ML19323E680
| ML19323E680 | |
| Person / Time | |
|---|---|
| Issue date: | 02/12/1976 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19323E675 | List: |
| References | |
| RTR-NUREG-75-087, RTR-REGGD-01.139, RTR-REGGD-1.139, TASK-EM-801-4, TASK-OS NUDOCS 8005270124 | |
| Download: ML19323E680 (5) | |
Text
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2/12/76 i.
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ENCLOSURE 1 f
4
' l WORKING PAPER GN RESIDUAL HEAT REMOVAL I.
Surmary of Procesal A revision to Standard Review Plant (SRP) 5.4.7 on the Residual Heat Removal (RHR) System is proposed to accomplish the following:
(1)
Approve a Branch Technical Position that documents the current NRR position on residual heat removal, from the reactor, and (2)
Clearly delineate the review responsibilities of the Reactor Systems and Auxiliary and Power Conversion System Branches regarding residual heat removal.
II.
Backer 22a1 An overall staff position on residual heat removal has been evolving for several years.
After a large number of ad hoc decisions on individual cases, a joint technical review -
projects position was reached and documented in Reference 1, in February 1974.
Although this position has been generally applied since that time, its application has not been con-sistent.
Apparently this is because Reference 1 was never formalized as a branch position or regulatory guide.
Some representative plants that have been required to satisfy many elements of the proposed position are CESSAR, WPPS 3 and 5, Floating Nuclear Power Plant.
The attempted imposition of the positions in Reference 1 to the Standard RESAR-41 and GESSAR plants led to appeals by General Electric and Westinghouse. At meetings the reactor manufacturer's position has been that the RHR system was not required to be designed as a safety system since:
(1)
The plant could remain at hot shutdown conditions indefinitely, and (2)
There are alternate (other non-safety grade) means of reducing the reactor coolant system temperature and pressure.
However, the positions stated by the reactor manufacturer's are not completely consistent with GDC 34.
General Design Criteria (GDC) 34 clearly states:
(1)
Removal of residual heat frem the reactor is a safety
- function, 8005270 4 (
e.
l' (2)
The safety function is to be acccmplished with only on-site or off-site power available, (3)
The safety function is to be acecmplished using only f
safety grade equipment, and i
(4)
The safety function is to be accomplished despite a single failure.
GDc 34 does not explicitly require that the plant be brought to a cold shutdown condition.
However, there is an tsplied requirement (based on reasonable engineering design) that the plant be able to be brought to a cold, depressurized condition in a reasonable length of time.
This step is necessary, if removal of fuel is to be accomplished.
The reactor manufacturer's position stated in the appeals meeting led, in turn, to a complete re-evaluation of all aspects of the position by the NRC staff.
The major '
conclusions of this staff re-evaluation were:
(1)
The requirements i= posed on the RHR system were generally supportable by the regulations, but in some cases were too inflexible.
(2)
The position considered only low. pressure RHR syste=s that were located outside of the containment.
(3)
Definitive design criter'- should be establishti for the systems and components tc
'd to lower the reactor coolant temperature and pressure,
values that permit operation of the RHR system.
A revised position that corrected these deficiencies was developed by the staff.
This po;ition was documented in the response to the reactor manufacturers' appeals.
(References 2 & 3).
III. Procosed Position The objective of the proposed Bran:h Technical Position is to establish definitive design requirements for all of the systems that are required to transfer residual heat from the reactor to the ulttnate heat sink.
In addition the position considers the possibility of high pressure RHR systems and low pressure RHR systems located inside of centainment, as well as the more typical low pressure RHR system that is located outside of the contain=ent.
o i
j -
n The overall position is presented in Branch Technical Position
'j RSB 5-1, " Design Requirements of the Residual Heat Removal System."
2 IV.
Value Assessment The proposed Branch Technical Position and revisions to SRP 5.4.7 define requirements for a safety grade system (s) to transfer fission product decay heat from the reactor to the environment.
The entire range of reactor coolant system temperature and pressures, frem nor=al operatiag valves to cold shutdown are considered in the proposed position.
Previous positions only treated the range of temperatures and pressures that occurred once the RHR system was placed into operation.
As noted in the following paragraph, the transfer of fission produce. decay heat to the environment over this entire range is important to safety.
The importance to safety of an operable method of transferring this heat is demonstrated by the results presented in the final draft of the Reactor Safety Study, WASH-1400.
That report shows, for PWR's, that the inability to remove decay heat from the reactor following a normal shutdown has a higher probability of resulting in a core melt than does a large LOCA'for all seven of the radioactive release categoriec associated with a core melt.
For BWR's, the report shows tha!. the inability to transfer decay heat from the reactor following a normal shutdown is the largest contributor to the core melt probability for the four highest radioactive release categories.
Therefcre, it is obvious that the ability to transfer heat from the reactor to the environ-
=ent is an extremely important safety function, for both PWR's and BUR's.
The promulgation of a definitive Branch Technical Position will also increase the efficiency of the review process.
- Recently, a series of ad hoc decisions have been made regarding specific deviations from the proposed position.
Each of these decisions have been preceded by a series of time consusing =eetings with the applicant and with various levels of management.
A definitive position should elisinate much of this effort.
V.
Imoact Assessment The Espact of the proposed position is anticipated to be relatively small.
Since the proposed position is intended to be applied only to Steadard Plants and future CP reviews, any required design changt. should be able to be acceplished as part of the normal plant design effort.
I.
4 i i 1
The anticipated design changes and analysis requirements are as follows:
(1)
For PWR's, the atmospheric dump valves would have to be designed to safety grade standards and would have to be provided with on-site and off-site power supplies.
An analysis would have to be provided to show that the plant could be trought to a cold shutdown condition (200*F) within a reasonable period of time with only on-site or off-site power available, assuming the most liniting single failure.
Since the RHR system, with no single failure, is designed to reduce the reactor coolant temperature to about 140 F in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, for the purpose of refueling, no significant difficulty is anticipated in satisfying this " reasonable period" requirement of bringing the plant to 200 F with a single failure.
The proposed revision to SRP 5.4.7 specifies 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> as being a reasonable period.
(2)
For BWR's, the reactor manufacturer has verbal'y stated that their design satisfies all of the requiremeras of the proposed position.
However, documentation is requicut to show that this is the case.
Since the design changes and additional efforts required are s=all, no schedule delays are anticipated.
The NRC staff does not have specific cost information; however, any hardware costs resulting from the proposed position are thought to be small.
VI.
Procosed Imolementation Plana Approval of the RRRC is requested to include the proposed position in the SRP as a Branch Technical Position and begin implementation in the review of custom CP applications docketed after March 1, 1976 and all standard plant applications.
SD also will be requested to initiate development of a Regulatory Guide.
When the Guide is
- issued, the SRP would be revised to delete the Branch Technical Position and reference the Guide, so that any changes in the position resulting from the development of the Guide would be incorporated.
VII. Backfittine Potential The position of URC regarding implementation of regulatcry guides and branch positions is expressed in Reference 4.
This letter, which received concurrence from Mr. Rusche and Dr. Knuth states that,
" Branch technical' positions...are used in the review of active applications.
As with regulatory guides, only in rare cases where
a 4
essential matters are involved will they be backfitted by applying them to plants already reviewed and then in accordance with 10 CFR 50.109."
Regarding Regulatory Guides, the letter states, "Only in rare cases where truly essential matters are involved do we plan to consider backfitting, cnd then based only on careful case-by-case reviews and in accordance with the requirements of 10 CFR Part 30.109."
Based on this stated NRC philosophy, the proposed position is not considered to be a subject of backfit requirements.
VIII.
Sagrdination The proposed Branch Technical Position has been extensively reviewed within NRR.
The position incorporates the require-ments stated in references 2 ahd 3 These letters had con-currence from the Director and appropriate Assistant Directors of Technical Review and Reactor Licensing.
References:
1.
Memorandum to R. C. DeYoung, V. Stello, et. al., from John Angelo entitled "RP-TR Staff Meeting of February 13, 1974 Regarding the Requirements on Shutdown Cooling Syntess," February 28, 1974.
2.
Letter to Mr. Clement Eiche1dinger, Westinghouse Electric Corporation from Roger Boyd, November 12, 1975.
3 Letter to Mr. Ivan Stuart, General Electric Company, free Roger Boyd, November 12, 1975.
4.
Letter to Mr. J. D. Geier, Illinois Power Company, from Robert Minogue, July 8, 1975.
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