ML19340E296
| ML19340E296 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 01/09/1981 |
| From: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8101130089 | |
| Download: ML19340E296 (10) | |
Text
.
4 SOUTH CAR 0tlNA EttcTRic a gas COMPANY po s t errect som re4 CotumsiA. SoVTH CAROLINA 29218 T. C. N icuc ts, J R.
January 9, 1981 vxi m w. m. t. co.
,,,c a.. cn.c.c.,
Mr. Harold R. Denton, Director Office of Nuclear P.eactor Regulation U. S. Nuclear Reg'.;atory Commission Washington, D. C. 20555 i
Subject:
Virgil C. Summer Nuclear Station Docket No. 50/395 j
Reactor Vessel Vent System
Dear Mr. Denton:
South Carolina Electric and Gas Company, acting for itself and as agent for South Carolina Public Service Authority submits forty-five (45) copics of our response to question 211.133 on the reactor vessel vent system (see attachment 1).
This information will be incorporated in FSAR Anendment 23.
If you have additional questions, please let us know.
/
Very truly yours, f
f,,
E
,9 T. C. Nichols, Jr.
NEC:TCN:rh Enclosures 4
cc:
V. C. Sumner w/o enclosures G. H. Fischer w/o enclosures T. C. Nichols, Jr. w/o enclosures i
E. H. Crews, Jr.
O. W. Dixon, Jr.
W. A. Williams, Jr.
O. S. Bradham D. A. Nauman R. B. Clary A. R. Koon A. A. Smith J. B. Knotts, Jr.
J. L. Skolds B. A. Bursey 2p g j",I
, li'// in,
NPCF/Whitaker (d.
File NDl;I
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ATTACilMENT I Q211.133 Your response to TMI-related requirement item II.B.1 is not sufficient. Provide all necessary information for your pro-posed Reactor Coolant System Vents including a detail system description, results of analyses, P& ids, operating procedures and technical specifications as required in the attached clarification for this item.
jesponse See revised Section 5.5.15 Operating procedures for use of the vents that include the information available to the operator for initiating or terminating vent usage are currently being developed. These procedures will be submitted by separate cover letter.
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5.5.15 REACTOR VESSEL HEAD VENT SYSTEM 5.5.15.1 Design Basic The basic function of the Reactor Vessel Head Vent System (RVHVS) is to remove noncondensable gases from the reactor vessel head. This system is designed to mitigate a possible condition of inadequate core cooling or impaired natural circulation resulting from the accumulation of noncondensable gases in the RCS.
The design of the RVHVS is in accordance with the requirements of NUREG-0578
.and subsequent definitions anu clacirications (reierences 2 and 3).
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5.5.15.2 Design Description and Evaluation
- i 5.3.15.2.1 Gencial Description i
"he RVHVS is designed to remove noncondensable gases from the reactor coolant system via remote manual operations from the control room. The system discharges i
to the pressureizer relief tank. The RVHVS is designed to vent a volume of hydro-gen at system design pressure and temperature approximately equivalent to one-half of the reactor coolant system volume in one hour.
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The flow diagram of the RVHVS is shown in Figure 5.5-13.
The equipment design parameters are listed in Table 5.5-16.
The active portion of the system consists of four two-inch motor operated isolation valves connected to the reactor vessel head vent pipe.
The isolation valves in j
series in each flow path are powered by opposite vital power supplies. The iso-lation valves are fail as is, active valves.
One normally closed isolation valve and one normally open valve are located in each flow path. Leakage past the vent valves during normal plant operation is detected by the acoustic leak monitoring system which is described in Section 7.6.9.
All of the isolation valves are qualified to IEEE-323-1974, 344-1975 and 382-1972 and to the requirements of Reg. Guide 1.48 as described in Appendix 3A.
4
~ j If one single active failure prevents a venting operation through one flow path, the redundant path is available for venting.
Similarly, the two isolation valves in each flow path provide a single failure method of isolating the venting system.
With two valves in series, the failure of any one valve or power supply will not inadvertently open a vent path. Thus, the combination of safety grade train assignments and valve failure modes will not prevent vessel head venting nor venting isolation with any single active failure.
The RVHVS has two normally de-energized valves in series in each flow path. Power
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lock out capability to all four ; solation valves is provided by administrative
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control at the motor control lo d center. This arrangement eliminates the possibi-lity of a spuriously opened flow path.
i The system is operated from the control room. The isolation valves have stem i
position switches. The position indication from each valve is monitored in the control room by status lights.
r The RVHVS is connected to the head vent pipe as shown on Figure 5.5-13.
The system is orificed to limit the blowdown from a break downstream of either of the orifices j
to within the capacity of one of the centrifugal charging pumps.
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A break of the RVHVS line upstream of the orifices would result in a small LOCA of not gres*er than one inch diameter. Such a break is similar to those analyzed in WCAP-9600 (refereace 4).
Since a break in the head vent line would behave similarly to the hot leg break case presented therein are applicable to a RVHVS line break. This postulated vent line break, therefore, results in no calculated core uncovery.
All piping and equipment from the vessel head vent up to and including the second isolation valve in each flow path are designed and fabricated in accordance with AS!E,Section III, Class 1 requirements. The remainder of the piping and equipment in,en-nuclear safety but is seismically supported up the 12" pressurizer relief line.
The system provides for venting the reactor vessel head by using only safety grade equipment. The RVHVS satisfies applicable requirements and industry standards including ASME Code Classification, safety classification, single-failure criteria, and environmental qualification.
5.5.15.2.2 Supports The vent system piping is supported to ensure that the resulting loads and stresses on the piping and one the vent connection to the vessel head are acceptable.
The support design for attaching the head vent system piping to the reactor vessel head lifting leg is shown in Figure 5.5-14.
The support is a two-part clamp con-figuration called a double bolt riser clamp. The clamp and associated bolts, nuts, spacers, and washers are made of stainless steel. A gap exists between the one inch head vent pipe and the support clamp to allow for thermal expansien in the vertical direction.
The support design for attaching the head vent system piping to the CRDM Seismic Support Platform is shown in Figure 5.5-15.
This support is a two-part clamp configuration, called a double bolt clamp bracket. This clamp support is used to rigidly support the piping in the radial direction. The clamp and associated bolts, nuts, spacers and washers are made of stainless steel, with high strength hold down bolts threaded into the deck of the CRDM Seismic Support Platform. A gap exists between the one inch head vent pine and the support clamp to allow for thermal expansion in the ax jl direction.
All supports and support structures comply with the requirements of the AISC Code, Part II.
5.5.15.3 Analytical Considerations The analysis of the reactor vessel head vent piping is based on the following plant operating conditions defined in the ASME Code Section III:
1.
Norma 3 Condition:
Pressure deadweight and thermal expansion analysis of the vent pipe during a) normal reactor operation with the two inboard vent isolation valves closed and b) post-refueling venting.
2.
Upset Condition:
Loads generated by the' Operating Basis Earthquake (OBE) response spectra.
i
3.
Faulted Condition:
Loads generated by the Safe Shutdown Earthquake (SSE) and by valve thrust during venting.
In accordance with ASME III, faulted conditions are not included in fatique evaluations.
The Class I piping used for the reactor vessel head vent is one inch schedule 160 and, therefore, in accordance with AMSE Section III, is analyzed following the procedures of NC-3600 for Class 11 piping.
For all plant operating conditions listed above, the piping stresses are shown to meet the requirements of equations (8), (9) and (10) or (11) of ASME Section III, NC-3600, with a design temperature of 650*F and a design pressure of 2485 psig.
5.5.16 REFERENCES 1.
Reactor Coolant Pump Integrity in LOCA, WCAP-8163, September 1973.
2.
Letter from D. B. Vassallo (NRC) to all Applicants for an Operating License " Followup Actions Resulting from the NRC Staff Reviews Regarding the Three Mile Island Unit 2 Accident',' and Enclosure 4:
Installation of Remotely Operated High Point Vents in the Reactor Coolant System, September 27, 1979.
3.
Letter from D. B. Vassallo (NRC) to all Applicants for an Operating License,
" Discussion of Lessons Learned Short Term Requirements", Enclosure 1, pr 44-49, Reactor Coolant System Venting, November 9, 1979.
4.
" Report on Small Break Accidents for Westinghouse NSSS System", WCAP-9600, June 1979, (specifically Case F, Section 3.2).
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TABLE 5.5-16 REACTOR VESSEL HEAD VENT SYSTEM EQUIPMENT DESIGN PARAMETERS VALVES I
Number (includes two manual valves) 6 Design pressure psig 2485 Design temperature, "F 650 PIPING Normal vent line, nominal diameter, in.
1-3/4 RVHVS flow path line, nominal diameter, in.
1 Design pressure, psig 2485 Design temperature, 'F 650
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