ML20049A462
| ML20049A462 | |
| Person / Time | |
|---|---|
| Issue date: | 01/28/1981 |
| From: | Murley T Office of Nuclear Reactor Regulation |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19219B002 | List: |
| References | |
| FOIA-81-417 NUDOCS 8103230692 | |
| Download: ML20049A462 (3) | |
Text
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ENCLO3URE Distribution Central File RBaer SHanauer AThadani JAN 2 81981 SPEB File RLobel PCheck DEisenhut TMurley JHannon Dross MErnst VPanciera FTPORA!:Pt'M FOR:
Harold R. renten, firecter, Cffice of Nucleer Reactor Reculatten FPO!':
Thoras E. f urley, Director, Division of Safety Technology, l'RP SUDJECT:
UST PEVIED OF FPC ST/fF SAFETY EVAll'ATIOF REPORT O!! EbR SCPA DISCHARGE SYSTEi'
References:
1.
!'crorandur for C. Lainas, T. i' oval:, P. Tedesco, l'SITC frer P. Check, I!SMRC, fe'R Scrar Discharge Syster Safety Evaluatien, tecember 1,1000.
2.
Icercrandur for Harold P. Centen, t'!HPC frer !!. Ernst, l'StiFC, PST Evaluation of the Auteratic Air Heater Curp en Poiling !!ater Peactors, Decerber 8, loPO.
3.
Anticirated Transients l'ithcut Scrar for Licht l'ater Peactors:
Resolutier of 1:nresolved Safety Issue T/P ;-9, PirREC-0460, l:St.RC Staff.
The Divisicn cf Safety Technolecy has reviewed the t:EC Staff Safety Evaluation Pepert (Sfr) entitled "P!'E Scrar Dischcrpe Systnr Safety fvalt+ tion," cf Decerter 1,19f 0 (Reference 1).
!!e have previcusly (Peference 2) previded yce with our ccreonts on the installation of an interir autoratic air header dien syster recorrended in that safety evaluation. We found that the addition of this syster could provide an irportant increase in Pd!R safety.
Our corrents on the rcrainder of tre SER ere oiven belcw.
The SEE pronoso<* a functicnal criterion and severel safety criteria, operatinc criteria, design criteria and surveillance criteria fer the EtlR scrar discherce syster.
The intent cf these criteria was to trovice cuidance to Pl!P licensees to assure that their screr:
thought to be previded when,these reactors were licensed.discharce systers prov Ratber than pro-posing specific solutions te the prchlens which were identified during the review of the Browns Ferry L: nit 3 partial scran event, these criteria are to be used as guidance te allcw the EilR licensees to resolve the problers in a way best suited to their specific designs.
These criteria vere first prcposed by a subcorrittee of the Cvners Grcup forred to ucrk with the I:RC on this problen.
The tTC staff rave one sienificant addi-tion to the criteria by recuiring thet the stran level instri.ventation be desicned fer cerron cause failure as wall as ronder failure (by the addition of diversity into the desien).
We agree uitb this additicnal criterico since cent.on cause failure redes arc, in general, sicnificant centriburcrs to the overall loss of function and also since instances of cerron cause failure of l
this instrerectation were actually cbserved (e.g., cruste, floats on level instrurentation),
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e Harold R. Denton JAN 2 81981 As noted above, the SER criteria for the Scram Discharge System were divided into safety criteria, design criteria, operating criteria and surveillance cri teria.
In at least one case it is not clear that the division of the criteria into different categories is useful. This case is Design Criterion I which states (in part):
The scram discharge headers shall be... hydraulically coupled to the instrumented volume (s) in a manner to pemit operability of the scram level instrumentation prior to loss of system function.
This appears to be a safety criterion as much as a design criterion Care should be taken to assure that all criteria are met regardless of whether they are called safety criteria or given another designation.
We have reviewed these criteria and find that they adequately aodress all the issues raised during the investigation of the Browns Ferry event.
The St.R lists appropriate ways of meeting these criteria (called " Acceptable Compliance") which will minimi;:e subsequent staff review. We have reviewed these methods of complying with the criteria and find these to be appropriate with the exception of the two alternatives listed for acceptaMe ' compliance with the level instrumentation diversity requirement (pages 3:-40 of the SER).
The first alternative requires level sensors employing a different operating principle for automatic scram from those currently used. The second alterna-tive requires that the cause of damaged floats be identified and corrected (or compensated for) and goes on to require either:
1.
Acditional (or substitute) level switches for automatic scram which are made by a different manufacturer; or 2.
Demonstration that the diverse indication of SDV water accumulation pro-vided to the operator by an alamed continuous monitoring system can pro-vide adequate backup protection if the level sensors (providing automatic scram) should fail. (The operator's response to a fast SDV fill event must be considered).
We re:ommend that the BWR licensees not be offered the alternative which involves operator action. A precedent for our recommendation is the ATWS requirement that no credit for operator action be given for at least 10 minutes (Reference 3).
In addition, we consider it doubtful that the licensee could show that the opera-tor could take timely action based on a level alarm. Therefore, we question whether this second alternative is really a choice at all. Furthemore, what i
choice would the operator actually have if the automatic system had not scrammed the reactor but the operator had received an alarm from the backup system? His only reasonable actiun 'would be to manually scram the reactor imediately. Since the reactor operator's first action upon receiving the alarm must be to manually trip the reactor, and he therefore will not have tir.e to diagnose the cause of the alam (e.g., to detemine if it is spurious) when the reactor has not tripped automatically, the alam does not seem to provide any benefit to the licensee.
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daroldR.Denton JAN 2 81981 The first alternative of two automatic scram systems based on sensors using different operating principles seems to us to be a better choice than level switches made by two different manufacturers because of the even greater diver-sity tnat it offers. Because of the importance of this system, we recommend that the licensees not be offered the choice of level switches made by a dif-ferent manufacturer as an option to the first alternative of two sensors based on different operating principles.
Experience with a sensor operating on a different principle than the currently used level switches has been limited so far to ultrasonic techniques. There have been many operating problems with systems using ultrasonic transducers but pro-gress is being made in solving thea.
In addition, at least one other civerse technique has been proposed. Therefore, it is our opinion that the first alter-native of two diverse level sensing systems based on different operating principles -
in the scram discharge system is preferable.
'Je did not attempt a cost benefit analysis af methods of acceptable compliance with these criteria; however, it is our judgement that such an analysis would show that the safety benefit of implementing these criteria would justify the cost of implementation.
Original Signed by T. F P.*urley Thomas L. hurley, Director Division of Safety Technology Office of fluclear Reactor Regulation n
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