ML20202G943
| ML20202G943 | |
| Person / Time | |
|---|---|
| Site: | Framatome ANP Richland |
| Issue date: | 12/05/1997 |
| From: | Edgar J SIEMENS POWER CORP. (FORMERLY SIEMENS NUCLEAR POWER |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 70-1257-97-202, JBE:97:173, NUDOCS 9712100150 | |
| Download: ML20202G943 (6) | |
Text
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SIEMENS December 5,1997 JB0:97:173.
.o U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 i
t Gentlemen:
[
Subject:
Reply to a Notice of Violailon i
Ref:
Letter, P. Ring to B.N. Femreite, "NRC Inspection Report 70-1257/97-202 and Notice
-of Violation," dated November 7,1997.
Below is Siemens Power Corporation's (SPC's) reply to the notice of violation accompanying the.
referenced letter, i
Violation Safety Condition S-1 of License 1227 authorizes the use of licensed materials in accordance with the statements, representations, and conditions in the License Application and Supplements.
Approved License Application Section 4.1.5, Operational and incident Reviews, states "All reported criticality safety violations, incidents, or abnormal conditions shall be reviewed and appropriate corrective actions taken."
Contrary to the above, as of October 10,1997, the April 1997 loss of moisture control incident at the Dry Conversion Pilot Plant was not adequately reviewed and appropriate corrective actions were not taken. The Siemens incident investigation Board review failed to detect a weakness within the Criticality Safety Analysis (CSA) regarding possible moisture migration from a geometry controlled portion of the system to a moderator controlled portion and failed to implement adequate controls to prevent such occurrence.
3 p p,0 0" 9712100150 971205 l l l j j!, l!!!ll h
P Siemens Power Corporation Nuclear Division 2101 Horn Rapids Road Tel:
(509) 375 8100 Engineering & Manufacturing P.o. Box 130 Fax:
(509)375-8402 Richland, WA 99352-o130
D: cum:nt C:ntrol D:sk JBE:97:173 December 5,1997 Pago 2 i
I SPC's Repiv Backoround Informatien The subject violation deals with inadequacies in SPC's investigatior, and corrective actions related to an April 1997 discovery of excessive moisture levels within equipment in SPC's Dry Convers!on Filot Plant. Since these inadequacies were revealed by a similar occurrence in September 19')7, background information on both occurrences is provided below.
The initial occurrence of excessive moisture was discovered on April 21,1997 when a small puddle of liquid was discovered just under the cap at the bottom end of a screw conveyer connecting the Pilot Plant pyrohydrolysis vessel (reactor) to the Pilot Plant calciner. The reactor at the time of discovery of the liquid was in hot standby; i.e., at operating temperature, a bed of UO present, but no incoming UF. flow. The calciner 2
was in an operating mode, meaning it was at temperature and ready to receive muterial via the screw conveyer from the reactor.
Upon discovery of the puddle of liquid, Operations immediately contacted Criticality
. Safety. The reactor and calciner were shut down and allowed to cool. Criticality Safety evaluated the discovery against the reporting requirements of NRC Bulletin 91-01 and determined the incident was not reportable. Removal of the screw conveyer cap and the -
emptying of all material in the conveyer revealed a sinall amount of free liquid ( 14 ml) plus a combination of " muddy" UO powder (0.6 kg), damp powder (0.68 kg), and dry 2
powder (3.65 kgs). Total moisture removed from the system in conjunction with the powder was about 194 grams, well below the 19,500 grams of water needed before criticality is possible with 5 wt.% enriched UO under optimum conditions.
2 SPC convened arilncident investigation Board (llB) to investigate the occurrence. The llB determined the specific cause of the occurrence to be condensation of steam that had backflowed from the calciner to the upstream and thermally cool calciner feed hopper and screw conveyer. The resulting condensate had flowed by gravity to the low end of the screw conveyer. This had occurred at a point in the startup process during which the reactor was at a substantially negative pressure with respect to the downstream calciner, and the intervening screw conveyer was both cool and empty. The backflow caused by this pressure differential exceeded the capacity of the nitrogen purge that had been installed in the bottom of the screw conveyer to provide separation of the calciner and reactor atmospheres when an intervening powder seal was not present; i.e., when the screw conveyer, rotary airlock valve, and reactor discharge tube contained no powder. Approximately 10 kg of powder in the screw conveyer was generally considered to provide such a seal.
The llB reported the root cause of the incident to be " Equipment Difficulty, Design, Design Specs, Problem Not Anticipated in that if there is no powder in the screw conveyor, the rotary air lock or the reactor discharge tube to isolate the atmosphere of
D: cum:nt C:ntrol D:sk JBE:97:173 December 5,1997 Page 3 the calciner.* tom the atmosphere of the reactor, the ser.ctor blower will produce enough vacuum to pull the calciner atmosphere over to the reactor. The nitrogen purge installed in the bottom of the screw conveyor does not have enough flow to holate the two atmospheres as desi ned."
0 Corrective actions recommended by the llB included instaliation of a magnehelic pressure Dauae on a dead leg of the screw conveyer to monitor pressure in the conveyer, revision of the Dry Conversion Pilot Startup SOP to reflect that stoem to the calciner would be tumed on last, and tasking of Manufacturing Technology to ensure that this condition will be preclufed in the new Dry Conversion Facility. These actions were completed as scheduled and were deemed adequate to ensure the safety of the Pilot Plant system.
The criticality safety group did not foresee any additional actions as being required to preclude moisture from reaching moderation controlled portions of the system upstream of the conveyor (i.e. the reactor) and therefore did not revise the Pilot Plant criticality safety analysis (CSA).
The shortcomings of the investigation and corrective actions related to the April 1997 occurrence were revealed by a similar occurrence in September 1997. More specifically, on September 16,1997, following maintenance activities, moist looking powder was observed inside a disassembled spool piece that connects the Pilot Plant reactor and rotary airlock valve to the screw conveyer that transports powder from the reactor to the calciner. Operations immediately notified Criticality Safety and initiated efforts tc determine both the source and extent of elevated moisture le';els within the system, including collection of samples for laboratory analysis. Further investigation revealed powder exceeding moisture limits in the rotary airlock valve, the lower portion of the screw conveyer, the calciner feed hopper, and the lower portion of the reactor itself.
The incident was evaluated for reportability per NRC Bulletin 91-01 criteria and subsequem!y reported to the NRC Operations Center on September 17. All material exceeding moisture limits was removed from the system and the Pilot Plant was maintained in the shutdown condition that existed at the time of the discovery.
As in the case of the April 1997 occurrence, an llB was convened to investigate this occurrencs. The investigation determined that the specific cause (caucal f actor) of this occurrenco was once again the backflow of calciner steam to cool upstream system components, with subsequent condensation. The circumstances, however, varied from those of the April occurrence in a key aspect, namely that the screw conveyer contained sufficient powder (~9.5 kgs) to form what was considered to be an effective seal, i.e. an effective barrier to the migration of calciner atmosphere to the upstream and moder6 tion-controlled reactor. The September occurrence therefore invalidated the assumption that the powder seal would serve as an effective moisture migration barrier. This assumption was erroneously accepted by the llB that investigated the April event and was reflected in an applicable Pilot Plant SOP. The September llR correctly recognized these inedequacies and its root cause conclusions recognized that, based on an incorrect assumption, controls were not identified properly and procedures were ambiguous.
i A
Docum;r$t C:ntrol Desk JBE:97:173 December 5,1997 Page 4 Based on the Set,tember occurrence, the Pilot Plant remained shut down and was tagged out of service, not to be restarted until proper corrective actions have been completed.
As corrective actions, the llB recommended a full evaluation of engineered barriers to prevent drawing moisture back into the reactor from the calciner. It was recognized that these engineered barriers willlikely be similar to the barriers applied in the new Dry Conversion Facility, which are considered to be adequate. Furthermore, all affected Pilot Plant SOPS would need to be revised to reflect any engint ered barriers and to correct and i
clarify any erroneous or ambiguous steps.
Reason for Violation The reason for the violation was acceptance of a faulty assumption relative to the operation of the Dry Conversion Pilot Plant, namely that a powder sealin the screw conveyer would preclude drawing calciner atmosphere back to the reactor. The corrective actions imposed by the April llB addressed operational conditions when the screw conveyer did not contain powder. Conditions during which the conveyer contained a powder seal were considered, but not deemed as requiring corrective actions. With respect to Criticality Safety leview, the liquid present in the lower (reactor) end of the screw conveyer was believed to have accumulated via gravity flow of condensate that formed in the calciner feed hopper and upper (downstream) end of the conveyer. Lacking any perceived mechanism to draw this accumulated liquid up into the reactor, Criticality Safcty concluded that no ravisions needed to be made to the CSA following the April event. Furthermore, Criticality Safety accepted the assumption of the efficscy of the powder seal under non-startup conditions.
Corrective Actions That Have Been Taken -
The Dry Conversion Pilot Plant has remained M a chutdown condition since ;he September 16,1997 occurrence.. The system will remain down until requhed engineered barriers has i been instslied. (As noted below under " Corrective Actions To Be Taken To Avoid Furthe Violations," adequate engineered barriers have been identified and installed in the new Dry Conversion Facility. Barriers for the Pilot Plant are anticipated to be the same or equivalent). Restart of the Pilot Plant will also be preceded by appropriate revisions to the aprlicat,le CSA and SOPS based on follow-up actions to the September 1997 occurrence.
Cerrective. Actions to be Taken to Avoid Further Violations As noted above, a thorough engirseering evaluation has been completed to verify that adequate controls are in plsee in the new Dry Conversion Facility to preclude the moisture migration pathway revealed by the Pilot Plant occurrences of April and September 1997. These controls include manual valving as well as pressure and temperature interlocks thet independently shut off calciner steam. They have been installed, received Criticality Safety review / concurrence, and are fully reflected in the applicable CSA, criticalit/ safety specifications (CSSs), and SOPS. As part of NRC's
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D:cument C:ntrcl D:sk JBE:97:173 December 5,1997 Page5 I
referenced inspection, the NRC inspectors " determined that appropriate lessons learned 4
from this incident were applied to the new DCF in that a manual valve between the calciner_ feed hopper and conveyer was installed, a reactor temperature calciner steam interlock was installed, and a reactor /calciner pressure steam interlock was also installed to prevent future occurrences. The inspectors verified that these items were in place
- and appeared to provide reasonable assurance that a similar esent would not occur in the i-new DCF."
The li'3 convened subsequent to the September occurrence also looked at generic 1
implicationc of both the April and September Pilot Plant occurrences to SPC production areas (ADU Conversion and Powder Prep) apart from the new Dr/ Conversion Facility; i.e., are there vessels in these aren into which steam is injected that are connected to-other vessels where condensate could form? The two such vessels identified were the Line 1 and Line 2 calciners in the UO, building, An in-depth review of these vessels by Plant Operations and Process Engineering is documented in the September llB report and concludes "that there are no plausible situations where steam injected into one vessel will cause moisture to be present in another vessel which would result in a criticality safety coricern."
Date When Full Comoliance Will be Achieved SPC is currently in compliance with regard to its operating processes. - As described above, any modifications to engineered barriers or operating nrocedures needed to assure r
the safety of the Dry Conversion Pilot Plant will be completed prior to startup of that 4
- facility, if you have any cuestions regarding these actions or require more information, please contact me at 509 375 8663.
Very truly yours, am B.
dgar-l Staff Engineer, Licensing
/pg
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- - Docum;nt Centrol Desk JBE:97:173 (December 5,1997 Page 6 l
' cc: U.S. Nuclear Regulatory Commission Regionsi Administrator, Region IV-Arlington, TX-U.S. Nuclear Reguietory Commission Region IV Field Office
~ Walnut Creek, CA y
U.S. Nuclear Regulatory Commission Chief, Fuel Cycle Operations Branch Division'of Fuel Cycle Safety and Safeguards, NMSS Washington, DC b
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