ML100250972
| ML100250972 | |
| Person / Time | |
|---|---|
| Issue date: | 03/31/2010 |
| From: | Bayssie M NRC/RES/DE/RGDB |
| To: | |
| Bayssie Mekonen/RES 251-7489 | |
| Shared Package | |
| ML100250009 | List: |
| References | |
| DG-1225 RG-1.011, Rev.1 | |
| Download: ML100250972 (4) | |
Text
Staff Responses to Public Comments on Draft Regulatory Guide DG-1225 INSTRUMENT LINES PENETRATING THE PRIMARY REACTOR CONTAINMENT (Proposed Revision 1 of Regulatory Guide 1.11)
(Public comments have been edited for clarity)
Strategic Teaming and Resource Sharing (STARS) Alliance Integrated Regulatory Affairs Group PO Box 1002 Glen Rose TX 76043 (ML093441087)
Comments NRC Comment Resolution DG-1225 Originator Specific Comment NRC Staff Response Section STARS-1 B & C.1 The following statement is contained on page 3 and is The wording was carried forward essentially repeated in Regulatory Position C. 1 on page 4: unchanged from the initial issue of the "Lines connected to instruments that are part of the guidance in 1971. The wording has been protection or safety systems are extensions of those changed to more clearly and affirmatively systems and should satisfy the requirements for convey that the instrument lines, as part of the redundancy, independence, and testability for those system to which the instruments belong, are systems to ensure that they accomplish their functions." required to support the systems achieving the This statement implies that instrument lines should design goals of redundancy, independence, satisfy requirements for redundancy, independence, and and testability. Lines connected to testability. However, designs of sensing lines to instruments that are part of the protection or instruments do not normally have redundant lines going safety systems are extensions of those to the same instrument, and if they did, they would not systems and should support those systems likely be independent. Similarly, testability does not achieving their requirements for redundancy, appear to apply to the line connected to the instrument, independence, and testability to ensure the but rather to the instrument itself or the systems that the systems safety functions are accomplished.
instrument supports.
The paragraph on page 3 following the above statement discusses providing a higher degree of isolation capability for lines connected only to instruments that are not part of the protection or safety systems. The intent of the guidance appears to be focused on the 3/26/2010 Page 1 of 4
capability of the systems supported by the instrument to perform their intended functions, instead of the requirements of the instrument sensing lines.
STARS recommends changing the wording to clarify the application of the guidance to the system function supported by the instrument, as follows:
"Lines connected to instruments that are part of the protection or safety systems are extensions of those systems and should satisfy not adversely impact the systems' requirements for redundancy, independence, and testability for those systems to ensure that they the systems supported by the instruments can accomplish their functions."
STARS-2 B & C.2.b. DG-1225, Section B. Discussion, states (also included NUREG-0800 Standard Review Plant (SRP) in Section C. Regulatory Position, item 2b): Sections 3.6.1, 3.6.2, 3.6.3 and associated "For those instrument lines that are part of the reactor Branch Technical Positions BTP 3-3 and BTP coolant boundary, it is also important to ensure that the 3-4 do not indicate that the normal reactor rate and the extent of coolant loss from the ruptured coolant makeup system capability is component are within the capability of the normal considered only during Modes 1 and 2. The reactor coolant makeup system." NUREG guidance does define normal plant STARS recommends adding underlined words as operating conditions as those that exist during follows: reactor startup, operation at power, hot "For those instrument lines that are part of the reactor standby, or reactor cooldown to cold coolant boundary, it is also important to ensure that the shutdown condition. The wording is the same rate and the extent of coolant loss from the ruptured as that of the initial issue of the RG 1.11 component at power are within the capability of the guidance in 1971 except that the term reactor normal reactor coolant makeup system such that reactor coolant makeup system was changed to trip would be avoided." normal reactor coolant makeup system.
Flow though a ruptured instrument line could vary This change was made to clarify that considerably depending on the state of the RCS system instrument line rupture was not to require fluid. Standard Review Plan 3.6 considers the capability ECCS operation to maintain coolant of the normal reactor coolant makeup system only inventory. (Staff recognizes that pumps used during MODES I and 2. During non-power modes, for normal charging at some plants may also methods other than normal reactor coolant makeup are have a safety related ECCS function.)
allowed. Limiting the design of instrumentation tubing to Similarly, the instrument line rupture should conditions at power is also acceptable since the length not cause a reactor trip as a result of the loss of time at power is much longer than time at non-power of coolant inventory, but the recommended (i.e., greatest probability of rupture). wording might be inferred as Staff guidance 3/26/2010 Page 2 of 4
that operators avoid tripping the reactor when responding to an instrument line rupture event. The recommended change was not incorporated.
STARS-3 B & C.2.d. DG-1225, Section B. Discussion, states (also similarly ANSI/ANS-51.1-83, Nuclear Safety Criteria included in Section C. Regulatory Position, item 2d): for the Design of Stationary Pressurized Because the likelihood of such a rupture is assumed to Water Reactor Plants, (and similarly for be high, the system is designed to result in calculated ANSI/ANS-52.1 for boiling water plants) were radiation doses from just such an instrument line failure incorporated into ANSI/ANS-18.2-74. These during normal operation being substantially below the standards identify plant conditions (PC) guidelines of 10 CFR Part 100, Reactor Site Criteria corresponding to best estimate frequency of (Ref. 2) and GDC 19, Control Room. occurrence. PC-1 corresponds to normal operation (expect to occur each year) and STARS recommends making the following changes: PC-2 corresponds to a frequency of once in Because the likelihood of such a rupture is assumed to 10 years or more often. The appendix B of be high, the system is designed to result in calculated these standards discusses the basis for the radiation doses from just such an instrument line failure plant condition criteria. In section B2, dose during normal operation being substantially below less limits are discussed and indicate PC-1 and than the guidelines of 10 CFR Part 100 50 Appendix I, PC-2 dose criteria are addressed by 10 CFR Reactor Site Criteria (Ref. 2) and GDC 19, Control 50 Appendix I with doses from all events in Room. Numerical Guides for Design Objectives and these plant condition categories summed and Limiting Conditions for Operation to Meet the Criterion best-estimate dose models and meterology As Low as is Reasonably Achievable for Radioactive used. Also stated is that the other plant Material in Light-Water-Cooled Nuclear Power Reactor condition categories have the dose limit Effluents. applied to individual events and dose The probability of a rupture is high and is consistent with consequences calculated using conservative the frequency of events categorized as PC-1 and PC-2 dose models and meterology. No specific (ANSI / ANS 18.2) and is similar to the limits of 10 CFR failure probability is assumed for instrument 50 Appendix I. The limits of 10 CFR Part 100 are much lines, but more than once in 10 years appears higher than 10 CFR 50 Appendix I since they consider higher than originally contemplated. An events of low probability with much greater instrument line failure event is at the border of consequence. These evaluations should use nominal PC-2 and PC-3. Changing the approach to plant and site parameters. Dose assessment should be determining dose consequences was not based on realistic estimates. contemplated and the likely impact of a guidance change to the different methodology 3/26/2010 Page 3 of 4
was not evaluated. The existing guidance results in calculated values that are compared to that which would be allowable in case of PC-3, -4, or -5 event. Although no specific numerical acceptance value has been provided, calculated dose values of less than or near ten percent of the 10 CFR 100 guidelines have generally been found acceptable. The recommended change was not incorporated.
STARS-4 B. DG-1225, Section B. Discussion, page 3 contains a list The four provisions listed from the Discussion of four actions to provide assurance that, for instrument Section B are incorporated into the regulatory lines without an isolation valve inside containment, the positions. The discussion section is provided lines from the containment out to and including the for explanation and regulatory positions are outside valve retains its integrity during normal reactor contained in a separate section. The operation and under accident conditions. proposed additional discussion section list action 5 is not directly replicated in a STARS recommends adding a fifth action to this list to regulatory position. However, Regulatory provide additional emphasis to component level design Position #5 does address consideration of the for post accident environmental conditions, as follows: jet impingement and missile generation
- 1. locating the valve as close to containment as concerns in a more general manner regarding practical, the instrument lines potential effect on one
- 2. adopting a conservative approach in the design of another. Also, this regulatory guide does not this section of the line, override the guidance of Reg Guide 1.89,
- 3. implementing suitable quality assurance provisions, Environmental Qualification of Certain and Electric Equipment Important to Safety for
- 4. performing suitable visual inservice inspections. Nuclear Power Plants, Reg Guide 1.151,
- 5. consider issues associated with environmental Instrument Sensing Lines, and requirements qualification, jet impingement and missile generation. of 10 CFR 50.49, Environmental Qualification of Electric Equipment Important to Safety for Nuclear Power Plants, regarding environmental qualification. The recommended change was not incorporated.
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