ML20125D424
| ML20125D424 | |
| Person / Time | |
|---|---|
| Issue date: | 09/29/1976 |
| From: | Bosnak R Office of Nuclear Reactor Regulation |
| To: | Novak T Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20125D401 | List: |
| References | |
| REF-GTECI-A-26, REF-GTECI-RV, TASK-A-26, TASK-OR NUDOCS 8001140295 | |
| Download: ML20125D424 (5) | |
Text
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C MEMORANDUM FOR: T. Novak, Chief, Reactor Systems Branch, Division of Systems Safety T ,y, FROM:
R. J. Bosnak, Acting Chief, Mechanical Engineering Branch, Division of Systems Safety ,
SUBJECT:
RSB BRANCH TECHNICAL POSITION ON REACTOR COOLANT SYSTEM OVERPRESSURE PROTECTION Your memorandum of September 7 to distribution requests comments to assist in formulating detailed requirements for the technical position RSB is developing regarding RCS overpressure protection under water solid conditions.
In response, attached to this memo are Mechanical Engineering Branch recommendations to assist in drafting the proposed BTP.
R. . Bosnak, Acting Chief Mec nical Engineering Branch Division of Systems Safety cc: R. Fluegge, SS H. Brammer, SS W. Minners, SS C. Berlinger, OR R. Bosnak, SS F. Cherny, SS .
D. Ross, SS !
S. Pawlicki, SS 90017158 l
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MECHANICAL ENGINEERING BRANCH DIVISION OF SYSTEMS SAFETY DESIGN CRITERIA RECOMMENDATIONS FOR RSB BRANCH POSITION ON OVERPRESSURE PROTECTION OF REACTOR COOLANT SYSTEM DURING WATER SOLID OPERATION Ref: T. Novak letter of 9/7/76 The September 7 letter request recommendations for input to the reference Branch Position that RSB is developing. It is our understanding the proposed position is intended for use in the review of licensing applications.
The particular overpressure problem to be addressed by the BTP has been prevalent in PWR's when they operate with the reactor It coolant system water is our understanding solid during plant start-up or shutdown conditions.
that there may be some system related modifications which can be made to eliminate this type of problem, such as perhaps not operating at all in the water solid cond1 tion. One way to accomplish this, which has been mentioned by utilities, is to maintain a nitrogen bubble in the pressuri::er during plant startup and shutdown phases. Our recom=endations are not directed at this type of protection mechanism.
We understand that two types of pressure relief valves are under discussion which may be able to provide the required protection. The purpose of such valves would be to relieve liquid at an appropriately determined pressure to prevent the system pressure from exceeding the Appendix G limit.
The two types of valves that have been mentioned are: (a) A_ spring actuated liqui _d relief valve which opens at a selected set pressure solely due to an increase in system pressure and (b) A power actuated relief valve which depends _on an external energy source and a separate pressure sensing device for actuation. The following are Mechanical Engineering Branch recommenda-tions for design criteria related to the use of these two types of valves.
We recotanend that any pressure relief valve installed for the specific purpose of providina protection against exceeding the Appendix G limit be designed and fabricated to ASME Code Section III Class 1 requirements.
This is commensurate with the quality level of the compo nt(s) for which the protection is being provided.
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i 2-Additionally, we recommend that consideration be given to the following when reviewing proposals for specific valve installations and their supporting analyses:
For Spring Actuated Liquid Valves:
(1) Such valves are not as yet officially recognized in ASME Section III for Class 1 service. As you are aware, overpressure protection requirements for ASME Class 1 components are provided in NB-7000 of ASME Section III. To date, the provisions of NB-7000 have been oriented toward presiding protection solely for FWR and BWR reactor coolant systems under power operating conditions which, until recently, has involved the relief of steam from the system to limit the pressure.
With the advent of such things as ATWS and the Clinch River Breeder reactor, it has been recognized that NB-7000 must be revised to address functional and certification requirements for Class 1 pressure relief devices which involve relief of fluids such as water, gas or air in addition to steam. Currently, the Section III Subgroup on Pressure Relief is rewriting and expanding the scope of NB-7000 to include such requirements.
Until these recuirements are published in the code,MEB recommends that spring actuated liquia relief valves intended for ASME Class 1 service, comply with the functional recuirements currently specified in the code for Class 2 licuid re14 a# valven;as specified in paragraphs NC-7614.1 and NC-7614.2. These are essentially the same reouirements that are being added to ME;7 04J *^* eh= class 1 valves. Analyses submitted by applicants to demonstrate that a proposed liquid relief valve installation is adequate to prevent system pressure excursions in excess of Appendix G limits should specifically take into account the tolerances permitted by NC-7614.1 and NC-7614.2 for such things Inis is or particular a_s popping point and valve full lif t pressure.
significance for system operation in the water solid condition where the rate of pressure increase resulting from fluid expansion can be quite high.
test or (2) Ehe relieving capacity of such valves should be certified by as permitted for Class 2 relief valves in NC-7811(b). If a @fication is performed by testing, code case 1700 provides an certi acceptable certification procedure for valves that relieve non-flashing liquid.
For Power Actuated Relief Valves:
(1) ME3 recommends that these valves meet all the requirements of paragraph NB-7630 of ASME Section III. The reliability record of such valves 90017160 i
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-3 i_s poor when compared to that of spring actuated valves. The staff recognized this curing the review of Anticipated Transients Without Scram by requiring vendors to consider one such valve as inoperable during the ATWS transient. This is consistent with the NB-7630 require-ment that when such valves are used for providing required system over-S. pr_ essure protection, rather than just for plant operational convenience, 0
8 as they generally are; redundant valves are to be used and safetv grade 8p sensing and control systems arefrequired) As f or tne(Fpring actuaq]p hg e v.2ve, including "wors case" tolerances 1 1 es, the response tim-bgp0I on va nd sen evices, should be taken into ace unt in analyses performed to emonstrate the adequacy of the protect n afforded by the valve. Such valves are not always rapid opening d ices. For example, it is our understanding that some valves of (KTs tvo - rr-tly in use on rWK pressurizers, require as long as three seconds to move from full closed to the tuli open position.
(2) Power Actuated Relief valves for use in liquid service should be certified as previously described for the spring actuated relief valves.
With regard to inservice testing to assure operational readiness, MEB does not feel there is any reason to test with a frequency anv dif ferent from what is specified in ASME Section XI for the cressurizer safety vnivos.
10 crx 50.55a (g) requires that either of these valve types be tested in accordance with Section XI.
For your information, the Section III Subgroup on Pressure Relief has aereed to add a requirement to the code which specifically addresses overpressure
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protection of components to protect against nossible nonductile f ailure.
The cet effect of this revision should be:
(1) The code will require that a determination be made at the system design stage as to whether pressure relief capacity should be added in order to protect one or more components in the reactor coolant system from possible non-ductile f ailure. This subject will be addressed in the ;
code required Overpressure Protection Report.
(2) If the review performed per 1 above indicates that some relief capacity is necessary to provide for protection against non-ductile failure,,the J code will require that pressure relief valves installed for this purpose !
must be recognized in article NB-7000 as an acceptable valve for Class 1 service and must meet all the requirements specified in the article for l that type of valve. ,
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- - Recommendations regarding an approerinta anfety limit for startuo and
_ shutdown will be f orthcoming from the Materials Engineering Branch in eparate corresponcence, i i h l'$$/
F. Cherny f Mechanical Engindering Branch Division of Systems Safety Approved Y i ed H. L. Brammer, Section Leader Mechanical Engineering Branch Division of Systems Safety 90017162
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