ML20113D701
| ML20113D701 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 07/01/1996 |
| From: | James Fisicaro ENTERGY OPERATIONS, INC. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| W3F1-96-0087, W3F1-96-87, NUDOCS 9607030277 | |
| Download: ML20113D701 (8) | |
Text
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y Enti: gy Oper:tions,Inc.
Killona. LA 70066 Tel 504 739 6242 s J. Fisicaro "2 Q"?
W3F1-96-0087 A4.05 PR July 1,1996 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555
Subject:
Waterford 3 SES Docket No. 50-382 i
License No. NPF-38 Request for Relief from 1971 ASME Boiler & Pressure Vessel Code Section Ill, Paragraph NC-7153 Gentlemen:
Entergy requests permanent relief from ASME Boiler & Pressure Vessel Code Section 111 (1971 Edition), paragraph NC-7153 as allowed under 10 CFR 50.55a(a)(3). Specifically, this permanent relief request (1S1-016) is to allow a manualisolation valve to remain installed downstream of a thermal overpressure relief device for Waterford 3's regenerative heat exchanger in the chemical and volume control system (CVCS). Strict compliance with paragraph NC-7153 would result in hardship without a compensating increase in quality and safety, it is the position of Waterford 3 that the plant's existing design configuration satisfies the intent of the ASME, Section 111, paragraph NC-7153 for overpressure protection for the subject condition and therefore provides an acceptable level of quality and safety. Similar relief was granted by the NRC for the Calvert Cliffs Nuclear Power Plant on November 29,1993.
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030082 gy 9607030277 960701 PDR ADOCK 05000382 P
Request for Relief From 1971 ASME Boiler & Pressure Vessel Code Section Ill, Paragraph NC-7153 W3F1-96-0087 Page 2 July 1,1996 Should you have any questions regarding this matter, please contact me at (504) 739-6242 or Tim Gaudet at (504) 739-6666.
Very truly yours, J.dw James J. Fisicaro Director Nuclear Safety JJF/DFUtjs Attachments cc:
L.J. Callan, NRC Region IV C.P. Patel, NRC-NRR R.B. McGehee N.S. Reynolds NRC Resident inspectors Office
Relief Request COMPONENT FOR WHICH RELIEF IS REQUESTED Permanent relief is requested for the manual isolation valve, CVC-220, being located downstream of check valve, CVC-219 (see attached figure). The unit's regenerative heat exchanger transfers heat from the hot, reactor coolant system (RCS) letdown fluid on the tube side of the heat exchanger to the cooler charging pump RCS fluid on the shell side of the heat exchanger. Spring-loaded check valve, CVC-219, provides thermal overpressure relief protection for the regenerative heat exchanger in the event the charging header is isolated and hot RCS fluid continues to flow through the heat exchanger. These two valves, the check and manual valves, are located in a bypass line arrangement around the charging line isolation valve, CVC-218A. The regenerative heat exchanger was designed to the 1971 Edition of the ASME, Section Ill, Class 2.
CODE REQUIREMENTS FROM WHICH RELIEF IS REQUESTED ASME Boiler and Pressure Vessel Code Section ill (1971 Edition), paragraph NC-7153 states:
"No stop valve or other device shall be placed relative to a pressure-relief device so that it could reduce the overpressure protection below that required by these rules, unless such stop valves are constructed and installed with positive controls and interlocks so that the relieving capacity requirements of NC-7400 are met under all conditions of operation of the system and the stop valves."
Strict compliance with this paragraph of the Code would require that the CVCS be modified to eliminate valve CVC-220 from the relief path of the spring loaded check valve CVC-219, or to provide an alternate means of relief protection.
PROPOSED ALTERNATIVE lt is proposed that the plant be maintained in its current system configuration. That is, valve CVC-220 will be maintained in the locked open position. This valve position is assured via the following:
The valve remains physically locked in position by a cable lock.
The valve is controlled by procedure OP-100-009, " Control of Valves and Breakers," which requires that the valve be monitored routinely for position and locked status.
I 5
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Background===
As a result of actions by Baltimore Gas and Electric Co. (BGE) for the Calvert Cliffs' Nuclear Power Plants (CCNPP), an issue was raised as to whether the location of a manualisolation valve downstream of a thermal overpressure relief valve for the regenerative heat exchanger complied with the originalintent of the ASME Code.
The CVCS at CCNPP was designed by Combustion Engineering, Inc. (CE).
Waterford Steam Electric Station, Unit 3, like the CCNPP, has the standard CE design for the CVCS. That is, a manual isolation valve, (CVC-220) exists downstream of a spring-loaded check valve (CVC-219), which is acting as a relief device. Thus, an evaluation was conducted to ascertain whether the current system configuration satisfies the intent of the Code with respect to overpressure protection.
The construction code for the regenerative heat exchanger is the 1971 Edition of the ASME Code. As described in FSAR, Section 9, the regenerative heat exchanger was designed to Class 2. A thorough review of the various ASME Code and Code interpretations for locating stop valves downstream of pressure relieving devices was performed in support of this relief request.
Section ill, Paragraph NC-7153, requires CVC-220 to be installed with positive controls and interlocks. While there are no interpretations of the NC-7153 phrase
" positive controls and interlocks" for the 1971 Edition, later versions of the ASME Code and Code Interpretations, issued post-construction for this plant, do address this issue. An interpretation registered in 1980 of Section ill, Division 1, NC-7142 (Ill-80-67) explicitly states that operating procedures can be part of mechanical controls of a locked valve. However a subsequent revision of the same interpretation (Ill-1-80-67R) in 1989, states that operating procedures are not acceptable.
Since it is not possible to clearly determine the 1971 Edition ASME Code, Section Ill, intent for the words " positive controls and interlocks," Entergy is seeking NRC recognition of the existing CVCS design in the form of Code relief.
Evaluation As previously stated, Entergy evaluated the existing system. It is believed that the current system configuration adequately controls and satisfies the intent of the ASME Code. The evaluation of the existing system condition considered three alternate arrangements. One alternative involved the removal of valve CVC-220 with no other change. However, the design of the system requires valve CVC-220 to be in its current location to facilitate maintenance activities. BGE has estimated that, as a consequence of this modification a cost of approximately $290,000 would be incurred to remove the valve. It is expected that the cost to Entergy would be comparable.
A second alternative was the possibikty of removing the bypass line (including valves CVC-220 and CVC-219) around valve CVC-218A, the charging isolation valve, and installing a dedicated, conventional spring loaded thermal relief valve for the regenerative heat exchanger. This would require a costly, major plant modification which can only be done during an extended outage. Based upon estimates prepared by BGE, this modification would ccst approximately $1 million, and would involve extended activities in a high radiation area. It is likely that similar cost would be incurred at this plant.
The third alternative that was evaluated was the possibility of installing electrical mechanical interlocks between valves CVC-220 and CVC-218A. This would require Control Room panel modifications. Based upon estimates prepared by BGE, the cost associated with this modification would be approximately $685,000, and likewise, involve high radiation exposure. It is expected that comparable costs would be required for this utility. This modification would also result in a more complicated system and additional potential single failures, as well as additional components to monitor in the plant's Equipment Qualification program.
The options available to upgrade the system configuration to current Code editions and interpretations would require either of the following: a.) removing CVC-220,-
b.) replacing CVC-220 and CVC-219 with a relief valve or c.) installing electronic or mechanicalinterlocks between CVC-220 and CVC-218A. All of these options present a significant hardship without a compensating increase in the level of plant quality or safety.
The opposing consequences of not changing the CVCS design are described in the following subsection.
Safety Significanca Valve CVC-219 provides thermal overpressure relief protection for the regenerative heat exchangers. The manual isolation valve, CVC-220, facilitates testing and maintenance of valve CVC-219. Valve CVC-220 is controlled in plant operating procedure OP-100-009, " Control of Valves and Breakers." There are administrative controls and physical restraints in place to prevent inadvertent closure of the stop valve. Valve CVC-220 can be manually closed to perform maintenance activities.
Controlling valve CVC-220 in this manner poses no threat to plant safety.
The concem associated with a manual isolation valve in the relief path is that if a thermal transient were to occur with all normal flow paths and the overpressure relief i
valve isolated, damage could occur to the regenerative heat exchanger. However, this would be a highly improbable occurrence. Also, inherent plant design and
, ~, - -, -
.w,
. existing operating procedures will mitigate the consequences should this improbable event occur.
In order for this to occur the manual valve would first have to be mispositioned closed. This would be a violation of plant procedure. Secondly, both charging flow paths would have to be isolated, simultaneous with the auxiliary spray flow path isolated as well. This is not a normal operating condition of the system; both charging line isolation valves are normally open valves. Inadvertent closure of these valves would only result from two coincident failures. Thirdly, the shell side of the regenerative heat exchanger would have to be isolated while the tube side, letdown flow is not isolated. Again, this is not a normal operating alignment of the CVCS.
In the unlikely event that the above sequence of events were to occur, the worst case damage to the regenerative heat exchanger would be an external rupture of the outer shell. In this situation, the event would be identifiable, when charging is returned to service, and isolable. The leak would be inside containment, thus minimizing external release possibilities. The event would be identifiable by a loss in RCS inventory such as a drop in pressurizer level, due to a mismatch in charging and letdown. The regenerative heat exchanger is capable of being isolated, via remote valves, and an alternate charging flow path can be aligned via the high pressure safety injection system header. This is described in the FSAR.
In the event that the charging header becomes unavailable during a LOCA event, due to this failure, alignment to the high pressure safety lojection (HPSI) system would not be affected. Regenerative heat exchanger failurs will not compromise the ability to align to the HPSI system.
If the component were to rupture internally (i.e. into the tubes), this would be i
inconsequential from a radiological release point of view, since this would not be a system boundary breach. Since the tube side of the regenerative heat exchanger (letdown) is isolated during an accident, leakage into the tubes would have no affect on the emergency boration safety function of the charging system.
It is noteworthy that the original Code classification of the regenerative heat exchanger as a Section Ill, Class 2 component versus Class 1 infers a reduced safety significance relative to failure of this component. Therefore, maintaining valve CVC-220 in its current configuration does not create a significant safety concern.
. -COMPENSATORY ACTIONS Waterford 3 will maintain the existing plant configuration. Valve CVC-220 will be maintained in the locked open position and will be assured so via the following:
The valve remains physically locked in position by a cable lock.
The valve is controlled by procedure OP-100-009," Control of Valves and Breakers," which requires that the valve be monitored routinely for position and locked status.
IMPLEMENTATION SCHEDULE lmplementation is immediate, as the requested relief represents the plant's CVCS in its current configuration with a manual isolation valve (CVC-220) located downstream of a thermal overpressure relief valve (CVC-219).
Simplified Schematic of CVCS Thermal Relief Valve Location Regen.
Letdown To From RCS ------+
M 54 To l-Aux.
y p4 Spray q
From l-To RCS 4
A N
VCT N
To RCS A
N i
i H
y W
Charging Pumps CVC-220 CVC-219 Thermal Relief Valve
-