degrees F, the setpoint increases linearly to 2335.psig at 4-2 degrees F.
When the reactor vessel is at low temperatures, with the loii pressure setpoint selected, a pressure transient is terminated below the Appendix G. limit by automatic opening of these relief valves.
A manual switch is used to enable and disable the low setpoint of each
. relief valve-An enabling alarm which monitors system pressure; the position of the enabling switch and the upstream isolation valve is pro-vided; The system low setpoint is enab')ed at'a pressure of 400.
3.1 E
psig during plant heatup.
Me find the pressurizer relief valves with a manually enabled low pressure setpoint to be an acceptable concept for an OtlS.
Air Su 1
3.2 The power operated. relief valves (PORVs) are spring-loaded-closed, air required to open the valves, which are supplied by a instrument air source.
To assure operability of the valves upon loss of control air, a backup air supply will be provided.
The backup air supply consists, of a'eismically mounted passive air accumualtor for each PORV.
Each tank contains enough air for a minimum of ten minutes operation.
Existing alanos in the control room alert the operator to loss of instrument air to the PORVs and associated accumulators.
The staff finds the backup air supply to be acceptable.
Electrical Controls The proposed overall approach to eliminating overpressure events incorporated administrative, procedural, and hardware controls with reliance upon the plant operator for the principal line of" defense.
Preventing administrative/procedural measures include (a,)
procedural'recautions, (b) deenergization of essentia')
components not required during the cold shutdown mode of operation, and (3) maintaini'ng a
nonwater-solid reactor coolant system condition whenever possible.
The basic design criteria that were applied in determining the adequacy of the electrical, instrumentation, and control aspects of the low temperature'verpressure protection system are those listed in 2.3 a'bove.
3.2.1 1n addition to complying with these criteri'a, the licensee has agreed to provide a variety of alarms to alert the operator to (a) manually enable the pressure protection system during cooldown, (b) indicate the occurrence of a pressure transient, and (c) indicate. closure of either power operated relief valve (PORY) isolation valve which ensures' complete pathway from the pressurizer to the oressurizer relief tank.
S,stem Electrical and Control Descri tion The 'OHS design for Turkey Point, Units 3
and 4 uses pressurizer PORVs with a variable low pressure setpoint as the pressure relief mechanism (Reference 1).
The variable low setpoint is energized and deenergized by two switches, one for each
- PORV, on the main control board..
The
variable low,.ressure setpoint is derived from reactor coolant system (RCS) wide range temperature using redundant transmitters.
The reactor "oolant pressure
'signal is ob'ainod forum redundant wide range pressure transmitters.
Below an RCS temperature of 300'F, the setpoint is a constant 415 psig.
Above 300'F, the setpoint increases linearly from 4'l5 psig a" 300'F to 2335 psig at 462'F.
Various alar."s are included in the ONS.
On decreasing
- pressure, an alarm and annunciator will acti vate at 390 psig.
This alarm alerts the operator to energize the ONS.
The alarm will not clear unless (a ) tne low pressure setpoi nt is energized, (b) the PORY mode selector switch is in AUTO, and (c) the motor oeprated valves (NOYs) upstream of the PORYs are indicated open.
This assures proper alignment of the ONS.
On increasing pressure an alarm and annunciator will actuate at 400 psig.
This alarm wil1 inform the operator that RCS pressure is approaching the PORV low setpoint.
Action can then be taken to remedy the cause of increasing
- pressure, or, if part of a normal heatup, to deenergize the ONS by placing the two iDTT control switches to the "Normal" position.
Should pressure continue to increase to the PORV setpoint, an alarm and annunciator will inform the operator that the PORVs have received a signal to open from the ONS.
The PORYs are spring-loaded closed and require air to open.
The air is presently supplied'by instrument air.
A redundant supply of air to the valves is included in the ONS.
Redundant accumulators, one dedicated to each PORY, will be added to the present air source.
Each accumulator will be sized to ensure a minimum of ten minutes operation of the ONS.
Redundant check valves will be provided for each accunmlator to prohibit backfeeding the instrument air system.
Existing alarms in the control room will alert the operator to a
loss of instrument air to the PORVs and associated accumulators.
Channel Se arabilit The ONS has two channels, one to control each PORV, 'that provide complete redundancy an are independent except for the use of common alarms and annunciators (as established by the single fai,lure analysis reported in Reference
- 8) which are isolated so that a
failure in i~he circuitry will not incapacitate either channel.
E ither one of the two PORYs provi des the reli ef capaci ty needed to protect the vessel, against a low-temperature ov'irpressurizat,ion event; the. other PORY provides redundant capacity.
The OHS setpoint and RCS pressure signals are derived from redundant temperature and pressu're transmi tters.
Each channel has its own ENABLE/DISABLE swich installed on the main control board.
The installation of the NS is in accordance with the sep'aration criteria used in the'design of 'the Turkey Point Plant.
Each of 'the'two channels uses an independent power supply from the transmitters to the solenoid valves controlling the air to the PROVs.
As discussed in the system description, the Ol5 has separate'ackup air supplies for each PORV.. These design features are in compliance with the single failure design criterion-3.2.1.2 Isolation Yalve and Set oint Alarms 3.2. 1.3 3.2.1.4
'As described in Paragraph 3.2.1, various alarms are included in the ONS.
Clearing of these alarms ensures proper alignment of the OPS.
The alarms provided meet the OMS design criterion.
0 erator Action 1
The Oi'1S is designed to perform its intended function for at least ten ininutes without operator action.
The most restrictive condition is the continued operation of a safety injection pump with an assumed loss of instrument air.
The redundant.
sources of air to the PORVs are sized to ensure a minimJm of ten minu'tes of operation after the loss of instrument
- air, and existing alarms alert the operator to this loss.'he system meets the design criterion, for operator action.
IEEE 279 Criteria The ONS meets the intent of IEEE 279, is designed against single failure, and has two channels that are electrically separate and meet the physical separation requirements used in the design of the electrical system for the Turkey Point Plant.
In addition, periodic testing of the OtiS prior to the need for its operation is i.ncluded to enhance system reliability.
The compliance of the design with the IEEE 279 design criteria is adequate.
3.2. 1.5 Testabilit Testability of the ONS is provided and the cooldown procedures include verification of ONS operability prior'to solid-system, low-temperature operation.
Testing will be accomplished by (a) closing the PORV isolatio'n
- valves, (b) enabling the
In this manner, OHS circuits as well as PORY operability will be verified-In addition, the associated instrumentation will be surveilled for calibration and proper. operation using the same methods followed for safety-related instrumentation.
These provisions and procedures for testability are adequate.
1 4
r 3.2.2 Pressure Transient Re ortin and Recordin Re uirements:
The staff. position on a pressure transient which causes the over-.
pressure protection system to function, thereby indicating the occurrence of a serious pressure transient, is that it is a 30-day reportable event.
In addition, pressure and temperature instrument-ation are required to provide a permanent record of the pressure tran-sient.
The response'times of the temperature/pressure recorders shall be compatible with a pressure transient increasing at a rate of approxi-mately 100 psi per second.
This instrumentation shall be operable
'henever.
the OMS is enabled.
'3-2.3 Disablin of Com onents Not Re uired Durin Cold Shutdown
- Except as required for brief intervals by operating procedures or Technical Specifications, the staff position requires that essential components not= required during cold shutdown. that could 'produce an overpresssurization event be disabled or isolated from the.RCS during cold shutdown, and'that the controls to disable, or isolate these com-ponents be incorporated in the, Technical 'Specifications. 'n particu-..
= lar, the safety injection accumulators and the high pressure. safety injection pumps are included in the components to be'disabled or isolated.
Valves and breakers used to dis'able essential equipment
= during cold shutdown est be tagged or locked to prevent inadvertent changes of state.
3.3. 'estabilit Testability is provided.
FPL has stated that verification of opera-bi)sty is possible prior to solid system, low temperature operation
'y use of the remotely operated isolation valve, enable/disable switch and normal electronics surveillance methodology.
Testing requirements will be incorporated in the Technical Specifications as discussed'n Section 4.2 of this evaluation.
x 3.4
~Aeedix.
G The Appendix G curve submitted by FPL for pur'poses of overpr'essure, transient analysis is based, on five effective full power years ir--'adi'ation.
The zero degree heatup curve is allowed since most pressure transients occur durinq isothermal metal conditions.
The Appendix G limit at 100 deqrees F according to-this curve is 510 psiq.-
The 'staff finds that use of this curve is acceptable as a basis for overpressure mitiqat'ing system performance.
3.5 Set oint Anal sis The one loop version of. the LOFTRAN (Reference 12 WCAP 7907) code was used to perform the mass input analyses.
'he four loop version was used for the heat input analysis.
Both versions require some input modeling and initialization changes.
LOFTRAN is currently under review by the staff and is judqed to be an acceptable code for treating problems of this type.
The results of this analysis are provided in terms of PORV setpoint overshoot.
The predicted maximum transient pressure is simply the sum of the overshoot magnitude and the setpoint maqnitude.
The PORV setpoint is adjusted so that given the setpoint overshoot, the re-sultant pressure is still below that allowed by Appendix G limits.
FPL presented the following Turkey Point Units 3 8 4 plant char-acteristi'cs to determine the pressure reached for the desiqn basis pressure transients:
SI Pump Flowrate 9 500 psig RCS Volume S
G Heat Transfer area Relief Valve setpoint 82.7,1b/sec 9343 ft3 44,430 ft2 415 psiq Westinghouse identified certain assumptions and input parameters as conservative with respect to the analysis.
Some of these are listed here.
1)
One PORV was assumed to fail.
2)
The RCS was assumed to be rigid with respect to. expansion.
3)
Conservative heat transfer coefficients were assumed for the steam generator.
The staff agrees that these are conservative assumptions.
~5 The inadvertent start of a safety injection pump with the plant in-a cold shutdown condition was selected as the limiting mass input case.
For this transient, a relief valve opening time of 2.0 seconds was used.
FPL has verified that this time is conservative..
3.5.
Westinghouse provided the licensee with a series of curves based on the LOFTRAN analysis of a generic plant design which indicates PORV setpoint overshoot for this transient as a function of system
- volume, relief valve opening time and relief valve setpoint.
These sensi-tivity analyses were then applied to the Turkey Point Units 3 8
4 plant parameters to obtain a conservative estimate of the PORV set-point overshoot.
The staff finds this method of analysis to be acceptable.
Using the Westinghouse methodology, the Turkey Point Units 3 8 4 PORV setpoint overshoot was determined to be 78 psi.
With a relief valve setpoint of 415 psig, a final pressure of 493 psig is reached for the worst case mass input transient.
Since the five EFPY Ap-pendix G limit at temperatures above 100 degrees F is above 510 psig, the staff concluded that the system performance was acceptable with a 415 psig low pressure relief valve setpoint.
Inadvertent startup of a reactor coolant pump with a primary to secondary temperature differential across the steam generator of 50 degrees F, and with the plant in a water 'solid condition, was selected as the limiting heat input case.
For the heat'nput
- case, Westinghouse provided the licensee with a series of curves based on the LOFTRAN analysis of a generic plant design to determine the PORV setpoint overshoot as a function of RCS volume, steam generator UA and.initial RCS temperature.
For this transient, a relief valve opening time of three seconds was assumed.
The calculated final pressure for the heat input transient For a
fixed zT of 50 degrees depends on the initial RCS temperature
'nd is given here:
RCS Tem erature Maximum Pressure
., '100 437 140 456 180 478 250 520 In all these
- cases, for the given RCS temperature, the Appendix G
limits are not exceeded.
The staff finds that the analyses of the limitinq mass input and heat input cases show a maximum pressure transient below that allowed by Appendix G limits and is therefore acceptable.
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11 3.6 Im lementation Schedule FPL installed the ONS in each unit in two phases.
Phase one included installation of the low pressure setpoint circuitry and pressure sensitive alarms.
Phase two included MOV interlocks and the backup air supply.
4.0, Administrative Controls To supplement the hardware modifications and to limit the magnitude of postulated pressure transients to within the bounds of the analysis provided by the licensee, a defense in depth approach is adopted usfna procedural and administrative controls.
Those. specific conditions required to assure that the plant is operated within the bounds of the analysis are spelled out in the Technical Specifications.
4.1 Procedures A number of provisions to prevent the initiation of pressure tran-sients are contained in the Turkey Point operating procedures.
.An effort has been made to minimize unnecessary RCP starts while the plant is in a water solid condition;
- However, when a
RCP start is required, procedures will require the operator to verify that I) if RCS temperature is above 212 deqrees F the steam pressure in the secondary side must be below the saturation pressure corres-ponding to the RCS temperature and 2) if RCS temperature is below 2l2 degrees F, that no significant vapor flow from the atmospheric dump valves will exist and that the recorded temperature difference between the hot leg and cold leg of each 1'oop is less than 20 de-grees F.
Phase two installation will include a thermocouole for measuring steam generator shell-side temperature prior to star+ina a reactor coolant pump.
In addition, to preclude inadvertent safety injection the hiqh pres-sure safety injection isolation valves and the safety injection accumulator valves are to be closed and de-energized by procedures below 1000 psig The staff finds that the procedural and administrative controls described are acceptable.
Ho'wever, the staff determined that certain procedu'ral and administrative controls should be included in the Technical Specifications.
These are listed, in the following section.
The licensee has agreed to these controls.
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a ) 4.2 Technical S ecifications To assure operation of the overpressure mitigating-system, the licensee has submitted for staff review, Technica1 Specifications
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to be incorporated into the license for Turkey Point Units 3
& 4.
These specifications are consistent with the intent of the statements listed below.
The licensee has assured that the Technical-Specifications proposed are compatible with other license requirements.
l.
Both PORIJ's must be operable whenever the RCS tempeature is less than the minimum pressurization temperature, except one PORV may be inoperable for seven days.
If these conditions are not met, the primarj system must be depressurized and vented to the atmos-phere or to the pressurizer relief tank within eight hours.
2.
Operability of the overpressure mitigation system requires that the low pressure setpoint will be selected, the upstream isolation valves open and the backup air supply charged.
3.
Ho nore than one high head SI pump injection va1ve may be energized at RCS temperatures below 380 degrees F, unless the vessel head is removed.
5.
A,reactor coolant pump may be started (or jogged) only if there is a steam bubble in the pressurizer, or the SG/RCS temperature is less than 50 degrees F.
I The overpressure mitigating system must be tested on a periodic basis consistent with the need for i-ts use.
5.0 6.
When the plant is in a cold shutdown condition the 'safety injection accumulators shall be isolated from the RCS by verifying that the accumulator isolation valves are in the closed position and power to the valve operators is removed.
~Summa@
The adminsi trative controls and hardware chan'ges proposed by Florida Power and Light Company provide protection for Turkey Point Units 3 and 4 from pressure transients at low temperatures by reducing the probability of initiation of a transient and by limiting the pressure of such a transient to below the limits set by Appendix G.
The staff finds that the overpressure mitigating system meets the criteria established by the NRC and is acceptable as a long term solution to the problem of overpressure transients.
- Also, any future revisions of Appendix G limits for Turkey Point Units 3 and 4 must be considered and the overpressure mitigating system setpoint adjusted accordingly with corresponding adjustments in the license.
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~ The electrical, instrumentation, and control aspects of the Turkey Point Units 3 and 4
OMS design are adequate on the basis that:
(a) the proposed control circuitry meets IEEE Std.
- 279, (b) the system is redundant and meets the single'failure criterion, (c) the design requires no operator action for ten minutes after the operator receives an over'pressure action alarm, (d) the system is testable on a periodic basis, and (e) the proposed changes to the Technical Specifications are in agreement with the recommended changes described in 4.2 above.
We find the licensee's proposed system acceptable.
Additionally, the licensee's proposed Technical Specifications are in agreement with the recommended changes described in Section 4.2'f this SER.
Environmental Consideration We have determined that the amendments do not authorize a change in effluent types or total amounts nor an increase i n power. level and will not result in any significant environmental impact.
Having made this determination, we have further concluded that the amendments involve an action wh'ich is insignificant'rom the standpoint of environmental impact and, pursuant to 10 CFR 55].5(d)(4), that an environmental impact statement or negative declaration and envi ron-mental impact appraisal need not be prepared in connection with the issuance of these amendments.
conclusion We have conc1uded, based on the considerations discussed
- above, that:
(1) because the amendments do not involve a significant increase in the probability or consequences of accidents previously considered and do not involve a significant decrease in a safety margin, the amendments do 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 compliance with the Commission's regulations and the'ssuance of these anendments will not be inimical to the comnon defense and security or to the health and safety of the public.
e Date:
March 14, 1980
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REFERENCES 1..Florida Power. and Light Company letter (Uhrig) to NRC (Lear) dated October 18, 1977.
2.
"Staff Discuss'ion of Fifteen Technical Issues listed in Attachment G
November 3, 1976'emorandum from Director NRR to NRR Staff."
NUREG-0138 November 1976; 3.
NRC letter (Lear) to'PL (Uhrig) dated August 11, 1976.
- 4. 'PL letter (Uhrig) to NRC (Lear) dated October 15, 1976.
5.
FPL letter (Uhrig) to NRC.(Lear) dated December 10, 1976.
6.
FPL letter (Uhrig) to NRC (Lear) dated March 1< 1977..
7.
FPL letter'(Uhrig) to NRC,(Lear) dated March, 16, 1977.
FPL letter (Uhrig) to NRC (Lear) dated March 31, 1977.-
9.
FPL'etter (Uhrig) to NRC (Lear) dated April 21, 1977.
10.
"Pressure Mitigating System Transient Analysis Results" prepar'ed by Westinghouse for the Westinghouse user's group" on reactor coolant system overpressurization, dated July 1977.
11.
FPL letter (Uhrig) to NRC (Lear) dated January 3, '1978.
12.
Loftran Code Description, WCAP-7907, October 1972.