ML20058J647
| ML20058J647 | |
| Person / Time | |
|---|---|
| Issue date: | 08/08/1990 |
| From: | Sheron B NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Beckjord E NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| Shared Package | |
| ML20058J272 | List: |
| References | |
| JCCCNRS-WG-6, NUDOCS 9012020140 | |
| Download: ML20058J647 (7) | |
Text
- _ _ _
g umiso starts I
8 NUCLEAR REGULATORY COMMISSION 4
F, wAsmworow,o.c. noses:
'AUG B 1990 MEMORANDUM FOR:
Eric S. Beckjord, Director Office of Nuclear Regula. tory Research-FROM:
Brian W. Sheron, Director Division of Systems Research.
Office of Nuclear Regulatory Research
SUBJECT:
TRIP REPORT - TRAVEL TO U.S.S.R.' JUNE 25-29, 1990 Please find enclosed my trip report.for travel to the U.S.S.R.
June 25-29, 1990. This trip report covers activities of JCCCNRS Working Group 6 (Severe Accidents) activities, J
O t
A Brian W. Sheron, Director Division of Systems Research Office of' Nuclear Regulatory Research
Enclosure:
As stated cc:
J. Taylor T. Speis J. Cortez J. Heltemes H. Denton E. Shomaker l
T. Theofanous l
P. North F. Harper j/
3 9012O20140 900823 PDR REV9P NRCUBUSR PDR
i
(
Summary of WG-6 Meeting in Moscow, U.S.S.R.
June 25-29, 1990 1
During the week of June 25-29, 1990, a meeting was held in Moscow, U.S.S.R.,
between the participants of the JCCCNRS Working Group 6 (severe accidents).
The subject areas discussed were thermal-hydraulics, corium-concrete i
inte actions, hydrogen behavior, accident management, and probabilistic risk assessments. The summaries that follow describe in detail the discussions l
held.
I Thermal.llykaulics Bcth cot ntriis presented overviews of their thermal-hydraulic research programs. Tle U.S. presented the U.S.S.R. with a copy of RELAP5/M002.
It was agreed that the U.S.S.R., through the Kurchatov Institute, would participate in the NRC's International Code Assessment Program (ICAP).
In order to determine the U.S.S.R.'s scope of effort for this agreement, the working group traveled to Electrogorsk on Tuesday, June 26, 1990, to visit the thermal-hydraulic experimental facilities there.
l The Electrogorsk test facility is located adjacent to the thermal power plant and uses steam and hot water from the plant for experiment purposes. The research and testing group at Electrogorsk are conducting studies in the following major areas:
1)
General thermal-hydraulics including integral systems tests and separate effects experiments such as dry-out and post-dryout heat-transfer experiments.
l 2)
The use of jet pumps in emergency cooling loops.
3)
Containment Thermophysics, including preparations for an experiment concerning core-concrete interaction.
4)
The best estimate analytic.and numerical modeling of two-phase flow, i
5)
Water chemistry and its influence on corrosion and also experiments on erosion.
6)
General thermal engineering equipment testing.
7)
Testing of control systems and simulators for future nuclear power plants.
While some of this work is in process, much of it appears to be in the i
planning and preparation stage. The following remarks concern a few of the major facilities or studies.
M g.
.) * *
, w. ;,, _
.;..g j
.)
- n. af.; %w,.
.. a
, iQ, :-.:
ik,
i W
VVER 1000 Thermal-Hydraulic Test Facility Although a larger facility is planned, the current VVER 1000 thermal-hydraulic test facility is volume and power scaled at approximately 1:2500 with full-i l
height simulation of major components and loop elevations.
It is an integral i
facility and is expected to be in operation at the end of CY 1990, i
l
'I l
The facility has an electrically heated core simulator with 19 fuel heater rods with full scale diameter and pitch and of full, 3.5 meter, length. The i
current heater roos os not have a built in axial power profile but instead are uniformly heated. The nominal overall power of the core is 1 MW but it can be driven to 1.8 MW in a transient fashion to simulate accidents. The downcomer i
is a separate pipe representation. The upper plenum of the nominal reactor vessel is also separate.
There are two active flow loops. One loop represents three intact loops in j
the full scale plant.
It contains three separate steam generators and a i
circulating pump.
The -second loop is scaled to represent a single loop in the full scale plant and represents the broken 100)..It contains a single U-tube steam generator, a circulating pump and a num)er of possible experimental small break connections. The complete system also contains a pressurizer.
0 The " steady state" operating conditions for the loop are 25 MPa and 400 C.
The transients are initiated from this condition.
Because of the full temperature operation and the disproportionately large surface area produced by the facility scaling, heat losses could be a significant experiment distortion.
It was reported that the local heat transfer measurements will be made at 100 points on the facility envelope (pressure boundary) and that heaters would be used to compensate for the heat losses. The precise nature of the heat loss compensation system was not clear and construction of the facility had not reached the stage where it could be shown.
The general loop is sparsely instrumented.
Differential pressure is measured I
at a number of locations (but probably not more than about 25 locations).
The core simulator contains 50 cladding thermocouples and 6 coolant thermocouples.
Flows are measured at several locations by means of venturis.
There is no evidence of 'nstruments such as gamma densitometers that would allow flow quality or flow regimes to be assessed.
Generally, the instrumentation appears to be a weakness in the facility.
The data acquisition system consists of 156 channels fed to two parallel P.C.
systems. The signal sample rate is 20 hertz. The facility has a standards laboratory available for calibration but the laboratory was not visited.
In summary, it appears doubtful that data useful for the assessment of-computational codes such as RELAP5 or TRAC can be achieved in this facility with its current instrumentation.
If the USNRC wishes to be of help to the Soviet effort, information on instrumentation, data acquisition systems,'and datt. validation and processing would be very useful to the Soviet group.
i i
l
-g
,m
,.u.
In addition'to the VVER 1000 test facility, we visited an apparatus used to test a jet pump passive cooling system.
Konstantin Soplenkov, head of the Thermal Hydraulics Safety Research Laboratory,.NPO Energia, discussed the experimental apparatus that will be used to investigate a jet pump passive core cooling approach.
In an accident situation, a valve will be opened presumably powered by compressed air or nitrogen) forcing flow through the l
et pump. A second flow loop that includes a passive heat exchanger provides.
cooler water to the jet pump. The system is designed to remove 30 50 MW of heat from the reactor for a day in the absence of any electrical power.
Core Concrete Interactions The U.S. (T. Theofanous)k in the U.S.gave a detailed presentation on.the status of corium-concrete interaction wor This was followed by a brief summary of a comparison of the U.S.S.R.'s prediction of the SURC-4 test by B. Sheron.
Presentations on corium-concrete work in the U.S.S.R. were then given.
Additional information on corium-concrete interaction experiments was provided during the June 26, 1990, visit to Electrogorsk.
These experiments were described as preliminary work in which steel (and/or corium) melts are delivered to concrete.
Core-concrete interaction-investigationsareunderwayforbgthlimestoneandgraniteconcretes,in which melts were delivered at 2200 C.
It was statec that work investigating fuel coolant interactions is planned.
Some preliminary work has also begun on the coolability of molten core debris in the lower head by immersion (of the reactor vessel) in water. This work will also include experiments.
Hydroaen 1.
Hydro en Generation New experimgntal results showing high reaction rates for temperatures over ~1,000 C.
The process seems to follow linear, rather than parabolic kinetics, and to be accompanied by a microstructure that is oriented (strata) in the direction of the reacting front rather than normal to it.
They employ a microbalance arrangement that allows continuous measurement of the sample weight and from these data we can obtain clearly reaction rate histories. There are some interesting observations of swelling (no internal pressure, oxidation on both sides) depending on the sequencing of the temperature of exposure, between 500 and 1100 C.
Theoretical interpretation remains to be made.
2.
Hydrogen Distribution l
Simple lumped parameter modelling of a VVER containment is used with 6 l
main compartments.
Also, simple experiments in a vessel 5.5M in height, by -3M in diameter (with internal compartments) are performed. Volume scaling is utilized, but no other details of scaling were given. They are planning more detailed modelling in the future.
v i
1 y
3.
Combustion, Detonation The Soviets gave an. interesting presentation spanning many aspects =of combustion phenomena. They discussed interesting applications for fires-l and explosions in the more general context of process industries and-chemical fuels. They have a way to calculate the detonation cell size i
and they think this is an improvement of the ZNO approach.
They_also
{
began to investigate mechanisms of acceleration, (i.e., stability of combustion fronts) but no detailed results were presented.' They can do temperature effects on the sensitivity to detonation, and they can also
-l consider non-uniformity in induction times, due to imposed conditions, i.e., hot particles,-radiation, etc..These are interesting experiments,
.l at large scale and different modes of-fuel fires and detonations.-They presently have the capability for large scale testing.
l Accident Manaaement The Soviets -gave several presentations on accident management, however it.
a) pears they define accident management very differently than the U.S. does.
T1ey seem to define it in the context of understanding the phenomena l
associated with severe accidents, and'do not consider it from the standpoint-of active intervention by operators and Operating staff to prevent or mitigate-the consequences of a severe accident.
The U.S. gave a presentation on current accident. management activities.'in the U.S., both regulatory and research. No specific agreements for future actions cre identified, and more interactions in th% area will be very useful.
i Summary of Probab;11stic Safety Analysis (PSA) Sessb The primary Soviet presentation during the PSA session addressed the topic of-data acquisition for use in PSAs. -The Soviets gave the impression >that they t
have a good mechanism for the acquisition of plant specific data,'although it was not clear whether the system had been in place long enough to provide r
information useful to current'PSAs.. The Soviets also have a good working knowledge of the data bases available to the. international PSA community (IAEA
' and others).
In the field of data acquisition, the Soviets seemed well coached by organizations such as the IAEA, but are not at the point ~at which_the U.S.
could profit from a technical interchange.
(We know what our data problems are.)
~
- Two other scheduled Soviet PSA presentations were cancelled.
l The U.S. (F. Harper) presented an overview of the NUREG-1150 methods and-results. During the overview the following three subjects were emphasized:
1)
The methods used to transfer information between the frontend analysis (consisting of the core damage frequency analysis) and backend analysis (consisting of the accident progression, source term, and consequence analyses).
W^
4 I
-.-, -., - - -,_ ---, - ~ ~ -. -...
-_i,
-1 l
l 1
g' 2)
The specifics of the logic models and the phenomenological treatment of example Level II phenomena (the logical treatment of hydrogen burns in l
the Mark III containment was discussed in detail).
l 3)
Options for performing reduced scope PSAs.
i The members of the Soviet delegation seemed knowledgeable in the field of PSA and asked many pertinent questions (mostly concerning the frontend NUREG-1150 analyses).
In the general field of PSA, as in the data acquisition area,-it l
appeared that the Soviets were well coached, but do not have the practical experience that could profit the U.S.
It is our understanding that they are currently in the proce'ss of completing their first PSA on a major nuclear plant, and may become a contributing member of the international PSA community i
shortly.
i i
f h
i i
l
?
I i
s,,r
-- -<ff.4 r
we t
l-l Working Group 10 Trip Report 4
'9 s
e
'f 5
f i
b I
m
,