ML20052B820
| ML20052B820 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 04/09/1982 |
| From: | Stolz J Office of Nuclear Reactor Regulation |
| To: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| References | |
| TAC-6710, NUDOCS 8205040003 | |
| Download: ML20052B820 (20) | |
Text
,
' APRIL 0 9 1982 DISTRIBUTION:
Docket File DEisenhut ACRS-10 NRCPDR MPadovan Gray File L PDR ADe Agazio H0rnstein ORB #4 Rd RIngram EBlackwood Docket No.g 50-312 OELD e
p - / "S AE0D 4
IE 9
Rggg,,gg gI,4PRI81982A '
Mr. J. J Mattimoe Q%ag Assistant General Manager and h*a Chief Engineer p
Sacramento Municipal Utility District 9
6201 S Street g
/
P. O. Box 15830 ru Sacramento, California 95813
Dear Mr. Mattimoe:
SUBJECT:
OVERPRESSURE PROTECTION SYSTEM FOR LOW TEMPERATURE OPERATION Our August 11, 1976 letter requested that you evaluate Rancho Seco's overpressurization protection system to assure that the pressure relieving systems function during low temperature operation.
Your October 14, 1976 and October 28, 1976 letters submitted a plant specific analysis to us, which was revised by your March 17, 1977 letter. Additional infomation was provided to us in your March 29, 1978 submittal.
i We have reestablished our review of your submittals and we find that l
additional infomation is necessary for us to coniplete our review.
l is a Request for Additional Infomation on the mechanical aspects of your overpressure protection (mitigation) system. The electrical and instrumentation and control (I&C) aspects of the system are discussed in Enclosure 2.
Within 60 days of receipt of this letter, please provide the following:
- 1) The infomation requested in Enclosure 1, with the exception of the requested Technical Specifications,
- 2) Address the recomendations provided in Section 5 of Enclosure 2, with the exception of the requested Technical Specifications, and l
- 3) A schedule for submitting the Technical Spec'fications requested l
in Enclosures 1 and 2.
If you cannot meet the 60 day submittal date, please inform your NRC Project Manager as soon as possible. The reporting requirements con-l 8205040003 omen
.. -....... ~. -.
SURNOME)
. ~.. - ~ ~. - a -
a
...-a-*~
~ a oeve>
....... ~....... -
.. -.. - ~ ~.. -
~ ~.. - - -. -
..~~~~~
' asc ronu sia no-soi nncu o24o OFFICIAL RECORD COPY usom mi-mesa
r i
l r
Mr. J. J. Mattimoe tained in this letter affect fewer than ten respondents; thus OMB clearance is not required under P. L.96-511.
Sincerely, FORIGI2iAL SIG'JD Fl goint F. STOLZ?
John F. Stolz, Chief Operating Reactors Branch f4 Division of Licensing
Enclosures:
1.
Request for Additional Information 2.
Technical Evaluation by EG&G Idaho, Inc.
t cc w/ enclosures:
See next page I
i l
l I
l l
I I
omce >... ORB #4: DL A.RB#4: DL C-0(R..M. 4:DL O
..3 Jstol an sun - e>
... 4./..%28.?.;.c.b.. 4/.a/.82........ 41..$.dR........
om, nac FORM 318 (10-80) NRCM 024o OFFICIAL RECORD COPY usom sees-m.eo
Sacramento Municipal Utility Ranch 3 Seco Docket No. 50-312 District cc w/ enclosure (s):
' David S. Kaplan, Secretary and Christopher Ellison, Esq.
J General Counsel Dian Grueufch, Esq.
Sacramento Municipal Utility California Energy Commission District 1111 Howe Avenue 6201 S Street Sacramento, California 95825 P. O. Box 15830 Sacramento, California 95813 Ms. Eleanor Schwartz California State Office Sacramento County 600 Pennsylvania Avenue, S.E., Rm. 201 Board of Supervisors Washington, D. C.
20003 827 7th Street, Room 424 Sacramento, California 95814 Docketing and Service Section Office of the Secretary Business and Municipal Department U.S. Nuclear Regulatory Commission Sacramento City-County Library Washington, D. C.
20555 828 I Street Resident Inspector / Rancho Seco Sacramento, California 95814 c/o U. S. N. R. C.
14410 Twin Cities Road Herald, CA 95638 Dr. Richard F. Cole Atomic Safety & Licensing Board Panel U.S. Nuclear Regulatory Commission Washington, D. C.
20555 Regional Radiation Eepresentative EPA Reaion IX Mr. Frederick J. Shon 215 Fremont Street Atomic Safety and Licensing Board l
San Francisco, California 94111 Panel U.S. Nuclear Regulatory Commission Mr. Robert B. Borsum Washington, D. C.
20555 Babcock & Wilcox Nuclear Power Generation Division Elizabeth S. Bowers, Esq.
Suite 220, 7910 Woodmont Avenue Chairman, Atomic Safety and Bethesda, Maryland 20814 Licensing Board Panel U.S. Nuclear Regulatory Comission Thomas Baxter, Esq.
Washington, D. C.
20555 Shaw, Pittman, Potts & Trowbridge 1800 M Street, N.W.
Washington, D. C.
20036 Herbert H. Brown, Esq.
Lawrence Coe Lanpher, Esq.
Hill, Christopher and Phillips, P.C.
1900 M Street, N.W.
Atomic Safety and Licensing Board Washington, D. C.
20036 Panel U.S. Nuclear Regulatory Commission Helen Hubbard Washington, D. C.
20555 P. O. Box 63 Sunol, California 94586
/
Sacramento Municipal Utiiity District Atomic Safety and Licensing Appeal Mr. Robert H. Engelken, Regional Administrator U. S. Nuclear Regulatory Comission Region V Board Panel U.S. Nuclear Regulatory Commission 1990 N. California Boulevard, Suite 202 Washington, D. C.
20555 Walnut Creek, California 94596 Alan S. Rosenthal, Chairman Atomic Safety and Licensing Appeal Board U. S. Nuclear Regulatory Connission Washington, D. C.
20555 Dr. John H. Buck Atonic Safety and Licensing Appeal Board U. S. Nuclear Regulatory Commission Washington, D. C.
20555 Christine H. Kohl Atomic Safety and Licensing Appeal Board U. S. Nuclear Regulatory Commission Washington, D. C.
20555 California Department of Health ATTN: Chief Environmental Radiation Control Unit Radiological Health Section 714 P Street, Room 498 Sacramento, California 95814
---w,x u-
i RC-1 i
REQUEST FOR ADDITIONAL INFORMATION l
1.
Branch Technical Position (SRP 5.2.2/RSB 5-2) specifies that the Rancho Seco, Unit 1 overpressure protection system (0PS) should prevent exceeding applicable Technical Specifications and 10 CFR 50 Appendix G limits.
In your analysis and system description, you use 550 psig as the low temperature operation PORV setpoint and as the value that RCS pressure is allowed to reach prior to any credited operator action.
a.
Does~ the 550 psig setpoint provide adequate assurance that the ll f
Appendix G curve limits will not be exceeded for all temperatures i
0 below 312 F (the minimum pressurization temperature)?
2.
The OPS is required to function assuming any single active component failure.
q O
The Rancho Seco overpressure protection system does not meet this criterion l
for the cases of (a) the makeup control valve failing in full open position, and (b) an inadvertent actuation of the high pressure injection (HPI) systs, either case with the PORV failing closed. You discussed several procedural and administrative controls used to prevent an inadvertent actuation of high pressure injection and the Branch Technical Position allows for such cases, if reviewed and approved on an individual basis, and if adequate controls to prevent the event are included in the plant Technical Specifications.
a.
Provide a copy of all Technical Specifications that deal with this subject, or propose appropriate ones.
l b.
List all procedural and administrative controls used during HPI systs tests to prevent violating Appendix G limits.
c.
Could an HPI isolation valve (SFV 23809, SFV 23810, SFV 23811, or SFV g
23812) be manually opened locally?
3.
In your March 29, 1978 submittal, you stated that you decided against using the pump trip feature in the Rancho Seco overpressure mitigating systs. You had used this feature as one of the diverse protective systems in your analysis of the makeup control valve failing full open. Address how you are going to meet all of the required criteria for this initiating I
event with the postulated failure (closed) of the single PORV. No credit can be taken for operator action until 10 minutes after the operator is aware of the transient.
ti 4.
In the March 29, 1978 letter from SMUD to Mr. Reid, you proposed eight modifications which involve adding equipment or modifying existing equipment or procedures in order to prevent overpressure events or mitigate them l
should they occur.
a.
What is the status of implementatior. if the eight proposed modifications?
b.
Would a single power source failure disable more than one of the alarm functions identified, or an alarm and the PORV?
The alarm for the HPI valves will actuate if any of the four valves 's c.
full open, however, the alann will not sound if any or all of the va' ves is partially open. This situation could result in overpressurization of the RCS f f an inadvertent actuation of an HPI pump occurred. Please discuss this scenario, s
L
h l'
. 2-i 5.
You take credit for operator action to mitigate a pressure transient for all analyzed events when a failure closed of the PORV is considered.
No credit can be taken for operator action until 10 minutes after the operator is aware that a pressure transient is in progress. For the most severe event that you analyzed, what audible alann will alert the operators that a pressure transient is occurring (alarms associated with the PORV cannot be used because it is assumed failed closed)?
We request that acceptable technical specification changes or. system modifications be proposed to increase your calculated operator time from 4.4 minutes to at least 10 minutes. -
(
6.
What training has been conducted at Rancho Seco to make the operating personn l
aware of overpressure incidents at other facilities' and possible overpressure situations at Rancho Seco?
problem during your licensing and retraining programs?How do you en k
7.
Provide current P& ids of the overpressure protection system.
4 8.
The administrative controls you use to ensure against the inadvertent opening of an HPI valve are not put into use until RCS temperature drops j
to 200 F during cooldown and they are removed once temperatures reach 200 F l
0 during system heatup.
(the minimu :
This leaves the time spent between 2000F and 3120F or a valve malfunction could result in a pressurc transient that cou exceed an Appendix G curve limit.
l the reactor coolant system between 200 F and 3120F.Please discuss the protec 9.
Provide the age of the primary system, in effective full power years (EFPY) at which the current Appendix G limits are calculated.
i 1
1825F r
o
! Y TECHNICAL EVALUATION
'h ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE LOW TEMPERATURE OVERPRESSURE MITIGATING SYSTEM RANCHO SECO UNIT 1 (Docket No. 50-312)
TAC 6710 D. A. Weber Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.
l:
4 CONTENT 3 1.
INTRODUCTION.
1 2.
DESIGN BASIS EVENTS (DBE)
\\
2 l
3.
OVERPRESSURE PROTECTION
...................... 2 3.1 Description.
2 3.1.1 Operator Action 8
3.1.2 Overpressure Mitigating System (OMS).
2 3.1.3 3
Transient Indications and Alarms l
3.1.4 Procedural Precautions.
3 4
3.2 Proposed HPI OMS Addition...................
4 4
EVALUATION OF THE EXISTING AND PROPOSED OMS 5
5.
RECOMMENDATIONS 8
5.1 Technical specifications 5.2 Existing OMS 8
5.3 Proposed OMS 9
. 10 6.
SUMMARY
10 l
7.
REFERENCES.
............................ 11 b
11
TECHNICAL EVALUATION ELECTRICAL, INSTRUMENTATION, AND CONTROL ASPECTS OF THE LOW TEMPERATURE OVERPRESSURE MITICATING SYSTEM RANCHO SECO UNIT 1 (Docket No. 50-312) 1.
INTRODUCTION lo I
By letter dated August 11, 1976, the NRC requested Sacrame.nto Mini-l cipal Utility District (SMUD) to evaluate the Rancho Seco Unit 1 "overpres-pure protection system designs to determine their susceptibility to over-pressurization events," and their ability to mitigate the consequences of these events.
It was also requested that operating procedures be examined and administrative controls be implemented to guard against initiating overpressure events at temperatures below the Nil Ductility Transition Temperature (hTTT).
l 2
3
'{
By letters dated October 14, 1976, and October 28, 1976, SMUD submitted to the NRC a plant specific analysis. The NRC questioned portions 0
I of this analysis in a letter dated December 10, 1976.
In responding, 0
SMUD, in a letter dated March 17, 1977, revised their analysis and answered the NRC questions. The NRC requested additional information regarding modifications in letters dated November 2, 19770, and March 13, 7
1978.
SMUD supplied the additional information in their letter of 8
March 29, 1978.
I The electrical, instrumentation, and control system aspects of the j
existing SMUD low temperature overpressure mitigating system (OMS) and the proposed design changes have been reviewed in this report.
Section 2 describes the two events which SMUD's analysis indicates would result in 4 '
overpressure transient.
Section 3 descrioes the Rancho Seco Unit 1 over-pressure protection and SMUD's proposed design change.
Section 4 provides I
an evaluation of the existing OMS and the proposed design change as they j
apply to the staff requirements. Section 5 lists recommendations as they
)
apply to Technical Specifications, the existing OMS, and the proposed design change.
Section 6 is a summary of this report.
l 1
-~
l
{
2.
DESIGN BASIS EVENTS (DBE) i SMUD has analyzed seven low temperature overpressure events to d mine whether they are applicable to Rancho Seco Unit eter-4 1
Based on the SMUD analysis, erroneous actuation of the high pressu injection (HPI) system and the makeup control valve (to RCS) f ili re have been identified as the limiting mass addition overpressure tran i a
ng open, which require action to prevent overpressurization within 10 minutes s ent f
initiation.
of Operation of an HPI pump, which is capable of delivering flow
}
against full system operating pressure, is required whenever a reactor
[
coolant pump is in operation (provides RCS pump seal water).
Since the h
discharge of an HPI pump is isolated from the reactor coolant system b single injection valve, ya a single error or equipment failure could open the injection valve and overpressurize the reactor coolant syste m (RCS).
Action would be required within 4.4 minutes to maintain the RCS pressu below Appendix G limits.
re For the event in which the makeup valve to the RCS fails full open, SMUD's analysis shows that action would be required within seven minutes to maintain the RCS pressure below the Appendix G limits 5, I
3.
OVERPRESSURE PROTECTION 3.1 Description For the Rancho Seco Unit 1, overpressure protection consists of oper-i ator action and the Overpressure Mitigating System (OMS).
The Decay Hest Removal (DHR) system can also provide some additional relief protecti from overpressure transients; however, on it is very small and intended only to provide ther=al relief.5 3
.1 Operator Action With a steam or nitrogen bubble in the pressurizer, the operator has 4.4 minutes or 7 minutes to prevent an overpressurization with a HPI open makeup valve transient, respectively.
, or an The operator action necessary 2
l 8
to prevent overpressurization is to determine the cause of the transient and to deenergize or control the responsible equipment before the RCS pressure reaches the PORV setpoint.
3.1.2 overpressure Mitigating system (OMS)
The OMS consists of a single, dual setpoint, power-operated relief
)
valve (PORV).
The valve has a high overpressure setpoint of 2255 psig for j
reactor operation and a low temperature overpressure setpoint of 550 psig f
for reactor cooldown and heatup. A manually operated switch under admini-strative control is provided to change the PORV setpoint.
An enabling alam alerts the control room operator to switch to the lower setpoint when the RCS pressure is below 550 psig.
SMUD has stated in their letter of March 17, 1977, that the PORV 5
has a steam (or nitrogen) relief capacity greater than the injection rate of two HPI trains, and a liquid relief capacity equal to or greater than I
the injection rate of one HPI train.
3.1.3 Transient Indications and Alar =s Alams and equipment which give indication that a transient is in progress include, wide-range pressure transmitters (0-2500 psig) used for actuation of the engineered safeguards syste=s; a pressure transmitter (0-600 psig) on the pressurizer sample line that controls the power-operated relief valve; two pressurizer level instruments and associated high and high-high level alams; a letdown storage tank low level alarm; makeup system flowrate indication; and mdkeup valve position indication.
SMUD provides three acoustic monitors, downstream of the PORV and each of the two press,cizer safety valves, to preiide direct indication of the positions of each valve. A single alarm is actuated if any~of the three monitors detects flow.
The operator then checks the indicators for each valve to determine which has lifted.
3 l
3.1.4 Procedural Precautions The staf f position with regard to the inadvertent operation of compo-nents capable of causing a low temperature overpressurization requires the deenergization and either lockout or alarming of unused equipment capable of causing the overpressurization.
Procedural steps requiring the removal of equipment from operation, o
e.g.,
the opening of pump and valve circuit breakers, require initialling 5
to indicate satisfactory completion of each step. Critical steps f
performed under administrative control are included.
e To prevent the erroneous action of an HPI train, circuit breakers for the closed HPI motor-operated valves are opened during plant cooldown and prior to start-up of the DHR system. This is accomplished by opening and tagging the valve circuit breakers at the motor control center.
These circuit breakers are not closed again until startup when RCS temperature is above 280 F.'
The operator has indication that power has been removed as the status lights in the control roo= will be off.
SMUD has incorporated changes into the valve indicator power supplies so the valve i
positions are indicated in the control room even though the circuit breakers have been opened.
3.2 Proposed RPI OMS Addition With the initial RCS conditions at NDTT and a pressure of 250 psig, the analysis has determined the time required for a pressure transient to I
t reach 550 psig (required relief setting) af ter initiation varies between 4.4 and 46.6 minutes, depending on the transient source.
Only a pressure transient caused by the actuation of an HPI train or on open makeup valve l
will reach the vessel overpressure point of 550 psig in less than ten minutes.
Therefore, SMUD proposes an overpressure protection system modification which provides control room annunciation for an over-pressurization incident caused by HPI system actuation, an open makeup valve, or when the PORV block valve is closed.0
/
4
'i i
l
l.
j Whsn tha racetor coolant system pressure drops below 550 pai, the control room operator receives an alarm to enable the low pressure setpoint circuit of the dual setpoint PORV. This is accomplished by closing a keylock switch which aligns the low pressure setpoint.
The switch also I
sets up four annunciator circuits.
An alarm is provided when (a) power is available to either of the two HPI pumps, (b) high flow to the RCS is 1
detected (which would be caused by the failure of a makeup valve in the full-open position), (c) either of the four motor-operated injection valves are open, and (d) the PORV block valve is closed, removing the PORV from J
service.0 lh 4.
EVALUATION OF THE EXISTING AND PROPOSED OMS 1
The OMS, present and proposed, as it is designed to respond to transi-is evaluated relative to the staff requirements as follows:
- ents, 1.
Requirement I
Operator Action - No credit can be taken for operator action until ten minutes after the operator is aware, through an alarm, that a pressure transient is in progress.
Evaluation The existing dual setpoint PORV OMS, when in service, will relieve all low temperature pressure transients.
However, it is not single failure free. The proposed OMS does not meet this requirement.
Operator action is required as the primary protection for two events, 1
i The events which would require operator action in less than ten minutes are an HPI transient and failure of the makeup valve in the full-open position.
i 5
2.
Requirenent Seismic and IEEE 279 Criteria - Ideally, the system should meet Seismic Category I and IEEE 279 criteria.
The basic objective is that the system should not be vulnerable to a com:non failure that would both initiate a pressure transient and disable the overpressure miti-j gation system.
l f
The original intent of the NRC staff was that at least two independent automatic low pressure prstection chan-nels should make up the OMS. Each channel should include separate sensors, alarms, power trains, and relief valves. Each channel should have complete elec-
]
trical and physical independence from each other to prevent common mode failures. The OMS should be oper-able upon loss of offsite power.
In addition, each OMS channel should not be susceptable to seismic events that could cause a transient and fail the channel at the same time.
Evaluation The existing and proposed Rancho Seco Unit 1 OMS does not comply with the IEEE 279 or Seismic criteria.
Regarding the IEEE 279 criteria, the existing and pro-posed OMS does not provide for a second independent autematic low-pressure. protection channel. The addition of the enabling alarm will assure proper alignment of the overpressure protection system. The four additional alarms will annunciate if powe:t is available to the HPI pumps, the injection valves are open, the makeup valve is open, and/or the PORV block valve is closed. These additional alarms do not qualify as a second automatic low pressure protection channel for the OMS. Regarding Seismic criteria, SMUD states that detailed
stress analyses have been performed for the pilot-actuated relief valve in accordance with ASME Sec-tion III, Class 1 requirements and have been found adequate for Class 1 applications. However, testing with simulated seismic loadings has not been performed l
as this was not a requirement at the time the plant was designed and constructed.5 o
3.
Requirement Single Failure - The system must be designed to relieve the pressure transient given a single failure in addi-tion to the failure that initiated the pressure transient.
ii f
Evaluation i
if The Rancho Seco OMS does not comply with the single i
failure criteria in that there is only one RCS low temperature overpressure protection channel, i.e.,
there is no channel redundancy.
4 Requirement Testability - The system shall include provisions for testing on a schedule consistent with the frequency that the system is relied upon for pressure protection.
I Evaluation The single existing PORV system is designed to allow testing of the system prior to its use.
l l
I 7
i
L' e
5.
RECOMMENDATIONS 5.1 Technical Specifications is the staff position that administrative controls shall appear in It the Technical Specifications as Limiting Conditions for Operation when administrative controls are used to limit overpressurization scenarios.
Therefore, it is recommended that the licensee be required to submit Tech-f nical Specification changes for Rancho Seco Unit I consistent with the following:
I 1.
Any operation or failure of the PORV to operate to
'9 relieve pressure transients must be reported to the NRC.
2.
The existing OMS and alarms must be operable (in oper-l ation) when the RCS temperature is below 280 F.
If the OMS modification is installed and in operation, then the system and its related alarms must be operable when the RCS temperature is below the minimum pressur-ization temperature.
If these conditions are not met, the primary system must be depressurized and vented to the atmosphere within eight hours.
3.
The four HPI motor-operated valves must be closed and the supplying circuit breakers open and tagged when the temperature is below 280 F and the reactor coolant is not vented to the atmosphere.
4 The low temperature overpressure protection system and added alarms must be tested on a periodic basis consis-tent with the need for its use.
A system functional test and a setpoint verification test shall be performed prior to enabling the overpressure protection system during cooldown and startup.
The system shall be cali-j ;
brated, and the PORV and related OMS alarm operations I
tested at refueling intervals.
The EPI valves will be i
I 8
allowed to be cycled only if (a) all HPI pumps are out of service, or vessel temperature is above the minimum value for which the vessel can be fully pressurized, or (b) the reactor vessel head is removed.
5.
Een the reactor vessel temperature is below the minimum value for which the vessel can be fully pressurized, the PORV may be removed from service for a maximum of y
two hours only if (a) charging pumps are out of service and all HPI injection valves are closed and power removed, or (b) the vessel head is removed.
k" 5.2 Existing OMS With regard to reco=mendatiens concerning the existing OMS, the licensee should:
1.
Submit Technical Specifications to comply with the requirements listed in Section 5.1 2.
Identify, in the Technical Specifications, the enabling 6
temperature and PORV setpoint 3.
Propose Technical Specifications related to system 6
testing 4.
Install pressure alarms to give the operator direct indication that a low temperature-pressure transient is in progress and that the RCS pressure has exceeded 550 psig 9
f I
J
l i
5.
Examine the maintenance and testing restrictions to assure compatibility with present/ proposed Technical Specifications regarding the operability and periodic testing of ECC and emergency boration system.0 i
5.3 Proposed OMS i
It is recommended that the following be required of the licensee:
l !
lI 1
1.
All alarms, instrumentation, control circuits, and power required by the operator to detect HPI overpressure transients should be electrically and physically separated from the PORV system (i.e., meet IEEE 279 criteria) 2.
Assure that the new equipment is seismic qualified and testable.
6.
SUMMARY
The NRC letter of August 11, 1976', regarding reactor vessel overpres-surization, requested the Sacramento Municipal Utility District to evaluate their low temperature overpressure mitigating systems for Rancho Sec o Unit I to determine their susceptibility to overpressure events The evaluation that S!!UD provided indicated that there were two events, a transient caused by the inadvertent operation of the high pressure injec-tion system and the makeup valve.failing full open, that would require operator action in less than the ten minutes allowed by the staff require ment to prevent overpressurization. On March 29, 1978, SMUD provided details of a proposed overpressure protection system modification in addi-tion to an existing PORV dual setpoint system that would provide control-room alarms if the PORV block valve was closed, the four motor-operated injection valves were open, power was available to the two HP1 injecti on pumps, and/or the makeup valve was open.
10 i
The existing and proposed system does not meet the staff positions regarding operator action for an overpressurization and the seismic and single f ailure requirements.
Although the Rancho Seco Unit 1 does not comply with all of the r
original staff positions, there are other factors which should be considered. The staff positions for an OMS vere originated for plants that are operated with the RCS in a water-solid condition during cooldown and d
startup. With a water-solid condition, a transient can cause an over-pressurization of the vessel within seconds of initiation. This step transient makes it impossible for an operator to detect a transEent and act in time to prevent overpressurization.
The B&W-designed plant never operates with a water-solid condition. A steam or nitrogen bubble is I
maintained in the reactor pressurizer at all times, which does not allow step transients to occur.
Instead, transients occur as a ramp function with the HPI transient or the makeup valve failing open transient reaching the overpressurization point 4.4 minutes and seven minutes or more after f
initiation and all other transients requiring over ten minutes. This delay allows the operator time to detect the transient and take action to prevent the RCS pressure from reaching the PORV relief point. There has been only one low temperature overpressurization at the B&W-designed plants.
In order that the Rancho Seco OMS be found acceptable in the areas of EI6C the licensee should be required to implement the additional changes described in Section 5.0 of this report.
i 7.
REFERENCES I
1.
R. W. Reid, NRC letter to SMUD, Re:
" Reactor Vessel Overpressurization in Pressurized Water Reactor Facilities," August 11, 1976.
2.
J. J. Mattimoe, " Evaluation of Potential Vessel Overpressurization,"
October 14, 1976.
11 L
I
i l.
3.
J. J. Mattimoe, " Reactor Vessel Overpressurization Events," October 28, 1976.
4.
R. W. Reid, NRC letter to SMUD, Re:
" Additional Information to Evalu-y ate Overpressure Mitigating System," December 10, 1976.
5.
J. J. Mattimoe, " Evaluation of Potential Vessel Overpressurization,"
l March 17, 1977.
e l
l 6.
i R. W. Reid, NRC letter to SMUD, Re:
"RCS Overpressurization,"
November 2, 1977.
il l
7.
R. W. Reid, NRC letter to SMUD, Re:
" Dual Setpoint PORV," March 13, 1978.
8.
J. J. Ma t t imoe, " Proposed Overpressure Protection System Modification,"
March 29, 1978.
i I
12
- -.