ML20054H877
| ML20054H877 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 06/15/1982 |
| From: | Kay J YANKEE ATOMIC ELECTRIC CO. |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20054H878 | List: |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.B.1, TASK-TM FYR-82-65, NUDOCS 8206250128 | |
| Download: ML20054H877 (7) | |
Text
jffE ATOMIC ELECTRIC COMPANY m.
_h 1671 Worcester Road, Framingham, Massachusetts 01701
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[, ANKEE g g, 6S United States Nuclear Regulatory Commission June 15, 1982 Washington, D. C. 20555 Attention:
Mr. Dennis M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing
References:
(a) License No. DPR-3 (Docket No. 50-29)
(b) USNRC Letter to YAEC dated February 25, 1982 l
Subject:
Reactor Coolant System Vent System
Dear Sir:
l The attached information has been prepared in response to Feference (b).
This information provides further clarification of NRC staff concerns l
pertaining to the design of the installed, but not opera tional, Reactor Coolant System (RCS) Vent System. In addition, the attached RCS Vent System Operational Cuidelines have been prepared, as requested. These guidelines are based on the guidelines prepared by the Westinghouse Owners Group effort, and describe when the operator should and should not manually vent the Reactor Coolant System.
Plant specific procedures for system operation will be wri tten upon acceptance of the system design and operational guidelines.
l l
If you have any questions or desire additional information, please contact us.
Very truly yours, YANKEE ATOMIC ELECTRIC COMPANY
'k
. A. Kay Senior Engineer - Licensing JAK/ kip
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50128 820615 ADOCK 05000029 PDR
YANKEE ATOMIC ELECTRIC COMPANY
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United States Nuclear Regulatory Commission June 15, 1982 Washington, D. C. 20555 Attention:
Mr. Dennis M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing
References:
(a) License No. DPR-3 (Docket No. 50-29)
(b) USNRC Letter to YAEC dated February 25, 1982
Subject:
Reactor Coclant System Vent System i
Dear Sir:
The attached information has been prepared in response to Reference (b).
This information provides further clarification of NRC staff concerns pertaining to the design of the installed, but not operational, Reactor Coolant System (RCS) Vent System.
In addition, the attached RCS Vent System Operational Cuide11nes have been prepared, as requested. These guidelines are based on the guidelines prepared by the Westinghouse owners Group effort, and describe when the operator should and should not manually vent the Reactor Coolant System.
Plant specific procedures for system operation will be written upon acceptance of the system design and operational guidelines.
j If you have any questions or desire additional information, please I
contact us.
l Very truly yours, i
i YANKEE ATOMIC ELECTRIC COMPANY J1 gyp i
. A. hy l
Senior Engineer - Licensing JAK/ kip
[
8206250128 820615 PDR ADOCK 05000029 P
ADDITIONAL INFORMATION REQUESTED FOR YANKEE RCSVS 1.
Demonstrate that the reactor coolant system vent system (RCSVS) flow restriction orifices are smaller than the size corresponding to the definition of a loss-of-coolant accident (10 CFR Part 50, Appendix A) by providing a calculation of the maximum rate of loss of reactor coolant through the RCSVS orifices (reference NUREG-0737, Item II.B.1 Clarification A.(4)).
Response
Each vent line has an orifice installed as close as possible to the tie-in to the existing system piping.
In the event of a break in the vent piping downstream of the orifice, the orifice has been sized to limit the leak rate to approximately 30 gpm.
This is within the makeup capacity of one charging pump, and is therefore less than the leakage rate corresponding to a loss-of-coolant accident. Detailed design calculations are available for NRC review in the plant files.
2.
The following items apply to the portions of the RCSVS that form a part of the reactor coolant pressure boundary, up to and including the second normally closed valve (reference NUREG-0737, Item II.B.1 Clarification A.(7)).
Provide the design temperature and pressure of the piping, a.
valves, and components.
Response
All piping, valves, and components are in accordance with the applicable piping class specified in the Specification for Piping for the Yankee plant; 2300 psig and 5500F.
b.
Verify that the piping, valves, components, and supports are classified Seismic Category I.
Response
Detailed piping, analysis and support design calculations are available for NRC review at Yankee Atomic Electric Company.
Describe the instrumentation that has been provided to detect c.
and measure RCSVS isolation valve seat leakage (reference Appendix A to 10 CFR Part 50, General Design Criterion 30).
Response
Both vent paths discharge into the pressurizer power-operated relief valve (PORV) discharge piping. This line has a temperature detector with indication and alarm in the main control room. This line also ties into the pressurizer safety valve discharge piping which also has a temperature detector with indication and alarm in the main control room. Any leakage by the RCSVS isolation valves will be collected in the low pressure surge tank (LPST). LPST tank I
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level, pressure and temperature are indicated and alarmed in the main control room.
d.
Describe the materials of construction and verify that they are compatible with the reactor coolant chemistry and will be f abricated and tested in accordance with SRP Section 5.2.3,
" Reactor Coolant Pressure Boundary Materials."
Response
All materials were purchased in accordance with the applicable piping class from the Specification for Piping for the Yankee plant. The system was fabricated and tested in accordance with applicable plant procedures. Details are available at the plant for NRC review.
Demonstrate that internal missiles and the dynamic ef f ects e.
associated with the postulated rupture of piping will not prevent the _ essential. operation of the. RCSVS (i.e._, _at least one vent path remains function'al) (reference 10 CFR Part 50 Appendix A, Ceneral Design Criterion 4).
Response
The reactor vent valves and piping are located outside of the pressurizer cubicle. There are no internal missile sources in this The pressurizer vent valves are located inside the a re a.
pressurizer cubicle. A 2 foot thick concrete wall is between the two vent paths.
The cross-connect line runs mostly along the wall, and is relatively well shielded from internal missiles generated inside the pressurizer cubicle. Because of the separation, at least one vent path would remain functional in the event of internal missiles and their effects.
3.
Verify that the following RCSVS failures have been analyzed and found not to prevent the essential operation of safety-related systems required for safe reactor shutdown or mitigation of the consequences of a design basis accident, Seismic failure of RCSVS components that are not designed to a.
withstand the safe shutdown earthquake.
Response
The only non-seismic portion of the RCSVS is the discharge piping downstream of the second isolation valve. This piping is only 1 inch, and no safety-related equipment is located in the same area.
b.
Postulated missiles generated by failure of RCSVS components.
Response
The only RCSVS components that could generate missiles are the vent valves. There are no safety-related systems located in the areas that would be affected by the potential missiles.
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Dynamic ef fects associated with the postulated rupture of RCSVS c.
piping greater than one-inch nominal size.
O
Response
All RCSVS piping is _6.1 inch.
d.
Fluid sprays from RCSVS component failures. Sprays from normally unpressurized portions of the RCSVS that are Seismic Category I and Safety Class 1, 2 or 3 and have instrumentation for detection of leakage from upstream isolation valves need not be considered.
Response
No safety-related equipment is located in areas that would be affected by fluid sprays from the RCSVS piping.
Verify'that all-RCSVS-valves -f ail closed upon loss of_ power, _or 4.
provide a reliability analysis consisting of a failure mode and
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ef fects analysis (FMEA) or equivalent qualitative analysis that shows that no single active component f ailure could result in failure to close af ter intentional opening of. an RCSVS path.
In particular, if the vent valves do not fail closed and if the cross-connect piping between the pressurizer and reactor vessel the head vent paths is being used, a power f ailure would prevent isolation of the vent path (reference NUREC-0737, Item II.B.1 Clarification A.(8)).
Response
The four valves used in the RCSVS are motor-operated and therefore fail as-is on a loss of power. Each vent path contains two valves in series, powered f rom dif ferent power supplies. Therefore, after venting has been initiated from either path, a loss of one power supply or a failure of one valve to close will not prevent the isolation of the vent path by the remaining valve.
The cross-connect piping and two valves powered f rom the same emergency power supply will only be utilized in the event of a failure of one emergency power supply before venting commences.
Before utilizing the cross-connect piping, the potential consequences of a loss of the remaining power supply and the the inability to terminate venting would have to be weighed against consequences of not venting. Again, the cross-connect is only utilized when a failure of one emergency power supply has occurred before venting has commenced.
14, 1981 submittal states that the pressurizer vent valve Your July 5
is powered f rom a nonemergency motor control center (MCC), which is powered by an emergency diesel in the event of a loss of off-site is unclear based on this whether Clarification A.(8) of power.
It NUREC-0737, Item II.B.1, requiring that each vent must have its power supplied by an emergency bus has been met.
Clarify the capability to provide emergency power to the pressurizer vent h
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a valve, including factors such as load-shed priorities, the time and manual actions necessary to connect the nonemergency MCC to the emergency diesel, and load sequencing delays.
Response
The plant procedure for " Loss of AC Supply" details the actions necessary to power nonemergency loads from an emergency diesel.
Before an emergency diesel can be used to supply nonemergency loads, the two major loads on that diesel must be secured - the high pressure and low pressure safety injection pumps. The " Loss of Main Coolant" procedure contains the criteria for securing safety injection pumps.
All of the manual actions required to power the nonemergency motor control center for the pressurizer vent valve from an emergency diesel are performed in the control room and the switchgear room, which is located directly under the control room. Only one operator is needed-to perform the electrical. switching. _Once_it __. _
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has been determined that this electrical alignment is needed and a diesel is available, the manual actions needed would require approximately 15 to 30 minutes to complete.
6.
Demonstrate, using engineering drawings (ineluding isometrics) and design descriptions as appropriate, that the rupture disk on the PORV discharge piping and the rupture diaphragm f rom the low pressure surge tank safety valves discharge into areas:
That provide good mixing with containment air to prevent the a.
accumulation or pocketing of high concentrations of hydrogen, and
Response
Figure 1, attached, details the air flows generated by the vapor container post-accident recirculation system. This drawing has also been marked with the approximate locations of the PORV discharge piping rupture disk and the rupture diaphragm from the low pressure surge tank (LPST).
In both cases, the discharge points are in areas that provide good mixing. The PORV discharge piping rupture disk is located at the lowest level of the pressurizer cubicle.
It discharges into an area that is below the bottom elevation of the compartment divider walls. This location af fords open communication with all of the other loop compartments. The LPST rupture diaphragm is located at a low elevation in the vapor container (V.C.) in the area between the biological shield and the outer skin. This area is completely open around the entire circumference of the V. C.
b.
In which any nearby structures, systems, and components essential to safe shutdown of the reactor or mitigation of a design basis accident, are capable of withstanding the effects of the anticipated mixtures of steam, liquid, and I
( 1
noncondensible gas discharging f rom the RCSVS (reference NUREG-0737 Item II.B.1 Clarification A.(9)).
RESPONSE
The two discharge points do not discharge in areas where components essential to safe shutdown of the reactor would be affected by the resulting sprays.
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