ML20070B940
| ML20070B940 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 06/29/1994 |
| From: | Horn G NEBRASKA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NSD940550, NUDOCS 9407010107 | |
| Download: ML20070B940 (10) | |
Text
v Y
fserk COOPER NUCLE AR STATON s
n M "4
P.O BOX 98, BROWNVILLE. NEBRASKA 68321
{Q 4 Nebraska Public Power District "in~i%C'""
g M M ____ _ _
NSD940550 June 29, 1994 U.S.
Nuclear Regulatory Commission Attention:
Document Control Desk washington, DC 20555 Gentlemen:
Subject:
Exemption Requests - LLRT of Globe and Stop-Check Globe Containment Isolation Valves in Reverse Direction Cooper Nuclear Station NRC Docket No. 50-298, License No. DPR-46 10 CFR 5 0, Appendix J,Section III.C establishes the leakage testing requirements for Type C tests on individual primary reactor containment penetrations.
This regulation requires, in part, that pressure shall be applied in the same direction as that when the valve would be required to perform its safety function, unless it can be determined that the results from the tests for a pressure applied in a different direction will provide equivalent or more conservative results.. " -
The Nebraska Public Power District (District) has recently initiated a design basis reconstitution effort for the primary containment at Cooper Nuclear Station (CNS). As a result, f our valves, two globe and two globe stop-check valves, were identified where the current local leak rate test (LLRT) method of applying pressure in the direction opposite to the accident direction, cannot be quantitatively determined to yield results that will provide equivalent or more conservative results to testing in the accident direction, as required by the above regulation. The current configurations of these valves does not allow testing to be performed in the accident direction.
On the basis of the information contained in the attachments to this letter, the District hereby requests permanent exemptions f rom the above identified Appendix J requirements for the four valves identified. The District requests that these exemptions remain effective until the expiration of the CNS Operating License, or until otherwise requested and granted.
10 CFR 50.12 (a) provides the Nuclear Regulatory Commission (NRC) a means of granting exemptions to the requirements of 10 CFR 50 if "special circumstances" are present and the exemptions, " authorized by law, will not present an undue risk to the public health and saf ety, and are consistent with the common defense and securi t y. "
On the basis of the information provided herein, the District concludes that "special circumstances" exist which justify the individual permanent exemptions for the subject valves under the standards of 10 CFR 50.12. to this letter identifies those special circumstances that are present and the bases f or why the requested exemptions will not present an undue risk to public health and safety because the underlying intent of Appendix J will continue to be met. contains other basic information regarding these valves.
9407010107 940629 PDR ADOCK 05000298 fl P
- l l-e,-,
e ym-y-r mememmyym-m fU!N.
O s 1n1
!)n A%wwwwks bs1LL xxkuwawwandD
_~.
1 V
\\
'U.S.
Nuclear Regulatory Commission June 29, 1994 Pagd 2 of 3 With respect to the schedule for review of these exemption requests, the District respectfully requests approval prior to July 8,
1994, which is the current projected end date of the current unplanned outage.
Since ely, Ho 0- -
(
rn ucl ar Power Group Manager GRH/GRS/dnm Attachments cc:
H.
R.
Borchert Department of Health State of Nebraska NRC Regional Office Region IV Arlington, TX NRC Resident Inspector Cooper Nuclear Station
)
I 1
'U.S. Nuclear Regulatory Commission June 29, 1994 Page 3 of 3 STATE OF NEBRASKA)
)
NEMAHA COUNTY
)
G.
R.
Horn, being first duly sworn, deposes and says that he is an authorized representative of the Nebraska Public Power District, a public corporation and political subdivision of the State of Nebraska; that he is duly authorized to submit this request on behalf of Nebraska Public Power District; and that the statemen s contained herein are true to the best of his knowledge and belief.
I I
- A L-~
c y.
R.
><ern b
Subscribed in my presence and sworn to before me this day of j
groa 1994.
hLOh / h')4tc U J b adLct M M m m omi NbTARY PUBLIC ME
4 NSD940550 Page 1 of 6 COOPER NUCLEAR STATION NRC DOCKET NO. 50-298 OPERATING LICENSE DPR-46 APPENDIX J EXEMPTION REQUESTS LLRT OF GLOBE AND STOP-CHECK GLOBE CONTAINMENT ISOLATION VALVES IN THE REVERSE DIRECTION Exemption Request Appendix J,Section III.
C.
1 states, in part:
Type C tests shall be performed by local pressurization.
The pressure shall be applied in the same direction as that when the valve would be required to perform its safety function, unless it can be determined that the results from the tests for a pressure applied in a different direction will provide equivalent or more conservative results.
In accordance with the requirements of 10 CFR 50.12, the Nebraska Public Power District (District) requests four permanent exemptions from the requirements of 10 CFR 50, Appendix J, Section III.C.1.
These permanent exemptions, if granted, need to be effective until the expiration of the CNS Operating License, or until otherwise requested and granted.
Discussion The District is applying for permanent exemptions for each of the following valves at CNS : RHR-MOV-MOl67A, RHR-MOV-MOl67B, RCIC-V-37, and HPCI-V-44. M0167A and MOl67B are globe valves. Valves RCIC-V-37 and HPCI-V-44 are stop-check globe valves.
A stop-check globe valve disk is not connected to the valve stem.
Normal flow comes from underneath the seat and pressure on the disk forces it off of the seat causing the valve to open. The disk is guided by a disk skirt in the valve.
Under backflow conditions, the pressurization of the torus (during accident conditions), in conjunction with gravity, forces the disk into the seat and closes the valve.
The four identified valves are not currently testable in the accident direction due to the inability to isolate the valves from the containment and the lack of test connections.
In general, LLRT testing of globe valves in the reverse direction is more conservative than testing in the accident direction with respect to seat leakage because the pressurization is under the seat.
- However, by testing in the reverse direction, the valve bonnet or packing are not exposed to the LLRT pressure and possible leakage would not show up in the LLRT results.
Ccattrary to the requirements of Appendix J, while the testing from the reverse direction of these valves would provide more conservative seat leakage, it cannot quantitatively be demonstrated to provide equivalent or more conservative valve leakage testing result due to the potential for leakage through the packing and bonnet gasket.
.__m
.._ _ ~-_.___ _ _
NSD940550 Page 2 of 6 t
However, there are several factors, discussed below, which provide a high level 3
of confidence that reverse direction pressure testing is acceptable, for the I
valves in question, and does not yield significantly dif ferent results than what j
would be expected in the accident direction.
i i
The first factor is that reverse testing of globe valves generally results in a i
conservative seat leakage rate.
The pressurization test applies force in the direction which would unseat the disk, thereby having a tendency to increase i
leakage.
This increase in seat leakage would offset the inability to measure j
leakage through the bonnet or the packing which are on the non-testable side of the valve.
The valve seats are nonflexible, close tolerance machined surfaces with a significant potential for degradation during the operating cycle from l
mechanisms, such as contact wear and flow-induced wear.
Packing is a flexible e
material, which conforms to the surfaces within the packing gland and is capable i
of sealing significant surface discontinuities. The bonnet gasket is installed with a preload on the bolts, which is determined such that unloading will not occur at f aulted pressure conditions; the gasket is also a somewhat flexible and l
conforming material. Although the bonnet and packing leakage rate could not be l
separately quantified with this testing methodology, maintenance history on these valves, along with the recent ILRT, have not provided any indication that bonnet or packing leakage exists or is significant. Additionally, industry experience has shown that leakage through these two paths is generally insignificant.
i The second factor is that all of the subject valves are tested in the accident l
direction during the ILRT, thus exposing all of the pressure retaining parts of the valves, including the bonnet and packing, to the design basis pressure (58 j
psig). Although there are vacuum breakers on the lines containing valves RCIC-V-l 37 and HPCI-V-44, the vacuum breakers are opened by the ILRT pressurization, thus subjecting these valves to the accident pressure. Valvec RHR-MOV-167A and B also
{
see a Type A pressure through the same path.
The 1991 ILRT yielded a total j
leakage rate for primary containment of 102.5 standard cubic feet per hour (sefh).
If a significant leak associated with one of these valves had existed,
[
the ILRT pressure test would have indicated cuch leakage.
f In taking the factors presented above into account, it should be noted that a considerable margin exists to account for additional leakage, if any, that may j
take place should the valves be called upon to retain the design basis pressure.
l This margin is based on data collected from both the 1991 ILRT and 1993 LLRT results for the subject valves. The total as-left minimum path leakage (reverse direction tested) measured in 1993 for these valves was 1.07 scfh. As of June i
22, 1994, the minimum path as left leakage for all type B and C tests, totaled
.[
- 1174 95 scfh (including the subject four penetrations). The 1991 ILRT, as stated
[
above, yielded results of 102.5 scfh.
Given the startup limit of 189 scfh and 316 scfh (total allowable limit), the local leakage rate for the valves in
)
question for startup or operation, would have to be approximately (total for the four valves) 71 scfh U and 198 sefh, respectively, to approach the Technical Specification limits. Therefore, the requirements of 10 CFR 50, Appendix J, and
{
the CNS Technical Specifications leakage restrictions, are continuing to be met.
l l
1.
It should be noted that a similar approach was utilized in the schedular exemption request l
f submitted to the NRC per District Letter dated June 7, 1993, "LLRT of Containment Isolation Valves in Reverse Direction". The data given above does not take into account the potential nonconservatisms discussed in the June 7, 1993 submittal.
i l
NSD940550 i
Page 3 of 6 I
I Aaditionally, all of the valves discussed in this exemption request are part of systems that are not normally subjected to flow, or major temperature or pressure transients. These valves normally remain at ambient temperature conditions, with the exception of the HPCI and RCIC stop-check globe valves, which are i
periodically subjected to mild service conditions either during normal operation i
or surveillance testing (20 psig and 260" F). Being fabricated f rom mineral fibers, the packing and bonnet gaskets do not contain materials which degrade under these type of service conditions.
The final factors are specifically applicable to valves RCIC-V-37 and HPCI-V-44.
These valves are Anchor globe stop-check globe valves. The stem is in the raised position which engages the backseat between the stem and the bonnet under the gland area, thus minimizing the potential leakage through the packing gland. In addition, the stem on these valves is only used during LLRTs.
Because of the inf requent use of these stems, the packing in these valves has a minimum of wear, thus should be highly reliable.
Furthermore, the bonnet of these valves is sealed using a flexitallic gasket.
Industry experience has demonstrated that flexitallic gaskets do not degrade while in service and that the reliability of these components is very high. The District will take measures to assure that the force applied to the valve disc during reverse direction testing will not exceed that which would be applied during design basis accident LOCA conditions.
Finally, the District has been able to observe these valvas during surveillance testing; no steam plumes or leakage from the insulation lagging have been identified during these surveillances.
l The District has evaluated several modifications in order to allow these valves to be Type C tested in the direction of the accident pressure.
For the stop-check globe valves, one of the options proposed consists of relocating the vacuum breakers, associated with the lines containing the subject valves, outside of the torus. This modification would create a water seal, thus removing the stop-check globe valves from the testing requirements.
This modification would involve considerable analyses, including computer modeling, design, and installation to maintain the Mark I attached piping structural standards, without a commensurate improvement in safety. For the RHR and the stop-check globe valves, the District has considered installing a block valve and test connections to allow accident direction testing. Addition of block valves and test connections would increase design complexity, provide additional potential leakage paths, and increase loading on torus attached piping.
The District recognizes that, while the factors discussed above provide a reasonable assurance that leakage through the packing and bonnet is not a problem for these four valves, additional actions are necessary to justify permanent exemption from the " equivalent or more conservative" results requirement of Appendix J..The District proposes that a soap bubble test be performed on the pressurized stem / bonnet boundaries of the valves during the Type A test.
Using the acceptance criteria of zero bubbles 'or this test, this would provide a direct indication of the leak-tightness of the packing and the bonnet. In between the Type A testo, the District will specifically observe valves RCIC-V-37 and HPCI-V-44 for indication of leakage through the insulation lagging during scheduled system surveillance tests which subject these valves to pressurization.
i NSD940550 Page 4 of 6 The following contains the 10 CPR 50.12 analysis. provides additional information regarding the four individual valves requiring permanent exemptions. This information consists of a brief description of the valves and the latest LLRT results.
10 CFR 50.12 Analysis The District concludes that the individual exemptions from the requirements of 10 CFR 50, Appendix J, are justified pursuant to 10 CFR 50.12, Sections (a) (1),
(a) (2) (ii), (a) (2) (iii), (a) (2) (v), and the second portion of (a) (2) (vi) in that:
These exemptions will not present an undue risk to the public health and safety.
The proposed exemptions do not change, modify, or restrict existing plant saf ety limits, saf ety settings, or operations. The exemptions do not impact the design basis of containment or significantly modif y its response during a design basis accident. The most recent LLRT results on the subject four valves provide conservative seat leakage because the testing methodology (reverse direction testing)
I tends to lift the valve disk off of the seat.
These results are expected to account for any potential leakage that could take place through the valve bonnet or packing.
Past LLRT and ILRT results, along with industry experience, for these valves have not indicated that bonnet and packing leakage is a problem.
Application of the regulation in the particular circumstances is not necessary to achieve the underlying purpose of the rule.
The LLRT Type C test information associated with the reverse pressure testing of the subject individual valves demonstrate generally equivalent results to what is required by Appendix J.
There is sufficient documented industry engineering judgment to conclude that any differences in leakage between testing of these valves in the accident direction versus reverse direction testing are not significant, and would provide confidence that leakage rates are within Appendix J limits.
Thus, the underlying purpose of the Appendix J,
which is to limit leakage from primary reactor containment through systems and components penetrating primary reactor containment so that it does not exceed allowable leakage rate values, as specified in the technical specifications or associated bases, has been met.
The NRC has evaluated and granted similar exemption requests and had concluded that permanent exemption from the " equivalent or more conservative results" requirement of Appendix J is justified.
Compliance would result in costs that are significantly in excess of those contemplated when the regulation was adopted.
NSD940550 Page 5 of 6 Until recently, the District believed that it was in full compliance with the requirements of Appendix J,Section III.C.1, based on the fact that testing in the reverse direction for globe valves generally results in conservative leakage results. The District has recently re-evaluated this methodology, as part of the primary containment design basis reconstitution effort, and has determined that reverse testing does not capture potential leakage paths through the valve packing and bonnet.
However, as stated above, literal compliance to Appendix J testing requirements for these valves is not required to demonstrate that the underlying intent of the rule has been met.
Addition of block valves and test connections to allow accident direction testing would increase design complexity, provide additional potential leakage paths, and increase loading on torus attached piping.
For these reasons, literal compliance to this rule would require a considerable amount of analyses, involving computer modeling, design, and additional testing requirements at an undue cost without a commensurate improvement in safety.
The licensee or applicant has made good-faith efforts to comply with the regulation.
The District has recently initiated a design basis reconstitution effort for the primary containment at CNS.
As a result, the District has identified several primary containment i
penetrations / valves that require modification to correct design deficiencies and to provide the capability to be tested per the requirement of 10 CFR 50, Appendix J,
or modified so that the testing requirements are no longer applicable.
The District has taken an aggressive effort to modify and test these penetrations, where applicable, prior to startup from the current unplanned j
outage.
Because of the District's aggressive efforts on this i
matter, the four valves identified in this exemption request are the only valves identified which the District does not believe modification is feasible or practical. The District has proposed to perform a soap bubble check on the pressurized stem / bonnet boundaries of the valves during future Type A tests.
The District i
also proposes to specifically observe the HPCI and RCIC stop-check globe valves during system surveillance tests that expose these valves to pressurization.
The District believes that
'he actions c
taken, along with actions to be taken, represent good f aith efforts to comply with the regulation.
Environmental Consideration The requested permanent exemptions change a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20.
As demonstrated in this attachment, the District has determined that the requested permanent exemptions I
involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, that they l
s-..
. --.~
.~
NSD940550.
[
Page 6 of.6 involve no significant hazards consideration, and that there is no significant increase in individual or cumulative occupational radiation exposure.
Accordingly, the proposed permanent exemptions meet the eligibility criteria for categorical exclusion set forth in 10 CFR Section
- 51. 22 (c) (9),
Pursuant to 10 CFR 51. 2 2 (b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the permanent exemptions.
In summary, the District has concluded that the four permanent exemptions for those valves, discussed above, are warranted under the standards of 10 CFR 50.12.
Continued improvements made during previous outages and those ongoing during the i
current unplanned outage represent the District's prudent steps to improve containment integrity testing and demonstrate the District's good-faith ef forts to satisfy the requirements of Appendix J.
With respect to the schedule for the review of this exemption request, the District respectfully requests approval of this request prior to July 8,
- 1994, i
which is the current projected end date of the current unplanned outage.
The four permanent exemptions are requested to remain until the expiration of the CNS i
Operating License, or until otherwise requested and granted.
v i
P 5
t i
i t
4 g..
e a
..e
NSD940550 Page 1 of 1 COOPER NUCLEAR STATION 10 CFR 50 APPENDIX J, SECTION III.C.1 INDIVIDUAL REQUESTS FOR PERMANENT EXEMPTIONS The District is applying for permanent exemptions from the requirements of 10 CFR 50 Appendix J, Section III.C.1 for the following valves:
RCIC-V-37, HPCI-V-44, i
RHR-MOV-M0167A, and RHR-MOV-MO-167B.
Provided below is additional information the four individual valves requiring permanent exemptions.
This information includes a brief description of the individual valves, 1993 LLRT results, and drawing information.
Additional Information on Valves Recuiring Individual Exemptions 1
l Penetration Number:
X-212, RCIC Turbine Exhaust Valve Number:
RCIC-V-37 l
1993 Min / Max Path LLRT: 0.0000 / 0.0000 scfh
==
Description:==
8",
300 lb, globe stop-check valve Drawings:
B5700 - 2043 (Flow), Anchor Valve Drawing 965-3 i
i Penetration Number:
X-214, HPCI Turbine Exhaust valve Number:
HPCI-V-44 j
1993 Min / Max Path LLRT: 1.0650 / 2.1250 scfh
==
Description:==
20",
300 lb, "Y-shaped" globe stop-check valve Drawings:
B5700 - 2044 (Flow), Anchor Valve Drawing 964-3 Penetration Number:
X-214, RHR Hx A and HX B Vents Valve Number:
RHR-MOV-M0167A 1993 Min / Max Path LLRT: 0.0000 / 0.0000 scfh
==
Description:==
Crane-Aloyco 1",
800 lb, globe valve Drawings:
B5700 - 2041 (Flow), Crane Valve Drawing K-8019A
+
Penetration Number:
X-214, RHR Hx A and Hx B Vents 1
I Valve Number:
RHR-MOV-M0167B 1993 Min / Max Path LLRT: 0.0025 / 0.0050 scfh
==
Description:==
Crane-Aloyco 1",
800 lb, globe valve Drawings:
B5700 - 2041 (Flow), Crane Valve Drawing K-8019A